Brunskog Rickard, Persson Mats, Jin Zihui, Danielsson Mats
The Royal Institute of Technology Stockholm, Physics of Medical Imaging, Stockholm, Sweden.
Karolinska University Hospital, MedTechLabs, BioClinicum, Solna, Sweden.
J Med Imaging (Bellingham). 2024 Jan;11(1):013503. doi: 10.1117/1.JMI.11.1.013503. Epub 2024 Feb 1.
Current photon-counting computed tomography detectors are limited to a pixel size of around 0.3 to 0.5 mm due to excessive charge sharing degrading the dose efficiency and energy resolution as the pixels become smaller. In this work, we present measurements of a prototype photon-counting detector that leverages the charge sharing to reach a theoretical sub-pixel resolution in the order of . The goal of the study is to validate our Monte-Carlo simulation using measurements, enabling further development.
We measure the channel response at the MAX IV Lab, in the DanMAX beamline, with a 35 keV photon beam, and compare the measurements with a 2D Monte Carlo simulation combined with a charge transport model. Only a few channels on the prototype are connected to keep the number of wire bonds low.
The measurements agree generally well with the simulations with the beam close to the electrodes but diverge as the beam is moved further away. The induced charge cloud signals also seem to increase linearly as the beam is moved away from the electrodes.
The agreement between measurements and simulations indicates that the Monte-Carlo simulation can accurately model the channel response of the detector with the photon interactions close to the electrodes, which indicates that the unconnected electrodes introduce unwanted effects that need to be further explored. With the same Monte-Carlo simulation previously indicating a resolution of around with similar geometry, the results are promising that an ultra-high resolution detector is not far in the future.
由于像素变得更小时电荷共享过多会降低剂量效率和能量分辨率,当前的光子计数计算机断层扫描探测器的像素尺寸限制在约0.3至0.5毫米。在这项工作中,我们展示了一种原型光子计数探测器的测量结果,该探测器利用电荷共享达到了理论上约为亚像素分辨率的水平。本研究的目标是通过测量来验证我们的蒙特卡罗模拟,以推动进一步的发展。
我们在MAX IV实验室的DanMAX光束线中,用35keV光子束测量通道响应,并将测量结果与结合了电荷传输模型的二维蒙特卡罗模拟进行比较。原型上仅连接了少数几个通道以保持引线键合数量较低。
当光束靠近电极时,测量结果与模拟结果总体上吻合良好,但随着光束移开,两者出现偏差。随着光束远离电极,感应电荷云信号似乎也呈线性增加。
测量结果与模拟结果之间的一致性表明,蒙特卡罗模拟可以准确地对探测器在光子相互作用靠近电极时的通道响应进行建模,这表明未连接的电极会引入需要进一步探索的有害影响。鉴于之前相同的蒙特卡罗模拟表明具有类似几何结构的探测器分辨率约为,这些结果预示着超高分辨率探测器在不久的将来有望实现。