Continuous depth-of-interaction encoding using phosphor-coated scintillators

Du, Heng; Yang, Yongfeng; Głodo, J.; Wu, Yue; Shah, K.S.; Cherry, Simon R.

doi:10.1088/0031-9155/54/6/023

Cited by 55 publications

(50 citation statements)

References 17 publications

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“…Most DOI detectors employ light sharing over several photosensors, utilize crystals with varied decay time constant, or deliberately alter light collection/wavelength along a scintillator crystal. [21][22][23][24][25][26][27][28][29] This, inevitably, in most cases slows the rise-time and reduces signal-to-noise ratio of the detector signal, compromising timing performance. 15 It is therefore, extremely challenging to fabricate a high performance TOF detector that also provides fine DOI resolution.…”

Section: Background and Theorymentioning

confidence: 99%

Side readout of long scintillation crystal elements with digital SiPM for TOF‐DOI PET

2014

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Purpose: Side readout of scintillation light from crystal elements in positron emission tomography (PET) is an alternative to conventional end-readout configurations, with the benefit of being able to provide accurate depth-of-interaction (DOI) information and good energy resolution while achieving excellent timing resolution required for time-of-flight PET. This paper explores different readout geometries of scintillation crystal elements with the goal of achieving a detector that simultaneously achieves excellent timing resolution, energy resolution, spatial resolution, and photon sensitivity. Methods: The performance of discrete LYSO scintillation elements of different lengths read out from the end/side with digital silicon photomultipliers (dSiPMs) has been assessed. Results: Compared to 3 × 3 × 20 mm 3 LYSO crystals read out from their ends with a coincidence resolving time (CRT) of 162 ± 6 ps FWHM and saturated energy spectra, a side-readout configuration achieved an excellent CRT of 144 ± 2 ps FWHM after correcting for timing skews within the dSiPM and an energy resolution of 11.8% ± 0.2% without requiring energy saturation correction. Using a maximum likelihood estimation method on individual dSiPM pixel response that corresponds to different 511 keV photon interaction positions, the DOI resolution of this 3 × 3 × 20 mm 3 crystal side-readout configuration was computed to be 0.8 mm FWHM with negligible artifacts at the crystal ends. On the other hand, with smaller 3 × 3 × 5 mm 3 LYSO crystals that can also be tiled/stacked to provide DOI information, a timing resolution of 134 ± 6 ps was attained but produced highly saturated energy spectra. Conclusions: The energy, timing, and DOI resolution information extracted from the side of long scintillation crystal elements coupled to dSiPM have been acquired for the first time. The authors conclude in this proof of concept study that such detector configuration has the potential to enable outstanding detector performance in terms of timing, energy, and DOI resolution. C 2014 American Association of Physicists in Medicine. [http://dx

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Section: Background and Theorymentioning

confidence: 99%

Side readout of long scintillation crystal elements with digital SiPM for TOF‐DOI PET

2014

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“…2b. Various methods were proposed to quantify the differences in the pulse shape, as follows: constant fraction discrimination (CFD); rise time discrimination (RTD); constant time discrimination (CTD); charge comparison (CC); and delayed charge integration (DCI) methods [25][26][27]. Based on the comparison of the different PSD methods, the performance of those methods depends on the radiation detector and the signal-to-noise ratio [26].…”

Section: Requirements For High Timing Resolutionmentioning

confidence: 99%

“…10b is a phosphor-coated crystal detector in which the upper-half crystal surface is coated by the thin layer of the phosphor powder [27]. The phosphor absorbs scintillation light with a relatively short decay time, and re-emits "phosphor-converted" light with a longer decay time.…”

Section: Continuous Doi Measurement By Single-ended Readoutmentioning

confidence: 99%

“…Although this approach utilizes the PSD method mentioned in the section of discrete DOI measurement (vide supra), it provides continuous DOI information. Using the delayed charge integration (DCI) method, the average DOI resolution (FWHM) obtained was 8.0 mm for 1.5 × 1.5 × 20 mm 3 LSO crystals (4 x 4 array) half-coated with YGG phosphor [27]. The use of unpolished crystal is necessary in this approach, and causes large light collection loss along the DOI position, so that the photoelectricpeak position in the energy spectrum decreases with an increase in the distance between the DOI position and PMT surface [27].…”

Section: Continuous Doi Measurement By Single-ended Readoutmentioning

confidence: 99%

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Positron emission tomography (PET) detectors with depth-of- interaction (DOI) capability

