A miniature SPECT using multi-pinhole collimator with vertical septa

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