Welander U, McDavid W D, Mörner A C, Tronje G, Tokuoka O, Fuchihata H, Nelvig P, Dove S B
Department of Oral Radiology, Karolinska Institutet, Stockholm.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1995 Sep;80(3):345-50. doi: 10.1016/s1079-2104(05)80393-2.
To study the noise characteristics of the Sens-A-Ray (Regam Medical Systems AB, Sundsvall, Sweden) system, 20 radiographs were obtained at each of three different exposure levels at 70 and 90 kVp with a homogeneous x-ray field. Exposures were measured with an ionization chamber. Noise power spectra were calculated over three areas within each radiograph, and ensemble averages were subsequently found from 60 data files at each exposure level. Noise equivalent quanta were calculated with the noise power spectra and modulation transfer function data from previous studies. Finally, the detective quantum efficiency was calculated by dividing the noise equivalent quanta by the estimated incident photon fluence at the different exposures. The system has a maximum detective quantum efficiency of approximately 0.030 at 70 kVp and 0.025 at 90 kVp. A broad maximum exists at approximately 2 cycles/mm, indicating that the signal-to-noise ratio is most favorable at this spatial frequency.
为研究Sens - A - Ray系统（瑞典松兹瓦尔Regam医疗系统公司）的噪声特性，在70和90 kVp的三种不同曝光水平下，使用均匀X射线场获取了20张X光片。曝光量用电离室测量。在每张X光片的三个区域计算噪声功率谱，随后从每个曝光水平的60个数据文件中求出总体平均值。利用先前研究中的噪声功率谱和调制传递函数数据计算噪声等效量子数。最后，通过将噪声等效量子数除以不同曝光量下估计的入射光子注量来计算探测量子效率。该系统在70 kVp时的最大探测量子效率约为0.030，在90 kVp时为0.025。在约2周期/毫米处存在一个较宽的最大值，表明在此空间频率下信噪比最为有利。
