Performance evaluation of a multi-pinhole collimator with vertical septa

Abstract

The authors have previously reported a simulation study on a novel multi-pinhole (MP) collimator that is able to provide improved angular sampling and an enlarged imaging field of view (FOV) when compared to a low-energy high-resolution parallel-hole (LEHR) collimator using a detector of equivalent size. The aim of this study was to develop a miniature single photon emission computerized tomography (SPECT) to verify the performance of the proposed MP collimator with lead vertical septa. A detector with a 70 mm×70 mm active area that consisted of a 6 mm-thick NaI(Tl) crystal coupled to a 127 mm-diameter position-sensitive photomultiplier tube (PSPMT) was used. A 7×7 pinhole collimator with a 2 mm-diameter pinhole and a focal length of 40 mm was fabricated to evaluate the performance as compared to a typical LEHR collimator. Additionally, a detector having a 50 mm×50 mm active area with 5×5 pinhole and LEHR collimators was investigated to evaluate the enlarged imaging FOV. Planar spatial resolution, sensitivity, and resolution for hot- and cold-rod phantom images were acquired. Images were reconstructed using a dedicated maximum likelihood expectation maximization (MLEM) algorithm with an unmatched projector/backprojector pair. The spatial resolution and sensitivity obtained with both collimators were 4.7 mm FWHM and 0.25 cps/μCi at a distance of 60 mm, respectively. Although the detector size was smaller than the phantom, the MP collimator allowed for imaging of the entire phantom while the image obtained with LEHR collimator suffered from a truncation artifact. The reconstructed images, using 60 and 30 projections with both 7×7 pinhole and LEHR collimators, yielded an image of similar quality to that, which was constructed using 120 projections. However, the images reconstructed with 10 projections using a 7×7 pinhole collimator showed better quality than those that used an LEHR collimator. The reconstructed images that used the MP collimator provided high-quality images with an enlarged imaging FOV, even when insufficient angular sampling data were used, which would be of use in the development of a stationary SPECT.