Board method Start with the clinical question, then tracer/stressor, acquisition validity, perfusion pattern, ventricular/high-risk findings, artifacts, and management implication. A beautiful reconstruction cannot rescue invalid raw data.
The whole field in one line · biology tagged with unstable atoms, reconstructed from escaping photons
Follow the atom
From nuclear reaction to clinical decision
A radiotracer is a physiologic question attached to an unstable atom. Its half-life governs delivery; its emission governs the camera; its molecular target governs the answer.
Actual antimatter · picogram chemistry · global logistics · quantitative physiology.
QuestionChoose the physiology.
ProbeMake + QC the tracer.
SignalGamma or annihilation photons escape.
ImageCounts → slices + curves.
DecisionValidate, interpret, act.
1
The 60-second nuclear read
sequence winsQuestion
Why image?
CAD diagnosis/risk, flow, viability, amyloid, inflammation, infection, function.
Why image?
CAD diagnosis/risk, flow, viability, amyloid, inflammation, infection, function.
Validity
Can I trust it?
Prep, stress, counts, motion, gating, attenuation registration, curves.
Can I trust it?
Prep, stress, counts, motion, gating, attenuation registration, curves.
Pattern
What is abnormal?
Location, extent, severity, reversibility; function and ancillary markers.
What is abnormal?
Location, extent, severity, reversibility; function and ancillary markers.
Meaning
What changes?
Integrate symptoms, ECG, anatomy, calcium, MBF/MFR, prior studies.
What changes?
Integrate symptoms, ECG, anatomy, calcium, MBF/MFR, prior studies.
2
Equations to write before the stem
units firstDecay
A = A₀e−λt
T½ = 0.693/λ
1/Teff = 1/Tphys + 1/Tbio
Perfusion score
SDS = SSS − SRS
% LV = score/68 × 100
17 segments × maximum score 4 = 68.
Flow & function
MFR = stress MBF/rest MBF
EF = (ED−ES)/ED × 100%
Counts require background correction.
Worked example SSS 12 and SRS 4 → SDS 8. Ischemic burden estimate = 8/68 = 11.8% of LV. This is a semiquantitative map—not a substitute for checking defect distribution, artifacts, function, and flow.
Stop 1Wrong patient, tracer, time or stress
Stop 2Infiltration or broken input curve
Stop 3Motion, truncation or low counts
Stop 4Bad gating or CT registration
Only thenInterpret physiology
Tip & trick On every calculation, ask: “Is the answer supposed to rise or fall?” If distance doubles, exposure falls to one quarter; if stress flow falls while rest flow is fixed, MFR must fall.
Nuclear cardiology advanced by changing the question — first “how fast does blood travel?”, then “where did the tracer go?”, then “how much flow is there?”, and now “which molecular deposit is present?”
A
Four eras that built the field
invention → clinical claim1927 · circulation by radiationBlumgart and Yens timed the transit of injected radium C from arm to opposite arm with an external detector. It was a number, not an image—and a conceptual ancestor of indicator-dilution physiology.PHYSIOLOGY BECOMES MEASURABLE
1958 · Anger cameraA scintillation camera localized many events at once. Collimation, crystal light, photomultipliers and position logic turned escaping gamma rays into a planar distribution.COUNTS BECOME AN IMAGE
1958 · the “moly cow”Brookhaven’s Mo-99/Tc-99m generator let a 66-hour parent travel while hospitals repeatedly eluted its 6-hour daughter. Geography and decay became part of clinical workflow.A SHORT-LIVED TRACER GOES LOCAL
1970s · injury and perfusionTc-99m PYP localized acute myocardial injury; Tl-201 supplied stress/redistribution perfusion biology. Early scans answered different questions with different mechanisms.TARGET CHOICE DEFINES THE TEST
Tomography + ECG gatingRotating cameras, reconstruction and later attenuation correction separated overlapping structures; gated datasets linked perfusion with wall motion, volumes and EF.2-D COUNTS → 3-D + FUNCTION
PET quantificationCoincidence detection, dynamic acquisitions and kinetic models turned tracer concentration over time into absolute MBF and flow reserve—not merely relative color.IMAGE → INPUT CURVE → PHYSIOLOGY
2005–2016 · amyloid pivotDPD phenotype separation, quantitative PYP work and the Gillmore multicenter pathway repurposed old bone tracers into a gated nonbiopsy ATTR diagnosis.OLD MOLECULE · NEW QUESTION
2024–2026 · long-lived PET MPIF-18 flurpiridaz gained U.S. approval for PET myocardial perfusion; its ≈110-minute half-life enables regional distribution and exercise workflows where infrastructure permits.PET REACHES BEYOND THE ON-SITE GENERATOR
B
Historical cases worth remembering
boards love repurposed tracersPYP: infarct → amyloid
Originally an adjunct for recent infarction because damaged myocardium can retain bone-seeking tracer. That history explains a modern false positive: recent MI can be focally PYP-avid.Hardware changes meaning
Planar overlap could not reliably distinguish myocardium from blood pool. SPECT—and often SPECT/CT—made “uptake in the wall” a defensible claim.Quantitation changes questions
Relative MPI finds regional imbalance; PET MBF can reveal globally reduced hyperemic flow even when every territory looks equally bright.Worked historical inference A patient scanned 10 days after an anterior MI has focal apical PYP uptake. Because the tracer’s infarct history predicts this pattern, do not call ATTR from the heart-to-contralateral ratio; localize on SPECT, review timing and complete the amyloid gates.
Factoid Technologic progress did not erase first principles: every result still depends on tracer biology, decay, collimation/coincidence physics, counting statistics and a clinical question specific enough to falsify.
A
Radioactive decay
exponential, not linear| Nuclide | Physical T½ | Board association | Emission used |
|---|---|---|---|
| Tc-99m | 6.02 h | Sestamibi/tetrofosmin SPECT | 140-keV gamma |
| Tl-201 | ≈73 h | Perfusion + redistribution | Hg x-rays ≈69–83 keV; 167 keV gamma |
| Rb-82 | ≈75 s | Generator PET perfusion | positron → 511-keV pair |
| N-13 | 9.97 min | Ammonia PET; cyclotron | positron |
| F-18 | 109.8 min | FDG; flurpiridaz | positron |
Where Tc-99m actually comes from · the most useful decay chain in medicine
Research reactorNeutrons fission a non-HEU uranium target.
Mo-99Separated, quality tested and shipped; T½ ≈66 h.
“Moly cow”Mo-99 binds alumina while daughter Tc-99m grows in.
EluteSaline removes pertechnetate; parent stays on column.
Cold kitChemistry turns Tc into sestamibi, tetrofosmin, PYP and more.
Parent → daughter clockMo-99 loses about 1% of activity each hour. After elution, Tc-99m grows back toward a maximum near 23 h while the parent also decays.The 66-h parent can travel; the 6-h daughter can be “milked” near the patient.Dirk Hünniger / Hbf878, CC BY-SA 3.0; source unmodified. Source · License
B
Photon interactions
contrast is a counting problemPhotoelectric
Photon is fully absorbed. Probability rises with absorber atomic number and falls strongly with photon energy; in tissue it removes useful photons and causes attenuation.Compton
Photon loses energy and changes direction. Scattered photons can enter the energy window in the wrong location, reducing contrast.Statistics
Poisson noise ≈ √N; relative noise ≈ 1/√N. Four times the counts roughly halves relative noise.Worked example 800 MBq with a 6-hour half-life: at 12 hours, two half-lives have elapsed → 800 × ½ × ½ = 200 MBq.
Worked effective half-life Tphys 6 h and Tbio 12 h act in parallel: 1/Teff = 1/6 + 1/12 = 1/4 → Teff = 4 h. Effective half-life is never longer than either input and is strictly shorter when both clearance processes are finite.
Factoid The generator was nicknamed the “moly cow.” Brookhaven’s parent–daughter column put short-lived Tc-99m inside hospitals without putting a reactor there.
A
Anger camera signal chain
localize, reject, countCollimator
direction selection
direction selection
NaI(Tl) crystal
gamma → light
gamma → light
Light guide/PMTs
amplify/localize
amplify/localize
Pulse-height analyzer
energy window
energy window
Computer
matrix + image
matrix + image
Pulse-height spectrumScatter continuum → 140-keV photopeak → reject out-of-window events.Widen window: sensitivity ↑, scatter contamination ↑.
B
Collimator trade-offs
no free sensitivity| Type | Best use | Trade-off / trap |
|---|---|---|
| LEHR / LEGP | Tc-99m cardiac imaging | High resolution costs sensitivity; septal penetration if energy too high. |
| Low-energy high-sensitivity | Low-count/dynamic situations | More counts, less spatial resolution. |
| Medium energy | Higher-energy emissions / penetration control | Thicker septa, lower sensitivity; protocol-specific. |
| Pinhole | Magnified small-organ imaging | Not routine adult MPI; inversion and limited field. |
Energy discrimination
Center a Tc-99m window near 140 keV; a typical 20% window spans about 126–154 keV. Exact windows are camera/protocol specific.Distance law of resolution
Parallel-hole resolution worsens as source-to-collimator distance grows. Keep the detector close without compromising safety.Worked examples A 20% window centered at 140 keV has half-width 14 keV → 126–154 keV. With 10,000 counts, relative counting noise is ≈1/√10,000 = 1%; 40,000 counts lowers it to 0.5%.
Longer holesresolution ↑
Smaller diameterresolution ↑
Thicker septapenetration ↓
More distanceresolution ↓
No free lunchsensitivity moves opposite
Tip & trick If the board moves the heart farther from the camera, choose worse spatial resolution—even if acquisition time and activity are unchanged.
A
Projection → volume
inspect before reconstructAcquire
180° or 360° validated orbit; close contour; enough views/counts.
180° or 360° validated orbit; close contour; enough views/counts.
Quality check
Cine projections, motion, truncation, extracardiac activity, ECG.
Cine projections, motion, truncation, extracardiac activity, ECG.
Reconstruct
FBP or iterative; filter; attenuation/scatter/resolution recovery.
FBP or iterative; filter; attenuation/scatter/resolution recovery.
Reorient
True LV long axis → short axis, vertical and horizontal long axis.
True LV long axis → short axis, vertical and horizontal long axis.
Each angular view is a line-integral projection—not a slice. Stacked views form a sinogram; an abrupt break in its normally smooth tracks flags motion before reconstruction turns the break into rings or edge defects.
| Choice | Benefit | Failure mode |
|---|---|---|
| Iterative reconstruction | Models system physics; noise/attenuation corrections | Wrong iterations/filter create over-smoothing or edge artifacts. |
| ECG gating | Wall motion, thickening, EDV/ESV/LVEF | Arrhythmia or wrong R-wave detection produces flashing/false function. |
| Attenuation correction | Reduces breast/diaphragm attenuation | Emission–CT misregistration manufactures defects. |
| Prone imaging | Can shift inferior attenuation | Supplement, not replacement; anterior attenuation may appear. |
Worked example Inferior defect disappears prone, has normal thickening, and raw cine shows diaphragmatic attenuation → artifact is favored. If fixed with absent thickening, scar remains more likely.
