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We present a preliminary study of list-mode likelihood reconstruction of images for a rectangular positron emission tomograph (PET) specifically designed to image the human breast. The prospective device consists of small arrays of scintillation crystals for which depth of interaction is estimated. Except in very rare instances, the number of annihilation events detected is expected to be far less than the number of distinguishable events. If one were to histogram the acquired data, most histogram bins would remain vacant. Therefore, it seems natural to investigate the efficacy of processing events one at a time rather than processing the data in histogram format. From a reconstruction perspective, the new tomograph presents a challenge in that the rectangular geometry leads to irregular radial and angular sampling, and the field of view extends completely to the detector faces. Simulations are presented that indicate that the proposed tomograph can detect 8-mm-diameter spherical tumors with a tumor-to-background tracer density ratio of 3:1 using realistic image acquisition parameters. Spherical tumors of 4-mm diameter are near the limit of detectability with the image acquisition parameters used. Expressions are presented to estimate the loss of image contrast due to Compton scattering.

Summary: Dynamic positron emission tomography with [ 18 Flfluorodeoxyglucose was used in six patients with Alzheimer's disease (AD) and seven healthy age-matched control subjects to estimate the kinetic parameters K 1*' k2 *, and k3 * that describe glucose transport and phospho rylation. A high-resolution tomograph was used to ac quire brain uptake data in one tomographic plane, and a radial artery catheter connected to a plastic scintillator was used to acquire arterial input data. A nonlinear iter ative least-squares fitting procedure that included terms for the vascular fraction and time delay to the peripheral sampling site was used to fit a three-compartment model to the brain data. Regions studied included frontal, tem poral, occipital, and the entire cortex and subcortical white matter. The values obtained for the individual rate constants and regional CMR g lc (rCMR g lc: calculated us ing regional values of the rate constants) were higher than those reported previously. A significant (p < 0.05) dePositron emission tomography (PET) has demon strated reduced regional CMRglc (rCMRg1J values in patients with Alzheimer ' s disease (AD). These findings predominate in temporal and parietal cor tical regions and have been reported by numerous laboratories (Benson et aI., 1983; Friedland et aI., 1983; Foster et aI., 1984; Duara et aI., 1986). De spite this agreement, however, the mechanisms and significance of these metabolic alterations are poorly understood.