Choi Yu-Na, Lee Seungwan, Kim Hee-Joung
Department of Radiological Science, College of Health Science and Research Institute of Health Science, Yonsei University, Wonju, Gangwon-do 220-710, Korea.
Phys Med Biol. 2016 Jan 21;61(2):N35-49. doi: 10.1088/0031-9155/61/2/N35. Epub 2016 Jan 6.
K-edge imaging with photon counting x-ray detectors (PCXDs) can improve image quality compared with conventional energy integrating detectors. However, low-energy x-ray photons below the K-edge absorption energy of a target material do not contribute to image formation in the K-edge imaging and are likely to be completely absorbed by an object. In this study, we applied x-ray filters to the K-edge imaging with a PCXD based on cadmium zinc telluride for reducing radiation dose induced by low-energy x-ray photons. We used aluminum (Al) filters with different thicknesses as the low-energy x-ray filters and implemented the iodine K-edge imaging with an energy bin of 34-48 keV at the tube voltages of 50, 70 and 90 kVp. The effects of the low-energy x-ray filters on the K-edge imaging were investigated with respect to signal-difference-to-noise ratio (SDNR), entrance surface air kerma (ESAK) and figure of merit (FOM). The highest value of SDNR was observed in the K-edge imaging with a 2 mm Al filter, and the SDNR decreased as a function of the filter thicknesses. Compared to the K-edge imaging with a 2 mm Al filter, the ESAK was reduced by 66%, 48% and 39% in the K-edge imaging with a 12 mm Al filter for 50 kVp, 70 kVp and 90 kVp, respectively. The FOM values, which took into account the ESAK and SDNR, were maximized for 8, 6 to 8 and 4 mm Al filters at 50 kVp, 70 kVp and 90 kVp, respectively. We concluded that the use of an optimal low-energy filter thickness, which was determined by maximizing the FOM, could significantly reduce radiation dose while maintaining image quality in the K-edge imaging with the PCXD.
与传统的能量积分探测器相比，采用光子计数X射线探测器（PCXD）的K边成像能够提高图像质量。然而，低于目标材料K边吸收能量的低能X射线光子对K边成像的图像形成没有贡献，并且很可能被物体完全吸收。在本研究中，我们将X射线滤光片应用于基于碲化镉锌的PCXD的K边成像，以减少低能X射线光子引起的辐射剂量。我们使用不同厚度的铝（Al）滤光片作为低能X射线滤光片，并在50、70和90 kVp的管电压下，以34 - 48 keV的能量区间实现碘K边成像。从信号差噪比（SDNR）、体表空气比释动能（ESAK）和品质因数（FOM）方面研究了低能X射线滤光片对K边成像的影响。在使用2 mm Al滤光片的K边成像中观察到最高的SDNR值，并且SDNR随滤光片厚度的增加而降低。与使用2 mm Al滤光片的K边成像相比，在50 kVp、70 kVp和90 kVp下，使用12 mm Al滤光片的K边成像的ESAK分别降低了66%、48%和39%。分别在50 kVp、70 kVp和90 kVp下，考虑到ESAK和SDNR的FOM值在使用8 mm、6至8 mm和4 mm Al滤光片时达到最大值。我们得出结论，通过使FOM最大化来确定的最佳低能滤光片厚度的使用，可以在使用PCXD的K边成像中显著降低辐射剂量，同时保持图像质量。
