Effect of MR contrast agents on quantitative accuracy of PET in combined whole-body PET/MR imaging
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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 18F-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.
KeywordsPET/MR Quantification Contrast agents Attenuation correction
We thank Mr. Gröper and Mr. Zeger (University of Tübingen, Germany) for performing the patient and volunteer scans and supporting the PET/MR phantom measurements. We also thank Julia Mannheim (University of Tübingen, Germany) for performing preliminary transmission scan measurements in a Siemens Inveon preclinical system (not discussed in the article). Finally, we thank L. Tellmann (FZ Jülich, Germany) for performing the transmission scan measurements and Brigitte Gückel (University of Tübingen, Germany) for managing the administration of the scientific study.
During the preparation of the manuscript C.L. and T.B. were supported in part by the Imaging Science Institute, a collaborative effort of Siemens Healthcare and the Department of Diagnostic and Interventional Radiology at the University of Tübingen.
Conflicts of interest
T.B. is founder and president of cmi-experts GmbH, but reports no conflicts of interest with the conduct of this study.
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