Nuclear Medicine and Molecular Imaging, KU Leuven, Leuven, Belgium
Nuclear Medicine and Molecular Imaging, KU Leuven, Leuven, Belgium.
J Nucl Med. 2018 Oct;59(10):1630-1635. doi: 10.2967/jnumed.117.204156. Epub 2018 Mar 1.
Methods for joint activity reconstruction and attenuation reconstruction of time-of-flight (TOF) PET data provide an effective solution to attenuation correction when no (or incomplete or inaccurate) information on attenuation is available. One of the main barriers limiting use of these methods in clinical practice is their lack of validation in a relatively large patient database. In this contribution, we aim to validate reconstruction performed with maximum-likelihood activity reconstruction and attenuation registration (MLRR) in a whole-body patient dataset. Furthermore, a partial validation (because the scale problem of the algorithm is avoided for now) of reconstruction performed with maximum-likelihood activity and attenuation (MLAA) is also provided. We present a quantitative comparison between these 2 methods of joint reconstruction and the current clinical gold standard, maximum-likelihood expectation maximization (MLEM) with CT-based attenuation correction. The whole-body TOF PET emission data of each patient dataset were processed as a whole to reconstruct an activity volume covering all the acquired bed positions, helping reduce the problem of a scale per bed position in MLAA to a global scale for the entire activity volume. Three reconstruction algorithms were used: MLEM, MLRR, and MLAA. A maximum-likelihood scaling of the single-scatter simulation estimate to the emission data was used for scatter correction. The reconstruction results for various regions of interest were then analyzed. The joint reconstructions of the whole-body patient dataset provided better quantification than the gold standard in cases of PET and CT misalignment caused by patient or organ motion. Our quantitative analysis showed a difference of -4.2% ± 2.3% between MLRR and MLEM and a difference of -7.5% ± 4.6% between MLAA and MLEM, averaged over all regions of interest. Joint reconstruction of activity and attenuation provides a useful means to estimate tracer distribution when CT-based-attenuation images are subject to misalignment or are not available. With an accurate estimate of the scatter contribution in the emission measurements, the joint reconstructions of TOF PET data are within clinically acceptable accuracy.
方法为联合活动重建和衰减重建的飞行时间（TOF）正电子发射断层扫描（PET）数据提供了一个有效的解决方案，当衰减没有（或不完整或不准确）信息是可用的。这些方法在临床实践中的主要障碍之一是缺乏在相对较大的患者数据库中的验证。在本贡献中，我们旨在验证全身患者数据集上使用最大似然活性重建和衰减配准（MLRR）进行的重建。此外，还提供了对使用最大似然活性和衰减（MLAA）进行的重建的部分验证（因为目前避免了算法的比例问题）。我们提出了一种定量比较这两种联合重建方法与目前的临床金标准，基于 CT 的衰减校正的最大似然期望最大化（MLEM）。每个患者数据集的全身 TOF PET 发射数据作为一个整体进行处理，以重建一个覆盖所有采集床位位置的活动体积，有助于将 MLAA 中每个床位位置的比例问题减少到整个活动体积的全局比例。使用了三种重建算法：MLEM、MLRR 和 MLAA。使用单散射模拟估计对发射数据的最大似然缩放进行散射校正。然后分析了各种感兴趣区域的重建结果。在由于患者或器官运动引起的 PET 和 CT 配准不良的情况下，全身患者数据集的联合重建提供了比金标准更好的定量结果。我们的定量分析显示，MLRR 和 MLEM 之间的差异为-4.2%±2.3%，MLAA 和 MLEM 之间的差异为-7.5%±4.6%，平均值为所有感兴趣区域。当基于 CT 的衰减图像配准不良或不可用时，活性和衰减的联合重建提供了一种有用的方法来估计示踪剂分布。通过对发射测量中的散射贡献进行准确估计，TOF PET 数据的联合重建在临床可接受的精度范围内。
