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Title: SU-F-I-54: Spatial Resolution Studies in Proton CT Using a Phase-II Prototype Head Scanner

Abstract

Purpose: To characterize the modulation transfer function (MTF) of the pre-clinical (phase II) head scanner developed for proton computed tomography (pCT) by the pCT collaboration. To evaluate the spatial resolution achievable by this system. Methods: Our phase II proton CT scanner prototype consists of two silicon telescopes that track individual protons upstream and downstream from a phantom, and a 5-stage scintillation detector that measures a combination of the residual energy and range of the proton. Residual energy is converted to water equivalent path length (WEPL) of the protons in the scanned object. The set of WEPL values and associated paths of protons passing through the object over a 360° angular scan is processed by an iterative parallelizable reconstruction algorithm that runs on GP-GPU hardware. A custom edge phantom composed of water-equivalent polymer and tissue-equivalent material inserts was constructed. The phantom was first simulated in Geant4 and then built to perform experimental beam tests with 200 MeV protons at the Northwestern Medicine Chicago Proton Center. The oversampling method was used to construct radial and azimuthal edge spread functions and modulation transfer functions. The spatial resolution was defined by the 10% point of the modulation transfer function in units of lp/cm. Results:more » The spatial resolution of the image was found to be strongly correlated with the radial position of the insert but independent of the relative stopping power of the insert. The spatial resolution varies between roughly 4 and 6 lp/cm in both the the radial and azimuthal directions depending on the radial displacement of the edge. Conclusion: The amount of image degradation due to our detector system is small compared with the effects of multiple Coulomb scattering, pixelation of the image and the reconstruction algorithm. Improvements in reconstruction will be made in order to achieve the theoretical limits of spatial resolution.« less

Authors:
; ; ;  [1]; ; ;  [2];  [3];  [4]
  1. University of California, Santa Cruz, Santa Cruz, CA (United States)
  2. Loma Linda University, Loma Linda, CA (United States)
  3. University of California, San Francisco, San Francisco, CA (United States)
  4. University of Wollongong, Wollongong, NSW (Australia)
Publication Date:
OSTI Identifier:
22632119
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; 60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; ALGORITHMS; COULOMB SCATTERING; HEAD; IMAGE PROCESSING; IMAGES; ITERATIVE METHODS; MODULATION; PHANTOMS; POLYMERS; PROTON COMPUTED TOMOGRAPHY; SCINTILLATION COUNTERS; SCINTILLATIONS; SIMULATION; SPATIAL RESOLUTION; STOPPING POWER; TRANSFER FUNCTIONS; FUNDAMENTAL INTERACTIONS

Citation Formats

Plautz, Tia E., Johnson, R. P., Sadrozinski, H. F.-W., Zatserklyaniy, A., Bashkirov, V., Hurley, R. F., Schulte, R. W., Piersimoni, P., and Giacometti, V.. SU-F-I-54: Spatial Resolution Studies in Proton CT Using a Phase-II Prototype Head Scanner. United States: N. p., 2016. Web. doi:10.1118/1.4955882.
Plautz, Tia E., Johnson, R. P., Sadrozinski, H. F.-W., Zatserklyaniy, A., Bashkirov, V., Hurley, R. F., Schulte, R. W., Piersimoni, P., & Giacometti, V.. SU-F-I-54: Spatial Resolution Studies in Proton CT Using a Phase-II Prototype Head Scanner. United States. doi:10.1118/1.4955882.
Plautz, Tia E., Johnson, R. P., Sadrozinski, H. F.-W., Zatserklyaniy, A., Bashkirov, V., Hurley, R. F., Schulte, R. W., Piersimoni, P., and Giacometti, V.. 2016. "SU-F-I-54: Spatial Resolution Studies in Proton CT Using a Phase-II Prototype Head Scanner". United States. doi:10.1118/1.4955882.
@article{osti_22632119,
title = {SU-F-I-54: Spatial Resolution Studies in Proton CT Using a Phase-II Prototype Head Scanner},
author = {Plautz, Tia E. and Johnson, R. P. and Sadrozinski, H. F.-W. and Zatserklyaniy, A. and Bashkirov, V. and Hurley, R. F. and Schulte, R. W. and Piersimoni, P. and Giacometti, V.},
abstractNote = {Purpose: To characterize the modulation transfer function (MTF) of the pre-clinical (phase II) head scanner developed for proton computed tomography (pCT) by the pCT collaboration. To evaluate the spatial resolution achievable by this system. Methods: Our phase II proton CT scanner prototype consists of two silicon telescopes that track individual protons upstream and downstream from a phantom, and a 5-stage scintillation detector that measures a combination of the residual energy and range of the proton. Residual energy is converted to water equivalent path length (WEPL) of the protons in the scanned object. The set of WEPL values and associated paths of protons passing through the object over a 360° angular scan is processed by an iterative parallelizable reconstruction algorithm that runs on GP-GPU hardware. A custom edge phantom composed of water-equivalent polymer and tissue-equivalent material inserts was constructed. The phantom was first simulated in Geant4 and then built to perform experimental beam tests with 200 MeV protons at the Northwestern Medicine Chicago Proton Center. The oversampling method was used to construct radial and azimuthal edge spread functions and modulation transfer functions. The spatial resolution was defined by the 10% point of the modulation transfer function in units of lp/cm. Results: The spatial resolution of the image was found to be strongly correlated with the radial position of the insert but independent of the relative stopping power of the insert. The spatial resolution varies between roughly 4 and 6 lp/cm in both the the radial and azimuthal directions depending on the radial displacement of the edge. Conclusion: The amount of image degradation due to our detector system is small compared with the effects of multiple Coulomb scattering, pixelation of the image and the reconstruction algorithm. Improvements in reconstruction will be made in order to achieve the theoretical limits of spatial resolution.},
doi = {10.1118/1.4955882},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Lutetium oxyorthosilicate (LSO) scintillation crystals coupled to avalanche photodiodes (APDs) have been proven to be an interesting detector module for high resolution positron emission tomography (PET). Compact detector modules were built to test their performance in a prototype tomograph. Each detector module consisted of sixteen 3.7 x 3.7 x 12.0 mm{sup 3} LSO crystals, which are one-to-one coupled to a two dimensional APD array (2 x 8 diodes, 3 mm {O}, 4 mm spacing). The signals were read out by a low noise, fast, charge sensitive preamplifier, a 50 ns shaping amplifier and CAMAC electronic modules. Two detector modules weremore » mounted on a rotatable gantry, to simulate a detector ring. Long term runs over 110 hours have shown that the detector remains stable over a long period of time. The energy resolution (FWHM) was 13.4% for 511 keV gamma rays and the intrinsic spatial resolution was 2.2 mm (FWHM). The gain dependence of the APD on temperature had been determined as 3.5%/K. The time resolution was 3.2 {+-} 0.1 ns (FWHM). Phantom measurements showed the suitability of the new LSO/APD detector for high resolution animal PET.« less
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  • In proton treatment planning, the use of protons instead of X-rays for computerized tomography (CT) studies has potential advantages, especially for medical applications. Proton CT requires accurate measurement of the energy loss of protons passing through the object. The resolution of a proton CT scanner is determined by the resolution of the energy loss measurement, which is limited by the inherent energy straggling of protons. An experiment with a doped CsI(Tl) crystal was designed to determine the resolution of the energy loss measurement of protons in the energy range from 40 MeV to 250 MeV experimentally. It was found that,more » in principle, the resolution of a proton calorimeter is adequate to CT studies with objects of realistic size.« less
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