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首页> 外文会议>Conference on Medical Imaging: Physics of Medical Imaging >Dark Current and DQE Improvements of Mercuric Iodide Medical Imagers
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Dark Current and DQE Improvements of Mercuric Iodide Medical Imagers

机译：暗流和DQE的Mercuric Iodide医疗成像仪的改进

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A new TFT array has been developed specifically for mercuric iodide (HgI_2) deposition. This new TFT array combined with a modified HgI_2 Physical Vapor Deposition (PVD) process provides less than 10 Pa/mm~2 dark current at room temperature (22°C) measured at 1 V/μm electrical field. This photoconductor (direct) imager was run at 10 fr/s framerate and gave a measured sensitivity of 19 μC/(R~*cm~2) using a RQA5 radiation quality x-ray beam (70kVp x-ray with 21 mm Al filtering). This sensitivity value is higher than the sensitivity reported by our group for any previous HgI_2 imagers. MTF, NPS and DQE values were also evaluated on this 13 cm × 13 cm size imager with 127 μm pixel pitch. The MTF value is higher than 40% at the Nyquist frequency (3.9 lp/mm). This is much better than the MTF of a 600 urn CsI scintillator/photodiode (indirect) imager, which is only 16% (Varian internal data) and it is similar to the MTF value of the a-Se (another photoconductor) imagers. The first frame image lag is less than 8% when the imager was run at a 10 fr/s framerate. The low dark current and some noise reduction in the detector electronics, made it possible for the DQE to be measured down to low fluoroscopic dose levels ( < 4 μR/fr). The DQE(0) value is over 50% at a dose of 35 μR/fr and still about 40% at 3.76 μR/fr. The 270 μm thick PVD HgI_2 layer only absorbs less than 75% of the ～51 keV mean energy X-ray photons (70 kVp RQA5 filtered beam). This means that if the thickness of the HgI_2 layer is increased to 500 μm (increasing the absorption up to over 90%) the DQE(0) should then increase to about 60- 65% (assuming everything else remains unchanged). This value is close to the 65 - 70 % DQE(0), measured for the indirect (CsI) imagers at higher doses. Such a high DQE value makes this material competitive both for fluoroscopic and for radiographic applications.
机译：已经专为Mercuric碘化物（HGI_2）沉积而开发了一种新的TFT阵列。该新型TFT阵列与改进的HGI_2物理气相沉积（PVD）工艺组合在1V /μm电场下测量的室温（22℃）提供小于10Pa / mm〜2暗电流。该光电导体（直接）成像器在10fr / s帧间运行，使用RQA5辐射质量X射线束（70kVP X射线，21mm Al滤波，测量为19μC/（R〜* cm〜2）的测量灵敏度）。这种敏感值高于我们对任何以前的HGI_2成像仪报告的灵敏度。还在具有127μm像素间距的13cm×13cm尺寸的成像器上评估MTF，NPS和DQE值。 MTF值在奈奎斯特频率（3.9磅/mm）处高于40％。这优于600瓮CSI闪烁体/光电二极管（间接）成像器的MTF，其仅为16％（Varian内部数据），类似于A-SE（另一光导体）成像器的MTF值。当成像器在10FR / S帧中运行时，第一帧图像滞后小于8％。检测器电子器件的低暗电流和一些降噪，使DQE能够测量到低荧光透视剂量水平（<4μR/ FR）。 DQE（0）值以35μR/ FR的剂量超过50％，仍然在3.76μR/ Fr下仍然约为40％。 270μm厚的PVD HGI_2层仅吸收小于〜51KeV的75％的〜51keV的平均能量X射线光子（70 kVP RQA5过滤梁）。这意味着如果Hgi_2层的厚度增加到500μm（增加吸收超过90％），则DQE（0）则应增加至约60-65％（假设其他一切保持不变）。该值接近于65-70％DQE（0），测量为较高剂量的间接（CSI）成像器。这种高DQE值使这种材料竞争荧光透视和用于放射线照相应用。

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