A Large Field of View Positron Emission Mammography Imager

Dedicated positron emission mammography (PEM) systems provide a potentially high sensitivity, high-resolution, low attenuation and lower cost alternative to whole body PET. We have designed, built, and performed initial evaluation of a large field-of-view PEM system. This system uses two 15 cm × 20 cm planar detectors. Each detector has an array of 3 mm × 3 mm × 10 mm LGSO (90% LSO, 10% GSO) scintillator crystals read out by an 6 × 8 array of 25 mm × 25 mm position-sensitive photomultipliers. The detectors are mounted on a gantry that is used in conjunction with an x-ray mammography unit such that when the film holder is rotated away the upper detector is above the compression paddle, which is used to compress the breast against the lower PEM detector. Several performance tests were done on the system with the LGSO crystals, as well as with 3 mm × 3 mm × 20 mm NaI crystals, for comparison purposes. Spatial resolution (coincidence) ranged from 4.1 to 4.7 mm FWHM for acceptance angles 10 degrees to 40 degrees (4.8 mm to 5.7 mm for NaI). Absolute sensitivity was 27-505 cps/uCi (9.0-165, NaI) for the same angular acceptance range. Images of a 12 cm diameter, 3 cm thick phantom with 8:1 concentration spheres demonstrate lesions as small as 4 mm for higher-count images.