Ganguly Arundhuti, Rudin Stephen, Bednarek Daniel R, Hoffmann Kenneth R
Toshiba Stroke Research Center, Department of Physics, State University of New York at Buffalo, Buffalo, New York 14214, USA.
Med Phys. 2003 Nov;30(11):3029-39. doi: 10.1118/1.1617550.
A micro-angiographic detector was designed and its performance was previously tested to evaluate its feasibility as an improvement over current x-ray detectors for neuro-interventional imaging. The detector was shown to have a modulation transfer function value of about 2% at the Nyquist frequency of 10 cycles/mm and a zero frequency detective quantum efficiency [DQE(0)] value of about 55%. An assessment of the system was required to evaluate whether the current system was performing at its full potential and to determine if any of its components could be optimized to further improve the output. For the purpose, in this study, the parallel cascade theory was used to analyze the performance of the detector under neuro-angiographic conditions by studying the output at the various stages in the imaging chain. A simple model for the spread of light in the CsI(Tl) entrance phosphor was developed and the resolution degradation due to K-fluorescence absorption was calculated. The total gain of the system was found to result in 21 e(-) (rms) detected at the charge coupled device per absorbed x-ray photon. The gain and the spread of quanta in the imaging chain were used to calculate theoretically the DQE using the parallel cascade model. The results of the model-based calculations matched fairly well with the experimental data previously obtained. This model was then used to optimize the phosphor thickness for the detector. The results showed that the area under the DQE curve had a maximum value at 150 microm of CsI(Tl), though when weighted by the squared signal in frequency space of a 100-microm-diam iodinated vessel, the integral DQE reached a maximum at 250 microm of CsI(Tl). Further, possible locations for gain increase in the imaging chain were determined, and the output of the improved system was simulated. Thus a theoretical analysis for the micro-angiographic detector was performed to better assess its potential.
设计了一种微血管造影探测器，之前对其性能进行了测试，以评估其作为神经介入成像中现有X射线探测器改进设备的可行性。该探测器在10线对/毫米的奈奎斯特频率下调制传递函数值约为2%，零频率探测量子效率[DQE(0)]值约为55%。需要对该系统进行评估，以判断当前系统是否发挥了其全部潜力，并确定其任何组件是否可以优化以进一步提高输出。为此，在本研究中，通过研究成像链中各个阶段的输出，使用并行级联理论分析了探测器在神经血管造影条件下的性能。建立了一个简单的模型来描述光在CsI(Tl)输入荧光体中的传播，并计算了由于K荧光吸收导致的分辨率下降。发现系统的总增益导致每吸收一个X射线光子在电荷耦合器件处检测到21个电子（均方根）。利用并行级联模型，根据成像链中量子的增益和传播从理论上计算了DQE。基于模型的计算结果与先前获得的实验数据相当吻合。然后使用该模型优化探测器的荧光体厚度。结果表明，在CsI(Tl)厚度为150微米时，DQE曲线下的面积有最大值，不过当以直径为100微米的碘化血管在频率空间中的平方信号加权时，积分DQE在CsI(Tl)厚度为250微米时达到最大值。此外，确定了成像链中可能增加增益的位置，并对改进系统的输出进行了模拟。因此，对微血管造影探测器进行了理论分析，以更好地评估其潜力。
