DocumentCode :
7102
Title :
PET Reconstruction From Truncated Projections Using Total-Variation Regularization for Hadron Therapy Monitoring
Author :
Cabello, Jorge ; Torres-Espallardo, Irene ; Gillam, John E. ; Rafecas, Magdalena
Author_Institution :
Inst. de Fis. Corpuscular, Univ. de Valencia, Valencia, Spain
Volume :
60
Issue :
5
fYear :
2013
fDate :
Oct. 2013
Firstpage :
3364
Lastpage :
3372
Abstract :
Hadron therapy exploits the properties of ion beams to treat tumors by maximizing the dose released to the target and sparing healthy tissue. With hadron beams, the dose distribution shows a relatively low entrance dose which rises sharply at the end of the range, providing the characteristic Bragg peak that drops quickly thereafter. It is of critical importance in order not to damage surrounding healthy tissues and/or avoid targeting underdosage to know where the delivered dose profile ends-the location of the Bragg peak. During hadron therapy, short-lived β+-emitters are produced along the beam path, their distribution being correlated with the delivered dose. Following positron annihilation, two photons are emitted, which can be detected using a positron emission tomography (PET) scanner. The low yield of emitters, their short half-life, and the wash out from the target region make the use of PET, even only a few minutes after hadron irradiation, a challenging application. In-beam PET represents a potential candidate to estimate the distribution of β+-emitters during or immediately after irradiation, at the cost of truncation effects and degraded image quality due to the partial rings required of the PET scanner. Time-of-flight (ToF) information can potentially be used to compensate for truncation effects and to enhance image contrast. However, the highly demanding timing performance required in ToF-PET makes this option costly. Alternatively, the use of maximum-a-posteriori- expectation-maximization (MAP-EM), including total variation (TV) in the cost function, produces images with low noise, while preserving spatial resolution. In this paper, we compare data reconstructed with maximum-likelihood-expectation-maximization (ML-EM) and MAP-EM using TV as prior, and the impact of including ToF information, from data acquired with a complete and a partial-ring PET scanner, of simulated hadron beams interacting with a polymethyl - ethacrylate (PMMA) target. The results show that MAP-EM, in the absence of ToF information, produces lower noise images and more similar data compared to the simulated β+ distributions than ML-EM with ToF information in the order of 200-600 ps. The investigation is extended to the combination of MAP-EM and ToF information to study the limit of performance using both approaches.
Keywords :
dosimetry; image reconstruction; ion beams; maximum likelihood estimation; medical image processing; patient monitoring; positron emission tomography; radiation therapy; tumours; Bragg peak; MAP-EM method; PET reconstruction; PET scanner; cost function; degraded image quality; dose distribution; hadron beams; hadron therapy monitoring; healthy tissue; ion beams; maximum likelihood expectation maximization; maximum-a-posteriori expectation maximization; polymethyl methacrylate target; positron annihilation; positron emission tomography; timing performance; total variation regularization; truncated projection; truncation effects; tumors; Cost function; Image reconstruction; Medical treatment; Noise; Positron emission tomography; Radiation effects; TV; Hadron therapy; in-beam PET; maximum- a-posteriori–expectation-maximization (MAP–EM) reconstruction; time-of-flight positron emission tomography (PET); total variation;
fLanguage :
English
Journal_Title :
Nuclear Science, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9499
Type :
jour
DOI :
10.1109/TNS.2013.2278121
Filename :
6596509
Link To Document :
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