Real-time cardiac MRI using DSP's

Potentials of Digitally Sampling Scintillation Pulses in Timing Determination in PET

We investigate the potentials of digitally sampling scintillation pulses techniques for positron emission tomography (PET) in this paper, focusing on the determination of the event time. We have built, and continue building, a digital library of PET event waveforms generated with various combinations of photo-detectors and scintillator materials, with various crystal sizes. Events in this digital library are obtained at a high sampling of 20 GSps (Giga-samples per second) so that their waveforms are recorded with high accuracy. To explore the potential advantages of digitally sampling scintillation pulses, we employ a dataset in the above-mentioned library to evaluate two methods for digitizing the event pulses and linear interpolation techniques to analyze the resulting digital samples. Our results show that the two digitization methods that we studied can yield a coincidence timing resolution of about 300 ps FWHM when applied to events generated by a pair of LSO + PMT detector units. This timing resolution is comparable with that is achieved by the same detector pair with a constant fraction discriminator (CFD). As a benchmark, regular-time sampling (RTS) method, usually implemented with very fast traditional analog-to-digital converters (ADCs) for digitizing scintillation pulses, is not feasible for a multi-channel system like a PET system. Digitizing scintillation pulses with multi-voltage threshold (MVT) method could be implemented at a reasonable cost for a PET system. With digitized PET event samples, various digital signal processing (DSP) techniques can be implemented to determine event arrival time. Our results have therefore demonstrated the promising potentials of digitally sampling scintillation pulses techniques in PET imaging.

A low-cost scalable multichannel digital receiver for magnetic resonance imaging

Commercial receivers used for parallel MR imaging often present researchers with hurdles such as high cost-per-channel, low scalability for multiple coils and non-accessibility to intermediate data for research. A novel low-cost multichannel digital receiver for use with MR scanners has been developed to alleviate these concerns. MR signals from up to 16 coils are bandpass sampled at RF, with all subsequent downconversion performed on a single-chip Field-Programmable Gate Array (FPGA). Downconverted information is buffered and can be downloaded over a network or onto flash memory for image reconstruction. Arrays with more than 16 coils can easily scale by using more than one of these economical receivers. A 2-channel prototype has been designed, built and tested successfully with a combination of real-world signals and simulated MR data.