2011

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Because positron emission tomography (PET) provides biochemical information in vivo with the sensitivity at the sub-pico-molar level, pre-clinical research using PET plays an important role in biological and pharmaceutical sciences. However, small animal imaging by PET has been challenging with respect to spatial resolution and sensitivity due to the small volume of the imaging objects. A DOI-encoding technique allows for pre-clinical PET to simultaneously achieve high spatial resolution and high sensitivity. Thus many DOI-encoding methods have been proposed. In this paper we describe why DOI measurements are important, what is required in DOI-encoding designs, and how to extract DOI information in scintillator-based DOI detectors. Recently, there has been a growing interest in DOI measurements for TOF PET detectors to correct time walk as a function of DOI position. Thus, the DOI-encoding method with a high time performance suitable for TOF detectors is now required. The requirements to improve the time resolution in DOI detectors are discussed as well.Keywords Positron emission tomography (PET), Depth of interaction (DOI), Multi-layer detector, Dual-ended readout, Single-ended readout THE IMPORTANCE OF DOI MEASUREMENT Simultaneous improvement in spatial resolution and sensitivityThe PET is an important pre-clinical imaging technique because PET provides biochemical information down to the sub-pico-molar level in vivo [1]. Thus, the development of pre-clinical PET scanners has been actively promoted. The major focus of the development is to obtain a similar quality in small animal images as human images, while the size of the imaging subject decreases and the amount of radiopharmaceutical injected into the small animals is limitedTo obtain a similar level of detail and SNR in mouse images as human images, spatial resolution and sensitivity should be increased. That is why many PET instrument researchers have been attempting for the pre-clinical PET to simultaneously achieve high spatial resolution and high sensitivity. The pre-clinical PET systems therefore have been designed by using very long and narrow crystals with small diameter ring geometry. However, such system structures cause the parallax error to become lager when providing no depth-of-interaction (DOI) information within crystals (general PETs can measure no DOI information), and bring the degradation of the radial resolution in the peripheral field of view (FOV). That is because the reconstruction algorithm, when drawing a line of response (LOR) without DOI information, usually assigns the interaction positions over all depths within a crystal to a single position (i.e. the center position on the front of the interacted crystals).

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“…Another approach involves the application of a special coating to scintillators and measurement of the pulse shape changes according to the gamma interaction position. 43 Here, we present a novel design and performance evaluation of a next generation PET detector yielding high spatial resolution, dense packaging, high detection sensitivity, and continuous DoI information. The detector is based on the readout of a fine pixelated scintillation block on two opposing sides by compact custom designed G-APD strip detectors.…”

Section: Introductionmentioning

confidence: 99%

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

Kolb¹,

Parl²,

Mantlik³

et al. 2014

Medical Physics

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Purpose: The aim of this study was to develop a prototype PET detector module for a combined small animal positron emission tomography and magnetic resonance imaging (PET/MRI) system. The most important factor for small animal imaging applications is the detection sensitivity of the PET camera, which can be optimized by utilizing longer scintillation crystals. At the same time, small animal PET systems must yield a high spatial resolution. The measured object is very close to the PET detector because the bore diameter of a high field animal MR scanner is limited. When used in combination with long scintillation crystals, these small-bore PET systems generate parallax errors that ultimately lead to a decreased spatial resolution. Thus, we developed a depth of interaction (DoI) encoding PET detector module that has a uniform spatial resolution across the whole field of view (FOV), high detection sensitivity, compactness, and insensitivity to magnetic fields. Methods: The approach was based on Geiger mode avalanche photodiode (G-APD) detectors with cross-strip encoding. The number of readout channels was reduced by a factor of 36 for the chosen block elements. Two 12 × 2 G-APD strip arrays (25 μm cells) were placed perpendicular on each face of a 12 × 12 lutetium oxyorthosilicate crystal block with a crystal size of 1.55 × 1.55 × 20 mm. The strip arrays were multiplexed into two channels and used to calculate the x, y coordinates for each array and the deposited energy. The DoI was measured in step sizes of 1.8 mm by a collimated 18 F source. The coincident resolved time (CRT) was analyzed at all DoI positions by acquiring the waveform for each event and applying a digital leading edge discriminator. Results: All 144 crystals were well resolved in the crystal flood map. The average full width half maximum (FWHM) energy resolution of the detector was 12.8% ± 1.5% with a FWHM CRT of 1.14 ± 0.02 ns. The average FWHM DoI resolution over 12 crystals was 2.90 ± 0.15 mm. Conclusions: The novel DoI PET detector, which is based on strip G-APD arrays, yielded a DoI resolution of 2.9 mm and excellent timing and energy resolution. Its high multiplexing factor reduces the number of electronic channels. Thus, this cross-strip approach enables low-cost, high-performance PET detectors for dedicated small animal PET and PET/MRI and potentially clinical PET/MRI systems.

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Continuous depth-of-interaction encoding using phosphor-coated scintillators

Cited by 55 publications

References 17 publications

Side readout of long scintillation crystal elements with digital SiPM for TOF‐DOI PET

Side readout of long scintillation crystal elements with digital SiPM for TOF‐DOI PET

Positron emission tomography (PET) detectors with depth-of- interaction (DOI) capability

Development of a novel depth of interaction PET detector using highly multiplexed G‐APD cross‐strip encoding

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