Radionuclide Ventriculography (MUGA / ERNA)
Equilibrium radionuclide angiography (MUGA/ERNA) with ⁹⁹ᵐTc-labelled red cells measures left-ventricular ejection fraction with high reproducibility, independent of geometric assumptions. Its main modern role is serial monitoring of chemotherapy cardiotoxicity (anthracyclines, trastuzumab), where small, reliable EF changes drive management.
The blood pool is labelled and imaged in ECG-gated equilibrium, so counts are proportional to volume — giving an accurate, operator-independent EF that is more reproducible than 2D echocardiography.
When to image
- Baseline and serial LVEF during cardiotoxic chemotherapy.
- Accurate EF when echocardiography is limited or discordant.
- Quantifying EF where reproducibility matters for treatment decisions.
How to read it
- Report LVEF and any interval change against thresholds for chemotherapy interruption.
- Assess regional wall motion qualitatively.
- Compare to the patient’s own prior studies (same technique).
Protocol
- In-vitro or in-vivo ⁹⁹ᵐTc red-cell labelling.
- ECG-gated equilibrium acquisition in the best septal LAO view.
- Consistent processing for serial comparability.
Pitfalls
- Poor red-cell labelling degrades the study.
- Arrhythmia degrades gating.
- Provides EF/function only — no perfusion or structural detail.
Evidence & guidelines
- ERNA is a highly reproducible EF method, valuable for serial cardiotoxicity monitoring.
- ESC 2022 cardio-oncology guidelines prefer echocardiography (ideally 3D) and CMR, reserving MUGA for when echo is non-diagnostic and CMR is unavailable.
In depth
- ⁹⁹ᵐTc-labelled red cells replaced ⁹⁹ᵐTc-albumin, which breaks down faster and gives poorer images; labelling efficiency is about 60–70% in vivo, about 90% with the modified in vivo/in vitro method and over 97% in vitro.
- Best-septal LAO is 40–50° (separates ventricles); frame-mode gated studies use 16–32 frames.
- Count-based LVEF needs no geometric assumptions; an LVEF of 50% or more is normal, and inter- and intra-observer variability is under 5%, so ERNA is more reproducible than echocardiography for serial monitoring.
- On exercise ERNA, an abnormal response is failure of LVEF to rise by at least 5 units (or a fall), a new regional wall-motion abnormality or an increase in end-systolic volume; stress ERNA is now rarely used, having been replaced by stress echocardiography and perfusion imaging.
- Doxorubicin cardiotoxicity is dose-dependent, with heart failure in an estimated 26% of patients at a cumulative 550 mg/m² and risk rising from about 400 mg/m²; trastuzumab toxicity is not dose-related and usually recovers after withdrawal (mean about 1.5 months).
- First-pass radionuclide angiography uses a compact high-activity bolus (e.g. ⁹⁹ᵐTc-DTPA when no equilibrium images are needed), acquired in the anterior or right anterior oblique view with a high-count-rate camera, as adequate count rates are essential for reliable ejection fractions.
- Gated blood-pool SPECT gives LVEF values about 8 units higher than planar ERNA because the left atrium is excluded; diastolic function (peak filling rate, normal above 2.5 end-diastolic volumes per second) needs higher temporal resolution, ideally 32 frames per cycle.
Sources: SNMMI/EANM gated equilibrium radionuclide angiography guideline 2020 (JNMT 2020 · 48:126) · Swain et al. Cancer 2003 (PMID 12767102) · Ewer et al. J Clin Oncol 2005 (PMID 16258084) · ASNC first-pass radionuclide angiography guideline (PMID 17174796) · Groch et al. J Nucl Med 2001 (PMID 11752072) · SNMMI/EANM ERNA guideline 2020 (JNMT 2020