Active pixel sensors in Nuclear Medicine imaging

Three CMOS active pixel sensors have been investigated to assess their potential application to Nuclear Medicine imaging. The first, Startracker, contained 525 × 525 pixels each 25 micron square and was coupled via a fiber optic stud to a 20mm × 20mm × 2mm thick segmented CsI(Tl) crystal. Imaging tests were performed using ^99mTc sources which emit 140 keV gamma rays together with various lead collimators. The system was interfaced to a PC via an FPGA-based DAQ and optical link enabling imaging rates of 10 frames per sec. System noise was measured to be ≫100e but the majority of this noise was found to be fixed pattern in nature. The intrinsic spatial resolution was measured as ∼80 microns and the system spatial resolution measured with a slit was ≪1mm. The second sensor, OPIC, had 64 × 72 pixels each 40 micron square and was used to evaluate noise characteristics of these sensors and to develop a method of differentiation between fixed pattern and statistical noise. The third sensor, Vanilla, had 520×520 pixels each 25micron square and a measured system noise of ∼25e. This sensor was coupled directly to the segmented phosphor. Results show that even at this lower level of noise the signal from 140 keV gamma rays is small as the light from the phosphor is spread over a large number of pixels. Suggestions for the ‘ideal’ sensor are made.