OpenPET: A Flexible Electronics System for Radiotracer Imaging

Abstract

We present the design for OpenPET, an electronics readout system designed for prototype radiotracer imaging instruments. The critical requirements are that it has sufficient performance, channel count, channel density, and power consumption to service a complete camera, and yet be simple, flexible, and customizable enough to be used with almost any detector or camera design. An important feature of this system is that each analog input is processed independently. Each input can be configured to accept signals of either polarity as well as either differential or ground referenced signals. Each signal is digitized by a continuously sampled ADC, which is processed by an FPGA to extract pulse height information. A leading edge discriminator creates a timing edge that is "time stamped" by a TDC implemented inside the FPGA. This digital information from each channel is sent to an FPGA that services 16 analog channels, and information from multiple channels is processed by this FPGA to perform logic for crystal lookup, DOI calculation, calibration, etc. As all of this processing is controlled by firmware and software, it can be modified / customized easily. The system is open source, meaning that all technical data (specifications, schematics and board layout files, source code, and instructions) will be publicly available.

Instrumentation for Time-of-Flight Positron Emission Tomography

“…Required characteristics for PET electronics are: (1) a large number of readout channels, (2) high bandwidth and low noise and (3) a high count rate [100]. In addition to these requirements, the cost and power consumption should be considered [101].…”

“…Therefore, numerous studies are being carried out using FPGA for the time-to-digital converter (TDCs) circuit [113,114]. These TDCs provide the solution to the shortcoming of the analog approach [100,102]. Most TDCs are designed on ASICs, which are very expensive and on the other hand have a limited number of channels and functionality.…”

“…An open source electronics system that can be used for data acquisition of nuclear medicine modalities is the Open-PET project [100].…”

Evolution of the design of a second generation FireWire based data acquisition system

“…Figure 3 shows a block diagram of the ANB. When used as a master or local controller the ADCs are replaced with jumper blocks to allow use of the signal connectors for high speed serial communications to the other boards in the system [9]. The components have been selected both for the needed functions to handle dMiCE and cMiCE data streams (including the real time position estimation algorithms use for the cMiCE detectors) as well as compatibility for eventual use of the cards within the bore of a 3T magnet.…”

“…Before undertaking a new electronics development effort we survived commercial offerings and the Open PET consortium effort [9] for alternatives. However, the demands for the cMiCE statistical estimation algorithms [8] requires a larger FPGA and more support memory than is available on the commercial devices we found nor the Open PET designs.…”