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- Borrarzo, Cristian, et al.
(författare)
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Monte Carlo Simulation to Evaluate Factors Affecting Imaging Performances of Compact Scintillation Gamma Camara
- 2016
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Ingår i: 2016 IEEE NUCLEAR SCIENCE SYMPOSIUM, MEDICAL IMAGING CONFERENCE AND ROOM-TEMPERATURE SEMICONDUCTOR DETECTOR WORKSHOP (NSS/MIC/RTSD). - : IEEE. - 9781509016426
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Konferensbidrag (refereegranskat)abstract
- In recent years, a new generation of compact gamma cameras, based on monolithic scintillation crystals, has become increasingly widespread. The main advantages of small FoV gamma cameras with respect to the standard ones are high portability, low cost and low weight, allowing several clinical applications, from scintimammography to intraoperative tumor localization. In gamma cameras based on continuous scintillation crystals, intrinsic Spatial Resolution (SR) is mainly affected by two factors: scintillation light collection efficiency and overall crystal thickness. The first affects the counting statistics, the latter impacts on the light distribution width. To fully investigate the potentiality of these devices we took advantage of Monte Carlo simulations as a valuable tool to physically characterize the imaging systems and to establish a priori reference values. GEANT4 toolkit allows to completely describe the phenomenon of light emission and propagation through the media, providing control to all second-order factors existing in real systems. Results show clearly that SR is dependent on the number of photoelectrons produced and on the light spread. Furthermore, the role of refractive index has been unambiguously identified as an important factor affecting light collection and consequently SR.
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| 2. |
- Borrazzo, Cristian, et al.
(författare)
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PET and MRI-guided focused ultrasound surgery for Neurological Applications
- 2016
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Ingår i: 2016 IEEE NUCLEAR SCIENCE SYMPOSIUM, MEDICAL IMAGING CONFERENCE AND ROOM-TEMPERATURE SEMICONDUCTOR DETECTOR WORKSHOP (NSS/MIC/RTSD). - : IEEE. - 9781509016426
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Konferensbidrag (refereegranskat)abstract
- Magnetic Resonance (MR) guided Focused Ultrasound Surgery (MRgFUS) technology, combined with High Intensity Focused Ultrasound (HIFU) beams, has opened to new therapeutic protocols for various pathological conditions. The success of this therapy relies on the accuracy of the guidance for therapy provided by thermal mapping of sonication, which is obtained with MR imaging. In addition, in recent years, multimodality Positron Emission Tomography and Magnetic Resonance Imaging (PET/MRI) imaging has been developed. This technique is able to provide simultaneous functional and soft tissue morphological imaging and, for this reason, it is particularly engaging for brain imaging. The key concept behind this work is to assess the feasibility of a brain-dedicated PET-and MRI-guided FUS device providing real-time evaluation of the outcome of the HIFU therapy. At first, a method to improve imaging capabilities of small-ring PET scanners will be presented. It will be showed that thanks to this method it is possible to obtain high tomographic spatial resolution with an affordable, brain-dedicated, PET scanner based on monolithic scintillation crystals and able to work as an insert in a MRI system. Moreover, simulations of an anthropomorphic phantom will be made in order to evaluate the effect of different HIFU protocols and, in addition, to investigate the capability of thermal maps provided by MRI for assessing the effect of the HIFU treatment. Finally, from the comparison of the spatial resolutions provided by each imaging technique (PET, MRI and thermal MRI) and the HIFU therapy, it will be possible to assess the feasibility of the proposed multimodality device. The system suggested in this work should be composed of a MRI scanner with a PET insert and a customized MRI-compatible focused ultrasound applicator. It could be very useful for the diagnosis and therapy of brain tumors thanks to the possibility of a real-time evaluation of the effect of the HIFU treatment. The protocol for the therapy could be executed in three main steps: the diagnosis of the pathological condition by means of fused anatomical imaging from MRI and functional imaging from PET (with different radiotracers) that allow to identify the region where apply the therapy, the ablation of the tumor by means of HIFU beams and the simultaneous evaluation of the thermal response of the tissues by means MRI thermal maps and, finally, the assessment of the outcome of the therapy by means, again, of PET/MRI hybrid imaging. The results suggest that PET and MRI-guided focused ultrasound surgery (PET/MRgFUS) could be an innovative, feasible and engaging technique for tumor ablation in the brain.
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| 3. |
- Pacilio, Massimiliano, et al.
(författare)
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Impact of SPECT corrections on 3D-dosimetry for liver transarterial radioembolization using the patient relative calibration methodology
- 2016
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Ingår i: Medical Physics. - : Wiley. - 0094-2405. ; 43:7, s. 4053-4064
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: Many centers aim to plan liver transarterial radioembolization (TARE) with dosimetry, even without CT-based attenuation correction (AC), or with unoptimized scatter correction (SC) methods. This work investigates the impact of presence vs absence of such corrections, and limited spatial resolution, on 3D dosimetry for TARE. Methods: Three voxelized phantoms were derived from CT images of real patients with different body sizes. Simulations of 99mTc-SPECT projections were performed with the SIMIND code, assuming three activity distributions in the liver: uniform, inside a "liver's segment," or distributing multiple uptaking nodules ("nonuniform liver"), with a tumoral liver/healthy parenchyma ratio of 5:1. Projection data were reconstructed by a commercial workstation, with OSEM protocol not specifically optimized for dosimetry (spatial resolution of 12.6 mm), with/without SC (optimized, or with parameters predefined by the manufacturer; dual energy window), and with/without AC. Activity in voxels was calculated by a relative calibration, assuming identical microspheres and 99mTc-SPECT counts spatial distribution. 3D dose distributions were calculated by convolution with 90Y voxel S-values, assuming permanent trapping of microspheres. Cumulative dose-volume histograms in lesions and healthy parenchyma from different reconstructions were compared with those obtained from the reference biodistribution (the "gold standard," GS), assessing differences for D95%, D70%, and D50% (i.e., minimum value of the absorbed dose to a percentage of the irradiated volume). γ tool analysis with tolerance of 3%/13 mm was used to evaluate the agreement between GS and simulated cases. The influence of deep-breathing was studied, blurring the reference biodistributions with a 3D anisotropic gaussian kernel, and performing the simulations once again. Results: Differences of the dosimetric indicators were noticeable in some cases, always negative for lesions and distributed around zero for parenchyma. Application of AC and SC reduced systematically the differences for lesions by 5%-14% for a liver segment, and by 7%-12% for a nonuniform liver. For parenchyma, the data trend was less clear, but the overall range of variability passed from -10%/40% for a liver segment, and -10%/20% for a nonuniform liver, to -13%/6% in both cases. Applying AC, SC with preset parameters gave similar results to optimized SC, as confirmed by γ tool analysis. Moreover, γ analysis confirmed that solely AC and SC are not sufficient to obtain accurate 3D dose distribution. With breathing, the accuracy worsened severely for all dosimetric indicators, above all for lesions: with AC and optimized SC, -38%/-13% in liver's segment, -61%/-40% in the nonuniform liver. For parenchyma, D50% resulted always less sensitive to breathing and sub-optimal correction methods (difference overall range: -7%/13%). Conclusions: Reconstruction protocol optimization, AC, SC, PVE and respiratory motion corrections should be implemented to obtain the best possible dosimetric accuracy. On the other side, thanks to the relative calibration, D50% inaccuracy for the healthy parenchyma from absence of AC was less than expected, while the optimization of SC was scarcely influent. The relative calibration therefore allows to perform TARE planning, basing on D50% for the healthy parenchyma, even without AC or with suboptimal corrections, rather than rely on nondosimetric methods.
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