Introduction: The most commonly used projection for pelvic and hip radiography is the supine AP projection, but some studies advocate that it would be better to perform it in erect position as this would provide more diagnostically useful information. According to a previous study they reported reduced image quality and increased radiation dose for erect pelvic imaging in larger patients as they compared it to the supine pelvic X-ray. Purpose: The purpose of this study is to determine whether the radiation dose and image quality differ between two different erect pelvic radiographic procedures, with and without fat tissue removal. Methods: The measurements were divided into two parts. In the first part we determined which band did not produce artefacts on the resultant X-ray image when displacing fat tissue on the phantom. The second part was performed on 60 patients referred for erect pelvic imaging. They were randomly divided into two equal groups, half of them removed the fat tissue from the region of interest and the other group did not. We measured waist and hip circumference, height, weight, DAP, primary field size, source-to-skin distance, mAs and kV. BMI, ESD and effective dose were subsequently calculated. The images were evaluated by three radiologists. Results: In the phantom study we found that a thin cotton triangular bandage does not show any visible artefacts. The waist circumference before and after tissue removal was statistically different (p<0.001), as the thickness decreased by 4.7%, while hip circumference before and after removal was not statistically different (p=0.211). DAP was 38.5% lower in a group of patients with tissue removal (p=0.001). The ESD was 44% lower in a group in which patients moved the fat tissue from the region of interest (p<0.001). The effective dose was reduced by 38.7% in a group of patients with soft tissue removal (p<0.001). Hip joints (p=0.001), trochanters (p=0.021), acetabula (p<0.001), femoral necks (p=0.021), medulla and cortex of the pelvis (p=0.009), sacrum and its foramina (p=0.008) and the pelvic/hip soft tissues (p=0.039) were more visible on images obtained with fat tissue removal and were also statistically different. We found no significant differences between groups in visualisation of sacroiliac joints (p=0.055), the iliac crests (p=0.060) and the pubic/ischial rami (p=0.166). The total image score was higher in the patients with fat tissue removal (p=0.004). Discussion and conclusion: In this study we found that when taking a pelvic radiograph in the erect position, while moving fat tissue from the region of interest, the patient dose area product, the entrance skin dose and the effective dose decreases. This also affects the image quality, as it increases with the removal of the tissue and most of the anatomical structures of the pelvis are better visualised.
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