Preliminary investigations of active pixel sensors in Nuclear Medicine imaging

Three CMOS active pixel sensors have been investigated for their application to Nuclear Medicine imaging. Startracker with 525×52525μm square pixels has been coupled via a fibre optic stud to a 2mm thick segmented CsI(Tl) crystal. Imaging tests were performed using 99mTc sources, which emit 140keV gamma rays. The system was interfaced to a PC via FPGA-based DAQ and optical link enabling imaging rates of 10f/s. System noise was measured to be >100e and it was shown that the majority of this noise was fixed pattern in nature. The intrinsic spatial resolution was measured to be ∼80μm and the system spatial resolution measured with a slit was ∼450μm. The second sensor, On Pixel Intelligent CMOS (OPIC), had 64×7240μm pixels and was used to evaluate noise characteristics and to develop a method of differentiation between fixed pattern and statistical noise. The third sensor, Vanilla, had 520×52025μm pixels and a measured system noise of ∼25e. This sensor was coupled directly to the segmented phosphor. Imaging results show that even at this lower level of noise the signal from 140keV 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.