Raw cinemotion + bowel
Sinogramabrupt discontinuity
Reconstructionfilter/noise
Axestrue LV long axis
Cross-checkgating + AC
Board trap Never interpret reconstructed slices without raw projection cine. Motion, bowel activity, truncation, and detector problems are often obvious only there.
A
Coincidence imaging
electronic collimationYes, PET is clinical antimatterp → n + e+ + νe
A proton-rich nucleus emits a positron—the electron’s antimatter twin. It loses kinetic energy over a tracer-dependent range, encounters an electron, and annihilates.
e+ + e− → 2γRest mass becomes two 511-keV photons: 1.022 MeV total. PET detects the photons, not the positron.
β+ decay
Positron travels a short range before interacting with an electron.
Positron travels a short range before interacting with an electron.
Annihilation
Two 511-keV photons depart approximately 180° apart.
Two 511-keV photons depart approximately 180° apart.
Coincidence
Near-simultaneous detectors define a line of response; TOF narrows localization.
Near-simultaneous detectors define a line of response; TOF narrows localization.
| Event/correction | Meaning | If uncorrected |
|---|---|---|
| True | Both photons from one annihilation, unscattered | Desired signal. |
| Scatter | One/both photons deflected | Wrong line; reduced contrast. |
| Random | Unrelated photons fall inside timing window | Background rises with count rate. |
| Attenuation | One photon absorbed removes the coincidence | Major quantitative bias; CT map needed. |
| Dead time / pile-up | System cannot process all high-rate events | Underestimated activity/flow; curve distortion. |
Spatial-resolution limits
Detector size, positron range, noncollinearity, reconstruction, motion. F-18 has shorter positron range than Rb-82.TOF
Does not alter the true line of response; it improves signal localization and image SNR, especially in larger patients.Worked TOF lab Localization uncertainty along the line of response is Δx = cΔt/2. At 400 ps: 3×108 m/s × 400×10−12 s ÷ 2 = 0.06 m = 6 cm. Better timing narrows—not eliminates—the uncertainty.
Count-rate factoid Random coincidences scale approximately as R ≈ 2τS1S2. Double both detector singles rates and randoms rise about fourfold—one reason “more activity” eventually degrades quantitative performance.
Antimatter factoid DOE notes that ordinary bananas emit roughly one positron every 75 minutes from natural K-40. PET turns the same category of particle into quantitative physiology.
Physics trap Pair production requires at least 1.022 MeV. A single 511-keV annihilation photon cannot create an electron–positron pair.
A
Quality control before interpretation
hardware → patient → software| Domain | Verify | Characteristic failure |
|---|---|---|
| Gamma camera | Energy peak/window, uniformity, center of rotation, detector geometry | Ring/ringlike or nonuniform defects; spatial misregistration. |
| PET | Normalization, calibration, blank/CT, timing, count-rate performance | Incorrect SUV/MBF, stripes, dead-time bias. |
| Hybrid CT | Registration, table position, breathing state, truncation/metal | Regional over- or undercorrection. |
| Patient | Identity, dose/time, position, motion, ECG leads, glucose/prep | Wrong protocol, curves, gating or interpretation. |
| Software | Correct tracer/model/database, axes, contours, beat acceptance | Precise-looking but invalid quantitation. |
B
Modern detectors
benefit without immunity
CZT SPECTDirect conversion: sensitivity/energy resolution ↑; normals remain system-specific.
Digital PETSiPM timing/count rate ↑; MBF still depends on calibration, motion and model.
Hybrid CTAC + anatomy; attenuation CT is not automatically diagnostic CCTA.
What the scanner really costs · five ledgers, not one price tag
CapitalCamera/PET-CT, shielding, electrical/HVAC, build-out and financing.
Physics + serviceAcceptance, calibration, preventive maintenance, software and downtime.
Tracer infrastructureGenerator, cyclotron access, radiopharmacy, QC, delivery and decay waste.
People + timeTechnologists, nurses, physicians, physicists, pharmacists and longer protocols.
Throughput riskNo-shows, failed injections and outages destroy perishable capacity.
Worked example A “new” lateral PET defect aligns exactly with a 12-mm emission–CT shift. After registration correction, perfusion normalizes → technical artifact, not interval CAD.
Economics factoid A short half-life makes unused capacity disappear. The marginal tracer may be inexpensive while the idle scanner, generator clock and staffed room dominate the true cost per completed study.
Tip & trick Ask whether the abnormality follows coronary anatomy or a hardware/registration boundary. Artifacts often respect the latter.
A
Perfusion tracer comparison
kinetics drive protocol| Tracer | Uptake/redistribution | Strength | Limitation |
|---|---|---|---|
| Tl-201 | Na/K-ATPase potassium analogue; redistributes | Delayed redistribution/reinjection can assess viability | Low photon energy, long half-life, higher dose burden, poorer counts. |
| Tc-99m sestamibi | Lipophilic cation; mitochondrial potential; minimal redistribution | High-count gated SPECT; stable distribution after injection | Hepatobiliary activity; separate rest/stress injections. |
| Tc-99m tetrofosmin | Lipophilic cation; minimal redistribution | Imaging may begin at 15 min under the current label; gated imaging | Separate rest/stress injections and protocol-specific timing still required. |
Extraction roll-off
At high coronary flow, tracer uptake rises less than linearly. Relative images can underestimate diffuse or balanced disease.Gating advantage
Tc-99m photon flux supports ventricular volumes, LVEF, motion and thickening—if rhythm and R-wave detection are valid.Tc-99m passportBirth: most conventional high-specific-activity Mo-99 supply comes from reactor fissionTravel: generator bridges continents → hospitalCost pressure: reactor schedule, processing, freight, generator utilization
Tl-201 passportBirth: cyclotron 203Tl(p,3n)201Pb → 201TlTravel: long 73-h half-life permits distributionCost pressure: target/processing + lower-count protocol time
Dated supply snapshot · 9 Apr 2026 DOE reported that the United States still imported all Mo-99 from producers in the Netherlands, Belgium, South Africa and Australia, while SHINE’s domestic facility remained under construction. A simultaneous foreign-reactor outage drove a major 2024 shortage—proof that “routine” Tc-99m begins with geopolitics and reactor uptime.
Worked example A severe reversible defect is injected at peak exercise, but imaging begins later. Tc distribution still reflects blood flow at injection because clinically meaningful redistribution is minimal.
Factoid Tl-201 imaging uses mercury x-rays produced after electron capture—not a 140-keV Tc photopeak.
A
Choose tracer by question and logistics
perfusion ≠ metabolism| Tracer | T½ / production | Core use | Board nuance |
|---|---|---|---|
| Rb-82 chloride | ≈75 s; Sr-82/Rb-82 generator | Rapid rest/stress PET + MBF | High throughput; lower extraction and longer positron range than N-13/F-18. |
| N-13 ammonia | 9.97 min; cyclotron | High-quality perfusion + MBF | U.S. labeling describes rest/pharmacologic-stress use; exercise workflows come from professional practice and require suitable logistics. Dynamic MBF is generally pharmacologic. |
| F-18 flurpiridaz | 109.8 min; regional distribution | FDA-approved 2024 rest/exercise or pharmacologic perfusion; MBF with validated pharmacologic acquisition/software | Mitochondrial complex-I binding; rest→stress ≥30 min pharmacologic or ≥60 min exercise. At exercise inject at ≥85% APHR or ischemic signs/symptoms and continue 1–2 min. |
| F-18 FDG | 109.8 min | Glucose metabolism: viability, inflammation/infection | Viability prep stimulates uptake; inflammation prep suppresses physiologic uptake. |
B
Targeted imaging
phenotype firstTc-PYP / DPD / HMDP
Bone-avid tracers for ATTR cardiac amyloid pathway; SPECT confirms myocardium and monoclonal-protein testing is mandatory.FDG inflammation
Cardiac sarcoid, prosthetic/device/graft infection. Preparation and pattern are disease-specific.Emerging targets
Innervation, fibroblast activation, thrombosis and other molecular targets are not interchangeable with established routine indications.Tracer passports · half-life writes the business model
Rb-82 · 75 sHigh-energy protons make Sr-82 from a RbCl target; the parent is loaded into an on-site generator.No dose delivery; throughput pays for the clock.
N-13 · 10 minOn-site cyclotron: 16O(p,α)13NExcellent physics; facility + radiochemistry intensive.
F-18 · 110 min18O(p,n)18F, regional cyclotronCan travel; synthesis, release testing and courier matter.
F-18 moleculesFDG tracks glucose; flurpiridaz targets complex I.Same isotope clock, different biology.
Current Rb-82 label CardioGen-82 stop-use limits are product-specific: 60 days, 17 L cumulative eluate, or specified Sr breakthrough limits—whichever occurs first. Minimum rest-to-stress interval is 10 min. Do not memorize an obsolete universal “42-day generator” rule.
Worked decay lab Rb-82 after 10 min has passed 8 half-lives → 0.39% remains. N-13 after 30 min → 12.4%; the radioactive N-13 atoms in a 10–20 mCi dose are ≈0.5–1.0 pmol—not the total ammonia/carrier mass. F-18 after 2 h → 46.9%; 213 MBq is the decay-only starting minimum to deliver 100 MBq then, so the real synthesis target must be higher for processing/transfer loss.
Tip & trick “FDG prep” is not one protocol. Always write the biologic goal: stimulate normal/viable myocardium or suppress physiologic myocardium.
A
Radiation quantities
do not mix units| Quantity | SI unit | Meaning | Legacy |
|---|---|---|---|
| Activity | Bq = disintegrations/s | Amount of radioactive transformation | 1 mCi = 37 MBq |
| Absorbed dose | Gy = J/kg | Energy deposited per mass | 1 Gy = 100 rad |
| Equivalent/effective dose | Sv | Radiation/tissue weighting; population risk model | 1 Sv = 100 rem |
| Exposure rate | context-specific | Falls with distance approximately as 1/r² for a point source | Use survey meter, not mental math, operationally. |
B
ALARA hierarchy
quality-preserving reductionJustify
Will the answer change diagnosis, prognosis, or management?
Will the answer change diagnosis, prognosis, or management?
Optimize
Stress-first/stress-only when validated; weight/camera-specific activity.
Stress-first/stress-only when validated; weight/camera-specific activity.
Avoid repeat
Prep, IV, timing, motion prevention, attenuation/gating QC.
Prep, IV, timing, motion prevention, attenuation/gating QC.
Protect
Time, distance, shielding, contamination controls and documentation.
Time, distance, shielding, contamination controls and documentation.
1 m82 m24 m0.5
Distance is a superpowerPoint-source approximation: rate ∝ 1/r².140 keV ≠ 511 keV. PET photons are more penetrating; shielding and workflow are modality-specific.Calculate for exams. Survey meters + the RSO control real work areas.
Worked example Exposure is 8 units at 1 m. At 2 m: 8 × (1/2)² = 2 units. At 4 m: 8 × (1/4)² = 0.5 unit.
Factoid ALARA does not mean “lowest possible counts.” It means the lowest exposure consistent with a diagnostic, management-relevant study.
A
Pregnancy and lactation
tracer-specific decisionsClarify
Pregnancy possibility, gestational age, breastfeeding, urgency and question.
Pregnancy possibility, gestational age, breastfeeding, urgency and question.
Consider alternative
Can echo/CMR or delayed imaging answer safely without losing benefit?
