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Title: Brain SPECT with short focal-length cone-beam collimation

Abstract

Single-photon emission-computed tomography (SPECT) imaging of deep brain structures is compromised by loss of photons due to attenuation. We have previously shown that a centrally peaked collimator sensitivity function can compensate for this phenomenon, increasing sensitivity over most of the brain. For dual-head instruments, parallel-hole collimators cannot provide variable sensitivity without simultaneously degrading spatial resolution near the center of the brain; this suggests the use of converging collimators. We have designed collimator pairs for dual-head SPECT systems to increase sensitivity, particularly in the center of the brain, and compared the new collimation approach to existing approaches on the basis of performance in estimating activity concentration of small structures at various locations in the brain. The collimator pairs we evaluated included a cone-beam collimator, for increased sensitivity, and a fan-beam collimator, for data sufficiency. We calculated projections of an ellipsoidal uniform background, with 0.9-cm-radius spherical lesions at several locations in the background. From these, we determined ideal signal-to-noise ratios (SNR{sub CRB}) for estimation of activity concentration within the spheres, based on the Cramer-Rao lower bound on variance. We also reconstructed, by an ordered-subset expectation-maximization (OS-EM) procedure, images of this phantom, as well as of the Zubal brain phantom, to allow visualmore » assessment and to ensure that they were free of artifacts. The best of the collimator pairs evaluated comprised a cone-beam collimator with 20 cm focal length, for which the focal point is inside the brain, and a fan-beam collimator with 40 cm focal length. This pair yielded increased SNR{sub CRB}, compared to the parallel-parallel pair, throughout the imaging volume. The factor by which SNR{sub CRB} increased ranged from 1.1 at the most axially extreme location to 3.5 at the center. The gains in SNR{sub CRB} were relatively robust to mismatches between the center of the brain and the center of the imaging volume. Artifact-free reconstructions of simulated data acquired using this pair were obtained. Combining fan-beam and short-focusing cone-beam collimation should greatly improve dual-head brain SPECT imaging, especially for centrally located structures.« less

Authors:
; ;  [1]
  1. Department of Radiology, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115 (United States)
Publication Date:
OSTI Identifier:
20726085
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 32; Journal Issue: 7; Other Information: DOI: 10.1118/1.1929208; (c) 2005 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ATTENUATION; BEAMS; BRAIN; COLLIMATORS; CONES; HEAD; IMAGES; OPTIMIZATION; PHANTOMS; PHOTONS; SENSITIVITY; SIGNAL-TO-NOISE RATIO; SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY; SPATIAL RESOLUTION

Citation Formats

Park, Mi-Ae, Moore, Stephen C, and Kijewski, Marie Foley. Brain SPECT with short focal-length cone-beam collimation. United States: N. p., 2005. Web. doi:10.1118/1.1929208.
Park, Mi-Ae, Moore, Stephen C, & Kijewski, Marie Foley. Brain SPECT with short focal-length cone-beam collimation. United States. https://doi.org/10.1118/1.1929208
Park, Mi-Ae, Moore, Stephen C, and Kijewski, Marie Foley. Fri . "Brain SPECT with short focal-length cone-beam collimation". United States. https://doi.org/10.1118/1.1929208.
@article{osti_20726085,
title = {Brain SPECT with short focal-length cone-beam collimation},
author = {Park, Mi-Ae and Moore, Stephen C and Kijewski, Marie Foley},
abstractNote = {Single-photon emission-computed tomography (SPECT) imaging of deep brain structures is compromised by loss of photons due to attenuation. We have previously shown that a centrally peaked collimator sensitivity function can compensate for this phenomenon, increasing sensitivity over most of the brain. For dual-head instruments, parallel-hole collimators cannot provide variable sensitivity without simultaneously degrading spatial resolution near the center of the brain; this suggests the use of converging collimators. We have designed collimator pairs for dual-head SPECT systems to increase sensitivity, particularly in the center of the brain, and compared the new collimation approach to existing approaches on the basis of performance in estimating activity concentration of small structures at various locations in the brain. The collimator pairs we evaluated included a cone-beam collimator, for increased sensitivity, and a fan-beam collimator, for data sufficiency. We calculated projections of an ellipsoidal uniform background, with 0.9-cm-radius spherical lesions at several locations in the background. From these, we determined ideal signal-to-noise ratios (SNR{sub CRB}) for estimation of activity concentration within the spheres, based on the Cramer-Rao lower bound on variance. We also reconstructed, by an ordered-subset expectation-maximization (OS-EM) procedure, images of this phantom, as well as of the Zubal brain phantom, to allow visual assessment and to ensure that they were free of artifacts. The best of the collimator pairs evaluated comprised a cone-beam collimator with 20 cm focal length, for which the focal point is inside the brain, and a fan-beam collimator with 40 cm focal length. This pair yielded increased SNR{sub CRB}, compared to the parallel-parallel pair, throughout the imaging volume. The factor by which SNR{sub CRB} increased ranged from 1.1 at the most axially extreme location to 3.5 at the center. The gains in SNR{sub CRB} were relatively robust to mismatches between the center of the brain and the center of the imaging volume. Artifact-free reconstructions of simulated data acquired using this pair were obtained. Combining fan-beam and short-focusing cone-beam collimation should greatly improve dual-head brain SPECT imaging, especially for centrally located structures.},
doi = {10.1118/1.1929208},
url = {https://www.osti.gov/biblio/20726085}, journal = {Medical Physics},
issn = {0094-2405},
number = 7,
volume = 32,
place = {United States},
year = {2005},
month = {7}
}