Cardiac Sympathetic Imaging (¹²³I-MIBG)
¹²³I-MIBG images cardiac sympathetic innervation. The planar heart-to-mediastinum ratio (HMR) and washout rate reflect sympathetic integrity: a delayed HMR <1.60 was associated with worse prognosis in heart failure (ADMIRE-HF). MIBG is also used to support dementia with Lewy bodies, where cardiac uptake is characteristically reduced.
MIBG is a noradrenaline analogue taken up by sympathetic nerve terminals. In heart failure and in Lewy-body disease, terminal dysfunction reduces cardiac uptake, lowering the HMR.
When to image
- Risk stratification in chronic heart failure.
- Supporting a diagnosis of dementia with Lewy bodies (reduced cardiac uptake).
- Research and selected clinical assessment of sympathetic function.
How to read it
- Compute early and delayed HMR and the washout rate.
- A low delayed HMR indicates impaired sympathetic function and higher risk.
- In suspected DLB, reduced cardiac MIBG uptake is an indicative biomarker.
Protocol
- Thyroid blockade; withhold interfering drugs where possible.
- Planar (± SPECT) at ~15 min (early) and ~4 h (delayed).
- Standardise HMR measurement (region placement, collimator).
Diagnostic performance
- ADMIRE-HF (961 patients, NYHA II–III, LVEF ≤35%): 2-year event rate 37% with delayed HMR <1.60 vs 15% with HMR ≥1.60 (HF progression, arrhythmic events, cardiac death).
- Reduced cardiac uptake is an indicative biomarker for DLB in the 2017 consensus criteria.
Pitfalls
- Many drugs (e.g. tricyclics, labetalol, sympathomimetics) alter uptake.
- HMR varies with camera/collimator — standardise and use local references.
- Interpret with the clinical context.
Evidence & guidelines
- Jacobson et al., ADMIRE-HF (JACC, 2010): prognostic value of ¹²³I-MIBG HMR in heart failure.
- Low cardiac MIBG uptake is an indicative biomarker in the 4th DLB consensus criteria (McKeith et al., 2017).
In depth
- ¹²³I-MIBG is taken up by the noradrenaline transporter (uptake-1) into sympathetic nerve terminals and stored in vesicles without being metabolised; it is FDA-approved to assist evaluation of NYHA class II–III heart failure with LVEF ≤35%.
- The heart-to-mediastinum (H/M) ratio uses a cardiac ROI and a 7×7-pixel upper-mediastinal ROI (excluding thyroid/lung/liver).
- In ADMIRE-HF (961 patients), the 2-year cardiac event rate was 15% with late H/M ≥1.60 versus 37% with H/M <1.60, and low H/M also predicted arrhythmic events and cardiac death; the prognostic separation persisted at 5 years.
- Washout between early (about 15 min) and late (about 4 h) images is normally below roughly 20–30%, but normal values depend on method and correction; late H/M falls slightly with age, whereas washout has not shown a consistent age effect.
- Stop interfering drugs (tricyclics, labetalol, sympathomimetics) and avoid vanillin/blue cheese/chocolate; give thyroid blockade (KI/Lugol’s).
- The only labelled contraindication is hypersensitivity to iobenguane; ask about prior reactions to iodine-containing products, weigh benefit in pregnancy, interrupt breastfeeding, and note that severe renal impairment increases radiation exposure and degrades images. The US labelled adult activity is 370 MBq (10 mCi); European and Japanese practice commonly uses 111–370 MBq.
- A regional innervation–perfusion mismatch (viable, perfused but denervated myocardium) is associated with a higher risk of ventricular arrhythmias. Cardiac MIBG uptake is reduced in about 90% of Parkinson's disease (pooled sensitivity 89%) and is usually preserved in multiple system atrophy and other atypical parkinsonism.
Sources: AdreView (iobenguane I-123) FDA prescribing information · ADMIRE-HF, Jacobson et al. JACC 2010 (PMID 20188504) · EANM/EACVI standardisation proposal, Flotats et al. EJNMMI 2010 (PMID 20577740) · Jacobson et al. JACC 2010 · 55:2212-21 (PMID 20188504) · Agostini et al. J Nucl Cardiol 2021 (PMID 31468379) · Asghar et al. Nucl Med Commun 2017 (PMID 27898646) · Nakajima et al. JSNM normal database (PMC5852176)