Freire Marta, Cañizares Gabriel, Echegoyen Sara, Gonzalez-Montoro Andrea, Gonzalez Antonio J
Instituto de Instrumentación para Imagen Molecular, Centro Mixto CSIC-Universitat Politècnica de València, Valencia, Spain.
Front Med (Lausanne). 2021 Nov 10;8:734476. doi: 10.3389/fmed.2021.734476. eCollection 2021.
In the past years, the gamma-ray detector designs based on the monolithic crystals have demonstrated to be excellent candidates for the design of high-performance PET systems. The monolithic crystals allow to achieve the intrinsic detector resolutions well below state-of-the-art; to increase packing fraction thus, increasing the system sensitivity; and to improve lesion detectability at the edges of the scanner field of view (FOV) because of their intrinsic depth of interaction (DOI) capabilities. The bottleneck to translate to the clinical PET systems based on a large number of monolithic detectors is eventually the requirement of mechanically complex and time-consuming calibration processes. To mitigate this drawback, several methods have been already proposed, such as using non-physically collimated radioactive sources or implementing the neuronal networks (NN) algorithms trained with simulated data. In this work, we aimed to simplify and fasten a calibration process of the monolithic based systems. The procedure consists of individually acquiring a 11 × 11 Na source array for all the detectors composing the PET system and obtaining the calibration map for each module using a method based on the Voronoi diagrams. Two reducing time methodologies are presented: (i) , where the calibration map of one detector is estimated and shared among all others, and (ii) , where the calibration map is slightly modified for each module as a function of their detector uniformity map. The experimental data from a dedicated prostate PET system was used to compare the standard calibration procedure with both the proposed methods. A greater similarity was exhibited between the methodology and the procedure; obtaining spatial resolution variances within 0.1 mm error bars and count rate deviations as small as 0.2%. Moreover, the negligible reconstructed image differences (13% deviation at most in the contrast-to-noise ratio) and almost identical contrast values were reported. Therefore, this proposed method allows us to calibrate the PET systems based on the monolithic crystals reducing the calibration time by approximately 80% compared with the procedure.
在过去几年中，基于整块晶体的伽马射线探测器设计已被证明是高性能正电子发射断层扫描（PET）系统设计的优秀候选方案。整块晶体能够实现远低于现有技术水平的固有探测器分辨率；提高填充率，从而提高系统灵敏度；并且由于其固有的相互作用深度（DOI）能力，能够改善扫描仪视野（FOV）边缘处病变的可检测性。将基于大量整块探测器的技术转化为临床PET系统的瓶颈最终在于需要复杂且耗时的机械校准过程。为了缓解这一缺点，已经提出了几种方法，例如使用非物理准直的放射性源或实施用模拟数据训练的神经网络（NN）算法。在这项工作中，我们旨在简化并加快基于整块晶体系统的校准过程。该程序包括为构成PET系统的所有探测器单独采集一个11×11的钠源阵列，并使用基于Voronoi图的方法为每个模块获取校准图。提出了两种减少时间的方法：（i）估计一个探测器的校准图并在所有其他探测器之间共享，以及（ii）根据每个模块的探测器均匀性图对校准图进行轻微修改。来自专用前列腺PET系统的实验数据用于将标准校准程序与这两种提出的方法进行比较。方法（i）与标准程序之间表现出更大的相似性；获得的空间分辨率方差在0.1毫米误差范围内，计数率偏差小至0.2%。此外，报告的重建图像差异可忽略不计（对比度噪声比偏差最大为13%）且对比度值几乎相同。因此，与标准程序相比，这种提出的方法使我们能够校准基于整块晶体的PET系统，将校准时间减少约80%。