Can echo/CMR or delayed imaging answer safely without losing benefit?
Justify + optimize
If essential, select protocol/activity with nuclear medicine and medical physics.
If essential, select protocol/activity with nuclear medicine and medical physics.
Counsel
Document dose estimate and tracer-specific breastfeeding interruption—not a generic interval.
Document dose estimate and tracer-specific breastfeeding interruption—not a generic interval.
Never improvise
Fetal dose and milk excretion differ by tracer, activity, timing and maternal clearance. Use institutional radiation-safety tables and a named expert.Risk communication
Explain expected benefit, alternatives, magnitude/uncertainty, and how protocol changes reduce exposure. Do not equate administered activity with fetal dose.B
Spill / contamination response
contain before cleanStop
Prevent spread; keep people away; remove contaminated gloves/clothing safely.
Prevent spread; keep people away; remove contaminated gloves/clothing safely.
Notify
Radiation Safety Officer and local emergency chain.
Radiation Safety Officer and local emergency chain.
Survey
Mark extent; decontaminate from edge inward; resurvey people/area.
Mark extent; decontaminate from edge inward; resurvey people/area.
Document
Nuclide, activity estimate, persons, readings, waste, follow-up.
Nuclide, activity estimate, persons, readings, waste, follow-up.
Worked example A Tc-99m syringe leaks on the floor. Do not carry supplies through clean halls. Control access, cover the spill, notify radiation safety, survey shoes/hands, and follow the site’s decontamination and waste pathway.
Stopfreeze the footprint
Containcover + control access
NotifyRSO / local chain
Surveypeople + area
Clearresurvey + document
Tip & trick On boards, “notify radiation safety” is usually earlier than attempting elaborate cleanup yourself.
Exercise is a diagnostic test plus a tracer-delivery method Preserve workload, symptoms, BP, HR, rhythm, ST response and recovery—not just the perfusion images.
A
Why exercise when feasible?
prognosis in the treadmillCapacity
Protocol, duration, peak workload/METs, limiting symptom and reason stopped.Hemodynamics
Chronotropic response, BP response, rate-pressure product and recovery.Electrical
ST shifts, arrhythmia, conduction and symptom–ECG concordance.Baseline12-lead ECG, BP, symptoms, IV patency and contraindication screen.T − 0
StageRecord workload, HR/BP and ECG at each stage; ask symptoms directly.every stage
Peak + injectInject while the patient is still at maximal achievable workload.peak stress
Keep movingContinue exercise ≈1–2 min when feasible so tracer sees peak physiology.+1–2 min
RecoveryContinue ECG/BP/symptoms until abnormalities resolve or are treated.document
| Step | Board-ready action | Common trap |
|---|---|---|
| Before | History, exam, ECG, medication/caffeine review, IV, emergency readiness | Exercise despite unstable symptoms, dangerous arrhythmia or decompensation. |
| Peak | Inject as close to maximal stress as possible; continue exercise ≈1–2 min when feasible | Inject after workload has fallen substantially. |
| Recovery | Continue ECG/BP/symptom surveillance and document resolution | Stopping observation when exercise stops. |
Stop exercise for safety Moderate/severe angina; marked dyspnea; pallor/poor perfusion; ataxia/near-syncope; patient request; sustained SVT/VT; ST elevation >1 mm in non-Q-wave leads; SBP fall >10 mmHg with ischemia; inability to monitor; or hypertensive response >250/115 mmHg.
Rate-pressure product
RPP = peak HR × peak SBP
Peak HR 131/min and SBP 180 mmHg → 23,580 mmHg·beats/min. It describes myocardial demand; interpret with workload, symptoms and medications.Chronotropic calculation
CI = (HRpeak−HRrest)/(APMHR−HRrest)
Age 60 → APMHR ≈160. Rest 70, peak 131 → CI = 61/90 = 0.68. Thresholds vary with beta-blocker use and protocol.Worked example This 60-year-old reaches 82% of age-predicted maximum HR but 11 METs, limiting angina and ischemic ST depression. “Below 85%” does not erase the positive, high-workload clinical data.
Board trap 85% of age-predicted maximum HR is an adequacy clue, not a universal target or automatic termination point. Stop for symptoms, diagnostic endpoints or safety criteria.
A
Doses and timing
memorize exactly| Agent | Dose | Tracer timing | Key pharmacology |
|---|---|---|---|
| Regadenoson | 0.4 mg rapid IV injection (about 10 s), then saline flush | Tracer 10–20 s after the saline flush | A2A-selective agonist; fixed dose. |
| Adenosine | 140 µg/kg/min continuous IV, usually 4–6 min | Commonly 3 min after start while infusion continues | Nonselective adenosine receptor agonist; half-life <10 s. |
| Dipyridamole | 0.56 mg/kg over 4 min | About 3–5 min after infusion | Raises endogenous adenosine; longer effects. |
A2A receptor: open the resistance bed
Regadenoson directly stimulates coronary A2A receptors; adenosine stimulates several receptor subtypes. Resistance-vessel dilation raises normal flow more than flow across a stenosis, producing relative heterogeneity.Competitive blockers and amplifiers
Caffeine and theophylline are methylxanthine antagonists that can blunt hyperemia. Dipyridamole inhibits adenosine uptake/metabolism, amplifying endogenous adenosine and prolonging effect.Caffeinehold ≥12 h
Theophyllinehold ≥12 h
Dipyridamolehold ≥48 h
If uncertainverify product + lab policy
B
Safety gates
screen before injectDo not proceed until resolved
Active bronchospasm; advanced AV block/sinus-node disease without a functioning pacemaker; unstable ischemia; symptomatic hypotension; or uncontrolled BP >200/110 mmHg. Verify the full agent-specific label and local emergency pathway.Relative: individualize
Severe symptomatic aortic stenosis is a relative—not absolute—contraindication to regadenoson. Weigh urgency, hemodynamic reserve, alternative imaging and monitored-lab capability; do not place it in the automatic “do not proceed” list.ScreenBronchospasm, conduction, BP, ischemic stability, caffeine and medicines.before dose
Regadenoson0.4 mg rapid IV injection over about 10 s.0 s
FlushFollow promptly with saline; watch ECG, BP and symptoms.≈10 s
TracerAdminister 10–20 s after the saline flush.≈20–30 s
Reverse if neededAminophylline 50–125 mg slow IV over 30 s for significant persistent nonseizure effects, generally ≥60 s after tracer if clinically safe. Repeat if needed to a cumulative maximum of 250 mg.tracer + ≥60 s
Emergency exception: reverse a very serious adverse event immediately and provide resuscitative care. Do not delay treatment to protect the scan. Reversal within the first minute may compromise stress perfusion, so document timing and reassess a reassuring result.
Worked example A patient drinks coffee 2 hours before regadenoson. Caffeine competitively antagonizes adenosine receptors → postpone or use an alternative validated stress strategy rather than accept a potentially false-negative study.
Seizure exception For a regadenoson-associated seizure, provide emergency support and urgent IV benzodiazepine/anticonvulsant per protocol; do not give aminophylline, which may worsen seizure activity.
Tip & trick Low-level exercise with vasodilator stress can reduce symptoms and bowel activity in selected patients, but do not use it with LBBB or pacing if tachycardia may worsen septal artifact.
A
Dobutamine pathway
when vasodilator is unsuitable5 µg/kg/minBaseline ECG/BP complete; begin infusion.0–3 min
10 µg/kg/minRecheck symptoms, rhythm, ST segments and BP.3–6 min
20 µg/kg/minContinue staged monitoring; prepare tracer timing.6–9 min
30 µg/kg/minAtropine may augment an inadequate HR response per protocol.9–12 min
40 µg/kg/minPeak stage; inject near endpoint, then recover under surveillance.≥12 min
Mechanismβ1 demand stress
MonitorECG + BP every stage
Injectnear peak physiology
Reversebeta-blocker if indicated
| Baseline condition | Preferred concept | Why |
|---|---|---|
| LBBB | Vasodilator MPI, preferably PET when available | Tachycardia/exercise can create septal perfusion artifact. |
| Ventricular pacing | Vasodilator rather than tachycardia-producing stress | Abnormal activation and septal artifact. |
| Active bronchospasm | Dobutamine if stress imaging is essential and appropriate | Adenosine-mediated bronchoconstriction risk. |
| High-grade AV block, no pacer | Avoid adenosine agonists; individualize alternative | Nodal suppression. |
Stop for danger
Limiting ischemic symptoms, significant ST change, sustained/severe arrhythmia, marked hypotension or severe hypertension → stop, stabilize and follow the lab emergency pathway.Stop for endpoint
Target/diagnostic endpoint or maximum validated dose is reached. “Target HR” never overrides a safety signal.Own recovery
Continue ECG, BP and symptom surveillance; treat persistent effects and document resolution. A beta-blocker may reverse dobutamine when clinically appropriate.Dose calculation
rate = weight × dose
A 70-kg patient at 40 µg/kg/min receives 70 × 40 = 2,800 µg/min = 2.8 mg/min. The pump rate then depends on the verified bag concentration.Why the ECG matters
Dobutamine may provoke ischemia, hypertension, hypotension or atrial/ventricular arrhythmia. Dose stage, endpoint, tracer time and recovery treatment belong in the report.Worked case Severe asthma with active wheeze plus LBBB creates competing hazards: vasodilator bronchospasm risk versus tachycardia-related septal artifact. Stabilize first; if imaging remains necessary, choose the modality/stressor that safely answers the question—often not routine SPECT.
Factoid Dobutamine increases demand; vasodilators create relative hyperemia. Both can reveal flow heterogeneity, but their contraindications and ECG artifacts differ.
A
Protocol selection
match patient + camera| Protocol | Best fit | Critical rule |
|---|---|---|
| Stress-first / stress-only | Low/intermediate risk, no known CAD, high-quality normal stress images | Omit rest only under a validated pathway with unequivocal normality. |
| 1-day rest–stress | Routine convenience | Second Tc-99m activity is generally ≈3× the first (≈3.5–4× with no inter-injection delay), using a validated camera/weight-specific protocol. |
| 1-day stress–rest | Stress-first triage | Rest only if stress abnormal/equivocal; avoid shine-through. |
| 2-day | Large body habitus or count limitations | Higher activity each day; confirm labeling/order and comparison. |
| Tl viability | Selected perfusion/redistribution question | Immediate + delayed/reinjection timing is not interchangeable with Tc. |
B
Three operational ledgers
quality has a costStress-only
lowest conditional burdenOne injection/acquisition if stress images are unequivocally normal after raw, gated and attenuation QC.Savings disappear if equivocal studies trigger recalls.One-day pair
throughput efficientTwo injections and acquisitions in one visit; residual first-dose counts demand adequate separation/activity ratio.Convenience trades against shine-through.Two-day pair
count-rich, time-heavyComparable higher activity each day can improve count statistics in large patients.Adds patient travel, scheduling and camera time.Before
Weight/body habitus, pregnancy/lactation, ECG/rhythm, caffeine/meds, IV and camera capacity.During
Stress adequacy, injection quality, exact activity/time, symptoms/ECG/BP, gating.After
Raw cine, counts, motion, extracardiac activity, prone/AC when validated, repeat only if needed.Shine-through arithmetic
A first Tc-99m dose of 10 mCi has ≈10 × (½)3/6 = 7.1 mCi physical activity remaining 3 h later. After a 30-mCi second dose, the first dose is still ≈7.1/(30+7.1) = 19% of combined physical activity before biologic/detection effects.Clinical consequence
Residual counts from the first study can mask a true change in the second. Waiting, an adequate second:first activity ratio, order selection and validated reconstruction reduce—but do not license ignoring—shine-through.Worked case Stress perfusion/function look normal, but severe motion crosses more than one pixel and creates a transient defect. Stress-only criteria are not met until motion is resolved and images are unequivocally diagnostic; an avoidable recall is both a quality and cost failure.
