Evaluation of estimation method for organ volume and uptake with single photon emission computed tomography (SPECT)

Estimation method for an organ volume and uptake was evaluated using five cylinder phantoms (113 cc - 1,539 cc) and two liver phantoms with all purpose (AP) and high resolution (HR) collimators. The volume was calculated from the summation of voxels in the region districted by equi-count threshold level at each section of the SPECT image, which were reconstructed with two attenuation correction methods: radial post correction (RPC) by Tanaka and precorrection (PRE) by Sorenson. The optimum equi-count threshold level (percentage to maximum count), which gave the nearest volume to true phantom volume, was estimated for all phantom images and the activity-count calibration curve was also generated. The optimum threshold level is tending downward as increasing the volume. Higher back ground gave higher optimum equi-count threshold level. Further, the optimum equi-count threshold level is changed with a kind of collimator, form of the phantom and attenuation correction methods. Estimated volume and activity are well correlated (r > 0.98) with their real values in the same situation. In RPC method than PRE method and in the estimation of activity than the estimation of volume, less dependence on the form of phantom was found from the present study comparing with cylinder and liver phantoms. In conclusion, the estimation for the volume and activity, furthermore uptake of pharmaceutical to the target organ with SPECT would be useful for clinical application, if the calibration study has done previously in the same situation as clinical one. (author)