The effects of patient positioning when interpreting CT dose metrics: A phantom study

Abstract

Proper patient positioning plays a large role in the function of TCM, and hence CTDI and SSDE. In addition, body mass distribution may affect how patients ought to be positioned within the scanner. Understanding these effects is critical in optimizing CT scanning practices.

The effect of vertical centering and scout direction on automatic tube voltage selection in chest CT: a preliminary phantom study on two different CT equipments

“…Several studies have shown that patient off-centering is a common and serious problem in CT with detrimental effects on patient dose and image quality [[20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]]. According to these publications, patients are typically positioned 1.7 cm–3.5 cm below the scan isocenter.…”

“…Despite the effective technical CT optimization tools, the role of user remains important to achieve optimal results both in terms of image quality and radiation dose. Several studies have previously shown remarkable effects of patient off-centering on patient radiation dose and image quality due to function of beam shaping filters and geometric magnification/minification resulted in the scout images (planning radiographs) [[20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]]. The function of a bowtie filter is to allow maximum x-ray intensity to the thickest part of a patient and to reduce x-ray intensity in peripheral areas with less attenuation, thereby reducing x-ray scatter and radiation dose of surface tissues [37].…”

Accuracy of automated patient positioning in CT using a 3D camera for body contour detection

“…Although radiographers can use laser beams to visually check the central positioning of the patient, this method is user-dependent and therefore patient positioning at a non-ideal table height is common [6, 7, 9, 10]. If the patient is positioned away from the isocenter (i.e., table positioned too high or too low), the localizer radiograph is either magnified or reduced in width and the radiation dose applied by the ATCM consequently increases or decreases, which might result in suboptimal image quality or an increase in dose [6–8, 10, 11]. In a study by Saltybaeva and Alkadhi, vertical off-centering by 20 mm in chest CT resulted in 7% organ dose differences, while off-centering of more than 40 mm was associated with significant dose differences of 20% and higher [12].…”

Precise and Automatic Patient Positioning in Computed Tomography

“…[5][6][7] Although the implementation of TCM varies between vendors, the applied tube current values always are based on estimates of patient size using information obtained from projection localizer radiographs (LRs). [8][9][10] Apparently, patient size in CT localizers varies with localizer type and patient positioning in the CT gantry, 11 resulting in variation in tube current values applied by the TCM system. This implies that inaccurate centering of patients may result in magnification of the acquired LR when the patient is positioned too close to the x-ray source, leading to overestimation of the patient size.…”