| 1. |
- Blackberg, Lisa, et al.
(author)
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Light Transport in PET Scintillator Detectors Fabricated Using Laser Induced Optical Barriers
- 2016
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In: 2016 Ieee Nuclear Science Symposium, Medical Imaging Conference And Room-Temperature Semiconductor Detector Workshop (Nss/Mic/Rtsd). - 9781509016426
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Conference paper (peer-reviewed)abstract
- Laser Induced Optical Barriers (LIOB) is a promising technique for fabrication of high resolution and high sensitivity scintillator detectors for Positron Emission Tomography (PET). With LIOB local changes in refractive index may be introduced inside the bulk of a monolithic crystal by using a tightly focused pulsed laser. One major advantage of LIOB compared to standard mechanical pixelation techniques is the flexibility in patterns that may be created in the crystal to redirect the scintillation light. With the aim of finding the optimal pattern of optical barriers for a single-side readout detector for small animal PET, we are performing simulations to study the light transport within laser-processed crystals. Here we report on results obtained with two 25.4x25.4x20.0 mm(3) LYSO:Ce crystals: 1) containing a 1 mm pitch pixel-like pattern throughout the crystal depth, and 2) pixel-like pattern in the top half of the crystal only. The crystal is coupled to an 8x8 photodetector array with 3.2 mm pixel pitch and the light spread functions are analyzed as a function of source location. Results suggest that 1 mm transversal spatial resolution is achievable using the LIOB technique. We further see that depending on the quality of the barrier/crystal interface and the barrier depth within the crystal, some level of DOI information may be obtained from the light response functions when using these simple patterns.
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| 2. |
- Bläckberg, Lisa, 1982-, et al.
(author)
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Light spread manipulation in scintillators using laser induced optical barriers
- 2018
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In: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 65:8, s. 2208-2215
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Journal article (peer-reviewed)abstract
- We are using the Laser Induced Optical Barriers (LIOB) technique to fabricate scintillator detectors with combined performance characteristics of the two standard detector types, mechanically pixelated arrays and monolithic crystals. This is done by incorporation of so-called optical barriers that have a refractive index lower than that of the crystal bulk. Such barriers can redirect the scintillation light and allow for control of the light spread in the detector. Previous work has shown that the LIOB technique has the potential to achieve detectors with high transversal and depth of interaction (DOI) resolution simultaneously in a single-side readout configuration, suitable for high resolution PET imaging. However, all designs studied thus far present edge effect issues similarly as in the standard detector categories. In this work we take advantage of the inherent flexibility of the LIOB technique and investigate alternative barrier patterns with the aim to address this problem. Light transport simulations of barrier patterns in LYSO:Ce, with deeper barrier walls moving towards the detector edge show great promise in reducing the edge effect, however there is a trade-off in terms of achievable DOI information. Furthermore, fabrication and characterization of a 20 mm thick LYSO:Ce detector with optical barriers forming a pattern of 1×1×20mm3 pixel like structures show that light channeling in laser-processed detectors in agreement with optical barriers with refractive index between 1.2 and 1.4 is achievable.
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| 3. |
- Bläckberg, Lisa, 1982-, et al.
(author)
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Scintillator-based Photon Counting Detector : is it feasible?
