I-123 MIBG Heart-to-Mediastinum Ratios Obtained by DNM530c CZT SPECT: Direct Comparison with Conventional Planar Imaging

229 Objectives I-123 Metaiodobenzylguanidine (MIBG) has been widely used in the fields of cardiology and neurology, but most studies have used planar imaging. Recently, some institutions have changed their equipment from Anger SPECT (A-SPECT) to CZT SPECT for cardiac studies, but conventional planar images are not available in the routine clinical setting. The aim of this study is to obtain the heart-to-mediastinum ratio (HMR) and washout rate (WOR) by CZT-SPECT and validate the utility of it in direct comparison with those measured by planar imaging by A-SPECT. Methods As an exploratory experiment, we conducted a series of phantom studies using an HL phantom (Kyoto-kaken Co., Japan), which were filled with several concentrations of I-123 activities in the cardiac, lung, mediastinum, and the liver compartments. Consecutive acquisitions were performed on a dual-head A-SPECT (Infinia) equipped with an extended LEGP collimator and a CZT-SPECT (DNM 530c) systems to obtain different HMR values. Then, clinical study included 84 consecutive patients with suspected Parkinson’s disease (43 males; mean age; 68±10 y.o.) were included. Ten min after injection of 111 MBq MIBG, early planar imaging with 8 min was performed first on A-SPECT, immediately followed by CZT-SPECT with 10 min. Delayed imaging with both modalities was performed in the same manner 5 hours after the injection. Eearly and delayed HMR on the planar images were analyzed with the conventional region-of-interest (ROI) technique. For the CZT-SPECT, transaxial images with 4mm thickness were reconstructed, then 70 coronal images were stacked using a Volumetrix softwere. On the summed coronal image, the heart ROI was manually drawn and the 3x5 pixels of the mediastinum ROI was set. HMR was calculated by dividing the mean counts in the heart voxel-of-interest (VOI) divided by the mean counts in the mediastinum VOI. Same VOIs were automatically set on the delayed coronal images. Results From the results of phantom studies, we found a scattering or reconstruction artifacts around outer circumferential borders of the quality field of view on transaxial images of CZT-SPECT. Therfore, we removed anterior and posterior slabs with artifacts from the stacked coronal images. Early HMR obtained from the planar imaging was 2.23±0.58, which was significantly higher than those of CZT SPECT (2.0±0.83, p Conclusions HMRs and WORs measured on the summed coronal image of CZT-SPECT with MIBG had a high correlation with those from the planar imaging of conventional A-SPECT, respectively. Calibrations between CZT-SPECT and planar imaging by A-SPECT are promising and the HMRs and WORs from either planar imaging or SPECT may be converted to comparable standardized values with an appropriate CC.