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Title: The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations

Abstract

z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposuremore » was normalized to CTDI{sub freeinair}. The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch=1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch=1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, z overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of z overscanning.« less

Authors:
; ; ; ;  [1]
  1. Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 1393, 71409 Iraklion, Crete (Greece)
Publication Date:
OSTI Identifier:
20726062
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 32; Journal Issue: 6; Other Information: DOI: 10.1118/1.1924309; (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; ABDOMEN; CHEST; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COMPUTERIZED TOMOGRAPHY; DOSIMETRY; IMAGE PROCESSING; IMAGES; IONIZATION CHAMBERS; MONTE CARLO METHOD; NECK; PATIENTS; PELVIS; PHANTOMS; PITCHES; RADIATION DOSES; RADIATION TRANSPORT; THERMOLUMINESCENT DOSEMETERS

Citation Formats

Tzedakis, A, Damilakis, J, Perisinakis, K, Stratakis, J, Gourtsoyiannis, N, and Department of Radiology, Faculty of Medicine, University of Crete, 71409 Iraklion, Crete. The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations. United States: N. p., 2005. Web. doi:10.1118/1.1924309.
Tzedakis, A, Damilakis, J, Perisinakis, K, Stratakis, J, Gourtsoyiannis, N, & Department of Radiology, Faculty of Medicine, University of Crete, 71409 Iraklion, Crete. The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations. United States. https://doi.org/10.1118/1.1924309
Tzedakis, A, Damilakis, J, Perisinakis, K, Stratakis, J, Gourtsoyiannis, N, and Department of Radiology, Faculty of Medicine, University of Crete, 71409 Iraklion, Crete. 2005. "The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations". United States. https://doi.org/10.1118/1.1924309.
@article{osti_20726062,
title = {The effect of z overscanning on patient effective dose from multidetector helical computed tomography examinations},
author = {Tzedakis, A and Damilakis, J and Perisinakis, K and Stratakis, J and Gourtsoyiannis, N and Department of Radiology, Faculty of Medicine, University of Crete, 71409 Iraklion, Crete},
abstractNote = {z overscanning in multidetector (MD) helical CT scanning is prerequisite for the interpolation of acquired data required during image reconstruction and refers to the exposure of tissues beyond the boundaries of the volume to be imaged. The aim of the present study was to evaluate the effect of z overscanning on the patient effective dose from helical MD CT examinations. The Monte Carlo N-particle radiation transport code was employed in the current study to simulate CT exposure. The validity of the Monte Carlo simulation was verified by (a) a comparison of calculated and measured standard computed tomography dose index (CTDI) dosimetric data, and (b) a comparison of calculated and measured dose profiles along the z axis. CTDI was measured using a pencil ionization chamber and head and body CT phantoms. Dose profiles along the z axis were obtained using thermoluminescence dosimeters. A commercially available mathematical anthropomorphic phantom was used for the estimation of effective doses from four standard CT examinations, i.e., head and neck, chest, abdomen and pelvis, and trunk studies. Data for both axial and helical modes of operation were obtained. In the helical mode, z overscanning was taken into account. The calculated effective dose from a CT exposure was normalized to CTDI{sub freeinair}. The percentage differences in the normalized effective dose between contiguous axial and helical scans with pitch=1, may reach 13.1%, 35.8%, 29.0%, and 21.5%, for head and neck, chest, abdomen and pelvis, and trunk studies, respectively. Given that the same kilovoltage and tube load per rotation were used in both axial and helical scans, the above differences may be attributed to z overscanning. For helical scans with pitch=1, broader beam collimation is associated with increased z overscanning and consequently higher normalized effective dose value, when other scanning parameters are held constant. For a given beam collimation, the selection of a higher value of reconstructed image slice width increases the normalized effective dose. In conclusion, z overscanning may significantly affect the patient effective dose from CT examinations performed on MD CT scanners. Therefore, an estimation of the patient effective dose from MD helical CT examinations should always take into consideration the effect of z overscanning.},
doi = {10.1118/1.1924309},
url = {https://www.osti.gov/biblio/20726062}, journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 32,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2005},
month = {Wed Jun 15 00:00:00 EDT 2005}
}