Department of Particle Physics, University of Santiago de Compostela, Campus Vida S/N, 15782 Santiago de Compostela, Spain.
Eur J Nucl Med Mol Imaging. 2012 Nov;39(11):1756-66. doi: 10.1007/s00259-012-2190-0. Epub 2012 Aug 14.
Clinical PET/MR acquisition protocols entail the use of MR contrast agents (MRCA) that could potentially affect PET quantification following MR-based attenuation correction (AC). We assessed the effect of oral and intravenous (IV) MRCA on PET quantification in PET/MR imaging.
We employed two MRCA: Lumirem (oral) and Gadovist (IV). First, we determined their reference PET attenuation values using a PET transmission scan (ECAT-EXACT HR+, Siemens) and a CT scan (PET/CT Biograph 16 HI-REZ, Siemens). Second, we evaluated the attenuation of PET signals in the presence of MRCA. Phantoms were filled with clinically relevant concentrations of MRCA in a background of water and (18)F-fluoride, and imaged using a PET/CT scanner (Biograph 16 HI-REZ, Siemens) and a PET/MR scanner (Biograph mMR, Siemens). Third, we investigated the effect of clinically relevant volumes of MRCA on MR-based AC using human pilot data: a patient study employing Gadovist (IV) and a volunteer study employing two different oral MRCA (Lumirem and pineapple juice). MR-based attenuation maps were calculated following Dixon-based fat-water segmentation and an external atlas-based and pattern recognition (AT&PR) algorithm.
IV and oral MRCA in clinically relevant concentrations were found to have PET attenuation values similar to those of water. The phantom experiments showed that under clinical conditions IV and oral MRCA did not yield additional attenuation of PET emission signals. Patient scans showed that PET attenuation maps are not biased after the administration of IV MRCA but may be biased, however, after ingestion of iron oxide-based oral MRCA when segmentation-based AC algorithms are used. Alternative AC algorithms, such as AT&PR, or alternative oral contrast agents, such as pineapple juice, can yield unbiased attenuation maps.
In clinical PET/MR scenarios MRCA are not expected to lead to markedly increased attenuation of the PET emission signals. MR-based attenuation maps may be biased by oral iron oxide-based MRCA unless advanced AC algorithms are used.
临床 PET/MR 采集方案需要使用磁共振对比剂（MRCA），这些对比剂可能会影响基于磁共振的衰减校正（AC）后的 PET 定量。我们评估了口服和静脉内（IV）MRCA 对 PET/MR 成像中 PET 定量的影响。
我们使用了两种 MRCA：Lumirem（口服）和 Gadovist（IV）。首先，我们使用 PET 透射扫描（ECAT-EXACT HR+，西门子）和 CT 扫描（PET/CT Biograph 16 HI-REZ，西门子）确定它们的参考 PET 衰减值。其次，我们评估了在存在 MRCA 的情况下 PET 信号的衰减。将在水中和（18）F-氟化物背景下含有临床相关浓度 MRCA 的体模进行成像，并使用 PET/CT 扫描仪（Biograph 16 HI-REZ，西门子）和 PET/MR 扫描仪（Biograph mMR，西门子）进行成像。第三，我们使用来自人类患者的 Gadovist（IV）的研究数据和志愿者研究中的两种不同的口服 MRCA（Lumirem 和菠萝汁），研究了临床相关体积的 MRCA 对基于 MR 的 AC 的影响。基于 Dixon 脂肪-水分割和外部图谱基于和模式识别（AT&PR）算法计算基于 MR 的衰减图。
在临床相关浓度下，IV 和口服 MRCA 的 PET 衰减值与水相似。体模实验表明，在临床条件下，IV 和口服 MRCA 不会对 PET 发射信号产生额外的衰减。患者扫描显示，在静脉内 MRCA 给药后，PET 衰减图没有偏差，但在使用基于分割的 AC 算法时，口服氧化铁基 MRCA 后可能会出现偏差。替代 AC 算法，如 AT&PR，或替代口服对比剂，如菠萝汁，可以产生无偏差的衰减图。
在临床 PET/MR 情况下，MRCA 预计不会导致 PET 发射信号明显增加的衰减。除非使用先进的 AC 算法，否则基于口服氧化铁的 MRCA 可能会使基于 MR 的衰减图产生偏差。
