Kaasalainen Touko, Mäkelä Teemu, Kortesniemi Mika
HUS Medical Imaging Center, Helsinki University Central Hospital, Finland.
Department of Physics, University of Helsinki, Finland.
Eur J Radiol Open. 2018 Dec 17;6:24-32. doi: 10.1016/j.ejro.2018.12.001. eCollection 2019.
To determine the effect of patient's vertical off-centering and scout direction on the function of automatic tube voltage selection (ATVS) and tube current modulation (TCM) in chest computed tomography (CT).
Chest phantom was scanned with Siemens and GE CT systems using three clinical chest CT protocols exploiting ATVS and a fixed 120 kVp chest protocol. The scans were performed at five vertical positions of the phantom (-6 to +6 cm from the scanner isocenter). The effects of scout direction (posterior-to-anterior, anterior-to-posterior, and lateral) and vertical off-centering on the function of ATVS and TCM were studied by examining changes in selected voltage, radiation dose (volume CT dose index, CTDI), and image noise and contrast.
Both scout direction and vertical off-centering affected ATVS. The effect differed between the vendors for the studied geometry, demonstrating differences in technical approaches. The greatest observed increase in CTDI due to off-centering was 91%. Anterior-to-posterior scout produced highest doses at the uppermost table position, whereas posterior-to-anterior scout produced highest doses at the lowermost table position. Dose varied least using lateral scouts. Vertical off-centering impacted image noise and contrast due to the combined effect of ATVS, TCM, structural noise, and bowtie filters.
Patient vertical off-centering and scout direction affected substantially the CTDI and image quality in chest CT examinations. Vertical off-centering caused variation also in the selected tube voltage. The function of ATVS and TCM methods differ significantly between the CT vendors, resulting in differences in CTDI and image noise characteristics.
确定患者垂直偏心和定位像扫描方向对胸部计算机断层扫描（CT）中自动管电压选择（ATVS）和管电流调制（TCM）功能的影响。
使用西门子和GE CT系统，采用三种利用ATVS的临床胸部CT协议以及固定的120 kVp胸部协议对胸部体模进行扫描。扫描在体模的五个垂直位置（距扫描等中心-6至+6 cm）进行。通过检查选定电压、辐射剂量（容积CT剂量指数，CTDI）、图像噪声和对比度的变化，研究定位像扫描方向（后前位、前后位和侧位）和垂直偏心对ATVS和TCM功能的影响。
定位像扫描方向和垂直偏心均影响ATVS。在所研究的几何结构中，不同厂商的影响有所不同，表明技术方法存在差异。观察到的由于偏心导致的CTDI最大增幅为91%。前后位定位像扫描在台面最上方位置产生的剂量最高，而后前位定位像扫描在台面最下方位置产生的剂量最高。使用侧位定位像扫描时剂量变化最小。由于ATVS、TCM、结构噪声和蝴蝶结滤波器的综合作用，垂直偏心影响图像噪声和对比度。
患者垂直偏心和定位像扫描方向在很大程度上影响胸部CT检查中的CTDI和图像质量。垂直偏心还会导致所选管电压发生变化。ATVS和TCM方法的功能在不同CT厂商之间存在显著差异，导致CTDI和图像噪声特征有所不同。