- 2016
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In: 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference And Room-Temperature Semiconductor Detector Workshop (Nss/Mic/Rtsd). - 9781509016426 - 9781509016433
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Conference paper (peer-reviewed)abstract
- By utilizing finely pitched scintillator arrays where the scintillator has high atomic number and density, fast decay time, and high light output, realizing a scintillator-based Photon Counting Detector (PCD) is conceptually feasible. Fabrication of fine-pitched scintillator arrays however, has been the bottleneck for realizing such detectors. Combining the novel scintillator fabrication technique called laser-induced optical barriers (LIOB) where optical barriers can be placed inside a transparent crystal and act as a reflector without removing the material, with laser ablation, we are now able to overcome the obstacles for developing scintillator-based PCD. In this regard, we are developing an LYSO-based PCD where the LYSO crystal is laser pixelated to sub-mm pixels. The scintillator array will be coupled to an application specific integrated circuit (ASIC) where each ASIC pixel has built-in photodiode, amplifiers and 3-4 energy windows and their associated counters. We have simulated light transport for different scenarios where the crystal is pixelated by a combination of LIOB and laser cut techniques, where the 2 mm thick crystal is first pixelated by LIOB to a depth and then the rest is pixelated by the ablation technique. We also simulated the fraction of collected light in the same scintillator pixel by modeling various surface properties of the pixel cuts as well as optical barrier surface roughness and refractive index (RI). Simulation results show that up to similar to 70% of the scintillation light will be contained in the same pixel when only using the LIOB technique with barrier refractive index of 1.0. These results suggest that laser processed arrays can potentially change the paradigm in PCD development as they can replace the traditional array production and thus allow for scintillator-based PCD development in a more robust and cost-effective manner.
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| 4. |
- Bläckberg, Lisa, 1982-, et al.
(author)
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Simulation study of light transport in laser-processed LYSO:Ce detectors with single-side readout
- 2017
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In: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 62:21, s. 8419-8440
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Journal article (peer-reviewed)abstract
- A tightly focused pulsed laser beam can locally modify the crystal structure inside the bulk of a scintillator. The result is incorporation of so-called optical barriers with a refractive index different from that of the crystal bulk, that can be used to redirect the scintillation light and control the light spread in the detector. We here systematically study the scintillation light transport in detectors fabricated using the laser induced optical barrier technique, and objectively compare their potential performance characteristics with those of the two mainstream detector types: monolithic and mechanically pixelated arrays. Among countless optical barrier patterns, we explore barriers arranged in a pixel-like pattern extending all-the-way or half-way through a 20 mm thick LYSO:Ce crystal. We analyze the performance of the detectors coupled to MPPC arrays, in terms of light response functions, flood maps, line profiles, and light collection efficiency. Our results show that laser-processed detectors with both barrier patterns constitute a new detector category with a behavior between that of the two standard detector types. Results show that when the barrier-crystal interface is smooth, no DOI information can be obtained regardless of barrier refractive index (RI). However, with a rough barrier-crystal interface we can extract multiple levels of DOI. Lower barrier RI results in larger light confinement, leading to better transverse resolution. Furthermore we see that the laser-processed crystals have the potential to increase the light collection efficiency, which could lead to improved energy resolution and potentially better timing resolution due to higher signals. For a laser-processed detector with smooth barrier-crystal interfaces the light collection efficiency is simulated to >42%, and for rough interfaces >73%. The corresponding numbers for a monolithic crystal is 39% with polished surfaces, and 71% with rough surfaces, and for a mechanically pixelated array 35% with polished pixel surfaces and 59% with rough surfaces.
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| 5. |
- Bläckberg, Lisa, 1982-, et al.
(author)
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Simulation Study of Partially Laser-Processed LYSO:Ce with Single-Side Readout
- 2017
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In: 2017 IEEE Nuclear Science Symposium And Medical Imaging Conference (NSS/MIC). - 9781538622827
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Conference paper (peer-reviewed)abstract
- Laser Induced Optical Barriers (LIOB) can be used to locally engineer the refractive index of a scintillator crystal, leading to the incorporation of so-called optical barriers. Given that the optical barriers may be placed in virtually any pattern inside the scintillator, light transport simulations are important tools for pattern optimization for a given end-application. In this work we simulate the light spread in a 20 mm thick LYSO:Ce detector with optical barriers in a pixel-like pattern half way through its thickness, read out by a photodetector array on one side. We compare the detector performance in terms of DOI and transversal resolution, depending on which side of the detector is chosen for light extraction. Our results show that reading the detector from the laser-processed side yields higher DOI resolution, at the expense of XY resolution, compared to the opposite configuration.
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| 6. |
- Sabet, Hamid, et al.
