Design of a High Resolution Positron Emission Tomograph

Abstract

The design of a high resolution positron emission tomograph is described. The scanner has four rings of detectors with an inside diameter of 38 cm and produces seven simultaneous slices, including three cross-slices. Each ring contains 128 bismuth germanate scintillation detectors with dimensions of 8.25 × 20 × 35 mm; adjacent crystals are separated by tapered tungsten septa that extend to within 7.5 mm of the front faces. The anticipated geometrical spatial resolution of the scanner is 4.5 mm full width at half maximum (FWHM) at the center of the image, and the sensitivity is 44,000 true counts/sec/ring (390,000 counts/sec total) for a uniform phantom 20 cm in diameter containing 1 μCi/cc activity. There are interchangeable collimators for use in high count rate studies, for narrowing the slice width from 1 cm FWHM to 5 mm FWHM, and for ultra-high resolution studies with a 2.5 mm FWHM geometrical point spread function. The electronic circuitry has separate timing and energy verification channels and can detect 95% of the coincidences with a timing window (twice the maximum time between two coincident pulses) of 14 nsec. The count rate capability of the electronics is 150,000 counts/sec/ring and 1.5 million counts/sec total.