Cardiac 123I-metaiodobenzylguanidine (MIBG) innervation imaging has been widely used to estimate cardiac sympathetic innervation in various forms of cardiac disorders. Although normal cardiac MIBG distribution includes a relatively low uptake in the inferior wall, the substantial uptake of the tracer in the liver could overlap the inferior left ventricular wall. Prone images might improve the relative tracer uptake in the inferior wall reducing diaphragmatic attenuation and avoiding intense uptake by the liver. This study assessed whether MIBG prone-position acquisition can change heart-to-mediastinum (H/M) values compared to supine acquisition.
Forty-five patients (34 men, mean age 58±15 years) were enrolled (34 patients with heart failure and 11 with Anderson Fabry disease). All patients underwent planar 123I-MIBG cardiac imaging after intravenous administration of 111 MBq. Ten-minute planar images were acquired from an anterior thoracic view 15 minutes (“early” image) and 3 hours and 50 minutes (“late” image) after tracer administration in both supine and prone positions. Early and late H/M ratios were computed and washout rate (WR) was calculated using the standard formula background and decay corrected. Using the mean relative uptake, the inferior to anterior uptake ratios were also calculated on early and late images for both supine and prone positions.
Early (1.8±0.3 vs. 1.9±0.3, p=0.3) and late (1.7±0.4 vs. 1.7±0.3, p=0.8) H/M ratios, and WR (35±17.6% vs. 35±16.4%, p=0.9) were not different between supine and prone position. On early images, inferior/anterior uptake ratio in the supine position was significantly lower as compared to prone position (0.96±0.12 vs. 1.01±0.08; p<0.02). Conversely, on late images inferior/anterior uptake ratio was not different between supine and prone positions (0.99±0.15 vs. 1.01±0.08, p= 0.4).
The results of the present study show that the prone-position acquisition did not change early and late H/M ratios and WR compared to supine-position acquisition. However, the inferior to anterior uptake ratio increased using the prone-position acquisition only in early images.