Timing Calibration in PET Using a Time Alignment Probe

Moses, W.W.; Thompson, Christopher J.

doi:10.1109/tns.2006.882797

Cited by 10 publications

(8 citation statements)

References 19 publications

(15 reference statements)

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“…The relationship between the event energy and the time to cross a pre-set threshold can be obtained by using a precision reference detector; data from the coincidence detector pair can be used to correct the detector of interest. In a real scanner, a calibration probe can be used as a reference detector [18]. In this case, the electronics either needs to be modified during the time-walk correction process, or requires provision for spare connections for the external probe.…”

Section: Introductionmentioning

confidence: 99%

A Time-Walk Correction Method for PET Detectors Based on Leading Edge Discriminators

Schmall

Judenhofer

et al. 2017

IEEE Trans. Radiat. Plasma Med. Sci.

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The leading edge timing pick-off technique is the simplest timing extraction method for PET detectors. Due to the inherent time-walk of the leading edge technique, corrections should be made to improve timing resolution, especially for time-of-flight PET. Time-walk correction can be done by utilizing the relationship between the threshold crossing time and the event energy on an event by event basis. In this paper, a time-walk correction method is proposed and evaluated using timing information from two identical detectors both using leading edge discriminators. This differs from other techniques that use an external dedicated reference detector, such as a fast PMT-based detector using constant fraction techniques to pick-off timing information. In our proposed method, one detector was used as reference detector to correct the time-walk of the other detector. Time-walk in the reference detector was minimized by using events within a small energy window (508.5 – 513.5 keV). To validate this method, a coincidence detector pair was assembled using two SensL MicroFB SiPMs and two 2.5 mm × 2.5 mm × 20 mm polished LYSO crystals. Coincidence timing resolutions using different time pick-off techniques were obtained at a bias voltage of 27.5 V and a fixed temperature of 20 °C. The coincidence timing resolution without time-walk correction were 389.0 ± 12.0 ps (425 –650 keV energy window) and 670.2 ± 16.2 ps (250–750 keV energy window). The timing resolution with time-walk correction improved to 367.3 ± 0.5 ps (425 – 650 keV) and 413.7 ± 0.9 ps (250 – 750 keV). For comparison, timing resolutions were 442.8 ± 12.8 ps (425 – 650 keV) and 476.0 ± 13.0 ps (250 – 750 keV) using constant fraction techniques, and 367.3 ± 0.4 ps (425 – 650 keV) and 413.4 ± 0.9 ps (250 – 750 keV) using a reference detector based on the constant fraction technique. These results show that the proposed leading edge based time-walk correction method works well. Timing resolution obtained using this method was equivalent to that obtained using a reference detector and was better than that obtained using constant fraction discriminators.

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Section: Introductionmentioning

confidence: 99%

A Time-Walk Correction Method for PET Detectors Based on Leading Edge Discriminators

Schmall

Judenhofer

et al. 2017

IEEE Trans. Radiat. Plasma Med. Sci.

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“…1 (right), due to accumulated time uncertainty and jitter from a larger number of clock distribution components, including cables. Constant skews may be automatically compensated by periodic calibration, along with trigger signal delay mismatches [13], [14], although calibration procedures are usually lengthy and costly [15], [16]. However, actual skew values are not entirely deterministic and may show small variations between power cycles, as well as fluctuate with variations in operating conditions.…”

Section: Introductionmentioning

confidence: 99%

PET System Synchronization and Timing Resolution Using High-Speed Data Links

Aliaga

Monzó

Spaggiari

et al. 2011

IEEE Trans. Nucl. Sci.

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Abstract-Current PET systems with fully digital trigger rely on early digitization of detector signals and the use of digital processors, usually FPGAs, for recognition of valid gamma events on single detectors. Timestamps are assigned and later used for coincidence analysis. In order to maintain a decent timing resolution for events detected on different acquisition boards, it is necessary that local timestamps on different FPGAs be synchronized. Sub-nanosecond accuracy is mandatory if we want this effect to be negligible on overall timing resolution. This is usually achieved by connecting all boards to a common backplane with a precise clock delivery network; however, this approach forces a rigid structure on the whole PET system and may pose scalability problems.As an alternative, we propose a backplane-less PET system architecture in which DAQ boards are connected by single fullduplex high-speed data links. Data encoding with embedded clock is used to correct frequency differences between local oscillators. Timestamp synchronization between FPGAs with clock period resolution is maintained by means of data transfers in a way similar to the IEEE 1588 standard. Finer resolution is achieved by reflection of received clocks and phase difference measurement on the transmitter. It is crucial that data transceivers have very low latency uncertainty in order to achieve the desired timestamp accuracy; we discuss the availability of off-the-shelf hardware for these implementations.

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“…In the former case, using long cables to transport sensitive sensor outputs degrades signal quality and timing [14], [15] and may require channelwise time alignment depending on implementation [16]. The latter case, on the other hand, requires transmission lines to be matched in length in order to obtain a fully balanced clock tree [17]- [19], which can be difficult when the number of acquisition nodes to be synchronized is large [20], forcing additional global timing calibrations [21]. Further problems arise when there is a large distance between system nodes, as fluctuating operating conditions such as temperature cause a variation of the delay of long lines [22].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a Modular PET System Architecture with Synchronization over Data Links

Aliaga

Bosch

Monzó

et al. 2014

IEEE Trans. Nucl. Sci.

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Abstract-A DAQ architecture for a PET system is presented that focuses on modularity, scalability and reusability. The system defines two basic building blocks: data acquisitors and concentrators, which can be replicated in order to build a complete DAQ of variable size. Acquisition modules contain a scintillating crystal and either a position-sensitive photomultiplier (PSPMT) or an array of silicon photomultipliers (SiPM). The detector signals are processed by AMIC, an integrated analog front-end that generates programmable analog outputs which contain the first few statistical moments of the light distribution in the scintillator. These signals are digitized at 156.25 Msamples/s with free-running ADCs and sent to an FPGA which detects single gamma events, extracts position and time information online using digital algorithms, and submits these data to a concentrator module. Concentrator modules collect single events from acquisition modules and perform coincidence detection and data aggregation. A synchronization scheme over data links is implemented that calibrates each link's latency independently, ensuring that there are no limitations on module mobility, and that the architecture is arbitrarily scalable. Prototype boards with both acquisition and concentration functionality have been built for evaluation purposes. The performance of a small PET system with two detectors based on continuous scintillators is presented. A synchronization error below 50 ps rms is measured, and energy resolutions of 19% and 24% and timing resolutions of 2.0 ns and 4.7 ns FWHM are obtained for PMT and SiPM photodetectors, respectively.

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Timing Calibration in PET Using a Time Alignment Probe

Cited by 10 publications

References 19 publications

A Time-Walk Correction Method for PET Detectors Based on Leading Edge Discriminators

A Time-Walk Correction Method for PET Detectors Based on Leading Edge Discriminators

PET System Synchronization and Timing Resolution Using High-Speed Data Links

Evaluation of a Modular PET System Architecture with Synchronization over Data Links

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