The utility of heart-to-mediastinum ratio using a planar image created from IQ-SPECT with Iodine-123 meta-iodobenzylguanidine

123I-labeled meta-iodobenzylguanidine (MIBG) has used a planar image to measure the heart-to-mediastinum ratio (HMR). However, planar images are not available from IQ-SPECT with SMARTZOOM collimator due to its multi-focal collimation. Since we created the planar-equivalent (IQ-planar) images by adding all slices of the IQ-SPECT coronal image. The aim of this study was to demonstrate the utility of the new method for calculating HMR. The planar image and transverse images of IQ-SPECT with attenuation and scatter corrections (ACSC) and without ACSC (NC) were obtained. Multi-planar reconstruction and ray-summation processing were applied to create IQ-planar images with NC and ACSC. Linear regression between the measured HMR from the planar image and the mathematically calculated HMR was used to calibrate HMR to standardized values. Scatterplots and linear regression lines between planar and IQ-planar HMRs before and after cross-calibration showed systematic differences in both NC and ACSC conditions. The IQ-planar HMR with NC and ACSC was significantly higher compared with that of the conventional planar image. However, the IQ-planar HMR with NC and ACSC after cross-calibration was similar to the standardized HMR calculated by planar image. The IQ-planar HMR using the new ray-summation processing method could be used along with the conventional planar HMR.