High resolution brain imaging with combined parallel-hole and pinhole collimation

A brain single photon emission computed tomography (SPECT) imager is simulated for obtaining high resolution brain scans for diagnosing brain ischemia. In this simulation the camera consists of one large field of view detector with parallel-hole collimation and a smaller field of view high resolution detector with pinhole collimation. The parallel-hole collimated detector images the whole brain and acquires data without truncation. It localizes areas of particular diagnostic interest, and also provides support information for the reconstruction of data acquired by the pinhole collimated detectors. The pinhole collimated detector images small regions of the brain. It provides high resolution truncated projections, from which a high resolution region of interest (ROI) is obtained. The reconstruction is performed using a maximum a posteriori (MAP) estimate with total variation regularization within the ROI. The low resolution image from the parallel-hole collimated detector is used as prior information. This improves the quantitation for the interior problem. The combination of a large field of view parallel-hole collimated detector and a smaller field of view high resolution pinhole detector improves the quantitation in the simulated brain imaging study. It makes use of the high sensitivity of the pinhole collimator while compensates for the degradation in the reconstructed image due to interior problem caused by the small field of view of the pinhole collimator. Our simulations show potential for clinical application, where the quantitation of cerebral blood flow (CBF) and cerebral vascular reactivity (CVR) are valuable in diagnosis of ischemia, and the quantitation of benzodiazepine receptor density is important in evaluating neuronal damage due to ischemic effects.