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FEATURED STORIES - JANUARY 2017

"Prompt Gamma Rays Detected With a BGO Block Compton Camera Reveal Range Deviations of Therapeutic Proton Beams"

by F. Hueso-González, G. Pausch, J. Petzoldt, K. E. Römer, and W. Enghard


The dose deposition profile of protons is interesting for tumour treatment due to the increased ionization density at the end of their track. However, the inaccurate knowledge of the proton stopping point limits the precision of the therapy. Prompt gamma rays, a by-product of the irradiation, are candidates for an indirect measurement of the particle range. Compton cameras have been proposed for prompt gamma ray imaging, but struggle with high trigger rates and low coincident efficiency. The feasibility in a clinical environment has yet to be proved. At Universitäts Protonen Therapie Dresden, two bismuth germanate (BGO) block detectors arranged face-to-face are deployed for imaging tests with a homogeneous target irradiated by a proton pencil beam. Shifts of the target, increase of its thickness and beam energy variation experiments are conducted. Each measurement lasts about 15 minutes at a low proton beam current. The effect of one centimetre proton range deviations on the backprojected images is analysed. The number of valid Compton events as well as the trigger rate expected in a realistic treatment plan with pencil beam scanning are estimated. The results support the use of a high density material despite its moderate energy resolution, in order to maximize the coincident efficiency. Nevertheless, they discourage the applicability of a two-plane Compton camera in a clinical scenario with usual beam currents. more...
 
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"Evaluation of a Sub-Millimeter Resolution PET Detector With a 1.2 mm Pitch TSV-MPPC Array One-to-One Coupled to LFS Scintillator Crystals and Inter-Crystal Scatter Studies With Individual Signal Readout"

by R. Ota, T. Omura, R. Yamada, T. Miwa, and M. Watanabe


To develop a small animal positron emission tomography (PET) scanner for whole body imaging of mice, a sub-millimeter resolution PET detector has been constructed and its performance evaluated. This PET detector is composed of a 1.2 mm pitch multi-pixel photon counter (MPPC) 8 × 8 array with through-silicon via (TSV) structure one-to-one coupled to Lutetium Fine Silicate (LFS) scintillator crystals of size 1.13 mm × 1.13 mm × 10 mm each. To evaluate the intrinsic spatial resolution and the energy resolution in coincidence events, the coincidence response functions (CRFs) of the detector pair, located facing each other at a distance of 80 mm, were measured by scanning a 0.25 mm diameter 22Na point source in 0.1 mm steps. The data were acquired by the computer automated measurement and control (CAMAC) system. The average full width at half maximum (FWHM) of the CRFs was 0.75 mm without point source size corrections. The average FWHM of the energy resolution was 16% at 511 keV. The coincidence timing resolution (CTR) was also evaluated by facing the detector and a fast photomultiplier tube (PMT) coupled with a BaF2 crystal. The expected average FWHM of the CTR between the detectors was 770 ps. Additionally, to improve detector efficiency while suppressing the positioning errors, we propose an interaction-order scheme based on Compton kinematics and adapt it to the same data. We also perform Monte Carlo simulations using GEANT4 10.01 to evaluate the accuracy of the proposed positioning scheme and compare it to that of a centroid calculation scheme. As a result, we demonstrate that the accuracy of the proposed positioning scheme is better than that of a centroid calculation scheme when inter-crystal scatter events occur. more...
 
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"Super-Resolution Reconstruction of 3D PET Images Using Two Respiratory-Phase Low-Dose CT Images

