Ladefoged Claes N, Benoit Didier, Law Ian, Holm Søren, Kjær Andreas, Højgaard Liselotte, Hansen Adam E, Andersen Flemming L
Department of Clinical Physiology, Nuclear Medicine and PET, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark.
Phys Med Biol. 2015 Oct 21;60(20):8047-65. doi: 10.1088/0031-9155/60/20/8047. Epub 2015 Sep 30.
The reconstruction of PET brain data in a PET/MR hybrid scanner is challenging in the absence of transmission sources, where MR images are used for MR-based attenuation correction (MR-AC). The main challenge of MR-AC is to separate bone and air, as neither have a signal in traditional MR images, and to assign the correct linear attenuation coefficient to bone. The ultra-short echo time (UTE) MR sequence was proposed as a basis for MR-AC as this sequence shows a small signal in bone. The purpose of this study was to develop a new clinically feasible MR-AC method with patient specific continuous-valued linear attenuation coefficients in bone that provides accurate reconstructed PET image data. A total of 164 [(18)F]FDG PET/MR patients were included in this study, of which 10 were used for training. MR-AC was based on either standard CT (reference), UTE or our method (RESOLUTE). The reconstructed PET images were evaluated in the whole brain, as well as regionally in the brain using a ROI-based analysis. Our method segments air, brain, cerebral spinal fluid, and soft tissue voxels on the unprocessed UTE TE images, and uses a mapping of R(*)2 values to CT Hounsfield Units (HU) to measure the density in bone voxels. The average error of our method in the brain was 0.1% and less than 1.2% in any region of the brain. On average 95% of the brain was within ±10% of PETCT, compared to 72% when using UTE. The proposed method is clinically feasible, reducing both the global and local errors on the reconstructed PET images, as well as limiting the number and extent of the outliers.
在没有透射源的情况下，利用正电子发射断层扫描/磁共振成像（PET/MR）混合扫描仪重建PET脑数据具有挑战性，此时磁共振图像用于基于磁共振的衰减校正（MR-AC）。MR-AC的主要挑战在于分离骨骼和空气，因为在传统磁共振图像中二者均无信号，并且要为骨骼赋予正确的线性衰减系数。超短回波时间（UTE）磁共振序列被提议作为MR-AC的基础，因为该序列在骨骼中显示出微弱信号。本研究的目的是开发一种新的临床可行的MR-AC方法，该方法能为骨骼提供患者特异性的连续值线性衰减系数，从而提供准确的PET图像重建数据。本研究共纳入164例[18F]FDG PET/MR患者，其中10例用于训练。MR-AC基于标准CT（参考）、UTE或我们的方法（RESOLUTE）。使用基于感兴趣区（ROI）的分析方法，在全脑以及脑内局部区域对重建的PET图像进行评估。我们的方法在未处理的UTE TE图像上分割空气、脑、脑脊液和软组织体素，并使用R（*）2值到CT亨氏单位（HU）的映射来测量骨骼体素的密度。我们的方法在脑内的平均误差为0.1%，在脑内任何区域均小于1.2%。平均而言，95%的脑区域在PETCT的±10%范围内，而使用UTE时这一比例为72%。所提出的方法在临床上是可行的，它既能减少重建PET图像的整体和局部误差，又能限制异常值的数量和范围。
