John E. Breeding

Performance comparison of a current LSO PET scanner versus the same scanner with upgraded electronics

Performance of an existing LSO PET scanner was compared to that of the same scanner with upgraded electronics. TDC step resolution decreased to 500 ps while background corrected system energy resolution increased to 18.89%. This allowed a lowering of the coincidence time window to 4.5 ns and an increase in the system LLD to 400 keV. Electronics dead time was reduced to 136 ns. Singles rates from each DEA were increased 100%. An almost 100% increase in NEC was achieved due to the increased electronics performance. The peak NEC was greater than 93,000.

Measuring the non-proportional response of scintillators using a Positron Emission Tomography scanner

A novel way of measuring the non-proportional response of scintillation materials, using a Positron Emission Tomography (PET) scanner, has been developed and tested. Using a Siemens Biograph mCT, a modified Compton coincidence technique is performed where the Compton scatter angular information data is collected by taking advantage of the fine angular sampling that is inherent to the PET scanner. Using the scatter angle information, the energy deposited in the sampled scintillator can be calculated. Comparing the calculated energy deposited versus the measured scintillator response yields the Compton electron non-proportional response.

Tracking coincidence events in pet even when count rates are extremely high: The Lost-Event Tally packet concept

We describe techniques that extend the usefulness of real-time data-handling architectures designed for clinical positron emission tomography (PET)-especially for instances of extremely high (>; 10 M events/s) count rate. As is widely known, Rubidium-82 (82Rb) with a 1.3-min half-life is often used in clinical PET. When used, 82Rb is more often applied for dynamic and/or gated studies-typically with little or no delay between tracer injection and start of acquisition. The use of 82Rb for short-duration-framed studies in clinical PET has its own set of challenges. For example, a “too large” dose may temporarily exceed the acquisition throughput. When such saturation occurs, coincidence events are lost. In the case of 82Rb, such loss is typically short-lived and limited to the count-rate peak. Such saturation also leads to a truncation of the count-rate profile-a truncation that often limits curve fitting essential for an accurate compartmental model across the entire study. The techniques offered here help to resolve this issue. By electronically keeping track of those events that are subject to saturation loss in the acquisition channel, the complete count-rate profile itself is preserved. Such tracking is done in real time with an accurate log of loss quantities added to the list-mode stream. This approach enables the clinician to raise the 82Rb dose without a specific concern over count-rate profile truncation. We describe a special 64-bit nonevent (i.e., “tag”) packet that is automatically inserted into the list-mode stream. The “Lost-Event Tally” tag packet stream enables a full recovery of the rate profile even when event packets are lost. During acquisition, this tag packet is repeatedly inserted into the stream to report the counted event-packet loss (up to 1 048 575) since the previous such tag packet was inserted.