Tip & trick “Low dose/high dose” is a relationship, not one universal pair of numbers. Camera type, patient size, acquisition time and local validation determine activity.
Current direction For patients selected for nuclear MPI, current expert guidance favors PET MPI with validated MBF when available because perfusion, function and flow are acquired together.
A
Dynamic flow acquisition
time zero is sacredPosition + CT
Center heart; attenuation CT; check breathing/registration.
Center heart; attenuation CT; check breathing/registration.
Dynamic rest
Accurate injection time/dose; capture arterial input and tissue phases.
Accurate injection time/dose; capture arterial input and tissue phases.
Rest analysis
Motion, curves, contours, rest MBF; consider rate-pressure product.
Motion, curves, contours, rest MBF; consider rate-pressure product.
Stress dynamic
Synchronize hyperemia and tracer; same QC → stress MBF + MFR.
Synchronize hyperemia and tracer; same QC → stress MBF + MFR.
ARTERIAL INPUT · EARLY / NARROW
▁▂▆█▅▂▁▁▁▁
MYOCARDIUM · LATER / BROADER▁▁▂▄▆██▆▄▂▁
time 0 ─────────────────────→ late framesCurve cockpit
Input peak: present + uncut
Tissue curve: smooth wash-in/out
Motion: frames aligned
Stress: timed to hyperemia
A plausible number cannot rescue an implausible curve.
| Invalidator | Clue | Action |
|---|---|---|
| Dose infiltration | Low/late input peak; injection-site activity | Do not trust MBF; document/repeat only if justified. |
| Missed time zero | Truncated input curve | Quantitation invalid even if static perfusion is interpretable. |
| Motion | Myocardium shifts across frames | Frame-wise correction only if validated; recheck contours. |
| Inadequate stress | High caffeine risk, weak response, globally low stress flow | Integrate prep/hemodynamics; avoid labeling diffuse disease reflexively. |
| Model mismatch | Wrong tracer/model or implausible curves | Reprocess correctly; use laboratory-specific normal ranges. |
Infiltrationsmall, broad input
Late startclipped input peak
Motionjagged tissue curve
Caffeinesubmaximal hyperemia
Wrong modelplausible-looking error
Worked example Rest MBF 0.9 and stress MBF 2.4 mL/g/min → MFR 2.67. If the input curve is intact and hemodynamics appropriate, global flow is preserved; regional perfusion still requires inspection.
Board trap A normal static perfusion image does not validate a broken dynamic acquisition. Report perfusion and flow as separate quality-controlled outputs.
A
Equilibrium radionuclide angiography
reproducible serial EFArea-normalized counts
b = BKGraw/NBKG pixels
EDcorr = EDraw − b·NED pixels
EScorr = ESraw − b·NES pixels
LVEF = (EDcorr−EScorr)/EDcorr
Scale background count density to each LV ROI area. Never subtract an arbitrary raw background-ROI total.
Strength
High count-based reproducibility for serial LV EF when acquisition, labeling, positioning, gating and analysis are consistent. Planar equilibrium RVEF is limited by chamber overlap; use first-pass or another dedicated validated method for RVEF.R-wave triggerEach accepted R–R interval opens a new cycle; review the beat-length histogram.gate
End diastoleHighest LV blood-pool counts/volume near the start of the cycle.ED frame
End systoleLowest LV counts/volume; contours and background still require inspection.ES frame
Next R waveTypical 16–32 bins trade temporal resolution against counts per frame; reject ectopy consistently.repeat + sum
| Problem | Effect | Recognition |
|---|---|---|
| Poor RBC labeling | Background/organ activity; weak blood pool | Low target-to-background; labeling method/context. |
| Arrhythmia | Mixed cycle lengths; distorted time–activity curve | Beat histogram/rejection; flicker or temporal blur. |
| LA/LV or RV/LV overlap | Erroneous ventricular counts | Review LAO angle and septal separation. |
| Background ROI error | Can raise or lower calculated EF | Position adjacent to LV without chamber/spleen overlap. |
B
First-pass and shunt concepts
time–activity curvesFirst-pass RNA
Tracks a compact bolus through right heart, lungs and left heart; useful for RV function or exercise when acquisition is technically robust.Left-to-right shunt
Pulmonary recirculation after the first pass raises the fitted pulmonary-to-systemic flow ratio; severe bolus dispersion undermines the curve.Worked counts Raw background ROI = 500 counts over 20 pixels → b = 25 counts/pixel. With 100-pixel ED and ES ROIs, scaled BKG = 2,500 counts—not 500. Raw ED 12,500 → 10,000 corrected; raw ES 6,500 → 4,000 corrected. EF = (10,000−4,000)/10,000 = 60%.
Tip & trick For serial cardiotoxicity surveillance, the smallest trustworthy change comes from repeating the same view, gating, labeling and analysis—not from assuming every EF method is interchangeable.
A
Read in a fixed order
do not start at polar map
Interpretation cockpit
Raw cine: motion + extracardiac activity
CT/AC: registration before correction
Slices: stress beside rest
Gate: motion + thickening + EF
Ancillary: TID, RV/lung, flow, calcium
Cardiac attenuation-correction example: Kieran Maher, public domain. Source
1 Quality
Raw cine/dynamic curves, motion, counts, gating, attenuation registration.
Raw cine/dynamic curves, motion, counts, gating, attenuation registration.
2 Perfusion
Location, extent, severity, reversibility; compare stress/rest side by side.
Location, extent, severity, reversibility; compare stress/rest side by side.
3 Function
LV/RV size, EDV/ESV, LVEF, motion, thickening, post-stress change.
LV/RV size, EDV/ESV, LVEF, motion, thickening, post-stress change.
4 Integrate
TID, lung/RV uptake, MBF/MFR, calcium/CT, symptoms/ECG and prior studies.
TID, lung/RV uptake, MBF/MFR, calcium/CT, symptoms/ECG and prior studies.
| Pattern | Perfusion | Function | Meaning after QC |
|---|---|---|---|
| Ischemia | Stress defect improves at rest | May show stunning/new dysfunction | Inducible flow limitation; quantify burden/severity. |
| Scar | Fixed defect | Reduced thickening/motion supports | Infarction likely; attenuation can mimic fixed defect. |
| Mixed | Fixed component + reversibility | Regional dysfunction common | Scar plus peri-infarct ischemia. |
| Balanced/diffuse | Relative images may look normal | TID/EF response may be abnormal | Use absolute MBF/MFR and clinical/anatomic context. |
Worked example Fixed inferior defect with normal gated thickening and resolution on prone/attenuation-corrected views → diaphragmatic attenuation favored over infarction.
Good-quality stress/rest MPI. Small mild fixed inferior reduction normalizes with attenuation correction and has normal gated thickening, favoring diaphragmatic attenuation; no convincing inducible ischemia. LV size and systolic function are normal.
Tip & trick Describe first, diagnose second. “Moderate, partially reversible inferolateral defect involving four segments” is auditable; “LCx disease” overstates certainty because territories vary.
A
17-segment scoring
0 normal → 4 absent1234567891011121314151617
AHA 17 segments: basal 1–6, mid 7–12, apical 13–16, cap 17. Territory assignment overlaps.
0Normal uptake
1Mildly reduced
2Moderately reduced
3Severely reduced
4Absent uptake
| Score | Formula | Interpretive role |
|---|---|---|
| SSS | Sum of 17 stress scores | Total stress perfusion abnormality. |
| SRS | Sum of 17 rest scores | Rest perfusion abnormality—not automatically scar. |
| SDS | SSS − SRS | Reversible component; estimate ischemic burden. |
| % LV | Summed score / 68 × 100% | 0–68 scale; semiquantitative, software/lab dependent. |
Extent / conventional SPECT bins Small defect <10% LV or 1–2 segments; medium 10–19% or 3–4; large ≥20% or ≥5. Traditional SSS: 0–3 normal, 4–8 mild, 9–13 moderate, >13 severe—label the tracer/software/lab context.
1 · Score each segment Stress scores are 2,2,2,2,2,2 in six inferolateral/inferior segments and 1,1,1,1 elsewhere; the other seven segments are 0. SSS = 16.
2 · Repeat at rest Three of the same segments remain 2 and all others normalize. SRS = 6; fixed burden estimate = 6/68 = 8.8% LV.
3 · Isolate reversibility SDS = 16 − 6 = 10; reversible burden estimate = 10/68 × 100 = 14.7% LV.
4 · Translate, do not automate Moderate-to-severe, predominantly reversible inferolateral/inferior abnormality. Check raw data, function, flow and anatomy before any cath/revascularization decision.
Six-segment inferolateral/inferior perfusion abnormality, predominantly reversible (SSS 16, SRS 6, SDS 10; semiquantitative reversible burden ≈15% LV); correlate with gating, artifacts, flow and coronary/graft anatomy.
Factoid LAD, LCx and RCA territories are defaults, not anatomy. Wraparound LAD, dominance, grafts and collaterals alter assignment; a segment can sit at a vascular border.
A
Gated data: function plus artifact adjudication
verify beat histogram| Finding | What it adds | Failure mode |
|---|---|---|
| Wall thickening | Normal thickening under fixed defect favors attenuation | Small hearts, low counts, gating errors can mislead. |
| Post-stress LVEF fall | May support stunning/extensive ischemia | Timing differs by tracer; compare like with like. |
| TID | Can mark diffuse subendocardial ischemia/high risk | Cutoff is protocol, tracer, camera, sex/database and software specific. |
| RV uptake/dilation | RV pressure/volume burden or severe lung disease | Relative increase may reflect reduced LV uptake. |
| Lung uptake | With applicable tracers, severe LV dysfunction/ischemia | Timing, tracer and ROI dependent. |
B
Risk rises with concordance
cluster ≠ isolated numberReassuringValid stress + normal perfusion + preserved function
InterrogateOne borderline TID, EF or flow value
ConcerningLarge or multiterritory ischemia; low EF or stress flow
High-risk clusterDefect + TID + stress EF fall + globally depressed flow
1 · Apparent signalRelative perfusion shows a large reversible anterior/lateral abnormality; post-stress EF is 47% versus 58% at rest, and TID exceeds the laboratory limit.
2 · Validate every inputBeat histogram is tight, LV contours are correct, stress was adequate, motion/attenuation registration are acceptable, and absolute flow is globally depressed.
3 · Integrated conclusionMultiple independent markers point in the same direction: high-risk ischemic physiology. Communicate promptly in the clinical context; do not reduce the finding to one TID number.
