Sundberg Christel, Persson Mats, Sjölin Martin, Wikner J Jacob, Danielsson Mats
KTH Royal Institute of Technology, Physics of Medical Imaging, Stockholm, Sweden.
Linköping University, Department of Electrical Engineering, Linköping, Sweden.
J Med Imaging (Bellingham). 2020 Sep;7(5):053503. doi: 10.1117/1.JMI.7.5.053503. Epub 2020 Oct 6.
Photon-counting silicon strip detectors are attracting interest for use in next-generation CT scanners. For CT detectors in a clinical environment, it is desirable to have a low power consumption. However, decreasing the power consumption leads to higher noise. This is particularly detrimental for silicon detectors, which require a low noise floor to obtain a good dose efficiency. The increase in noise can be mitigated using a longer shaping time in the readout electronics. This also results in longer pulses, which requires an increased deadtime, thereby degrading the count-rate performance. However, as the photon flux varies greatly during a typical CT scan, not all projection lines require a high count-rate capability. We propose adjusting the shaping time to counteract the increased noise that results from decreasing the power consumption. To show the potential of increasing the shaping time to decrease the noise level, synchrotron measurements were performed using a detector prototype with two shaping time settings. From the measurements, a simulation model was developed and used to predict the performance of a future channel design. Based on the synchrotron measurements, we show that increasing the shaping time from 28.1 to 39.4 ns decreases the noise and increases the signal-to-noise ratio with 6.5% at low count rates. With the developed simulation model, we predict that a 50% decrease in power can be attained in a proposed future detector design by increasing the shaping time with a factor of 1.875. Our results show that the shaping time can be an important tool to adapt the pulse length and noise level to the photon flux and thereby optimize the dose efficiency of photon-counting silicon detectors.
光子计数硅条探测器正吸引着人们在下一代CT扫描仪中的应用兴趣。对于临床环境中的CT探测器，期望具有低功耗。然而，降低功耗会导致更高的噪声。这对于硅探测器尤其不利，因为硅探测器需要低噪声本底以获得良好的剂量效率。可以通过在读出电子设备中使用更长的整形时间来减轻噪声的增加。这也会导致脉冲更长，从而需要增加死时间，进而降低计数率性能。然而，由于在典型的CT扫描过程中光子通量变化很大，并非所有投影线都需要高计数率能力。我们建议调整整形时间以抵消因降低功耗而增加的噪声。为了展示增加整形时间以降低噪声水平的潜力，使用具有两种整形时间设置的探测器原型进行了同步加速器测量。从测量中，开发了一个模拟模型并用于预测未来通道设计的性能。基于同步加速器测量，我们表明将整形时间从28.1纳秒增加到39.4纳秒可降低噪声并在低计数率下将信噪比提高6.5%。利用开发的模拟模型，我们预测在未来提出的探测器设计中，通过将整形时间增加1.875倍，可实现功耗降低50%。我们的结果表明，整形时间可以成为使脉冲长度和噪声水平适应光子通量从而优化光子计数硅探测器剂量效率的重要工具。
