High resolution detectors based on continuous crystals and SiPMs for small animal PET

Cabello, Jorge; Barrillon, P.; Barrio, John; Bisogni, Maria Giuseppina; Guerra, A. Del; Lacasta, C.; Rafecas, M.; Saikouk, Hajar; Solaz, C.; Solevi, P.; Taille, C. De La; Llosá, G.

doi:10.1016/j.nima.2012.08.094

Cited by 31 publications

(32 citation statements)

References 7 publications

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“…Moreover, over-estimation is higher for the 10 mm thick crystal than for the 5 mm thick crystal due to the higher aspect ratio. Such effects were reproduced in previous simulation studies of these detectors [9] and also observed in a thorough simulation study investigating different crystal sizes with different aspect ratios [15].…”

Section: A Detector Intrinsic Resolutionsupporting

confidence: 63%

“…While pixelated crystal detectors are standard, the use of continuous crystals has demonstrated increased sensitivity [1]- [9]. However, the estimation of the interaction position of photons in continuous crystals with high resolution requires a sophisti cated algorithm.…”

mentioning

confidence: 99%

“…In this work, the interaction position coordinates including Dol are estimated using a model [7] with no additional detector hardware or training data set, that has already been validated with the current system using Monte Carlo simulations [9]. Sub millimetric detector intrinsic spatial resolution is obtained with continuous crystals, and superior point source full-width at half maximum (FWHM) after image reconstruction is achieved when the continuous nature of the detection space is exploited, com pared to an artificially discretized data space.…”

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confidence: 99%

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Monolithic crystals on SiPM arrays in a prototype system with depth of interaction estimation

Cabello

Gillam

Oliver

et al. 2012

2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)

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Increased sensitivity is one of the major challenges in novel detector development. While pixelated crystals are standard, the use of continuous crystals can provide increased active volume and thus sensitivity. Accurate estimation of the interaction positions of photons in continuous crystals requires a sophisticated algorithm. Additionally, including depth of interaction (Dol) in the reconstruc tion process can mitigate parallax effects near the edges of field of view, therefore Dol estimation is highly desirable. In this work, the interaction position coordinates in 3D are estimated adapting an already existing analytical model to our system with no additional hardware, training data sets or Monte Carlo simulations. The algorithm is implemented in a two-detector-head system comprised of continuous crystals coupled to SiPM arrays. Acquired data is stored in list-mode where the continuous nature of the interaction position is preserved. For image reconstruction, since the crystal is continuous, pre-computation of the system matrix elements would require discretization of the detected measurements. To avoid data discretization the system matrix elements are calculated on-the fly. Spatial information is later on retained in the reconstruction algorithm by using a Sid don-like algorithm where the ray end-points correspond to the estimated interaction positions in continuous space, introducing the interaction position estimation uncertainty in the calculation of the system matrix elements. Reconstruction using continuous data is compared to reconstruction using artificially discretized data. Results show that the spatial resolution measured from a reconstructed point source using ML-EM obtained with a continuous crystal is superior to the spatial resolution obtained with a pixelated crystal. Index Terms-Continuous detector, monolithic detector, depth of interaction, SiPM. I. I NTRODUCTION INCREASED sensitivity is one of the major challenges in detector development, particularly in application to emission imaging in nuclear medicine where data sets can be statistically limited. While pixelated crystal detectors are standard, the use of continuous crystals has demonstrated increased sensitivity [1]-[9]. However, the estimation of the interaction position of photons in continuous crystals with high resolution requires a sophisti cated algorithm. There exists a variety of methods: those based on previous calibrations, statistical methods or neural networks among them. Some methods provide only the two coordinates in the surface plane of the detector. However, including depth of interaction (Dol) in the reconstruction process mitigates parallax effects near the edges of field of view (Fo V), hence reducing the typical anisotropic blurring observed in those regions and the compression effect towards the centre of the Fo V. Dol estimation is highly desirable for high resolution PET. Some works estimate the Dol information using an analytical model from a resistive network [2], phoswich structures [lO] or several read-out ...

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Section: A Detector Intrinsic Resolutionsupporting

confidence: 63%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Monolithic crystals on SiPM arrays in a prototype system with depth of interaction estimation

Cabello

Gillam

Oliver

et al. 2012

2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC)

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“…The slightly higher average values obtained in the present work can be attributed to the increased influence of the intermediate and edge regions in a detector with a smaller surface area. Cabello et al [12] reported a spatial resolution of mm FWHM and mm FWTM for a detector based on a mm mm mm LYSO crystal and a pixels analog SiPM array. These excellent results may have been due to the small photosensor pixel size of mm mm, which enables a very fine sampling of the light distribution.…”

Section: B Spatial Resolutionmentioning

confidence: 99%

“…For example, several research groups have obtained spatial resolutions better than 2 mm FWHM in crystals with a thickness of 10 mmmm [10]- [12], while coincidence resolving times (CRT) well below 200 ps FWHM have recently been achieved with 10 mm and 20 mm thick LSO:Ce(Ca) crystals [13]. Moreover, monolithic scintillator detectors provide good energy resolution [11], [14], show better sensitivity compared to high-resolution crystal matrices due to the absence of dead space, and can estimate the depth of interaction (DOI) from the shape of the light distribution [15]- [20].…”

Section: Introductionmentioning

confidence: 99%

Experimental Validation of an Efficient Fan-Beam Calibration Procedure for <formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula>-Nearest Neighbor Position Estimation in Monolithic Scintillator Detectors

Borghi

Tabacchini

Seifert

et al. 2015

IEEE Trans. Nucl. Sci.

