Establishing an evidence-base for erect pelvis radiography : positioning, radiation dose and image quality

Alzyoud, K

Abstract

Purpose: Pelvic radiography using X-ray imaging has traditionally been used for the identification of hip joint changes, including the identification of pathologies such as osteoarthritis. For patients suffering from hip pain, the supine pelvis X-ray examination is one of the initial diagnostic steps. Despite this, many recent studies have recommended that the position should now be undertaken erect and not supine to reflect the functional appearances of the hip joint. This thesis aims to establish an evidence base for erect pelvis radiography, and it will include assessing radiographic positioning, radiation dose and image quality.
Methods: The experimental work described in this thesis was conducted in three phases. Each phase has its own methods with the purpose of achieving a specific set of aims. Phase One was the evaluation of the postural effects of different erect (standing) positions in order to recommend an optimal one for erect pelvic radiography. Eight different erect positions were investigated. A sample group of 67 healthy people participated, and a range of spinal and pelvis measurements were acquired using a 3D video rasterography system (Diers) and an inclinometer.
Phase Two was a phantom study evaluating the potential changes to radiation dose and image quality when moving between supine and erect imaging. Phase two was undertaken using three experiments (experiment #1, experiment #2 and experiment #3). Experiment #1 evaluated the impact of increased patient size on the radiation dose and image quality. In this experiment, animal fat was positioned anteriorly on a pelvic anthropomorphic phantom and the thickness increased incrementally in 1cm steps from 1 to 15cm. Image quality was evaluated physically and visually. The effective dose was calculated using Monte Carlo simulation software (PCXMC). During experiment #2, the anterior thicknesses for 109 patients, with a range of BMIs, who were referred for pelvis radiography, was measured in the erect and supine position. Experiment #3 evaluated the potential differences between the positions (supine and erect) in terms of image quality and radiation dose by modelling patient thickness changes between positions using the data obtained in experiment #2. An anthropomorphic phantom was used and modified (by adding additional fat) to simulate tissue changes for both erect and supine X-ray positions. Visual grading analysis was used (VGA) to evaluate image quality. The effective dose and absorbed dose were calculated using PCXMC.
During Phase Three, 60 patients were imaged in erect and supine positions. The paired pelvis X-ray images were then compared, taking into account radiation dose and image quality.
Results: Phase One demonstrated no statistical differences between the eight-different standing positions for pelvic and spine metrics (P>0.05). Results also demonstrated no significant postural differences between BMIs across all eight standing positions (P>0.05). Also, no differences (P>0.05) were identified in the pelvis and spinal metrics when comparing between males and females .Standing relaxed with feet internally rotated by 20°and the upper arms supported was a recommendation derived from this phase. Results from Phase Two showed an increase in effective dose (E) as the fat thickness increased. Also, all physical and visual image quality metrics decreased as fat thickness increased. Physical and visual image quality measures also decreased for erect images when compared to supine images, and the E also increased. 90kVp, 130/145 SID, using both outer chambers, were the recommended exposure parameters settings for obtaining erect pelvis X-ray images. Results from Phase Three showed that anterior patient thickness was 17% (P<0.001) higher in an erect position .The DAP and absorbed dose were 46% and 45% (P<0.001) greater in the erect position. Also, the effective dose was 67% (P<0.001) higher in the erect position when compared with supine. In regard to the image quality (IQ), that of the erect position decreased by 10% when compared with supine (P<0.001).
Conclusion: The eight proposed standing positions could theoretically be suitable for erect pelvis imaging. People in a relaxed standing position, with their feet internally rotated by 20°and their upper arms supported would be recommended. In terms of IQ and radiation dose for erect positions, this position decreases image quality (both physical and visual) and increased radiation dose. Changes were largely due to the effect of gravity on the anterior soft tissue distribution. These issues should be considered and optimised more fully when deciding if to move from supine to erect pelvis imaging.

Citation

Alzyoud, K. Establishing an evidence-base for erect pelvis radiography : positioning, radiation dose and image quality. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 9, 2019
• Publicly Available Date: Oct 9, 2019
• Additional Information: Funders : Hashemit University