Ultra-high resolution SPECT with a semiconductor detector and a diverging collimator

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The development of semiconductor detectors such as CdTe, which works at room temperature, has facilitated the development of a new SPECT system. These semiconductor detectors have a high energy resolution. Moreover, they are used as pixellated detectors, and so the intrinsic resolution can be equal to the size of the pixel used for measurement. The detector pixel is as small as 0.5mm, and so the spatial resolution of a reconstructed SPECT image can be less than 3mm FWHM. To clarify the feasibility of an ultra-high resolution SPECT system, we conducted some simulations and evaluated the quality of images. In these simulations we used a diverging collimator to enlarge the field of view of the detector and compared the quality of the reconstructed images of a pixellated SPECT system with a conventional SPECT system with a scintillation detector and parallel-hole collimator under the same sensitivity and reduced sensitivity. The results showed that the improvement of the spatial resolution in the pixellated semiconductor detector yielded high quality images even under the low sensitivity condition due to the small size of the pixels. With the above results we built a prototype semiconductor SPECT system with a diverging collimator. In this system we made the diverging collimator by using several hundreds of thin tungsten plates. With this proposed ultra-high resolution system we established the reconstruction of rod phantoms(hot rod phantom and cold rod phantom) with the spatial resolution of 1.0mm for the hot rods and 1.6mm for the cold rods. The obtained results with the simulation and experiment showed that the ultra-high resolution SPECT system was available with the semiconductor detector and a parallel-hole collimator or a diverging collimator with holes of a small size.