Stamatakis H C, Welander U, McDavid W D
Department of Oral Radiology, Karolinska Institutet, Box 4064, S-141 04 Huddinge, Sweden.
Dentomaxillofac Radiol. 2000 Jan;29(1):28-34. doi: 10.1038/sj/dmfr/4600497.
To determine physical properties of the Digora digital intra-oral radiographic system (Soredex Orion Corporation, Helsinki, Finland) for different calibration settings and beam energies.
The line spread function (LSF) and the modulation transfer function (MTF) were determined from radiographs of a slit. Noise power spectra (NPS) were determined from radiographs exposed to homogeneous radiation fields at 10, 50 and 100% of the calibration exposure for three tube potentials. All calculations were performed using relative values of exposure comprised of gray level, the signal at the photomultiplier tube and the amplified signal in order to confirm agreement between these different approaches. Noise equivalent quanta (NEQ) were calculated from the one-dimensional NPSs and the MTF. Detective quantum efficiencies (DQE) were determined from the NEQs and representative values of the photon fluence. Signal-to-noise ratios (SNR) were calculated for different signal contrasts applying the NEQs.
The MTF of the system exhibited typical characteristics and falls to a value close to zero at the Nyquist frequency of about 7 cycles/mm. Noise as expressed by the NPS was found to be relatively low, i.e. about 10(-5) to 10(-6) mm2 depending on exposure and frequency. There was no significant difference between data obtained at different beam energies. The NEQ and hence the DQE were relatively high. DQE decreased with increased exposure. For exposures in the clinical range of the DQE reached a peak value of about 25%. SNRs are favorable.
The physical properties of the Digora intra-oral system indicate that it is suitable for digital intra-oral radiography.
确定Digora数字化口腔内放射成像系统（芬兰赫尔辛基Soredex Orion公司）在不同校准设置和射线能量下的物理特性。
通过狭缝的射线照片确定线扩展函数（LSF）和调制传递函数（MTF）。在三种管电压下，从校准曝光量的10%、50%和100%的均匀辐射场曝光的射线照片中确定噪声功率谱（NPS）。所有计算均使用由灰度级、光电倍增管处的信号和放大信号组成的曝光相对值，以确认这些不同方法之间的一致性。从一维NPS和MTF计算噪声等效量子数（NEQ）。根据NEQ和光子注量的代表性值确定探测量子效率（DQE）。应用NEQ计算不同信号对比度下的信噪比（SNR）。
该系统的MTF表现出典型特征，在约7周期/mm的奈奎斯特频率处降至接近零的值。发现由NPS表示的噪声相对较低，即根据曝光和频率约为10^(-5)至10^(-6) mm²。在不同射线能量下获得的数据之间没有显著差异。NEQ以及因此的DQE相对较高。DQE随曝光增加而降低。对于临床范围内的曝光，DQE达到约25%的峰值。SNR良好。
Digora口腔内系统的物理特性表明它适用于数字化口腔内放射摄影。
