Intra-vendor clinical SPECT/CT system activity validation of 99mTc in phantom studies

Abstract

This study was to establish various conversion factors and its impact on the quantitative accuracy of an absolute activity in phantom between 2 variant clinical SPECT/CT system from the same vendors in different centre. Multiple series of uniform phantom scans were performed with 370 MBq filled activity in the uniform phantom using different isotropic voxel sizes (64 × 64 × 64, 128 × 128 × 128, and 256 × 256 × 256). For activity validation purpose, single anthropomorphic phantom scan with different activities ratios for different organs (0:0:1:10, lung: spine: background: liver), matrix sizes and iterations were performed. Various conversion factor (in cps/Bq or Bq/cps) estimated from various matrix sizes (CF64, CF128, and CF256) were applied to generate the activity concentration of distribution in SPECT/CT images. The measured activities for background and liver were then compared to an absolute activity distribution and reported as a percentage difference, while for lung and spine region were reported as activity relative errors percentage. The identical methods were replicated in the other system and the differences between the system were evaluated. Both systems produced an identical trend of CF curves over the different iterations number and voxel sizes. Both systems were capable to estimate the activity distribution within 10% and 15% of error for the liver and background respectively using 256 × 256 × 256 voxel sizes. Furthermore, the relative error percentage was within 10 to 15% of error. Different variant of SPECT/CT system from the same vendor could be able to estimate an accurate activity distribution in phantom according to an identical procedure of CF establishment.