Borderline alone
A TID of 1.23 with a laboratory limit of 1.20, normal perfusion and an obviously too-small rest LV contour should trigger reprocessing. Partial-volume/edge detection can underestimate ESV and inflate EF.First question: is the measurement real?Concordant cluster
Large/multiterritory reversibility plus a valid stress-EF fall, abnormal ventricular response and low global flow carries more weight than any single marker.Second question: what urgent consequence follows?Board trap There is no universal TID cutoff. Use the laboratory’s validated tracer, stress protocol, camera, sex/database and software limit.
A
Artifact fingerprint table
raw data are evidence| Artifact | Clue | Resolution |
|---|---|---|
| Breast / chest wall | Compare raw rest/stress cine: a shift in breast position can move a camera-fixed attenuation defect and mimic reversibility. | Match position; inspect body contour, gated thickening, and AC vs non-AC; reposition and reacquire when possible. Quantitation cannot repair a mismatched acquisition. |
| Diaphragm | Inferior fixed defect, often male/large abdomen | Prone/AC and function; confirm no true defect. |
| Motion | “Hurricane”/ring, axial shift on cine, noncoronary edge defect | Motion correction only if validated; repeat when necessary. |
| Subdiaphragmatic activity | Hot liver/bowel adjacent to inferior wall; normalization error | Delay, hydration/food or repeat per protocol; inspect unnormalized slices. |
| Gating failure | Beat-histogram tails, flashing, implausible EF/volumes | Fix leads/window; interpret nongated perfusion if valid. |
| PET/CT misregistration | Defect follows CT boundary, not coronary territory | Re-register, regenerate the attenuation map and reconstruct; moving only the display overlay does not correct AC. |
B
Four-question adjudicator
true defect or manufactured?Raw?
Motion, attenuation, truncation, extracardiac activity?
Motion, attenuation, truncation, extracardiac activity?
Gated?
Does wall motion/thickening agree?
Does wall motion/thickening agree?
Corrected?
AC vs non-AC; prone; CT registration?
AC vs non-AC; prone; CT registration?
Physiology?
Coronary territory, ECG, MBF, calcium, prior?
Coronary territory, ECG, MBF, calcium, prior?
Worked example Apparent apical defect is tiny, fixed and has preserved thickening; apex is thin on CT and defect remains at the true apex → apical thinning is favored. Confirm quality and clinical context before excluding a small infarct.
The workstation cannot reacquire the patient. Gating can help separate fixed attenuation from scar; it cannot prove that a rest/stress position mismatch is not ischemia, because post-stress wall motion may already have normalized. Quantitation scores the departure—it does not name or repair the cause. A mismatched camera, collimator, tracer, position, correction, reconstruction, software database, axes, or contours can also manufacture disease; inspect the source slices and segmentation.
Flow is quantitative physiology, not a binary stenosis detector Absolute MBF and MBFR (also called MFR) integrate focal epicardial stenosis, diffuse atherosclerosis, microvascular function, resting workload and technical validity. MBFR = stress MBF/rest MBF.
A
Interpret rest MBF, stress MBF and MBFR together
three numbers, one physiology| Pattern | Relative perfusion | Flow pattern | Favored physiology after QC |
|---|---|---|---|
| Focal epicardial | Regional reversible defect | Regional stress MBF/MFR reduced | Flow-limiting stenosis in matching territory. |
| Balanced multivessel | May look uniform | Global stress MBF and MFR depressed | Diffuse severe epicardial disease; integrate calcium/anatomy. |
| Microvascular/diffuse | Normal or mild diffuse heterogeneity | Global reduction without focal defect | CMD/diffuse atherosclerosis after excluding inadequate stress/technical cause. |
| High resting flow | Often normal | Low MFR but preserved stress MBF | Tachycardia, hypertension, anemia or other increased rest workload. |
B
ASNC 2025 MBFR bins
Rb-82-focused practice guidance| Global MBFR | Practice interpretation | Relative risk |
|---|---|---|
| >2.0 | Normal | Low |
| 1.7–2.0 | Mildly abnormal | Intermediate |
| 1.2–<1.7 | Abnormal | High |
| <1.2 + perfusion defect | Highly abnormal | Very high |
| <1.2 without perfusion defect | Consider nondiagnostic/indeterminate | First exclude failed hyperemia/QC |
Transport warning These ASNC 2025 bins are Rb-82-focused practice guidance, not universal constants. Use tracer-, kinetic-model-, camera-, reconstruction- and software-specific validation plus the laboratory’s normal database; report the actual rest/stress values and technical validity.
Board trap A low MBFR is a ratio, not a diagnosis. A focal numerator failure, globally blunted hyperemia, or an inflated resting denominator can produce the same number.
A
Perfusion–metabolism matrix
FDG needs uptake stimulationPerfusion NORMAL · FDG NORMALnormal match Concordant preserved delivery and glucose use: viable myocardium.
Perfusion ↓ · FDG PRESERVED/↑mismatch Hibernating but metabolically viable myocardium favored—the classic salvageable pattern.
Perfusion ↓ · FDG ↓matched defect Scar favored; grade depth and extent because mild reduction is not the same as absent uptake.
Perfusion NORMAL · FDG ↓reverse mismatch Nonspecific: consider LBBB, remodeling, insulin resistance or failed metabolic preparation.
B
Make the FDG study diagnostic
stimulate viable cellsScreen & fastDocument fasting, diabetes drugs/insulin, HF stability, IV access and a hypoglycemia rescue plan.BEFORE ARRIVAL / CHECK-IN
Baseline glucoseMeasure—do not guess. Choose the validated oral-glucose/insulin algorithm or euglycemic clamp pathway.T = 0
Load & recheckGive glucose/insulin only per protocol; remeasure and correct safely. Record every value, dose and time.PROTOCOL-DEFINED
FDG → uptake → scanAdminister when metabolic conditions are acceptable; quiet uptake and acquisition commonly follow about 45–60 min later, per site protocol.LOCAL VALIDATION RULES
Diagnostic metabolism
Diffuse, adequately stimulated myocardial uptake with interpretable perfusion allows segment-by-segment matching.The biology is visible.Failed preparation
Globally poor or patchy uptake can mimic scar or reverse mismatch. Check glucose, insulin, timing, infiltration and motion before assigning tissue fate.Repeat may be safer than overcalling scar.Worked example Inferior perfusion score 3 but FDG score 1 → a two-grade mismatch supports viable hibernation. This semiquantitative difference is descriptive; it does not by itself prove revascularization will improve survival or symptoms.
Tip & trick Viability is one input to a Heart Team decision. Coronary anatomy, completeness of revascularization, scar burden, LV remodeling, comorbidity, symptoms and patient goals remain decisive.
A
Choose the test that answers the next question
patient-centered, not modality-centered| Clinical feature | Best nuclear contribution | Selection nuance |
|---|---|---|
| Exercise-capable | Symptoms, ECG, workload and hemodynamics plus perfusion | Exercise ECG alone may suffice in selected low-risk patients. |
| Prior CAD / CABG | Ischemic burden, scar, flow and serial comparison | Map graft/native anatomy; cath when high-risk actionable anatomy is the immediate question. |
| LBBB, pacing, attenuation risk | Vasodilator PET when available; modern AC/CZT SPECT where validated | Choose by local quality, body habitus, rhythm and anatomy. |
| Possible diffuse CAD / CMD | PET MBF/MBFR directly tests global and regional physiology | Requires a validated flow program; invasive coronary-function testing or stress CMR may fit the pathway. |
Unit-dose Tc-99m SPECTRadiopharmacy/delivery + dose clock; longer camera/room time
Rb-82 generator PETGenerator/service are time-linked fixed costs; fast throughput spreads them
F-18 PETCyclotron/radiochemistry or regional delivery; geography and decay set usable yield
B
Three money ledgers—never substitute one for another
cost ≠ payment ≠ patient price1 · True lab cost
OPERATIONS LEDGERCapital/lease, service, facility, QC/compliance, tracer and delivery, stress drug, consumables, staff/reader time, decay/no-shows, nondiagnostic repeats and downtime.Ask: cost per completed diagnostic study at actual throughput?2 · Payer reimbursement
CONTRACT / POLICY LEDGERFacility and professional payment, HCPCS/APC packaging, site of service, payer contract, coverage and add-ons. Payment can be above or below the lab’s cost.A CMS threshold or code is not a market quote for tracer.3 · Patient out-of-pocket
BENEFIT-DESIGN LEDGERDeductible, copay/coinsurance, network, authorization, site and supplemental coverage. Estimate from the patient’s plan and performing facility.Never infer the patient bill from acquisition cost or Medicare payment.Average cost/completed study = [Fperiod + ΣVcompleted + Wdecay/no-show + Rrepeat] / Ncompleted diagnostic studies
Throughput changes the fixed-cost denominator; short half-lives make schedule gaps and failed studies economically visible.
Throughput changes the fixed-cost denominator; short half-lives make schedule gaps and failed studies economically visible.
CY 2026 Medicare HOPD payment policy—not a price list The OPPS diagnostic-radiopharmaceutical packaging threshold is $655 per day. HCPCS C9176 provides a $10 per study-dose add-on when qualifying Tc-99m uses Mo-99 with at least 50% domestically produced, non-HEU source. These are payment-policy parameters—not tracer acquisition cost, chargemaster price, patient out-of-pocket amount or a reimbursement guarantee.
Worked decision Persistent angina, nonobstructive CCTA, diabetes and normal relative SPECT: PET MPI with validated MBF/MBFR can answer diffuse-disease/CMD physiology. Appropriateness identifies a useful test; access, local validity, radiation, alternatives and patient cost still shape the final choice.
A
Post-PCI / CABG interpretation
territories are remodeledKnow anatomy
Native stenoses, graft origins/targets, stents, dominance, infarcts and time since procedure.Expect complexity
Competitive flow, graft/native disease, collateralization and peri-infarct ischemia blur default territories.Compare
Use identical slices/protocol where possible; state whether defect, flow, EF or volumes truly changed.1 · Draw the plumbing LIMA→LAD, SVG→OM and SVG→RPDA; a known inferior infarct gives a stable SRS of 8. Default native-vessel polar-map borders are now only a starting hypothesis.
2 · Anchor the baseline Six months after CABG, same tracer/stressor/reconstruction: SSS 8, SRS 8, SDS 0. Inferior scar is fixed; no convincing reversibility.
3 · Quantify the new symptom study Three years later: SSS 13, SRS 8, SDS 5 ≈ 7.4% LV reversible, concentrated in two anterolateral segments; motion, gating and attenuation correction are valid.
4 · Report change + consequence New limited anterolateral ischemia versus the post-CABG baseline; correlate with the OM graft/native LCx and current symptoms. Do not label it “LCx ischemia” without the operative/anatomic map.
Compared with the [date] post-CABG study, inferior scar is unchanged; a new two-segment anterolateral reversible abnormality is present (SDS 5, ≈7% LV), with preserved [or changed] LV function. Correlate with SVG–OM/native LCx anatomy.
