Low-dose or better resolution ultrafast cardiac SPECT: NCAT reconstruction and GATE study

Abstract

SPECT is primarily used in the clinic for cardiac myocardial perfusion imaging. However, for SPECT, sensitivity is impaired due to the need for collimation. System resolution is poor as well. New systems including those with multi-pinhole collimation has shown high sensitive acquisitions. Our previous work showed that using a curved detector instead of flat we can obtain resolution improvements as much as 29% on the average or else can sensitivity gains as much as 2.25 for similar resolutions. Here we use our voxel-driven MLEM reconstruction algorithm on an NCAT phantom for pinhole reconstruction to evaluate a lower dose or a higher resolution setting. The detector behind each pinhole can be flat or curved. We show that with the curved detector system (at the higher sensitivity setting, for equivalent resolution as the flat detector system), we can reduce the dose by about a factor of 1/2 still obtain equivalent image-quality as the flat-detector. Alternatively we have a better resolution compared to flat-detector system. In the second part of the study we investigated a practicable trapezoidal detector with the same height as our paraboloid detector using GATE SPECT simulator for pinhole geometry. Using point sources we investigated the sensitivity of the trapezoidal and an equivalent base flat detector for the same pinhole aperture size of 4mm. We then compared the sensitivity of each point to the approximate expected value for each point We also measured the FWHM of each point and obtained the average resolution gain of the trapezoidal over the flat detector. This constitutes the better resolution design. On the average we obtained a 31.3% improvement of resolution Then we used the trapezoidal detector with a larger pinhole aperture to match the flat-detector resolution on the average to obtain a higher sensitivity design, obtaining a sensitivity gain factor of 2.26, for similar average resolution for the two systems.