The piecewise-linear dynamic attenuator reduces the impact of count rate loss with photon-counting detectors.
The piecewise-linear dynamic attenuator reduces the impact of count rate loss with photon-counting detectors.
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DOI：
10.1088/0031-9155/59/11/2829
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发表时间：
2014-06-07
影响因子：
3.5
通讯作者：
Pelc NJ
中科院分区：
文献类型：
--
作者：
Hsieh SS;Pelc NJ
光子计数X射线探测器（PCXD）与标准的能量集成X射线探测器相比具有几个优点，但也面临重大挑战。一个关键的挑战是CT所需的高计数率。在高计数率下，PCXD表现出计数率损失，并且在信号丰富（或高通量）测量中显示出降低的检测量子效率。为了降低计数率要求，可以使用动态波束成形滤波器来重新分布入射到患者上的通量。我们研究了分段线性衰减器与PCXD没有能量歧视能力。我们检查了三种检测器模型：经典的非瘫痪和瘫痪检测器模型，以及“混合”检测器模型，该模型是两种检测器模型的加权平均值，近似于现有的真实的检测器（Taguchi et al，Med Phys 2011）。我们推导出这些探测器的CT测量的方差的解析表达式。这些表达式与从腹部和胸部的DICOM图像文件估计的原始数据一起使用，以估计动态衰减器和静态波束成形（“蝴蝶结”）滤波器的重建图像中的方差。通过重新分配通量，动态衰减器在不增加理想探测器峰值方差的情况下将剂量降低了40%。对于非理想的PCXD，计数率损失的影响也降低了。不可瘫痪的检测器显示计数率损失的影响很小，但是对于可瘫痪的模型，计数率损失导致可以用动态衰减器控制的噪声条纹。利用混合模型，在噪声条纹主导重建之前所需的特征计数率减少了2到3倍。我们得出结论，分段线性衰减器可以降低计数率的要求，除了提高剂量效率的PCXD。这种减少的幅度取决于检测器，与paralyzable检测器表现出更大的好处比nonparalyzable检测器。
Photon counting x-ray detectors (PCXDs) offer several advantages compared to standard, energy-integrating x-ray detectors but also face significant challenges. One key challenge is the high count rates required in CT. At high count rates, PCXDs exhibit count rate loss and show reduced detective quantum efficiency in signal-rich (or high flux) measurements. In order to reduce count rate requirements, a dynamic beam-shaping filter can be used to redistribute flux incident on the patient. We study the piecewise-linear attenuator in conjunction with PCXDs without energy discrimination capabilities. We examined three detector models: the classic nonparalyzable and paralyzable detector models, and a “hybrid” detector model which is a weighted average of the two which approximates an existing, real detector (Taguchi et al, Med Phys 2011). We derive analytic expressions for the variance of the CT measurements for these detectors. These expressions are used with raw data estimated from DICOM image files of an abdomen and a thorax to estimate variance in reconstructed images for both the dynamic attenuator and a static beam-shaping (“bowtie”) filter. By redistributing flux, the dynamic attenuator reduces dose by 40% without increasing peak variance for the ideal detector. For non-ideal PCXDs, the impact of count rate loss is also reduced. The nonparalyzable detector shows little impact from count rate loss, but with the paralyzable model, count rate loss leads to noise streaks that can be controlled with the dynamic attenuator. With the hybrid model, the characteristic count rates required before noise streaks dominate the reconstruction are reduced by a factor of two to three. We conclude that the piecewise-linear attenuator can reduce the count rate requirements of the PCXD in addition to improving dose efficiency. The magnitude of this reduction depends on the detector, with paralyzable detectors showing much greater benefit than nonparalyzable detectors.
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影响因子：
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