B
Heart failure and cardiotoxic therapy
phenotype, do not over-attributeWhat ERNA does well
Count-based serial LVEF when labeling, projection, gating, background correction and software are kept constant. It is useful when acoustic windows are poor or a highly repeatable legacy series already exists.Trend one validated method.What it does not supply
No strain, valves, tissue characterization, pericardium or full HF phenotype; planar chamber overlap limits RV assessment. Integrate echo/CMR, biomarkers, symptoms and therapy timing.EF is one surveillance signal.BaselineSinus rhythm; same-camera ERNA LVEF 61%; labeling, contours and background valid.PRE-THERAPY
Early trendSame method LVEF 58%; no technical warning. Preserve the acquisition/analysis recipe.CYCLE 4
Apparent fallLVEF 52%, but new AF, broad beat rejection and flicker make the number noncomparable.CYCLE 6 · INVALID TREND POINT
Adjudicated repeatAfter rate/rhythm stabilization, valid same-method LVEF 54%. Now report a confirmed 7-point decline and integrate with echo/GLS, biomarkers and oncology/HF decisions.PROMPT REPEAT
Tip & trick Never average a technically invalid EF into a trend. Show the serial values, flag rhythm/acquisition differences, and state whether change exceeds expected laboratory repeatability.
The trial question matters more than the scan label. Prognostic association, diagnostic accuracy, test strategy and treatment selection are different claims. A high-risk image can predict events without proving that an imaging-triggered procedure improves survival.
A
What the landmark studies actually established
result + boundary| Study | Question and result | Practice lesson · do not overclaim |
|---|---|---|
| DIAD · 2009 n=1,123 | Screen asymptomatic type 2 diabetes with adenosine SPECT MPI? Event rates were low and screening did not reduce cardiac death/nonfatal MI. | Do not screen low-risk asymptomatic diabetes routinely. This did not test symptomatic or otherwise high-risk patients. |
| WOMEN · 2011 n=824 | In low-risk women able to exercise, initial exercise ECG versus exercise SPECT yielded similarly low 2-year event rates. | Use the lower-cost, no-radiation exercise ECG strategy when the ECG is interpretable and exercise is adequate. |
| COURAGE MPI n=314 substudy | PCI + optimal medical therapy reduced ischemia more than medical therapy alone; ≥5% ischemia reduction tracked with better outcomes in exploratory analyses. | Selected substudy, not a randomized proof that ischemia reduction itself mediates a survival benefit. |
| ISCHEMIA · 2020 n=5,179 | Moderate/severe ischemia: an initial invasive strategy did not lower the main composite or all-cause death versus a conservative strategy over the initial follow-up. | Ischemic burden alone is not an automatic PCI mandate; symptoms, anatomy, LV function and exclusions still govern. |
| PARR-2 · 2007 n=430 | FDG PET-assisted management in severe LV dysfunction did not significantly reduce the primary composite overall; benefit signals appeared with adherence and experienced-center use. | A viability test cannot help if its recommendation is ignored—and the subgroup signal is not the primary result. |
| STICH viability long-term follow-up | Viable myocardium tracked with EF improvement regardless of assignment; viability did not identify CABG survival benefit, and EF improvement was not associated with survival. | Do not use viability as a solitary yes/no gate for CABG; anatomy, scar, remodeling, surgical risk and goals remain central. |
| AURORA · 2023 578 evaluable | F-18 flurpiridaz PET had higher sensitivity than SPECT and noninferior specificity for CAD, with improved ROC performance including women and patients with obesity. | A diagnostic-accuracy trial supported the 2024 U.S. approval; it was not a randomized outcomes trial. |
B
A five-question trial decoder
read before quotingPopulationsymptomatic? known CAD? LV dysfunction? exclusions?
Randomized what?test, treatment, or test-guided strategy?
Endpointaccuracy, ischemia change, symptoms, MI, death?
Adherencewas advice followed and crossover handled?
Interactiondid the biomarker truly select treatment benefit?
Prognostic evidence
“More ischemia predicts more events” can be true. It establishes risk association after adjustment and within the studied population.Useful for risk; not automatically causal.Predictive evidence
To claim imaging selects a treatment benefit, look for a randomized treatment-by-imaging interaction—not merely better outcomes among patients whose scan improved.Selection claims demand interaction evidence.Worked board stem A stable patient with moderate ischemia, preserved EF and controlled symptoms asks whether PCI prolongs life. ISCHEMIA argues against promising survival benefit from an automatic invasive strategy; review left-main exclusion/anatomy, symptom burden, medical therapy and shared goals.
Memory hook DIAD/WOMEN restrained testing; PROMISE found no outcome advantage for an initial anatomic versus functional strategy (not a nuclear-specific treatment trial); ISCHEMIA restrained automatic invasion; PARR-2/STICH restrained viability as a lone revascularization gate; AURORA advanced tracer accuracy.
The planar image suggests; tomography localizes. Every study needs SPECT, preferably SPECT/CT where available, to prove that activity is in the ventricular wall rather than blood pool, ribs or sternum. Amyloid: illustrated localization examples · diagnostic discussion.
A
Tracer passports and acquisition
do not transfer cutoffsTc-99m PYP
U.S./Canada predominantPlanar visual grade + SPECT localization. H/CL has validated adjunctive use only under a PYP protocol.
Tc-99m DPD
Europe and elsewhereVisual Perugini grade + SPECT. Do not import PYP H/CL thresholds.
Tc-99m HMDP/HDP
regional availabilityVisual grade + SPECT under tracer-specific guidance; not numerically interchangeable with PYP.
Tc-99m MDP
ordinary bone agentNot an accepted substitute for PYP/DPD/HMDP in the ATTR nonbiopsy pathway.
Inject10–20 mCi (370–740 MBq) PYP, DPD or HMDP; record tracer, activity, time and infiltration.T = 0
Acquire at 2–3 hPlanar chest plus SPECT/SPECT-CT is the standardized default. A validated 1-h PYP pathway may be used by experienced centers.PROTOCOL-DEFINED
Delay if blood poolIf 1-h images show persistent cavity activity or uncertainty, repeat at 3 h rather than forcing a grade.QUALITY GATE
Localize before gradeReview transaxial/short-axis and orthogonal planes: wall, cavity, ribs, sternum, infarct and calcification.SPECT REQUIRED
B
Perugini visual grade
compare heart with ribs| Grade | Myocardium versus ribs | Meaning |
|---|---|---|
| 0 | No myocardial uptake | Does not exclude all amyloid |
| 1 | Less than ribs | Equivocal |
| 2 | Equal to ribs | Potential ATTR only after localization + AL screen |
| 3 | Greater than ribs | Same diagnostic gates apply |
H/CL is an adjunct—not the diagnosis
For PYP only, ≥1.5 at 1 h or ≥1.3 at 3 h may support interpretation after SPECT confirms myocardial uptake. Do not calculate a diagnostic H/CL when uptake is only blood pool; a definite visual grade 2/3 does not require it.How to draw it
Place a circular/elliptical ROI over the heart on anterior planar imaging; mirror the same shape and area over the contralateral chest, avoiding sternum/ribs when possible. H/CL = mean heart count density ÷ mean contralateral count densityWorked H/CL Heart ROI mean count density 24,600 and mirrored chest mean count density 16,000 → H/CL = 24,600/16,000 = 1.54. At 1 h this crosses the adjunctive PYP threshold, but nonbiopsy ATTR-CM requires definite grade 2/3 myocardial uptake on SPECT/SPECT-CT, a compatible phenotype and the complete negative monoclonal screen.
Blood pool masquerade
Cavity-centered activity fills LV/RV chambers, follows vessels and often diminishes on delayed imaging. Low output and renal dysfunction make it common.Activity inside the chamber—not the ventricular wall.True myocardial retention
Orthogonal tomograms show activity in the ventricular wall, circumferentially or regionally—not merely inside the cavity. SPECT/CT can resolve rib/sternal overlap.Activity in the walls.Factoid PYP’s U.S. label historically centers on bone imaging, acute myocardial infarction and blood-pool applications; its ATTR role comes from a guideline-defined evidence pathway. The binding mechanism is still incompletely explained—microcalcification and fibril composition probably contribute.
Nonbiopsy ATTR-CM is a three-gate diagnosis — compatible phenotype + definite grade 2/3 myocardial uptake on SPECT/SPECT-CT + no monoclonal protein by the complete screen. Fail any gate and tissue typing or further evaluation replaces the shortcut. Amyloid: recognition & diagnostic pathway · tissue & strain atlas.
A
The diagnostic pathway
exclude AL urgently1 · Recognize
HFpEF/LVH, apical-sparing strain, low voltage relative to wall thickness, bilateral carpal tunnel, spinal stenosis, biceps rupture, neuropathy or family history.
HFpEF/LVH, apical-sparing strain, low voltage relative to wall thickness, bilateral carpal tunnel, spinal stenosis, biceps rupture, neuropathy or family history.
2 · Screen for AL
Serum free light-chain κ/λ ratio interpreted with eGFR + serum immunofixation + urine immunofixation. SPEP/UPEP alone is inadequate. The combined screen has ≈99% sensitivity for detecting the abnormal precursor in AL, not a universal 99% negative predictive value.
Serum free light-chain κ/λ ratio interpreted with eGFR + serum immunofixation + urine immunofixation. SPEP/UPEP alone is inadequate. The combined screen has ≈99% sensitivity for detecting the abnormal precursor in AL, not a universal 99% negative predictive value.
3 · Localize tracer
PYP/DPD/HMDP with definite myocardial grade 2/3 on SPECT or SPECT-CT. Planar grade or H/CL alone does not pass.
PYP/DPD/HMDP with definite myocardial grade 2/3 on SPECT or SPECT-CT. Planar grade or H/CL alone does not pass.
4 · Type and act
All gates pass → ATTR-CM without biopsy; then TTR sequencing and counseling regardless of age. Discordant/equivocal → CMR and/or biopsy with mass-spectrometry typing.
All gates pass → ATTR-CM without biopsy; then TTR sequencing and counseling regardless of age. Discordant/equivocal → CMR and/or biopsy with mass-spectrometry typing.
When a monoclonal process is possible
Positive immunofixation, a low κ/λ ratio or a clonal/otherwise concerning FLC pattern prevents the shortcut. A borderline high ratio in CKD needs renal-range and hematology review; if clonality cannot be excluded, obtain tissue with definitive typing. Grade 2/3 uptake can occur in AL.Negative or grade 1 scan
Does not exclude early ATTR, AL, or certain TTR variants. If phenotype is convincing, proceed with expert review, CMR and biopsy rather than reassuring from scintigraphy alone.B
Mimics and misses
pattern predicts the trap| Pattern / cause | Why it misleads | Rescue move |
|---|---|---|
| Blood pool | Low output, renal dysfunction or early timing leaves cavity activity that overlaps myocardium on planar views. | Orthogonal SPECT/SPECT-CT; delay to 3 h when needed. |
| Injury / toxicity | Recent MI, pericarditis and hydroxychloroquine or other drug-associated myocardial injury can retain PYP. | Map pattern to anatomy, medication and timing; do not relabel focal or inflammatory uptake as diffuse ATTR. |
| Rib/sternum | Fracture, metastasis or normal bone projects over the heart. | Review rotating data and CT anatomy; redraw ROIs if used. |
| AL / rare amyloids | Bone-tracer uptake is not absolutely TTR-specific. | Complete monoclonal testing and biopsy typing when abnormal or discordant. |
| Early/variant ATTR | Some variants and early disease may have little bone-tracer retention. | Do not stop at grade 0/1 when phenotype/genotype is compelling. |
Case A · scan positive, gate failsGrade 3 PYP with definite wall uptake; serum immunofixation detects an M-protein. Not nonbiopsy ATTR. Urgent tissue typing is required because AL remains possible.