(author)
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A sub-mm spatial resolution LYSO : Ce detector for small animal PET
- 2015
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In: 2015 Ieee Nuclear Science Symposium And Medical Imaging Conference (Nss/Mic). - : IEEE. - 9781467398626
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Conference paper (peer-reviewed)abstract
- Current high-resolution scintillators are fabricated using mechanical pixelation technique. However the fabrication cost of finely pitched scintillator arrays together with their lack of flexibility to accommodate new depth of interaction designs has remained a significant issue with mechanical pixelation. Another pitfall of mechanically pixelated scintillators is their relatively large inter-pixel gaps that adversely affect their sensitivity to the incident gamma-ray. The main objective of our ongoing efforts is to fabricate high-spatial resolution and high sensitivity PET detectors with depth of interaction (DOI) capability and single-side readout in a cost-effective manner using laser-induced optical barriers (LIOB) technique. We have simulated the behavior of simple optical barriers in LYSO:Ce crystal using the DETECT simulation code. We have also created optical barriers with different size and barrier density in LYSO:Ce at various depths up to 20 mm to form pixel-like shapes similar to mechanically pixelated crystals. In order to process 20mm thick crystals we corrected for laser beam defocusing effect and its adverse effect on laser energy density which results in smaller barrier size and reflectivity. The fabrication time for 10x10x1 and 10x10x20 mm3 LYSO crystals (with lmm pixels) was similar to 8 and 95 minutes respectively.
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| 7. |
- Sabet, Hamid, et al.
(author)
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Novel laser-processed CsI:Tl detector for SPECT
- 2016
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In: Medical physics (Lancaster). - : Wiley. - 0094-2405. ; 43:5, s. 2630-2638
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Journal article (peer-reviewed)abstract
- PURPOSE:The aim of this work is to demonstrate the feasibility of a novel technique for fabrication of high spatial resolution CsI:Tl scintillation detectors for single photon emission computed tomography systems.METHODS:The scintillators are fabricated using laser-induced optical barriers technique to create optical microstructures (or optical barriers) inside the CsI:Tl crystal bulk. The laser-processed CsI:Tl crystals are 3, 5, and 10 mm in thickness. In this work, the authors focus on the simplest pattern of optical barriers in that the barriers are created in the crystal bulk to form pixel-like patterns resembling mechanically pixelated scintillators. The monolithic CsI:Tl scintillator samples are fabricated with optical barrier patterns with 1.0 × 1.0 mm(2) and 0.625 × 0.625 mm(2) pixels. Experiments were conducted to characterize the fabricated arrays in terms of pixel separation and energy resolution. A 4 × 4 array of multipixel photon counter was used to collect the scintillation light in all the experiments.RESULTS:The process yield for fabricating the CsI:Tl arrays is 100% with processing time under 50 min. From the flood maps of the fabricated detectors exposed to 122 keV gammas, peak-to-valley (P/V) ratios of greater than 2.3 are calculated. The P/V values suggest that regardless of the crystal thickness, the pixels can be resolved.CONCLUSIONS:The results suggest that optical barriers can be considered as a robust alternative to mechanically pixelated arrays and can provide high spatial resolution while maintaining the sensitivity in a high-throughput and cost-effective manner.
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| 8. |
- Uzun-Ozsahin, Dilber, et al.
(author)
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GATE Simulation of a High-performance Stationary SPECT System for Cardiac Imaging
- 2016
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In: 2016 Ieee Nuclear Science Symposium, Medical Imaging Conference And Room-Temperature Semiconductor Detector Workshop (Nss/Mic/Rtsd). - 9781509016426
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Conference paper (peer-reviewed)abstract
- In this work we report on GATE simulation studies of DC-SPECT, a body contouring system designed for cardiac imaging applications. The design concept of the DC-SPECT is based on multiple simultaneous view of the heart enabled by the use of laser processed CsI:T1 detector modules with high intrinsic detector resolution. Our theoretical and GATE simulation results show that we can obtain similar to 0.081% system sensitivity and -10.0 mm FWHM system spatial resolution without point spread function (PSF) modeling or other correction techniques. Image reconstruction of a Derenzo-like phantom suggest that the DC-SPECT system can resolve activity rods smaller than 10 mm diameter with no correction techniques applied.
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