Haba Tomonobu, Koyama Shuji, Aoyama Takahiko, Kinomura Yutaka, Ida Yoshihiro, Kobayashi Masanao, Kameyama Hiroshi, Tsutsumi Yoshinori
Department of Radiology, Fujita Health University Hospital, 1-98 Dengakugakubo, Kutsukake-cho, Toyoake, Aichi, Japan.
Brain & Mind Research Center, Nagoya University, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya, Aichi, Japan.
Phys Med. 2016 Jul;32(7):905-13. doi: 10.1016/j.ejmp.2016.06.010. Epub 2016 Jun 29.
Patient dose estimation in X-ray computed tomography (CT) is generally performed by Monte Carlo simulation of photon interactions within anthropomorphic or cylindrical phantoms. An accurate Monte Carlo simulation requires an understanding of the effects of the bow-tie filter equipped in a CT scanner, i.e. the change of X-ray energy and air kerma along the fan-beam arc of the CT scanner. To measure the effective energy and air kerma distributions, we devised a pin-photodiode array utilizing eight channels of X-ray sensors arranged at regular intervals along the fan-beam arc of the CT scanner.
Each X-ray sensor consisted of two plate type of pin silicon photodiodes in tandem - front and rear photodiodes - and of a lead collimator, which only allowed X-rays to impinge vertically to the silicon surface of the photodiodes. The effective energy of the X-rays was calculated from the ratio of the output voltages of the photodiodes and the dose was calculated from the output voltage of the front photodiode using the energy and dose calibration curves respectively.
The pin-photodiode array allowed the calculation of X-ray effective energies and relative doses, at eight points simultaneously along the fan-beam arc of a CT scanner during a single rotation of the scanner.
The fan-beam energy and air kerma distributions of CT scanners can be effectively measured using this pin-photodiode array.
X射线计算机断层扫描（CT）中的患者剂量估算通常通过对人体模型或圆柱形体模内光子相互作用进行蒙特卡罗模拟来完成。准确的蒙特卡罗模拟需要了解CT扫描仪中配备的蝴蝶结滤波器的影响，即沿CT扫描仪扇形束弧的X射线能量和空气比释动能的变化。为了测量有效能量和空气比释动能分布，我们设计了一种针状光电二极管阵列，该阵列利用八个X射线传感器通道沿CT扫描仪的扇形束弧等间隔排列。
每个X射线传感器由两个串联的平板型针状硅光电二极管（前光电二极管和后光电二极管）以及一个铅准直器组成，该铅准直器仅允许X射线垂直照射到光电二极管的硅表面。X射线的有效能量由光电二极管的输出电压之比计算得出，剂量则分别使用能量和剂量校准曲线从前光电二极管的输出电压计算得出。
针状光电二极管阵列能够在CT扫描仪单次旋转期间，沿着其扇形束弧的八个点同时计算X射线有效能量和相对剂量。
使用这种针状光电二极管阵列可以有效地测量CT扫描仪的扇形束能量和空气比释动能分布。
