Evolution of PET Detectors and Event Positioning Algorithms Using Monolithic Scintillation Crystals

González-Montoro, Andrea; González, Antonio J.; Pourashraf, Shirin; Miyaoka, Robert S.; Bruyndonckx, Peter; Chinn, Garry; Pierce, Larry A.; Levin, Craig S.

doi:10.1109/trpms.2021.3059181

Cited by 64 publications

(55 citation statements)

References 161 publications

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“…A different approach is the monolithic scintillator detector, which consists of a large (typically several cm 3 ) single crystal read out by SiPM array(s) coupled to one or more of its surfaces [ 211 ]. The 3D position of interaction in the crystal is decoded from the measured light intensity map(s), while multiple timestamps (typically one per SiPM pixel) are available to estimate the time of interaction.…”

Section: Future Of Tof In Petmentioning

confidence: 99%

Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography

Schaart

Schramm

Surti

2021

IEEE Trans. Radiat. Plasma Med. Sci.

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The first time-of-flight positron emission tomography (TOF-PET) scanners were developed as early as in the 1980s. However, the poor light output and low detection efficiency of TOF-capable detectors available at the time limited any gain in image quality achieved with these TOF-PET scanners over the traditional non-TOF PET scanners. The discovery of LSO and other Lu-based scintillators revived interest in TOF-PET and led to the development of a second generation of scanners with high sensitivity and spatial resolution in the mid-2000s. The introduction of the silicon photomultiplier (SiPM) has recently yielded a third generation of TOF-PET systems with unprecedented imaging performance. Parallel to these instrumentation developments, much progress has been made in the development of image reconstruction algorithms that better utilize the additional information provided by TOF. Overall, the benefits range from a reduction in image variance (SNR increase), through allowing joint estimation of activity and attenuation, to better reconstructing data from limited angle systems. In this work, we review these developments, focusing on three broad areas: (1) timing theory and factors affecting the time resolution of a TOF-PET system, (2) utilization of TOF information for improved image reconstruction, and (3) quantification of the benefits of TOF compared to non-TOF PET. Finally, we offer a brief outlook on the TOF-PET developments anticipated in the short and longer term. Throughout this work, we aim to maintain a clinically-driven perspective, treating TOF as one of multiple (and sometimes competitive) factors that can aid in the optimization of PET imaging performance.

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Section: Future Of Tof In Petmentioning

confidence: 99%

Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography

Schaart

Schramm

Surti

2021

IEEE Trans. Radiat. Plasma Med. Sci.

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“…Monolithic detectors provide high spatial, timing, energy resolution, and sensitivity, while the single detector is significantly cheaper compared to a pixelated crystal with the same resolution (Borghi et al 2016b, Marcinkowski et al 2016, Gonzalez-Montoro et al 2021. The unit cost for e.g.…”

Section: Introductionmentioning

confidence: 99%

High-resolution monolithic LYSO detector with 6-layer depth-of-interaction for clinical PET

et al. 2021

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The system spatial resolution of whole-body positron emission tomography (PET) is limited to around 2 mm due to positron physics and the large diameter of the bore. To stay below this 'physics'limit a scintillation detector with an intrinsic spatial resolution of around 1.3 mm is needed. Currently used detector technology consists of arrays of 2.6-5 mm segmented scintillator pixels which are the dominant factor contributing to the system resolution. Pixelated detectors using smaller pixels exist but face major drawbacks in sensitivity, timing, energy resolution and cost. Monolithic continuous detectors, where the spatial resolution is determined by the shape of the light distribution on the photo detector array, are a promising alternative. Without having the drawbacks of pixelated detectors, monolithic ones can also provide depth-of-interaction (DOI) information. In this work we present a monolithic detector design aiming to serve high-resolution clinical PET systems while maintaining high sensitivity. A 50 x 50 x 16 mm 3 Lutetium-Yttrium oxyorthosilicate (LYSO) scintillation crystal with silicon photomultiplier (SiPM) back side readout is calibrated in singles mode by a collimated beam obtaining a reference dataset for the event positioning. A mean nearest neighbour (MNN) algorithm and an artificial neural network for positioning are compared. The targeted intrinsic detector resolution of 1.3 mm needed to reach a 2 mm resolution on system level was accomplished with both algorithms. The neural network achieved a mean spatial resolution of 1.14 mm FWHM for the whole detector and 1.02 mm in the centre (30 x 30 mm 2 ). The MNN algorithm performed slightly worse with 1.17 mm for the whole detector and 1.13 mm in the centre. The intrinsic DOI information will also result in uniform system spatial resolution over the full field of view.

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“…Furthermore, this configuration provides a higher sensitivity than pixelated approaches, and a good and not intrinsically limited spatial resolution. 4 However, the timing capabilities of monolithic scintillators are usually more challenging than in pixelated crystals due to the spreading of the scintillation light inside the crystal. To achieve good timing capabilities, a high number of photons need to be collected in a single photosensor.…”

Section: Introductionmentioning

confidence: 99%

Timing evaluation of a PET detector block based on semi‐monolithic LYSO crystals

et al. 2021

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Purpose: Detectors for positron emission tomography (PET) typically use two types of scintillation crystals, pixelated or monolithic. A variant of these types of scintillators are the so-called semi-monolithic crystals. They consist of a monolithic crystal segmented in one direction in pieces called slabs. These scintillators have the potential to successfully combine the benefits of pixelated and monolithic configurations, providing good timing and spatial resolutions as well as the capacity to decode the depth of interaction (DOI) information. In this work, the timing performance of a detector based on semi-monolithic crystals was studied in depth. The energy response was also evaluated. Methods: The semi-monolithic detector consists of 1 × 24 LYSO slabs of 25.4 × 12 × 0.95 mm 3 each. The bottom surface of the slabs is coupled to an array of 8 × 8 silicon photomultipliers (SiPMs) of 3 × 3 mm 2 active area, 50 μm cell size and 3.2 mm pitch. The 64 output signals were independently readout by the TOFPET2 ASIC. In order to achieve the best coincidence time resolution (CTR), four different time walk corrections were tested. Additional work investigated the best method of combining the timestamps belonging to the same event.Results: The resolvability of the slabs in the measured flood maps improves with the thickness of a light guide placed in between the scintillators and photosensors. The energy resolution does not change significantly with values as good as 13.7%. Regarding the CTR, values of 335.8, 363, 369.8, and 402.5 ps have been obtained for the whole detector for no light guide, 0.5, 1.0, and 1.5 mm thickness light guide cases, respectively. These values further improve to 276.1, 302.6, 305.6 and 336.2 ps, respectively, when energy-weighted averaging of timestamps is applied. Conclusions: We have shown both an excellent timing resolution and good energy resolution for a PET detector based on semi-monolithic crystals. The use of light guides of different thicknesses does not significantly affect the energy resolution of the whole detector, but the timing capabilities slightly worsen with the increasing thickness of the light guide.

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Evolution of PET Detectors and Event Positioning Algorithms Using Monolithic Scintillation Crystals

Cited by 64 publications

References 161 publications

Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography

Time of Flight in Perspective: Instrumental and Computational Aspects of Time Resolution in Positron Emission Tomography

High-resolution monolithic LYSO detector with 6-layer depth-of-interaction for clinical PET

Timing evaluation of a PET detector block based on semi‐monolithic LYSO crystals

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