Jain Amit, Kuhls-Gilcrist Andrew, Bednarek Daniel R, Rudin Stephen
Toshiba Stroke Research Center, University at Buffalo, Buffalo 14214 NY USA (telephone: 716-829-5417,
Toshiba Stroke Research Center, University at Buffalo, Buffalo 14214 NY USA (telephone: 716- 829-5409,
IEEE Nucl Sci Symp Conf Rec (1997). 2009 Dec 31;2009:3012-3016. doi: 10.1109/NSSMIC.2009.5401587.
Although in radiological imaging, the prevailing mode of acquisition is the integration of the energy deposited by all x-rays absorbed in the imaging detector, much improvement in image spatial and contrast resolution could be achieved if each individual x-ray photon were detected and counted separately. In this work we compare the conventional energy integration (EI) mode with the new single photon counting (SPC) mode for a recently developed high-resolution Micro-Angiographic Fluoroscopic (MAF) detector, which is uniquely capable of both modes of operation. The MAF has 1024×1024 pixels of 35 microns effective size and is capable of real-time imaging at 30 fps. The large variable gain of its light image intensifier (LII) provides quantum limited operation with essentially no additive instrumentation noise and enables the MAF to operate in both EI and the very sensitive low-exposure SPC modes. We used high LII gain with very low exposure (<1 x-ray photon/pixel) per frame for SPC mode and higher exposure per frame with lower gain for EI mode. Multiple signal-thresholded frames were summed in SPC mode to provide an integrated frame with the same total exposure as EI mode. A heavily K-edge filtered x-ray beam (average energy of 31 keV) was used to provide a nearly monochromatic spectrum. The MTF measured using a standard slit method showed a dramatic improvement for the SPC mode over the EI mode at all frequencies. Images of a line pair phantom also showed improved spatial resolution with 12 lp/mm visible in SPC mode compared to only 8 lp/mm in EI mode. In SPC mode, images of human distal and middle phalanges showed the trabecular structures of the bone with far better contrast and detail. These improvements with the SPC mode should be advantageous for clinical applications where high resolution and/or high contrast are essential such as in mammography and extremity imaging as well as for dual modality applications, which combine nuclear medicine and x-ray imaging using a single detector.
尽管在放射成像中，目前的采集模式是对成像探测器中吸收的所有X射线沉积的能量进行积分，但如果能对每个单独的X射线光子进行检测和计数，图像的空间分辨率和对比度分辨率将会有很大提高。在这项工作中，我们将传统的能量积分（EI）模式与新的单光子计数（SPC）模式进行了比较，使用的是最近开发的高分辨率微血管造影荧光（MAF）探测器，该探测器独特地具备两种操作模式。MAF有1024×1024个像素，有效尺寸为35微米，能够以30帧/秒的速度进行实时成像。其光像增强器（LII）的大变增益提供了量子极限操作，基本没有附加仪器噪声，使MAF能够在EI和非常灵敏的低曝光SPC模式下运行。在SPC模式下，我们使用高LII增益和每帧极低的曝光（<1个X射线光子/像素），在EI模式下使用较低增益和每帧较高的曝光。在SPC模式下，对多个信号阈值化的帧进行求和，以提供与EI模式总曝光相同的积分帧。使用经过强K边滤波的X射线束（平均能量为31 keV）来提供近乎单色的光谱。使用标准狭缝法测量的调制传递函数（MTF）表明，在所有频率下，SPC模式相对于EI模式都有显著改善。线对模型的图像也显示，SPC模式下的空间分辨率有所提高，可见12线对/毫米，而EI模式下仅为8线对/毫米。在SPC模式下，人体远端和中间指骨的图像显示出骨骼的小梁结构，对比度和细节要好得多。SPC模式的这些改进对于乳腺摄影和肢体成像等高分辨率和/或高对比度至关重要的临床应用以及使用单个探测器结合核医学和X射线成像的双模态应用应该是有利的。
