Quantitative 123I - MIBG SPECT/CT assessment of cardiac sympathetic innervation in patients with congestive heart failure

Abstract

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Objectives: Myocardial scintigraphy with 123I – MIBG (MIBG) allows for visual assessment and semi-quantitative analysis using the heart to mediastinum ratio (HMR)of the sympathetic cardiac innervation. Impaired cardiac MIBG clearance may occur in patients (pts) with congestive heart failure (CHF). The purpose of present study was to develop and validate a quantitative index for the assessment of cardiac MIBG uptake kinetics using SPECT/CT for diagnosis of CHF.

Methods: Nineteen pts (7 M, 12 F; mean age, 57.7±21 y) who performed MIBG scintigraphy for assessment of known or suspected neuroendocrine tumors were recruited. Pts were interviewed and examined for the presence of CHF or other cardiac-related diseases. Pts received an i.v. injection of 148MBq MIBG. Dedicated cardiac imaging was performed in addition to the routine scintigraphic protocol for neuroendocrine tumors, included planar scintigraphy of the chest at 5 minutes after tracer injection, further used for measurement of HMR. A sequence of three SPECT/CT studies (Infinia & Hawkeye, GE Healthcare) of the chest was performed at 15 minutes, 4 and 24 hours post-injection. SPECT was followed by acquisition of low dose CT used for attenuation and scatter correction, and for precise localization of the heart on SPECT. Total cardiac MIBG counts (cts) were measured with boundaries of the heart delineated on the CT component for each SPECT/CT study, using fully automatic, in-house developed software. The percent of injected dose/cc (%ID/cc) over the heart was also calculated for each time point using a calibration curve derived from phantom studies, relating cts and injected doses, corrected for decay. Slope values were calculated using the three consecutive time point measurements for each patient. The quantitative MIBG clearance slopes and HMR were compared between subgroups of pts with and without CHF using the non-parametric Mann-Whitney test.

Results: Five pts had CHF and 14 pts had neither CHF nor other cardiac disease. The total MIBG heart count clearance slope in pts with CHF was 0.0113±0.0003 as compared with 0.0163±0.0004 cts/hour in pts without CHF (p<0.05). The %ID/cc clearance slope in pts with CHF was 0.161±0.05 vs. 0.313±0.09 %ID/cc/hour in pts without CHF (p<0.05). The HMR was 1.43±0.14 in pts with CHF vs. 1.54±0.25 in pts without CHF (p not significant).

Conclusions: Patients with CHF show slower MIBG clearance as compared to pts without CHF. SPECT/CT measured MIBG clearance may potentially represent an accurate index for early diagnosis of CHF and be used in future for monitoring response to treatment.