by Il Jun Ahn, Ji Hye Kim, Yongjin Chang, Woo Hyun Nam, and Jong Beom Ra


Positron emission tomography (PET) images usually suffer from incorrect quantification of the radioactive uptake of small lesions due to low spatial resolution. To improve the spatial resolution, we previously proposed super-resolution (SR) algorithms based on wobble scanning. The proposed algorithms, however, require mechanical motion of the patient bed or a system gantry for wobble scanning. In this paper, we propose a framework for SR reconstruction of 3D PET images based on the use of respiratory motion rather than wobble motion. As in the conventional protocol of PET imaging, gated list-mode PET data are acquired in a free breathing condition. In addition, we acquire two low-dose CT images in a breath-hold manner at exhale and inhale phases, without increasing the radiation burden to a patient. Using the two low-dose CT images, we estimate the 4D motion vector field (MVF) and correspondingly generate a virtual 4D CT image that are matched to the 4D PET image. The 3D CT images have much better spatial resolution than PET images and therefore the corresponding estimated 3D MVFs can be considered reliable for PET SR reconstruction. We then estimate space-variant point spread functions (PSFs) in the imaging field of view using a minimum number of PSFs obtained through Monte-Carlo simulations. Finally, SR reconstruction is performed by incorporating the estimated 3D MVFs and spacevariant PSFs. In the SR reconstruction, to avoid the resolution degradation in the evenly spaced parallel-beam rebinning and to reduce the computational time on the graphics processing unit, we introduce a parallel-friendly spanned line of response reconstruction technique based on fan-beam reordering. The proposed framework is evaluated via Monte-Carlo simulations with the digital XCAT phantom and via experiments with several patient datasets including moving lung lesions. Both the simulation and experiment results show that the proposed framework provides much clearer organ boundaries as well as more accurate quantitative lesion information than the conventional methods, with a considerable reduction of computational time. more...
 
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A PUBLICATION OF THE IEEE NUCLEAR AND PLASMA SCIENCES SOCIETY

JANUARY 2017   |  VOLUME 1  |  NUMBER 1  |  ITRPFI  |  (SSN 2469-7311)

EDITORIAL
The Birth of a New and Unique Journal: IEEE Transactions on Radiation and Plasma Medical Sciences . . . . . . . . . . . . . . . . . . D. Visvikis

SCINTILLATORS AND DETECTORS
Hybrid Pixel-Waveform (HPWF) Enabled CdTe Detectors for Small Animal Gamma-Ray Imaging Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A. Groll, K. Kim, H. Bhatia, J. C. Zhang, J. H. Wang, Z. M. Shen, L. Cai, J. Dutta, Q. Li, and L. J. Meng
Evaluation of a Sub-Millimeter Resolution PET Detector With a 1.2 mm Pitch TSV-MPPC Array One-to-One Coupled to LFS
     Scintillator Crystals and Inter-Crystal Scatter Studies With Individual Signal Readout
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. Ota, T. Omura, R. Yamada, T. Miwa, and M. Watanabe
Scintillation and Spectroscopic Characteristics of 90%Lu LGSO With Variable Decay Times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Loignon-Houle, C. M. Pepin, and R. Lecomte
Performance of a 0.4 mm Pixelated Ce:GAGG Block Detector With Digital Silicon Photomultiplier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E. Pratiwi, H. T. Leem, J. H. Park, Y. Choi, S. Yamamoto, K. Kamada, A. Yoshikawa, and J. Y. Yeom

CAMERA DESIGN AND IMAGING PERFORMANCE
A Comparison Between GATE and Accelerated Convolution-Based Forced Detection SIMIND for Low- and Medium-Energy
     Collimators: A Simulation Study
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M. I. Karamat and T. H. Farncombe

IMAGE RECONSTRUCTION AND DATA PROCESSING
Super-Resolution Reconstruction of 3D PET Images Using Two Respiratory-Phase Low-Dose CT Images . . . . . . . . . . . . . . . . . . . . . . . . . .
     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. J. Ahn, J. H. Kim, Y. Chang, W. H. Nam, and J. B. Ra
Low Dose CT Filtering in the Image Domain Using MAP Algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R. J. Geraldo, L. M. V. Cura, P. E. Cruvinel, and N. D. A. Mascarenhas
Does Noise Weighting Matter in CT Iterative Reconstruction? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G. L. Zeng and W. Wang

RADIOTHERAPY
Prompt Gamma Rays Detected With a BGO Block Compton Camera Reveal Range Deviations of Therapeutic Proton Beams . . . . . . . . . . .
     . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F. Hueso-González, G. Pausch, J. Petzoldt, K. E. Römer, and W. Enghardt
In Beam PET Acquisition on 75 MeV.u−1 Carbon Beam Using Sampling-Based Read-Out Electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
     . . . . . . . . . . . . . . . . L. Lestand, G. Montarou, P. Force, B. Joly, D. Lambert, M. Magne, F. Martin, A. Rozes, P. E. Vert, and R. Chadelas
An Image Reconstruction Framework and Camera Prototype Aimed for Compton Imaging for In-vivo Dosimetry of Therapeutic
     Ion Beams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S. Schoene, W. Enghardt, F. Fiedler, C. Golnik, G. Pausch, H. Rohling, and T. Kormoll

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