Measurements of wavelength shifting (WLS) fibre readout for a highly multiplexed, depth-encoding PET detector

Du, Heng; Yang, Yongfeng; Cherry, Simon R.

doi:10.1088/0031-9155/52/9/011

Cited by 20 publications

(15 citation statements)

References 18 publications

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“…A similar but more complex readout scheme than ours uses perpendicular arranged wavelength shifter fibers and PMTs instead of cross strip G-APDs. 48 Unfortunately, this LSO-based detector has not been evaluated according to dE/E and CRT. However, this detector allows a multiplexing from N 2 crystals into 2 × N decoding channels.…”

Section: Discussionmentioning

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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Section: Discussionmentioning

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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“…In Fig. 7b, the wavelength shifting (WLS) optical fibers are placed orthogonally on the top and botton of the scintillator array, and photosensors are coupled to one end of the WLS fibers for signal readout [52]. Since the WLS fibers readout the signals over row or column, that can reduce the number of photosensors.…”

Section: Continuous Doi Measurement By Dual-ended Readout Detectorsmentioning

confidence: 99%

“…Accordingly, this approach is advantaged to build large-ring systems, and applied to develop a whole-body clinical PET/CT scanner, although the signals from WLS fibers at present are used to improve detector identification and energy resolution (compared with block detector design), rather than to acquire DOI information [51]. For acceptable performance, however, it is critical to maximize collection of light photons from the ends of the fibers and to minimize the optical crosstalk between adjacent fibers [52]. The use of optical fibers degrades time performance.…”

Section: Continuous Doi Measurement By Dual-ended Readout Detectorsmentioning

confidence: 99%

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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“…A promising approach for obtaining higher DOI resolution is to read out the scintillation light by placing photodetectors at both ends of the crystal array and use the ratio of the 2 photodetector signals to measure the DOI (22)(23)(24)(25)(26). An alternative approach being used to estimate DOI for monolithic scintillator crystals measures the distribution of the scintillation light signal on a positionsensitive photodetector array (27,28).…”

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confidence: 99%

A Prototype PET Scanner with DOI-Encoding Detectors

Yang¹,

Wu²,

Qi³

et al. 2008

J Nucl Med

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Detectors with depth-encoding allow a PET scanner to simultaneously achieve high sensitivity and high spatial resolution. Methods: A prototype PET scanner, consisting of depth-encoding detectors constructed by dual-ended readout of lutetium oxyorthosilicate (LSO) arrays with 2 position-sensitive avalanche photodiodes (PSAPDs), was developed. The scanner comprised 2 detector plates, each with 4 detector modules, and the LSO arrays consisted of 7 · 7 elements, with a crystal size of 0.9225 · 0.9225 · 20 mm and a pitch of 1.0 mm. The active area of the PSAPDs was 8 · 8 mm. The performance of individual detector modules was characterized. A line-source phantom and a hot-rod phantom were imaged on the prototype scanner in 2 different scanner configurations. The images were reconstructed using 20, 10, 5, 2, and 1 depth-of-interaction (DOI) bins to demonstrate the effects of DOI resolution on reconstructed image resolution and visual image quality. Results: The flood histograms measured from the sum of both PSAPD signals were only weakly depth-dependent, and excellent crystal identification was obtained at all depths. The flood histograms improved as the detector temperature decreased. DOI resolution and energy resolution improved significantly as the temperature decreased from 20°C to 10°C but improved only slightly with a subsequent temperature decrease to 0°C. A full width at half maximum (FWHM) DOI resolution of 2 mm and an FWHM energy resolution of 15% were obtained at a temperature of 10°C. Phantom studies showed that DOI measurements significantly improved the reconstructed image resolution. In the first scanner configuration (parallel detector planes), the image resolution at the center of the field of view was 0.9-mm FWHM with 20 DOI bins and 1.6-mm FWHM with 1 DOI bin. In the second scanner configuration (detector planes at a 40°angle), the image resolution at the center of the field of view was 1.0-mm FWHM with 20 DOI bins and was not measurable when using only 1 bin. Conclusion: PET scanners based on this detector design offer the prospect of high and uniform spatial resolution (crystal size, ;1 mm; DOI resolution, ;2 mm), high sensitivity (20-mm-thick detectors), and compact size (DOI encoding permits detectors to be tightly packed around the subject and minimizes number of detectors needed). Over the past decade, many small-animal PET scanners have been developed (1-12), and this technology has played a very important role in the rapidly growing field of molecular imaging. High sensitivity is needed to increase signal-to-noise ratio of the images to reliably detect lower levels of radiotracer uptake and to reduce the injected dose (reducing radiation dose to the subject) (13) and scan time (increasing temporal resolution for dynamic studies). High spatial resolution is required to detect small structures and lesions and to improve quantification by reducing the partialvolume effect. A compromise between sensitivity and spatial resolution due to depth-of-interaction (DOI) effects always exists in small-ani...

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Measurements of wavelength shifting (WLS) fibre readout for a highly multiplexed, depth-encoding PET detector

Cited by 20 publications

References 18 publications

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

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

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

A Prototype PET Scanner with DOI-Encoding Detectors

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