University Hospitals of Derby and Burton NHS Foundation Trust, Staffordshire, UK.
Research and Development Imaging Support Unit, Nottingham University Hospitals NHS Trust, Nottingham, UK.
Radiography (Lond). 2024 Oct;30(6):1517-1523. doi: 10.1016/j.radi.2024.09.051. Epub 2024 Sep 19.
Computed Tomography (CT) chest, abdomen and pelvis research demonstrates a relationship between vertical phantom positioning and radiation dose. Moving the phantom closer or further from the x-ray source results in magnification or minimisation of the localiser. As automatic tube current modulation (ATCM) algorithms use localisers to estimate patient size and calculate required tube current, magnification or minimisation results in the incorrect provision of radiation dose. Radiation dose changes also depend on localiser orientation, changes with anteroposterior (AP) and posteroanterior (PA) localisers demonstrating an inverse relationship. However, within CT head literature often attributes radiation dose changes on impaired function of the bow-tie filter instead. The current study investigated the role of miscentering on ATCM function within CT head, paying particular attention to localiser orientation.
Head scanning was performed with an anthropomorphic phantom at the isocentre, alongside ten vertically miscentered positions. This was performed three times, with an AP, PA and lateral localiser. CT dose index values at each miscentered level were compared across conditions.
Vertical miscentering altered radiation dose in both AP and PA conditions, radiation dose linearly increasing (up to 17.05%) when positioning the phantom closer to the x-ray source and decreasing when positioning away (up to -13.13%). Changes across AP and PA conditions demonstrated an inverse relationship. Radiation dose was unaffected in the lateral condition.
Miscentering during CT head alters ATCM function due to magnification/minimisation of the localiser image, causing ATCM algorithms to misinterpret patient size and miscalculate required tube current.
Radiographers should be accurate when centering for CT head, avoiding any potential radiation dose changes. Further research into vertical miscentering and image quality during CT head is recommended.
计算机断层扫描（CT）胸部、腹部和骨盆研究表明，垂直体模定位与辐射剂量之间存在关系。将体模靠近或远离 X 射线源会导致定位器的放大或缩小。由于自动管电流调制（ATCM）算法使用定位器来估计患者的大小并计算所需的管电流，因此放大或缩小会导致辐射剂量的不正确提供。辐射剂量的变化还取决于定位器的方向，前后（AP）和后前（PA）定位器的变化呈反比关系。然而，在 CT 头部文献中，通常归因于蝴蝶结滤线器功能障碍引起的辐射剂量变化。本研究调查了在 CT 头部中体模错位对 ATCM 功能的影响，特别注意定位器的方向。
在等中心位置使用人体模型对头部进行扫描，同时在十个垂直错位位置进行。这是三次进行的，使用了 AP、PA 和侧位定位器。在每个错位水平比较了各个条件下的 CT 剂量指数值。
垂直错位改变了 AP 和 PA 条件下的辐射剂量，当将体模靠近 X 射线源定位时，辐射剂量呈线性增加（高达 17.05%），而当远离时则减少（高达-13.13%）。AP 和 PA 条件下的变化呈反比关系。在侧位条件下，辐射剂量不受影响。
CT 头部的体模错位会改变 ATCM 功能，因为定位器图像的放大/缩小会导致 ATCM 算法错误地解释患者的大小并错误地计算所需的管电流。
放射技师在进行 CT 头部扫描时应准确定位，避免任何潜在的辐射剂量变化。建议进一步研究 CT 头部的垂直错位和图像质量。
