Improved quantitative 90Y bremsstrahlung SPECT/CT reconstruction with Monte Carlo scatter modeling
Improved quantitative 90Y bremsstrahlung SPECT/CT reconstruction with Monte Carlo scatter modeling
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DOI：
10.1002/mp.12597
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发表时间：
2017-12-01
期刊：
影响因子：
3.8
通讯作者：
Fessler, Jeffrey A.
中科院分区：
文献类型：
--
作者：
Dewaraja, Yuni K.;Chun, Se Young;Fessler, Jeffrey A.
用途：在Y-90微球放射性栓塞（RE）中，准确的治疗后成像剂量测定对于建立吸收剂量与结局关系以制定未来治疗计划策略非常重要。此外，准确评估微球分布是重要的，因为关注肝脏外的意外活性沉积。通过SPECT或PET进行定量Y-90成像具有挑战性。在Y-90 SPECT模型为基础的方法是必要的散射校正，因为能量窗口为基础的方法是不可行的连续韧致辐射能谱。这项工作的目的是实现和评估一个散射估计方法，准确的Y-90韧致辐射SPECT/CT imaging.Methods：由于完全蒙特卡罗（MC）的方法Y-90 SPECT重建计算上是非常苛刻的，在本研究中，由MC模拟器产生的散射估计相结合的3D OS-EM重建模型中的分析投影仪。一个单一的窗口（105至195千电子伏）用于采集和投影仪建模。对具有肝内病变和低摄取肝外物体的肝/肺躯干体模进行成像，以评价无散射校正和有散射校正的SPECT/CT重建。临床应用表明，通过应用重建方法，以确定病变和正常的肝脏活性浓度与RE治疗的患者使用（肝脏）相对calibration.Results：有收敛的散射估计后，只需两次更新，大大降低了计算要求。在体模研究中，与无散射校正的重建相比，使用MC散射建模，肝内病变（从> 55%到> 86%）、正常肝脏（从113%到104%）和肺（从227%到104%）的活性恢复有实质性改善，噪声仅略有下降（13% vs. 17%）。同样，通过散射建模，对比度在视觉上和可检测性指数方面都得到了显著改善，这与低摄取肝外物体尤其相关。在患者研究中也观察到了体模的趋势，其中与仅使用两次MC散射更新的重建相比，不使用散射校正的SPECT的病变活动浓度和病变与肝脏浓度比较低：在11个病灶中，平均摄取为4.9 MBq/mL vs. 7.1 MBq/mL（P = 0.0547），平均正常肝脏摄取为1.6 MBq/mL vs. 1.5 MBq/mL（P = 0.056），平均病灶-肝脏摄取比为2.7 vs. 4.3（P = 0.0402）分别为无散射校正和有散射校正的重建。Y-90韧致辐射成像的定量精度可以大大提高MC散射建模，而不会显着降低图像噪声或密集的计算要求。(C)2017年美国医学物理学家协会
Purpose: In Y-90 microsphere radioembolization (RE), accurate post-therapy imaging-based dosimetry is important for establishing absorbed dose versus outcome relationships for developing future treatment planning strategies. Additionally, accurately assessing microsphere distributions is important because of concerns for unexpected activity deposition outside the liver. Quantitative Y-90 imaging by either SPECT or PET is challenging. In Y-90 SPECT model based methods are necessary for scatter correction because energy window-based methods are not feasible with the continuous bremsstrahlung energy spectrum. The objective of this work was to implement and evaluate a scatter estimation method for accurate Y-90 bremsstrahlung SPECT/CT imaging.Methods: Since a fully Monte Carlo (MC) approach to Y-90 SPECT reconstruction is computationally very demanding, in the present study the scatter estimate generated by a MC simulator was combined with an analytical projector in the 3D OS-EM reconstruction model. A single window (105 to 195-keV) was used for both the acquisition and the projector modeling. A liver/lung torso phantom with intrahepatic lesions and low-uptake extrahepatic objects was imaged to evaluate SPECT/CT reconstruction without and with scatter correction. Clinical application was demonstrated by applying the reconstruction approach to five patients treated with RE to determine lesion and normal liver activity concentrations using a (liver) relative calibration.Results: There was convergence of the scatter estimate after just two updates, greatly reducing computational requirements. In the phantom study, compared with reconstruction without scatter correction, with MC scatter modeling there was substantial improvement in activity recovery in intrahepatic lesions (from > 55% to > 86%), normal liver (from 113% to 104%), and lungs (from 227% to 104%) with only a small degradation in noise (13% vs. 17%). Similarly, with scatter modeling contrast improved substantially both visually and in terms of a detectability index, which was especially relevant for the low uptake extrahepatic objects. The trends observed for the phantom were also seen in the patient studies where lesion activity concentrations and lesion-to-liver concentration ratios were lower for SPECT without scatter correction compared with reconstruction with just two MC scatter updates: in eleven lesions the mean uptake was 4.9 vs. 7.1 MBq/mL (P = 0.0547), the mean normal liver uptake was 1.6 vs. 1.5 MBq/mL (P = 0.056) and the mean lesion-to-liver uptake ratio was 2.7 vs. 4.3 (P = 0.0402) for reconstruction without and with scatter correction respectively.Conclusions: Quantitative accuracy of Y-90 bremsstrahlung imaging can be substantially improved with MC scatter modeling without significant degradation in image noise or intensive computational requirements. (C) 2017 American Association of Physicists in Medicine