Department of Radiology, Beijing Tongren Hospital, Capital Medical University, China.
AJNR Am J Neuroradiol. 2011 Nov-Dec;32(10):1783-8. doi: 10.3174/ajnr.A2609. Epub 2011 Aug 18.
MDCT has some specific scan parameters that may systematically increase or decrease radiation dose to patients. This study explored the scan protocol parameters that impact radiation dose in temporal bone MDCT and determined the optimal scan parameters that balance radiation dose with diagnostic image quality.
Using exsomatized cadaveric heads, traditional axial scanning, and helical scanning were performed with different detector collimations. Helical scans of the same scan region were then acquired by using the determined optimal detector collimation and various tube voltages, whereas other scan parameters remained fixed. Next, the scans were repeated by using various tube current-time products by using the determined optimal tube voltage. Last, with fixed tube current-time product, the scans were repeated with various pitches. All thin-section, helically acquired scans were reformatted to axial and coronal images with respect to the relevant scanning baseline. In each of the image volumes, the mean and SD HU values in regions of interest were measured in the central section of the internal auditory canal, and CNR values were calculated.
In agreement with theory, wider detector collimations such as 16 × 0.625 mm and 64 × 0.625 mm were associated with lower radiation doses than narrower collimations due to their lower overbeaming and higher geometric efficiency. In helical scanning, the detector collimation of 16 × 0.625 mm had higher image quality and the minimum DLP. Axial and coronal images acquired by using a 140-kVp tube voltage had significantly lower noise than scans acquired at 120 or 80 kVp with equivalent volume CT dose index. Diagnostic image quality was achieved when using a minimum tube current-time product of 120 mAs. Noise, CNR, and dose were jointly optimized with a pitch of 0.685.
Temporal bone CT scanning parameters may be optimized by following a systematic procedure that allows for the optimization of diagnostic image quality and the minimization of radiation dose. One such procedure for a particular 64-section MDCT scanner has been presented.
多层螺旋 CT（MDCT）有一些特定的扫描参数，这些参数可能会系统地增加或减少患者的辐射剂量。本研究旨在探讨影响颞骨 MDCT 辐射剂量的扫描方案参数，并确定在平衡辐射剂量和诊断图像质量方面的最佳扫描参数。
使用离体尸头，进行传统的轴位扫描和不同探测器准直的螺旋扫描。然后，使用确定的最佳探测器准直和不同的管电压对同一扫描区域进行螺旋扫描，同时保持其他扫描参数不变。接下来，使用确定的最佳管电压，通过改变不同的管电流-时间乘积来重复扫描。最后，使用固定的管电流-时间乘积，通过改变不同的螺距来重复扫描。所有薄层、螺旋采集的扫描均通过与相关扫描基线相对应的轴向和冠状位图像进行重建。在每个图像容积中，在内部听觉道中央节段的感兴趣区域测量平均和标准偏差 HU 值，并计算 CNR 值。
与理论相符，较宽的探测器准直（如 16×0.625mm 和 64×0.625mm）比较窄的准直（如 16×1.25mm 和 64×1.25mm）辐射剂量更低，这是由于前者的过射束更低，几何效率更高。在螺旋扫描中，16×0.625mm 的探测器准直具有更高的图像质量和最小的剂量长度乘积（DLP）。使用 140kVp 管电压获得的轴向和冠状位图像噪声明显低于使用 120kVp 或 80kVp 管电压并具有等效容积 CT 剂量指数的扫描。使用最小管电流-时间乘积 120mAs 可获得诊断图像质量。噪声、CNR 和剂量可以通过 0.685 的螺距进行联合优化。
颞骨 CT 扫描参数可以通过遵循系统的程序进行优化，从而优化诊断图像质量并最小化辐射剂量。已经提出了一种针对特定 64 层 MDCT 扫描仪的程序。
