Fayad Hadi, Schmidt Holger, Wuerslin Christian, Visvikis Dimitris
INSERM, UMR1101, LaTIM, CHRU Morvan, Université de Bretagne Occidentale, Brest, France; and
Diagnostic and Interventional Radiology, Department of Radiology, University Hospital of Tübingen, Tübingen, Germany.
J Nucl Med. 2015 Jun;56(6):884-9. doi: 10.2967/jnumed.114.153007. Epub 2015 Apr 23.
Simultaneous PET and MR imaging is a promising new technique allowing the fusion of functional (PET) and anatomic/functional (MR) information. In the thoracic-abdominal regions, respiratory motion is a major challenge leading to reduced quantitative and qualitative image accuracy. Correction methodologies include the use of gated frames that lead to low signal-to-noise ratio considering the associated low statistics. More advanced correction approaches, previously developed for PET/CT imaging, consist of either registering all the reconstructed gated frames to the reference frame or incorporating motion parameters into the iterative reconstruction process to produce a single motion-compensated PET image. The goal of this work was to compare these two—previously implemented in PET/CT—correction approaches within the context of PET/MR motion correction for oncology applications using clinical 4-dimensional PET/MR acquisitions. Two different correction approaches were evaluated comparing the incorporation of elastic transformations extracted from 4-dimensional MR imaging datasets during PET list-mode image reconstruction to a postreconstruction image-based approach.
Eleven patient datasets acquired on a PET/MR system were used. T1-weighted 4D MR images were registered to the end-expiration image using a nonrigid B-spline registration algorithm to derive deformation matrices accounting for respiratory motion. The derived matrices were subsequently incorporated within a PET image reconstruction of the original emission list-mode data (reconstruction space [RS] method). The corrected images were compared with those produced by applying the deformation matrices in the image space (IS method) followed by summing the realigned gated frames, as well as with uncorrected motion-averaged images.
Both correction techniques led to significant improvement in accounting for respiratory motion artifacts when compared with uncorrected motion-averaged images. These improvements included signal-to-noise ratio (mean increase of 28.0% and 24.2% for the RS and IS methods, respectively), lesion size (reduction of 60.4% and 47.9%, respectively), lesion contrast (increase of 70.1% and 57.2%, respectively), and lesion position (changes of 60.9% and 46.7%, respectively).
Our results demonstrate significant respiratory motion compensation using both methods, with superior results from a 4D PET RS approach.
同时进行正电子发射断层扫描（PET）和磁共振成像（MR）是一项很有前景的新技术，它能融合功能（PET）和解剖/功能（MR）信息。在胸腹部区域，呼吸运动是一个主要挑战，会导致定量和定性图像准确性降低。校正方法包括使用门控帧，但考虑到相关的低统计量，这会导致信噪比降低。先前为PET/CT成像开发的更先进的校正方法，要么是将所有重建的门控帧配准到参考帧，要么是将运动参数纳入迭代重建过程以生成单个运动补偿PET图像。这项工作的目的是在PET/MR运动校正的背景下，使用临床四维PET/MR采集数据，比较这两种先前在PET/CT中实施的校正方法在肿瘤学应用中的效果。评估了两种不同的校正方法，将PET列表模式图像重建期间从四维MR成像数据集中提取的弹性变换纳入与基于重建后图像的方法进行比较。
使用在PET/MR系统上采集的11例患者数据集。使用非刚性B样条配准算法将T1加权四维MR图像配准到呼气末图像，以得出考虑呼吸运动的变形矩阵。随后将导出的矩阵纳入原始发射列表模式数据的PET图像重建中（重建空间[RS]方法）。将校正后的图像与通过在图像空间中应用变形矩阵（图像空间[IS]方法）然后对重新对齐的门控帧求和产生的图像，以及未校正的运动平均图像进行比较。
与未校正的运动平均图像相比，两种校正技术在处理呼吸运动伪影方面均有显著改善。这些改善包括信噪比（RS和IS方法分别平均提高28.0%和24.2%）、病变大小（分别减少60.4%和47.9%）、病变对比度（分别增加70.1%和57.2%）以及病变位置（分别变化60.9%和46.7%）。
我们的结果表明，两种方法都能显著补偿呼吸运动，四维PET RS方法的效果更佳。
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