Variability of MDCT Dose Due to Technologist Performance: Impact of Posteroanterior Versus Anteroposterior Localizer Image and Table Height With Use of Automated Tube Current Modulation

Harri, Peter A.; Moreno, Courtney C.; Nelson, Rendon C.; Fani, Negar; Small, William; Duong, Phuong-Anh T.; Tang, Xiangyang; Applegate, Kimberly E.

doi:10.2214/ajr.13.11608

Cited by 29 publications

(25 citation statements)

References 14 publications

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“…Our observations indicate that, despite trying to vertically center the phantom as accurate as possible, the attenuation centering was on average too low. Similar findings according to the patient vertical centering were previously reported (9,11,17).…”

Section: Discussionsupporting

confidence: 91%

“…The phantom was fixed on the couch and carefully adjusted to place the geometric center of the phantom in the center of the rotating gantry. For this, lateral localizer radiography was performed to obtain a side view for adjusting the table height, with the aim of placing the phantom in the vertical center as recently shown (11). CT scans were obtained in the craniocaudal direction from the apex of the lungs to the diaphragm with the following protocol parameters: pitch, 1.2; collimation, 0.6 3 96 mm with use of the z-flying focal spot; and gantry rotation time, 0.5 second.…”

Section: Discussionmentioning

confidence: 99%

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Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation

2017

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Purpose To calculate the effect of localizer radiography projections to the total radiation dose, including both the dose from localizer radiography and that from subsequent chest computed tomography (CT) with tube current modulation (TCM). Materials and Methods An anthropomorphic phantom was scanned with 192-section CT without and with differently sized breast attachments. Chest CT with TCM was performed after one localizer radiographic examination with anteroposterior (AP) or posteroanterior (PA) projections. Dose distributions were obtained by means of Monte Carlo simulations based on acquired CT data. For Monte Carlo simulations of localizer radiography, the tube position was fixed at 0°and 180°; for chest CT, a spiral trajectory with TCM was used. The effect of tube start angles on dose distribution was investigated with Monte Carlo simulations by using TCM curves with fixed start angles (0°, 90°, and 180°). Total doses for lungs, heart, and breast were calculated as the sum of the dose from localizer radiography and CT. Image noise was defined as the standard deviation of attenuation measured in 14 circular regions of interest. The Wilcoxon signed rank test, paired t test, and Friedman analysis of variance were conducted to evaluate differences in noise, TCM curves, and organ doses, respectively. Results Organ doses from localizer radiography were lower when using a PA instead of an AP projection (P = .005). The use of a PA projection resulted in higher TCM values for chest CT (P < .001) owing to the higher attenuation (P < .001) and thus resulted in higher total organ doses for all investigated phantoms and protocols (P < .001). Noise in CT images was lower with PA localizer radiography than with AP localizer radiography (P = .03). The use of an AP projection allowed for total dose reductions of 16%, 15%, and 12% for lungs, breast, and heart, respectively. Differences in organ doses were not related to tube start angles (P = .17). Conclusion The total organ doses are higher when using PA projection localizer radiography owing to higher TCM values, whereas the organ doses from PA localizer radiography alone are lower. Thus, PA localizer radiography should be used in combination with reduced reference tube current at subsequent chest CT.

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Section: Discussionsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation

2017

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“…(b)]. For all of the configurations (male, female, overweight male) the phantom was positioned on the CT scanner table and was carefully adjusted in the center of the rotating gantry by using two orthogonal LRs as recently proposed …”

Section: Methodsmentioning

confidence: 99%

Vertical off‐centering affects organ dose in chest CT: Evidence from Monte Carlo simulations in anthropomorphic phantoms

Saltybaeva

Alkadhi

2017

Medical Physics

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“…Owing to the divergence of the X-ray beam, a magnification or demagnification of the patient may occur if the patient is miscentred, leading to the attenuation of the patient being misjudged. 14 An operator-controlled image quality reference parameter (IQ reference parameter) is used to adjust the amount of applied ATCM during a scan. Prior to a scan, the CT scanner determines which tube current to apply at different locations throughout a scan from the attenuation characteristics of the patient, the IQ reference parameter and the selected technique parameters.…”

Section: Methodsmentioning

confidence: 99%

Evaluating the impact of scan settings on automatic tube current modulation in CT using a novel phantom

Merzan¹,

Nowik²,

Poludniowski³

et al. 2017

BJR

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Objective: The aim of this study was to make a comprehensive evaluation of how variable scan settings can affect the performance of automatic tube current modulation (ATCM) in recent CT scanners from the four major manufacturers. Methods: A phantom was designed and manufactured for the purpose of evaluating ATCM. The phantom was scanned with four categories of systematically varied settings (scan projection radiograph, technique and reconstruction parameters and phantom miscentring). The performance of ATCM, in terms of applied tube current and noise uniformity, for the scans with varied settings was compared with a reference scan using subjective and quantitative approaches. Results: The ATCM implemented by each manufacturer is based on different principles and any affect to the performance of the ATCM, when varying scan settings, will manifest differently among the vendors. The results are summarized in four tables corresponding to the categories of varied settings. Conclusion: The developed phantom proved useful for evaluating the ATCM. It is important to understand how different implementations (vendor specific) of ATCM perform in order to make informed decisions about the selection of scan settings when designing protocols. The resulting tables can serve as a reference for understanding the different implementations of ATCM and highlight settings that should be taken into consideration when adjusting an imaging protocol. Advances in knowledge:The results from this work can serve as a reference for how changes in geometry or scan settings can affect the performance of ATCM, in terms of tube current and noise.

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Variability of MDCT Dose Due to Technologist Performance: Impact of Posteroanterior Versus Anteroposterior Localizer Image and Table Height With Use of Automated Tube Current Modulation

Abstract: Patient off-centering closer to the x-ray source resulted in patient magnification in the posteroanterior localizer image, leading to higher tube currents with ATCM and increased DLP. Differences in technologist, arm position, and overscanning also resulted in dose variability.

Cited by 29 publications

References 14 publications

Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation

Effect of Localizer Radiography Projection on Organ Dose at Chest CT with Automatic Tube Current Modulation

Vertical off‐centering affects organ dose in chest CT: Evidence from Monte Carlo simulations in anthropomorphic phantoms

Evaluating the impact of scan settings on automatic tube current modulation in CT using a novel phantom

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