Multiplexed Eighty Channel PMT List-Mode Data Acquisition System for 27–511 keV Gamma Ray Imaging

All channels of the read-out system have a gated integrator to determine the charge per event. Each 16 channels are multiplexed to a 12-bit 40 MS/s pipelined ADCs. Using multiplexing only 5 ADCs are needed which share a commercial USB 2.0 interface board to send the event data to the computer.
The signal input range is up to 120 pC with a noise level of 57 fC. The integral non-linearity is better than 1% for all channels, while the channel response has a gain non-uniformity less than 2.4% for the different channels. The crosstalk between channels is better than 64 dB. The dead time is 2.5 s , including a 760 ns integra- tion period. The system can handle a sustained event rate of 155 kcps on the USB 2.0 bus.

Connected to a clinical gamma camera we show that the isotopes 125I (27–35 keV), 99mTc (140.5 keV) and 22Na (511 keV) can all be imaged without electronic adjustments thus enabling, for instance, simultaneous pinhole PET/SPECT. With this PMT list-mode acquisition system, advanced offline event positioning and energy estimation with e.g. maximum likelihood methods are enabled.