13.2 Cardiac Function, Viability, and Special Studies
Key Takeaways
- First-pass radionuclide angiography measures right and left ventricular EF and wall motion from a tight IV bolus; MUGA (ERNA) uses labeled RBCs for high-precision LVEF at rest (± stress) and SPECT blood-pool options
- Cardiac shunt quantification compares systemic vs pulmonary flow using first-pass curves when ordered
- Tc-99m PYP planar + SPECT for ATTR cardiac amyloidosis: image ~1 h and/or 3 h; semi-quantitative visual grades and H/CL (heart-to-contralateral lung) ratio concepts support interpretation
- Cardiac sarcoidosis evaluation favors FDG PET with strict dietary/prep protocols; I-123 MIBG assesses cardiac sympathetic innervation
- Viability: Tl-201 rest–redistribution (or stress-redistribution-reinjection pathways) vs FDG PET metabolic imaging after glucose loading/insulin euglycemia prep
13.2 Cardiac Function, Viability, and Special Studies
Quick Answer: First-pass = bolus EF/wall motion (RV & LV). MUGA/ERNA = Tc-99m labeled RBCs, high-precision serial LVEF. Shunt studies use first-pass curve analysis. PYP = ATTR amyloid (1 h / 3 h, visual grade, H/CL). FDG PET = sarcoid (prep!) and viability. MIBG = innervation. Tl-201 rest-redistribution or FDG for viability when revascularization is considered.
Order these studies for function, infiltrate/inflammation, innervation, or hibernating myocardium—not routine CAD screening alone.
First-Pass Radionuclide Angiography
A compact IV bolus (often Tc-99m DTPA, pertechnetate, or lab-chosen first-pass agent) is imaged with rapid frames as activity traverses SVC → RV → lungs → LV → aorta.
| Output | Teaching value |
|---|---|
| RVEF / LVEF | Count-based ejection fractions from time-activity curves |
| Wall motion | Regional qualitative assessment during transit |
| Shunt clues | Abnormal recirculation patterns |
Tech keys: large vein, bolus integrity (no infiltrate, rapid flush), high frame rate, correct ROIs. A fragmented bolus invalidates quantitative EF.
Gated Blood Pool (MUGA / ERNA)
Equilibrium radionuclide angiocardiography (ERNA/MUGA) uses Tc-99m labeled autologous RBCs (in vivo, modified in vivo, or in vitro). After mixing, ECG-gated planar images (classic best septal LAO for EF) sum many beats into one representative cycle.
| Setting | Notes |
|---|---|
| Rest MUGA | Serial LVEF (e.g., chemotherapy cardiotoxicity) |
| Stress MUGA | Exercise or pharmacologic stress with gating |
| SPECT blood pool | Tomographic volumes/wall motion |
| Typical activity | Often ~20–30 mCi Tc-99m RBCs |
Why MUGA endures: excellent LVEF reproducibility when labeling and ROI methods stay consistent. QC includes labeling efficiency, arrhythmia rejection, count density, and background ROI. Highly irregular AF degrades frames—document and apply lab filters.
Labeling pitfalls matter: poor RBC tag leaves free Tc-99m (stomach, thyroid, soft tissue) and undercuts chamber contrast. Verify the labeling method on the order (in vitro kits often give higher efficiency) and image only after adequate equilibration.
Cardiac Shunt Evaluation
Left-to-right shunts alter pulmonary transit on first-pass curves; quantitative methods estimate Qp/Qs. Right-to-left shunts may use Tc-99m MAA (systemic foci after venous injection). Match agent and analysis to the ordered shunt direction.
Cardiac Amyloidosis: Tc-99m PYP
ATTR cardiac amyloid is often Tc-99m PYP-avid; AL is less so—labs combine imaging with monoclonal protein workups. Technologists still must execute timing and SPECT correctly.
| Protocol element | Teaching practice |
|---|---|
| Activity | Often ~10–25 mCi Tc-99m PYP IV |
| Imaging times | ~1 hour and/or ~3 hours planar + SPECT/SPECT-CT |
| Visual grading | Heart vs rib (0–3 style; grade ≥2 at 3 h supports ATTR pattern when criteria met) |
| H/CL ratio | Heart / contralateral lung counts; elevated ratio (classic teaching near ~1.5 at 1 h—use lab cutoffs) supports abnormal retention |
| SPECT role | Confirms myocardial, not blood-pool, uptake |
Note recent MI (classic infarct-avid use of PYP) and keep ROIs consistent.
Planar-only reading can mistake blood-pool activity for myocardial uptake—SPECT (or SPECT/CT) is required to localize tracer to myocardium. Time both 1 h and 3 h sets the same way each visit so visual grades and H/CL ratios remain comparable.
Cardiac Sarcoidosis PET
F-18 FDG PET/CT (± perfusion imaging) detects active myocardial inflammation. Prep is strict and lab-specific: prolonged high-fat, low-carbohydrate diet, fasting, sometimes heparin, to suppress normal myocyte glucose uptake. Failed prep → diffuse physiologic FDG that mimics or masks disease. This is not a casual oncology FDG instruction set.
Cardiac MIBG
I-123 MIBG maps sympathetic innervation (heart-to-mediastinum ratios, washout). Hold interfering drugs per lab list; follow iodine thyroid-protection rules when applicable. MIBG is not a substitute for MPI ischemia mapping.
Myocardial Viability
| Approach | Concept | When chosen |
|---|---|---|
| Tl-201 rest–redistribution | Rest uptake + 3–4 h (sometimes 24 h) fill-in = viable hibernation | SPECT viability without FDG |
| Tl-201 stress–redistribution ± reinjection | Stress defect with later uptake | Combined ischemia + viability |
| F-18 FDG viability PET | FDG-avid tissue in a perfusion defect = mismatch (hibernating); matched severe reduction = scar | Metabolic gold standard when available |
| Tc-99m rest uptake (supportive) | Preserved rest perfusion favors viability | Adjunct, less definitive |
FDG viability prep uses glucose loading/insulin euglycemia to stimulate myocyte FDG uptake—the opposite goal of sarcoid suppression prep. Swapping those preps is a classic board trap.
When reporting viability language at the tech level, remember: perfusion-metabolism mismatch suggests hibernating myocardium that may improve after revascularization; matched severe reduction suggests scar with less recovery potential. Actual revascularization decisions remain clinical.
Choosing the Study
| Clinical question | Nuclear package |
|---|---|
| Serial LVEF on cardiotoxic chemo | Rest MUGA |
| RV function / shunt / bolus EF | First-pass |
| ATTR amyloid | Tc-99m PYP 1 h/3 h + SPECT, H/CL |
| Cardiac sarcoid inflammation | FDG PET with suppression prep |
| Sympathetic denervation | I-123 MIBG |
| Hibernation before revascularization | Tl-201 redistribution and/or FDG viability |
| Daily CAD ischemia vs scar | MPI (± gating) first (§13.1) |
Bottom line: name the question, pick the agent and prep, and defend bolus quality, labeling, timing, and ratios.
A patient needs highly reproducible serial LVEF measurements during anthracycline chemotherapy. Which study is the classic nuclear medicine choice?
For Tc-99m PYP imaging of suspected ATTR cardiac amyloidosis, which technical/interpretive package is most appropriate?
How does patient preparation for F-18 FDG cardiac sarcoidosis PET differ in purpose from preparation for FDG myocardial viability PET?