Gantry Angulation Effects on Ct Dose Along the Z-Axis Direction in Head Examinations

Parsi, Masoumeh; Sohrabi, Mehdi; Mianji, Fereidoun A.; Paydar, Reza

doi:10.1093/rpd/ncx064

Cited by 4 publications

(2 citation statements)

References 15 publications

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“…The source was attached to an arbitrary geometrical volume and was rotated in the circular path to define a total of 100 projections in one slice. A total of 10 8 photons were emitted toward the isocenter in one slice (15) .…”

Section: Ct Scanner and Phantom Modelingmentioning

confidence: 99%

Analysis of size-specific dose profiles beyond the scan range in water phantoms undergoing computed tomography examinations

2021

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Background:The purpose of this study is to analyze the cumulative dose profile tail beyond the scan lengths of 10-90 cm in CT examinations on central and peripheral axes of water phantoms (10-50 cm diameter). The analysis includes extension, trend, and dependency of the tails on the scan length and phantom diameter. Materials and Methods: A validated Monte Carlo model of a GE LightSpeed 16-slice CT scanner was used to obtain a dose profile from narrow beam collimation (1µm). The cumulative dose profile tail was developed by applying the well-known "convolution method", i.e. convolving a dose profile with a RECT function. The tails were analyzed according to the phantom diameter and scan length statistically. Results: For all phantoms, the statistical analysis shows no significant differences between tails of scan lengths of 10-90 cm for peripheral axis and those of scan lengths > 30 cm for the central axis. The tails have an exponential falloff from the scan edge modeled by D(z)=Ae -Bz . The A and B are related to the falloff speed and amplitude of the tails. By increasing the phantom diameter, the amplitude and falloff speed decrease 82% and 59% on the central axis and 65% and 31% on the peripheral axis respectively. Conclusion: A simple equation was suggested for dose calculation at any point beyond the scan range on the central and peripheral axes of water phantoms. The equation is independent of scan length and is useful for evaluating the dose of organs located at the edge or outside of the scan region.

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Section: Ct Scanner and Phantom Modelingmentioning

confidence: 99%

Analysis of size-specific dose profiles beyond the scan range in water phantoms undergoing computed tomography examinations

2021

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“…11 The gantry tilt is the angle between the vertical plane to the isocenter and the CT gantry. 12,13 It is often performed for clinical purposes and is set manually by the operator. It can be performed from angles of -30° to +30° in 0.5° increments according to the specifications of the CT scanner and specific examination.…”

Section: Introductionmentioning

confidence: 99%

Automatic validation of the gantry tilt in a computed tomography scanner using a head polymethyl methacrylate phantom

Noviliawati

Anam

Sutanto

et al. 2021

Polish Journal of Medical Physics and Engineering

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The purpose of this study was to develop an automatic method for validating the computed tomography gantry tilt. A head polymethyl methacrylate phantom with a diameter of 16 cm was used. Gantry tilt angles were measured both manually and automatically. Manual measurements were performed by measuring the length of the anteroposterior and lateral diameters from acquired images using electronic calipers. Automatic measurements consisted of a number of steps: phantom segmentation, determination of the center of the phantom, measurement of the anteroposterior and lateral diameters, and computation of the gantry tilt angle. The method was implemented on the gantry angles from 0° to 15°. The proposed method of measuring gantry angles produced accurate gantry tilt angles. The differences with the angles displayed on the gantry were less than 1°. The results of the automatic method were the same as those of the manual method (R2 > 0.98).

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Study on a Specific Test Method for Dosimetric Characterization of Ultra-Wide Detector Computed Tomography

Zhang

et al. 2021

Radiation Protection Dosimetry

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The purpose of this study was to establish a specific test method for dosimetric characterization of wide-beam computed tomography (CT). For a wide beam, the dose distribution curve and the area of the curve were obtained by using pencil-like ionization chamber, a long CT dose profiler probe, a head phantom and a body phantom. The absolute dose conversion coefficient was multiplied to obtain the total integration integral of the absolute dose distribution, and then the computed tomography dose index (CTDI) value under any wide beam condition was obtained by dividing the collimation width. It was calculated that the absolute dose conversion coefficient was 1.135 under the narrow beam of 8 mm. To a 160 mm-wide beam, the value of CTDI was 7.57 mGy/100mAs after normalized in the head 80 kV CT scanning, and it was 9.80 mGy/100mAs after normalized in the body 120 kV CT scanning. The specific test method solves the problem that the previous measurement method underestimates the CTDI value.

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Gantry Angulation Effects on Ct Dose Along the Z-Axis Direction in Head Examinations

Cited by 4 publications

References 15 publications

Analysis of size-specific dose profiles beyond the scan range in water phantoms undergoing computed tomography examinations

Analysis of size-specific dose profiles beyond the scan range in water phantoms undergoing computed tomography examinations

Automatic validation of the gantry tilt in a computed tomography scanner using a head polymethyl methacrylate phantom

Study on a Specific Test Method for Dosimetric Characterization of Ultra-Wide Detector Computed Tomography

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