Section of Medical Physics, Cleveland Clinic, Cleveland, OH 44112, USA.
AJR Am J Roentgenol. 2012 Sep;199(3):670-6. doi: 10.2214/AJR.10.6153.
This CT study evaluates image noise and radiation dose using a modified CT dose index phantom to approximate pediatric abdominal shape. Contrast-to-noise ratio (CNR) and radiation dose were measured.
The oval shape was simulated by fixing 1000-mL saline bags aside cylindric phantoms with variable circumferences. The doses at the center and peripheral holes in the phantom were recorded. Measurements were obtained at 50-400 mAs and 80-140 kVp. Diluted iodine contrast agent filled the center hole, and distilled water filled the peripheral holes. CNR was defined as the difference in CT number between diluted iodine and water divided by the standard deviation (SD) of CT number of water.
Dose increased linearly with increases in tube current-exposure time product and by a power function (proportional to kVp(n), where n = 2.64-3.09) for increases in kilovoltage. A range of scanning parameters was established for each circumference from which technique optimization curves were created to determine the best tube current-time product and kilovoltage pairs when noise was less than 20 HU and dose was less than 2.5 cGy. CNR increased by 40% as kilovoltage was reduced from 140 to 80 kVp. A dose reduction of 70% was observed for 140 versus 80 kVp for the same CNR.
Because pediatric patients of the same age and weight come in all shapes and sizes, abdominal circumference is a useful clinical parameter on which to base CT scan techniques controlling radiation output--namely kilovoltage and tube current-time product. Low-kilovoltage techniques for patients with small circumference show better iodine CNR.
本 CT 研究使用改良的 CT 剂量指数体模评估图像噪声和辐射剂量，以模拟儿科腹部形状。测量对比噪声比（CNR）和辐射剂量。
通过将 1000 毫升生理盐水袋固定在具有不同周长的圆柱形体模旁边来模拟椭圆形。记录体模中心和外围孔的剂量。在 50-400 mAs 和 80-140 kVp 下进行测量。中心孔中填充稀释碘造影剂，外围孔中填充蒸馏水。CNR 定义为稀释碘与水之间的 CT 数差值除以水的 CT 数标准差。
剂量随管电流-曝光时间乘积的增加而线性增加，并随千伏的幂函数（与 kVp(n)成正比，其中 n = 2.64-3.09）增加。为每个周长确定了一系列扫描参数，以创建技术优化曲线，以确定噪声小于 20 HU 且剂量小于 2.5 cGy 时的最佳管电流-时间乘积和千伏对。当千伏从 140 降低到 80 kVp 时，CNR 增加了 40%。对于相同的 CNR，140 与 80 kVp 相比，剂量降低了 70%。
由于相同年龄和体重的儿科患者有各种形状和大小，因此腹部周长是控制辐射输出的 CT 扫描技术的有用临床参数，即千伏和管电流-时间乘积。对于周长较小的患者，低千伏技术显示出更好的碘 CNR。