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Monolithic scintillator detectors can achieve excellent spatial resolution and coincidence resolving time. However, their practical use for positron emission tomography (PET) and other applications in the medical imaging field is still limited due to drawbacks of the different methods used to estimate the position of interaction. Common statistical methods for example require the collection of an extensive dataset of reference events with a narrow pencil beam aimed at a fine grid of reference positions. Such procedures are time consuming and not straightforwardly implemented in systems composed of many detectors. Here, we experimentally demonstrate for the first time a new calibration procedure for -nearest neighbor ( -NN) position estimation that utilizes reference data acquired with a fan beam. The procedure is tested on two detectors consisting of mm mm mm and mm mm mm monolithic, Ca-codoped LSO:Ce crystals and digital photon counter (DPC) arrays. For both detectors, the spatial resolution and the bias obtained with the new method are found to be practically the same as those obtained with the previously used method based on pencil-beam irradiation, while the calibration time is reduced by a factor of . Specifically, a FWHM of mm and a FWTM of mm were obtained using the fan-beam method with the 10 mm crystal, whereas a FWHM of mm and a FWTM of mm were achieved with the 20 mm crystal. Using a fan beam made with a MBq point-source and a tungsten slit collimator with 0.5 mm aperture, the total measurement time needed to acquire the reference dataset was hours for the thinner crystal and hours for the thicker one.Index Terms-Calibration, fan beam, monolithic scintillator detector, nearest neighbor method, PET, positron emission tomography.

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Performance evaluation of side‐by‐side optically coupled monolithic LYSO crystals

et al. 2022

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Background: Significant interest has been recently shown for using monolithic scintillation crystals in molecular imaging systems, such as positron emission tomography (PET) scanners. Monolithic-based PET scanners result in a lower cost and higher sensitivity, in contrast to systems based on the more conventional pixellated configuration. The monolithic design allows one to retrieve depth-of -interaction information of the impinging 511 keV photons without the need for additional hardware materials or complex positioning algorithms. However, the so-called edge-effect inherent to monolithic-based approaches worsens the detector performance toward the crystal borders due to the truncation of the light distribution, thus decreasing positioning accuracy. Purpose: The main goal of this work is to experimentally demonstrate the detector performance improvement when machine-learning artificial neuralnetwork (NN) techniques are applied for positioning estimation in multiple monolithic scintillators optically coupled side-by-side. Methods: In this work, we show the performance evaluation of two LYSO crystals of 33 × 25.4 × 10 mm 3 optically coupled by means of a high refractive index adhesive compound (Meltmount, refractive index n = 1.70). A 12 × 12 silicon photomultiplier array has been used as photosensor. For comparison, the same detector configuration was tested for two additional coupling cases: (1) optical grease (n = 1.46) in between crystals, and (2) isolated crystals using black paint with an air gap at the interface (named standard configuration). Regarding 2D photon positioning (XY plane), we have tested two different methods: (1) a machine-learning artificial NN algorithm and (2) a squared-charge (SC) centroid technique. Results: At the interface region of the detector, the SC method achieved spatial resolutions of 1.7 ± 0.3, 2.4 ± 0.3, and 2.6 ± 0.4 mm full-width at half -maximum (FWHM) for the Meltmount, grease, and standard configurations, respectively. These values improve to 1.0 ± 0.2, 1.2 ± 0.2, and 1.2 ± 0.3 mm FWHM when the NN algorithm was employed. Regarding energy performance, resolutions of 18 ± 2%, 20 ± 2%, and 23 ± 3% were obtained at the interface region of the detector for Meltmount, grease, and standard configurations, respectively. Conclusions: The results suggest that optically coupling together scintillators with a high refractive index adhesive, in combination with an NN algorithm, reduces edge-effects and makes it possible to build scanners with almost no gaps in between detectors.

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High resolution detectors based on continuous crystals and SiPMs for small animal PET

Cited by 31 publications

References 7 publications

Monolithic crystals on SiPM arrays in a prototype system with depth of interaction estimation

Monolithic crystals on SiPM arrays in a prototype system with depth of interaction estimation

Experimental Validation of an Efficient Fan-Beam Calibration Procedure for <formula formulatype="inline"><tex Notation="TeX">$k$</tex></formula>-Nearest Neighbor Position Estimation in Monolithic Scintillator Detectors

Performance evaluation of side‐by‐side optically coupled monolithic LYSO crystals

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