基于层间无金属滤波片的双层平板探测器X射线及CT成像性能评估

Evaluation of X-ray and CT imaging using a dual-layer flat-panel detector without interlayer metal filter

目的双层平板探测器在单次X射线曝光下即可获得高低能投影时空匹配俱佳的能谱数据,应用前景广阔。本文针对一款层间无金属滤波片、等晶体厚度(550μm CsI)的双层平板探测器,在桌面CT平台上测量和评估了其X射线及CT成像性能。方法首先,基于CATPHAN标准模型和平场扫描,测量了该双层平板探测器的空间分辨率和噪声功率谱;其次,通过对KYOTO拟人胸腔模型的X射线摄影,分析了其双能透视成像性能;最后,使用窄束准直X射线对GAMMEX多能模体做计算机断层成像(Computed Tomography,CT)扫描,经过投影域基材料物质分解和CT图像重建,评估了其双能CT能谱成像潜力。结果在2×2像素合并模式(0.3×0.3 mm^(2))下,双层平板探测器顶层所得CT图像的空间分辨率可达21 lp/cm,底层可达17 lp/cm;二维透视成像实验研究表明,散射校正后的双层平板探测器高低能数据经过加权运算,可较好地实现骨头和软组织的有效分离;三维断层成像实验研究表明,双层平板探测器能谱成像有望获得准确的物质成分信息(窄束准直下,基材料分解平均误差在10%以内)。结论本文完成了基于一款新型双层平板探测器的X射线及CT成像性能的初步分析与评估,结果表明层间无金属滤波片、等晶体厚度的双层设计有望实现高质量双能能谱成像。

Purpose A dual-layer flat-panel detector(DL-FPD)can obtain high-and low-energy projections with excellent spatial and temporal matching under a single shot of X-ray exposure,leading to a great potential in medical and industrial applications.In this paper,the X-ray and CT imaging performance of a DL-FPD prototype with equal scintillator crystal thickness(550μm CsI)and no interlayer metal filter was measured and evaluated on a tabletop CT platform.Methods Firstly,the spatial resolution and noise power spectrum(NPS)of the DL-FPD were measured based on a CATPHAN phantom and flat field scans.Then,the dual energy fluoroscopic imaging performance was analyzed by using a KYOTO anthropomorphic thorax phantom.Finally,a Computed tomography(CT)scan was conducted on a GAMMEX multi-energy phantom using a narrow-collimated X-ray beam,and its dual-energy CT spectral imaging potential was evaluated after a projection-domain material decomposition and CT image reconstruction.Results In a 2×2 binning mode(0.3×0.3 mm^(2)),the spatial resolution of the CT image obtained from the top layer can reach 21 lp/cm,and the bottom layer can reach 17 lp/cm.The two-dimensional(2 D)fluoroscopic imaging experiment shows that,after scatter correction and weighted subtraction,the high-and low-energy projections of the DL FPD can be used to effectively separate bone from soft tissue.Experimental studies on the three dimensional(3 D)CT show that,the spectral imaging of DL FPD can obtain accurate material components information(the average error of material decomposition is within 10%in a narrow-collimated beam scan.).Conclusions In this paper,a preliminary analysis and evaluation of X-ray and CT imaging based on a new DL-FPD prototype are conducted.The results show that the DL-FPD design with no interlayer metal filter and equal scintillator crystal thickness is promising to achieve high-quality dual-energy spectral imaging.