Case B · scan negative, phenotype persistsGrade 0 PYP in a patient with pathogenic TTR variant, neuropathy and CMR evidence of infiltration. Negative does not end the workup. Expert review and biopsy may be appropriate.
Definite diffuse myocardial [PYP] uptake on SPECT, visual grade 3 at [3 h]. Findings are strongly suggestive of ATTR cardiac amyloidosis only if serum free light-chain ratio interpreted with eGFR and serum/urine immunofixation exclude a monoclonal process.
True myocardial uptake is [grade 1 / uncertain grade 1 versus 2], with [persistent blood pool / focal rib overlap]. This study cannot establish nonbiopsy ATTR-CM. Correlate with complete monoclonal testing and consider repeat optimized imaging, CMR or biopsy according to clinical suspicion.
Monitoring trap Routine serial bone-tracer scans are not established for treatment response. Group-level change does not overcome substantial patient-level variability; follow clinical status, biomarkers and cardiac structure/function while research standards mature.
Cardiac amyloid PET is promising but investigational/off-label. Brain amyloid-tracer approval does not create a cardiac indication. No universal cardiac positivity cutoff or validated routine treatment-response threshold exists. Amyloid: established diagnostic pathway.
A
Two tracer families answer different questions
bone affinity ≠ fibril bindingBone-avid SPECT · PYP/DPD/HMDP
Best-established nonbiopsy lane for ATTR after AL exclusion; inexpensive/widely accessible in many regions. Uptake is indirect, AL sensitivity is poor, early/variant ATTR may be missed and serial burden is unreliable.Clinical strength: gated ATTR diagnosis.Amyloid-binding PET
Targets amyloid fibrils more directly and can show signal in AL as well as ATTR, with dynamic/whole-body quantitation. Blood-pool correction, tracer-specific thresholds, availability and outcome validation remain unresolved.Research promise: detection + burden + change.C-11 PiB
T½ ≈20 minClassic amyloid-binding PET research tracer; requires an on-site cyclotron and rapid synthesis.
Florbetapir / florbetaben
T½ ≈110 minBrain β-amyloid agents studied off-label in cardiac AL/ATTR; regional delivery is practical.
Flutemetamol
fibril-binding PETCardiac research results depend on tracer, subtype, timing and analytic method; do not pool thresholds.
Evuzamitide / AT-01
investigational pan-amyloidPeptide PET designed to bind systemic amyloid deposits; long-lived I-124 enables multiorgan imaging but adds dosimetry/logistics.
B
How PET tries to measure burden
validate every denominator| Measure | What it attempts | Main failure mode |
|---|---|---|
| SUV / SUV ratio | Static tissue concentration, normalized to injected activity/body metric; target-to-blood or target-to-background may improve contrast. | Timing, residual blood pool, body-size convention and scanner calibration change the number. |
| Retention index | Myocardial activity relative to integrated arterial input over time. | Requires valid dynamic framing, input curve, motion correction and model assumptions. |
| Kinetic binding | Separate delivery/washout from binding using compartment or graphical models. | Complexity, low counts, metabolites and no standardized clinical normal range. |
| Whole-body burden | Map heart plus soft tissue, nerve, kidney, liver or marrow deposits. | Organ-specific background and subtype biology make one universal threshold unlikely. |
Potentialdetect AL as well as ATTR
Potentialearlier signal than wall thickening
Potentialquantify whole-body burden
Unknownminimum meaningful serial change
Requiredoutcome-linked prospective validation
Worked discordance PYP is grade 0, an investigational amyloid PET scan is positive, and a monoclonal protein is present. This does not establish ATTR; it raises suspicion for amyloid (including AL) and should direct expert biopsy with definitive typing.
Registry check · 17 Oct 2026 CArdiag (NCT05184088; florbetaben in cardiac AL) and REVEAL (NCT06788535; I-124 evuzamitide) are listed complete but without posted results. A florbetaben test–retest study (NCT06790394) and a systemic evuzamitide study (NCT05758493) are recruiting. Completion status is not efficacy evidence.
A
Suppress physiologic myocardium
prep quality is diagnostic qualityDiet
Validated high-fat, very-low/no-carbohydrate meals—often two meals with >35 g fat and <3 g carbohydrate each.
Validated high-fat, very-low/no-carbohydrate meals—often two meals with >35 g fat and <3 g carbohydrate each.
Fast
Then fast 4–12 h; an alternative is prolonged fast >18 h per validated pathway.
Then fast 4–12 h; an alternative is prolonged fast >18 h per validated pathway.
Optional heparin
UFH 50 IU/kg IV ≈15 min before FDG only if no contraindication/HIT; incremental suppression benefit is uncertain.
UFH 50 IU/kg IV ≈15 min before FDG only if no contraindication/HIT; incremental suppression benefit is uncertain.
Pair
Document adherence/glucose; pair FDG with rest perfusion and inspect extracardiac disease.
Document adherence/glucose; pair FDG with rest perfusion and inspect extracardiac disease.
Example prep-day menu
Meal 1: 3 eggs cooked in 2 Tbsp olive oil or butter + plain salmon; water. Meal 2: plain beef or chicken + 2 eggs, prepared/finished with 2 Tbsp olive oil; water. These portions exceed 35 g fat before counting the meat/fish; confirm <3 g carbohydrate and exact macros against the lab sheet. Then follow the lab’s fast. Avoid bread/cereal, rice/pasta/potatoes, fruit, dairy, sweets, sweetened drinks, alcohol and sugary sauces. Local instructions, allergy needs and diabetes plans supersede this example.Why optional heparin?
Unfractionated heparin acutely releases endothelial lipoprotein lipase, which hydrolyzes circulating triglycerides and raises free fatty acids. The normal myocardium shifts toward fatty-acid oxidation (the glucose–fatty-acid/Randle cycle), helping suppress physiologic FDG uptake. The incremental benefit beyond excellent diet/fasting is uncertain; screen bleeding risk and prior HIT.Factoid The intent of UFH here is metabolic—not treatment of sarcoidosis or thrombosis—but it remains pharmacologically anticoagulant, with bleeding, thrombocytopenia and HIT risk. It cannot rescue a carbohydrate-containing meal, and many validated protocols omit it.
B
Read perfusion and metabolism as a pair
original pattern atlas◎○
Normal P · no FDGSuppressed myocardium with normal perfusion. No active pattern detected.
◐○
Defect P · no FDGFixed perfusion loss without inflammation signal. Scar favored; exclude infarct/artifact.
◎•
Normal P · focal FDGFocal or multifocal noncoronary uptake after good suppression. Inflammation favored; etiology unresolved.
◐•
Defect P · focal FDGInflammatory activity at/around injured myocardium. Inflammation + injury; high risk, not specific.
Diffuse, homogeneousfailed suppression until proved otherwise
Focal, multifocalmap noncoronary distribution
RV uptakeraises risk in the right context
Extracardiacnodes/lung can corroborate and guide biopsy
Serial scanmatch prep, timing and treatment state
Worked example Basal septal perfusion defect with matching focal/multifocal noncoronary FDG and RV uptake after excellent suppression → active inflammatory disease with scar and a high-risk pattern. FDG supports inflammation, not sarcoid etiology by itself: exclude CAD/hibernation/artifact and integrate CMR, rhythm/device data and extracardiac pathology.
Tip & trick Compare serial studies only when preparation, uptake time, acquisition and treatment state are sufficiently similar. SUV change alone is not treatment success.
A
Where nuclear infection imaging adds value
anatomy + microbiology remain central| Scenario | FDG PET/CT value | Major limitation |
|---|---|---|
| Prosthetic valve | Perivalvular infection and extracardiac embolic/source survey | Recent surgery, adhesives and inflammation can be false positive. |
| CIED | Pocket vs lead involvement; metastatic infection | Small lead vegetations and postoperative uptake; antibiotics reduce sensitivity. |
| LVAD | Driveline, pump/pocket and cannula distribution | Metal attenuation artifact; sterile inflammation. |
| Vascular graft | Focal/intense heterogeneous graft uptake and extent | Diffuse linear postoperative uptake may persist. |
| Native valve | Extracardiac complications may help | Limited sensitivity for small mobile vegetations; TEE/blood cultures dominate. |
B
FDG versus labeled leukocytes
biology changes workflow and costFDG PET/CT · one perishable molecule
PrepareCardiac suppression when myocardium is in the field; check glucose.hours before
Inject + distributeFDG delivery has a decaying clock; uptake interval is protocol-defined.same day
AcquireHigh-resolution whole-body survey; verify suspected device/prosthesis uptake on non-AC images.one visit
Labeled WBC SPECT/CT · the patient’s own cells
Draw + labelSeparate leukocytes, radiolabel ex vivo under controlled blood-handling conditions.laboratory intensive
ReinjectReturn labeled cells with identity, sterility and radiation controls.same day
Serial imagesEarly/delayed ± next-day acquisition according to tracer and validated acquisition guidance.multiple slots
FDG clock
decay + courierMissed slots waste a prepared dose; nearby production and throughput matter.PET efficiency
whole bodyOne acquisition can map the cardiac focus, emboli and an extracardiac source.Cell laboratory
blood handlingSeparation, labeling, QC and reinjection add skilled labor and biosafety complexity.Serial SPECT
time + capacityMultiple acquisitions consume patient time and camera slots. Actual price/payment is site- and payer-specific.Worked example Focal FDG at a prosthetic sewing ring plus splenic and vertebral foci strongly supports disseminated prosthetic-valve infection, but cultures, TEE/CT anatomy and surgical evaluation still define management.
Board trap A negative FDG study after prolonged antibiotics does not exclude infection. Report treatment timing and test limitations.
A
Patterns beyond epicardial CAD
nuclear phenotype needs context| Phenotype | Potential nuclear finding | Integrate with |
|---|---|---|
| Hypertrophic CM | Regional ischemia, reduced MFR, apical/midventricular scar-related defects | Echo/CMR morphology, gradients, symptoms and arrhythmia risk. |
| Dilated CM | Patchy defects, LV dilation/dysfunction, reduced global flow | CCTA/cath when CAD question remains; CMR tissue phenotype. |
| RV pressure load / PH | Perfusion-tracer RV uptake, dilation, septal flattening context | Echo and right-heart catheterization; not a PH subtype test. |
| Amyloid / sarcoid | Targeted tracer patterns | Disease-specific gates on pages 27–30. |
| Autonomic innervation | I-123 MIBG heart-to-mediastinum ratio and washout in selected settings | Protocol/system standards; not routine universal HF testing. |
B
I-123 MIBG sympathetic innervation
uptake-1 + vesicular storageWhat the tracer follows
Iobenguane resembles norepinephrine: presynaptic uptake-1 transport, vesicular storage and release/washout reflect cardiac sympathetic nerve integrity. Reduced uptake and faster washout are adverse signals in studied HF populations.It images nerve biology, not perfusion.Why numbers do not travel freely
Collimator energy response, scatter correction, ROI placement, acquisition timing and calibration alter H/M. Use validated camera-specific conversion/normal limits and the applicable jurisdictional indication.Standardize before serial comparison.Heart-to-mediastinum ratio
H/M = mean heart count density ÷ mean upper-mediastinal count densityDraw reproducible planar ROIs; record early/delayed time and collimator. H/M is not an ejection fraction.
