Phantom measurements and simulations of cardiac and brain studies using a multipinhole collimator with 20 apertures

SPECT, despite its success, has an uncertain future This is partly due to the continued use of parallelhole collimators. These collimators possess poor geometric sensitivity which leads to increased study times and higher dose requirements. In recent years there has been activity investigating dedicated SPECT cameras which attempt to build on the strengths of SPECT while addressing its weaknesses. Here we present measurements of a cardiac and Hoffman brain phantom (Data Spectrum, Hillsborough, NC) performed with a pair of focusing 20-pinhole collimators with 7.5 mm diameter tungsten apertures mounted on an Infinia Hawkeye 4 dual-head SPECT/CT system (GE Healthcare, Chalfont St. Giles, UK). Comparisons are made with measurements taken with LEHR parallelhole collimators. We also present an assessment of point source sensitivity and image resolution. The cardiac and brain phantoms contained 3.8 mCi and 1.5 mCi of 99mTc-pertechnetate (140 keV), respectively. The cardiac phantom was imaged with six 300 s views over 180° and the brain phantom was imaged with eight 300 s views over 360°. The gantry orbit was circular with a radius of rotation between 22.5 cm and 25.0 cm. Shortened study times were simulated by scaling the projection data and adding Poisson noise. The multipinhole projection data were then reconstructed with 300 iterations of MLEM. We find that despite the relatively large pinhole sizes we obtain image quality comparable to that obtained with LEHR collimators at a fraction the acquisition time. For the cardiac phantom good quality images are obtained in 10 minutes, while for the brain phantom comparable image quality is attained in 10 minutes. The measured point source sensitivity near the central field of view is 7.4 × 10^-4, and optimal resolution is between 9 mm and 13 mm. These results indicate that imaging performance approaching that capable with dedicated SPECT cameras may be possible with these collimators while le- eraging the existing SPECT install base.