The Measurement, Reporting, and Management of Radiation Dose in CT

A Hindmarsh‐Rose model perceptibility phantom containing inserts with various in vitro atherosclerotic plaque compositions was constructed and imaged on a clinical 64 slice multidetector (MDCT) system using 80 and 120 kVp settings and two other cone‐beam (CBCT) systems at 80 kVp. Perceptibility of the simulated lipid‐fibrotic plaque solutions in the images was evaluated by six observers. The effective doses of the protocols employed were estimated using phantom CTDI‐vol measurements placed at identical settings. The CBCT system allowed reduction in effective dose in comparison with the conventional MDCT system for imaging of the carotid plaque phantoms without degrading image quality. The CBCT dose was less than MDCT, with a mean dose of 1.14±0.01 mSv and 1.11±0.02 mSv for MDCT using two measuring techniques vs. 0.35±0.01 mSv for CBCT. The image quality analysis showed no significant differences in the contrast‐detail (C‐D) curves of the best performing CBCT vs. clinical MDCT false(p>0.05false) using a Mann‐Whitney U test. Results indicate that low‐tube‐potential CBCT may produce comparable C‐D resolution for phantom‐based representations of soft plaque types with respect to MDCT systems. This study suggests that the utility of low kVp CT techniques for evaluating carotid vulnerable atherosclerotic plaque merits further study.PACS numbers: 87.53.Bn, 87.57.N‐, 87.57.Q‐, 87.57.cj

“…A reasonable estimate, independent of scanner type, was obtained by employing the proper weighting factor, k, which is only dependent on the body region being exposed: (19)

Effective Dose = normalk \times DLP

where k is the weighting factor in

mSv . {mGy}^{- 1} . {cm}^{- 1}

, and DLP is the dose length product in mGy.cm. The weighting factor used in this study to estimate the effective dose was

0.0059 mSv . {mGy}^{- 1} . {cm}^{- 1}

for the neck region, as per the values reported in AAPM Report 96 (20) …”

Section: Methodsmentioning

confidence: 97%

Characterization of atherosclerotic plaque: a contrast‐detail study using multidetector and cone‐beam computed tomography

Kasraie

Mah

Keener

et al. 2014

“…Unfortunately, in CT, the current scanner output dose metrics, such as volume CT dose index (CTDI vol ), do not reflect the dose the patient actually receives . The CTDI vol only represents the system's radiation output for a very specific set of conditions in a cylindrical acrylic polymethyl methacrylate (PMMA) phantom with diameters of 16 or 32 cm in a contiguous axial or helical examination . Ideally, a method would exist to normalize these dose values to make them reflect the dose a patient actually receives.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of AAPM Reports 204 and 220: Estimation of effective diameter, water‐equivalent diameter, and ellipticity ratios for chest, abdomen, pelvis, and head CT scans

Burton

Szczykutowicz

2017

PurposeTo confirm AAPM Reports 204/220 and provide data for the future expansion of these reports by: (a) presenting the first large‐scale confirmation of the reports using clinical data, (b) providing the community with size surrogate data for the head region which was not provided in the original reports, and additionally providing the measurements of patient ellipticity ratio for different body regions.MethodA total of 884 routine scans were included in our analysis including data from the head, thorax, abdomen, and pelvis for adults and pediatrics. We calculated the ellipticity ratio and all of the size surrogates presented in AAPM Reports 204/220. We correlated the purely geometric‐based metrics with the “gold standard” water‐equivalent diameter (DW).ResultsOur results and AAPM Reports 204/220 agree within our data's 95% confidence intervals. Outliers to the AAPM reports’ methods were caused by excess gas in the GI tract, exceptionally low BMI, and cranial metaphyseal dysplasia. For the head, we show lower correlation (R2 = 0.812) between effective diameter and DW relative to other body regions. The ellipticity ratio of the shoulder region was the highest at 2.28 ± 0.22 and the head the smallest at 0.85 ± 0.08. The abdomen pelvis, chest, thorax, and abdomen regions all had ellipticity values near 1.5.ConclusionWe confirmed AAPM reports 204/220 using clinical data and identified patient conditions causing discrepancies. We presented new size surrogate data for the head region and for the first time presented ellipticity data for all regions. Future automatic exposure control characterization should include ellipticity information.

“…At present,

{CTDI}_{vol}

is still used to account for helical scanning parameters in clinical setting. The “dose equilibrium” proposed by AAPM is yet to be accepted to replace the traditional CTDI dosimetry approach (1,4) . In this study, it is shown that the excess percentage radiation doses decreased as a function of (increasing) nominal gantry rotation time.…”

Section: Discussionmentioning

confidence: 80%

“…Because of the continued growth in CT utilization in recent years, an increased emphasis has been placed on the importance of quality assurance/control and patient radiation dose assessment during CT examinations (9) . To design appropriate scanning protocols, it is important to understand not only the variable settings, but also the methodology to assess accurate radiation dose (1,4,10) …”

Section: Discussionmentioning

confidence: 99%

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Evaluation of gantry rotation overrun in axial CT scanning

Fukuda

Lin

Matsubara

et al. 2014

The purpose of this study was to develop and evaluate a simple method to assess gantry rotation overrun in a single axial CT scanning. The exposure time in the axial scanning was measured at selected nominal rotation times (400, 700, and 1000 ms) using a solid‐state detector, the RTI's CT dose profiler (CTDP). CTDP was placed at the isocenter and the radiation dose rate signal (profile) was recorded. Subsequently, the full width of this profile was determined as the exposure time (Taxial). Next, CTDP was positioned on the inner cover of the gantry with a sheet of lead (1 mm thick) placed on top of the detector. Gantry rotation time (Thelical) was determined by the time between two successive radiation peaks during continuous helical scanning. The gantry overrun time (Toverrun) is, thus, determined as Taxial‐Thelical. The exposure times in the axial scanning, Taxial, obtained with CTDP for nominal rotation times of 400, 700, and 1000 ms were 409.5, 709.6, and 1008.7 ms, respectively. On the other hand, the measured gantry rotation times, Thelical, were 400.0, 700.3, and 999.8 ms, respectively. Therefore, the overruns were 9.5, 9.3, and 8.9 ms for nominal rotation times of 400, 700, and 1000 ms, respectively. The evaluation of overrun in axial scanning can be accomplished with the measurements of both the exposure time in axial scanning and the gantry rotation time. It is also noteworthy that in this context, overrun implies overexposure in axial scanning, which is still used, particularly, in head CT examination.PACS number: 87.57.Q‐