The potential to perform attenuation and scatter compensation (ASC) in single-photon emission computed tomography (SPECT) imaging without a separate transmission scan is highly significant. In this context, attenuation in SPECT is primarily due to Compton scattering, where the probability of Compton scatter is proportional to the attenuation coefficient of the tissue and the energy of the scattered photon and the scattering angle are related. Based on this premise, we investigated whether the SPECT scattered-photon data acquired in list-mode (LM) format and including the energy information can be used to estimate the attenuation map. For this purpose, we propose a Fisher-information-based method that yields the Cramer-Rao bound (CRB) for the task of jointly estimating the activity and attenuation distribution using only the SPECT emission data. In the process, a path-based formalism to process the LM SPECT emission data, including the scattered-photon data, is proposed. The Fisher information method was implemented on NVIDIA graphics processing units (GPU) for acceleration. The method was applied to analyze the information content of SPECT LM emission data, which contains up to first-order scattered events, in a simulated SPECT system with parameters modeling a clinical system using realistic computational studies with 2-D digital synthetic and anthropomorphic phantoms. The method was also applied to LM data containing up to second-order scatter for a synthetic phantom. Experiments with anthropomorphic phantoms simulated myocardial perfusion and dopamine transporter (DaT)-Scan SPECT studies. The results show that the CRB obtained for the attenuation and activity coefficients was typically much lower than the true value of these coefficients. An increase in the number of detected photons yielded lower CRB for both the attenuation and activity coefficients. Further, we observed that systems with better energy resolution yielded a lower CRB for the attenuation coefficient. Overall, the results provide evidence that LM SPECT emission data, including the scattered photons, contains information to jointly estimate the activity and attenuation coefficients.

中文翻译：

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列表模式 SPECT 发射数据的 Fisher 信息分析，用于联合估计活动和衰减分布


在单光子发射计算机断层扫描 (SPECT) 成像中无需单独的透射扫描即可执行衰减和散射补偿 (ASC) 的潜力非常显着。在这种情况下，SPECT中的衰减主要是由于康普顿散射，其中康普顿散射的概率与组织的衰减系数成正比，并且散射光子的能量与散射角相关。基于这个前提，我们研究了以列表模式（LM）格式获取并包含能量信息的SPECT散射光子数据是否可以用于估计衰减图。为此，我们提出了一种基于 Fisher 信息的方法，该方法产生 Cramer-Rao 界（CRB），用于仅使用 SPECT 发射数据联合估计活动和衰减分布的任务。在此过程中，提出了一种基于路径的形式来处理LM SPECT发射数据，包括散射光子数据。 Fisher 信息方法在 NVIDIA 图形处理单元 (GPU) 上实现以进行加速。该方法用于分析模拟 SPECT 系统中 SPECT LM 发射数据的信息内容，其中包含一阶散射事件，其参数通过二维数字合成和拟人体模的真实计算研究对临床系统进行建模。该方法还适用于包含合成模型二阶散射的 LM 数据。使用拟人模型进行的实验模拟了心肌灌注和多巴胺转运蛋白 (DaT)-扫描 SPECT 研究。结果表明，获得的衰减系数和活动系数的 CRB 通常远低于这些系数的真实值。 检测到的光子数量的增加会导致衰减系数和活度系数的 CRB 降低。此外，我们观察到具有更好能量分辨率的系统产生的衰减系数 CRB 更低。总体而言，结果提供了证据，表明 LM SPECT 发射数据（包括散射光子）包含联合估计活动和衰减系数的信息。