Comparison of inferior myocardial defect between planar and SPECT image of 123I-metaiodobenzylguanidine cardiac scintigraphy

Discordant findings of inferior MIBG defect between SPECT and planar images were sometimes observed in the clinical studies. In this study, we compared inferior myocardial findings between planar and SPECT image of 123I-metaiodobenzyl-guanidine (MIBG) cardiac scintigraphy in 29 patients. All patients were estimated as normal in anterior accumulation of MIBG. The patients were divided into 3 groups according to the visual finding of inferior defect in the planar and SPECT image; normal group (normal inferior accumulation of MIBG both in the planar and SPECT image, N = 10), discordance group (inferior MIBG defect was only observed in the SPECT image, but was not observed in the planar image, N = 7), inferior defect group (inferior MIBG defect was observed both in the planar and SPECT image, N = 12). Inferior/anterior count ratio of SPECT and planar image were 0.96 +/- 0.11 vs. 0.97 +/- 0.05 in normal group, 0.59 +/- 0.21 vs. 0.99 +/- 0.13 in discordance group, 0.46 +/- 0.13 vs. 0.82 +/- 0.04 in inferior defect group. Liver/heart count ratio was significantly higher in the discordance group (2.07 +/- 0.49) than that in the normal (1.14 +/- 0.15) and inferior defect group (1.45 +/- 0.39). In phantom study, it has been reported that increased liver accumulation of MIBG causes artifactual inferior defect adjacent to the liver. These data indicate that increased liver/heart count ratio may cause artifactual inferior defect on MIBG SPECT image in the clinical studies. Planar image evaluation may be helpful to distinct the artifactual inferior defect on SPECT image.