Effect of MR contrast agents on quantitative accuracy of PET in combined whole-body PET/MR imaging.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Department of Particle Physics, University of Santiago de Compostela, Campus Vida S/N, 15782 Santiago de Compostela, Spain. crisloisg@gmail.com
Cristina
C
Lois
Ilja
I
Bezrukov
Holger
H
Schmidt
Nina
N
Schwenzer
Matthias K
MK
Werner
Jürgen
J
Kupferschläger
Thomas
T
Beyer
D061605:Administration, Intravenous; D000284:Administration, Oral; D003287:Contrast Media / Q000008:administration & dosage*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000008:administration & dosage; D009942:Organometallic Compounds / Q000008:administration & dosage; D049268:Positron-Emission Tomography / Q000379:methods*; D012833:Siloxanes / Q000008:administration & dosage; D051598:Whole Body Imaging
D003287:Contrast Media; D058185:Magnetite Nanoparticles; D009942:Organometallic Compounds; D012833:Siloxanes; D019788:Fluorodeoxyglucose F18; C090600:gadobutrol; C088769:ferumoxsil