Septal penetration in iodine-123 metaiodobenzylguanidine cardiac sympathetic imaging using a medium-energy collimator.

ABSTRACT

BACKGROUND: Septal penetration of high-energy photons affects the estimation of the heart-to-mediastinum (H/M) ratio in cardiac (123)I-metaiodobenzylguanidine (MIBG) imaging, and the use of a medium-energy (ME) collimator has been shown to improve quantitative accuracy. We investigated the effect of septal penetration on the estimation of H/M ratios using an ME collimator. METHODS AND RESULTS: Point sources of (99m)Tc and (123)I were imaged using various collimators, which indicated that the effect of high-energy photons with the ME collimator was relatively small but larger than that with the high-energy (HE) collimator. Four hours after (123)I-MIBG injection, 20 patients underwent planar anterior chest imaging by different methods in succession. The ME collimator gave lower H/M ratios (mean 2.52) than the HE collimator (2.57), indicating influence of septal penetration in the ME collimator; however, the difference was limited. Although narrowing the energy window from 20% (2.51) to 15% (2.54) increased the H/M ratios in imaging with the ME collimator, the difference was quite limited. CONCLUSIONS: Septal penetration affects the estimation of the H/M ratios using an ME collimator; however, this influence is small and would not have clinical significance.