Washout rate
DCF = 2Δt/13 h; Clate,corr = (Hlate−Mlate) × DCFWR = [(Hearly−Mearly) − Clate,corr] ÷ (Hearly−Mearly) × 100%
Use the same background-corrected count-density and ROI method at both times.
Worked H/M Delayed heart ROI mean 180 counts/pixel and mediastinum 100 → H/M = 1.80. It is interpretable only against a system- and protocol-specific normal database; a textbook cutoff copied across collimators is unsafe.
Worked WR Early H−M = 200−50 = 150; late H−M = 130−40 = 90 at Δt = 4 h. DCF = 24/13 ≈ 1.24, so corrected late counts = 90×1.24 = 111.6 and WR = (150−111.6)/150 = 25.6%. Match the laboratory’s validated timing and method.
Repaired TOF caveat Increased perfusion-tracer RV uptake may reflect true RV hypertrophy/pressure work, residual RVOT obstruction or pulmonary-regurgitation volume load—or simply low LV uptake. It is not RV volumetry, does not prove ischemia or VSD-patch scar, and is no standalone pulmonary-valve-replacement trigger; integrate echo/CMR RV size/function, residual lesions, exercise and rhythm data.
Registry status checked · 17 October 2026. “Recruiting” means a question is being studied. “Completed” means data collection ended. Neither means the result is positive, peer reviewed or ready for practice.
A
The newest change already in practice
approval ≠ outcome benefitPhase 3 · AURORA730 enrolled; 578 evaluable. Flurpiridaz PET sensitivity was 80.3% versus 68.7% for SPECT; specificity was noninferior (63.8% versus 61.7%). ROC performance improved, including in women and patients with obesity.
Regulatory step · 27 Sep 2024The FDA approved F-18 flurpiridaz for rest/stress PET MPI in adults with known or suspected CAD, using pharmacologic or exercise stress.
Procedure standard · 2025SNMMI/ASNC/SCCT published acquisition, exercise/pharmacologic stress, image-quality and reporting guidance. Local validation still governs quantitative flow.
Next unanswered claimWill broader access, exercise PET and quantitative MBF improve selection, equity, downstream testing or outcomes compared with high-quality existing strategies?
B
Amyloid studies with data to watch
registry status, not results| Study · status | Question | What could change practice |
|---|---|---|
| CArdiag NCT05184088 completed · no posted results | F-18 florbetaben in cardiac AL; actual enrollment 244, registry completion May 2026. | Prospective diagnostic performance, standardized quantitation and incremental value versus current biopsy/imaging pathways. |
| REVEAL NCT06788535 completed · no posted results | I-124 evuzamitide cardiac amyloid imaging; actual enrollment 204, registry completion April 2026. | Subtype-aware accuracy against a credible reference standard plus reproducible burden measures. |
| Florbetaben retest NCT06790394 recruiting | Small test–retest cardiac amyloid study; estimated enrollment 15. The estimated September 2026 completion has passed, but the registry still reports recruiting. | Repeatability tight enough to distinguish biology from measurement noise—a prerequisite for therapy monitoring. |
| Evuzamitide systemic NCT05758493 recruiting | Whole-body I-124 evuzamitide across systemic amyloid; estimated enrollment 150, expected completion 2028. | Validated organ-specific interpretation and proof that quantified burden adds actionable information. |
C
What would earn routine adoption?
five evidence gatesAccuracyprospective + blinded reference standard
Repeatabilityscanner/tracer/site reproducibility
Incrementadds beyond labs, echo, CMR, PYP or biopsy
Actionresult changes a defined decision
Outcomebetter care, not merely prettier images
Other promising targets
FAPI PET for fibroblast activation, novel infection/thrombus probes, total-body dynamic PET and digital-detector advances can reveal new biology.Interesting signal; indication-specific validation required.Board-safe language
Name tracer, target, indication, jurisdiction and study status. Say “investigational” when appropriate and date pipeline claims.Never convert an abstract or registry date into a guideline.Factoid An old tracer can produce a new standard (PYP), and a new tracer can remain only an attractive picture. Clinical maturity depends on the evidence chain, not the isotope’s novelty.
A
Report skeleton
answer the indicationINDICATION — symptoms/diagnosis; known CAD/revascularization; comparison __.
STRESS — exercise protocol/workload or drug/dose; symptoms; HR/BP; ECG; adequacy; reversal __.
TRACER/ACQUISITION — tracer, activity, timing; SPECT/PET; gating; AC/CT; image quality and limitations __.
PERFUSION — location, extent, severity, reversibility; SSS/SRS/SDS or quantitative burden __.
FUNCTION — LV/RV size; EDV/ESV; LVEF; motion/thickening; post-stress change; TID using local normal __.
FLOW — rest/stress MBF + MFR by territory/global; model and technical validity; hemodynamic context __.
CT — coronary calcium when valid; actionable extracardiac findings __.
IMPRESSION — normal/abnormal; ischemia/scar burden; high-risk features; comparison; precise next implication __.
STRESS — exercise protocol/workload or drug/dose; symptoms; HR/BP; ECG; adequacy; reversal __.
TRACER/ACQUISITION — tracer, activity, timing; SPECT/PET; gating; AC/CT; image quality and limitations __.
PERFUSION — location, extent, severity, reversibility; SSS/SRS/SDS or quantitative burden __.
FUNCTION — LV/RV size; EDV/ESV; LVEF; motion/thickening; post-stress change; TID using local normal __.
FLOW — rest/stress MBF + MFR by territory/global; model and technical validity; hemodynamic context __.
CT — coronary calcium when valid; actionable extracardiac findings __.
IMPRESSION — normal/abnormal; ischemia/scar burden; high-risk features; comparison; precise next implication __.
B
Closed-loop quality
the report is not the finishUrgent communication
Large high-risk ischemia, severe stress instability, new severe dysfunction or other critical finding → named recipient, time, read-back and action documented.Laboratory metrics
QC completion, nondiagnostic/repeat rates, dose, stress events, report turnaround, discrepancies, normal databases and peer review.Incidental CT
Define CT quality and scope. Route actionable lung, aortic, breast or other findings; do not overread an attenuation-only scan.Abnormal, high-risk study: moderate-size, severe reversible anterior/anteroseptal defect (≈18% LV) with transient ischemic dilation and stress LVEF fall. Dr X notified at 14:32; result and recommended urgent clinical review were read back.
Relative perfusion is diagnostic and shows no regional defect. Quantitative MBF/MBFR is uninterpretable because the rest input curve is truncated despite reprocessing; no flow-based risk claim is made. Consider repeat flow acquisition only if it would change care.
Recognizecritical result or active stress emergency
Stabilizestop stress and activate emergency pathway when acute
Reachnamed responsible clinician; escalate if unavailable
Read backfinding, urgency and expected action
Documentrecipient, time, response and escalation
Tip & trick State what is technically valid. If MBF failed but perfusion is diagnostic, report diagnostic perfusion and explicitly mark flow as uninterpretable.
Tc-99m
T½ 6.02 h · 140-keV γMost high-specific-activity Mo-99 comes from reactor fission → generator eluate → cold kit; alternative routes exist.
Rb-82
T½ ≈75 s · β+ → 511 keVSr-82/Rb-82 generator; no delivered daily dose. Rapid PET perfusion + dynamic MBF.
N-13 ammonia
T½ 9.97 min · β+ → 511 keVOn-site cyclotron/radiochemistry. High-extraction PET perfusion + MBF.
F-18
T½ 109.8 min · β+ → 511 keVRegional cyclotron distribution can support FDG and flurpiridaz workflows.
A
Last-minute board grid
numbers + guardrails| Prompt | Answer | Guardrail |
|---|---|---|
| Annihilation | Two 511-keV photons, near 180°, coincidence | Correct attenuation, scatter, randoms, motion and dead time. |
| Vasodilators | Regadenoson 0.4 mg; adenosine 140 µg/kg/min; dipyridamole 0.56 mg/kg/4 min | Screen caffeine, block, bronchospasm, hypotension and agent risks. |
| Scoring | 17 segments; 0–4; SDS=SSS−SRS; score/68×100 | Semiquantitative; adjudicate artifacts. |
| Flow | MBFR (MFR) = stress MBF/rest MBF | Inspect absolute rest + stress MBF and QC before the ratio. |
| ATTR | FLC ratio interpreted with eGFR + serum/urine IFE; then grade 2/3 myocardium on SPECT/SPECT-CT | Positive IFE or clonal FLC pattern → tissue typing; CKD-borderline ratio needs renal-range review. |
| Sarcoid | Suppress myocardium; focal FDG ± perfusion defect | Diffuse homogeneous uptake usually failed prep. |
| Infection | FDG PET/CT for prosthesis/device/LVAD/graft; WBC more specific | Post-op inflammation, antibiotics, native-valve sensitivity. |
| ASNC 2025 Rb-82-focused global MBFR guidance | Interpretation | Risk / next check |
|---|---|---|
| >2.0 | Normal | Low risk |
| 1.7–2.0 | Mildly abnormal | Intermediate |
| 1.2–<1.7 | Abnormal | High |
| <1.2 + defect | Highly abnormal | Very high |
| <1.2, no defect | Consider nondiagnostic/indeterminate | Exclude failed vasodilation/technical failure |
Scope the bins These are Rb-82-focused practice guidance, not universal physiologic constants. Tracer extraction, kinetic model, software implementation, stress adequacy, normal database and local validation can shift interpretation; inspect rest/stress MBF and QC before the ratio.
B
Source hierarchy and reference shelf
current guidance controlsClinical hierarchy
1. Current society guideline/consensus and regulator-approved protocol.2. Multisociety practice points/technical standards.
3. Primary evidence and validated normal limits.
4. Textbooks for durable physics, syllabus and board framing. When thresholds conflict, current guidance wins.
Reference shelf
Jaber & Cerqueira, Nuclear Cardiology Review: A Self-Assessment Tool, 2nd ed (2018) and 1st ed (2013). Used to audit topic coverage only; all prose, schematics, examples and review prompts here are original.Visual media: complete CC/public-domain attribution ledger.
C
The answer that passes
validity before certaintyCan I trust it?
Prep, stress, counts, curves, motion, gating, registration.
Prep, stress, counts, curves, motion, gating, registration.
What is the pattern?
Perfusion/metabolism/targeted uptake with extent and severity.
Perfusion/metabolism/targeted uptake with extent and severity.
Does physiology agree?
Function, MBF/MFR, calcium/anatomy, symptoms and ECG.
Function, MBF/MFR, calcium/anatomy, symptoms and ECG.
What changes?
Risk, urgent communication, next test or management question.
Risk, urgent communication, next test or management question.
Worked example “Regional ischemia is supported by a reversible inferolateral defect and matching low stress MBF; acquisition and attenuation registration are valid. Preserved global MFR lowers concern for balanced disease. Correlate with coronary anatomy and symptoms.”
Final mantra Physics explains the image. Quality control earns the right to interpret it. Integration turns it into patient care.