Abstract
BackgroundSimultaneous PET/MR imaging depends on MR-derived attenuation maps (mu-maps) for accurate attenuation correction of PET data. Currently, these maps are derived from gradient-echo-based MR sequences, which are sensitive to susceptibility changes. Iron oxide magnetic nanoparticles have been used in the measurement of blood volume, tumor microvasculature, tumor-associated macrophages, and characterizing lymph nodes. Our aim in this study was to assess whether the susceptibility effects associated with iron oxide nanoparticles can potentially affect measured 18F-FDG PET standardized uptake values (SUV) through effects on MR-derived attenuation maps.MethodsThe study protocol was approved by the Institutional Animal Care and Use Committee. Using a Siemens Biograph mMR PET/MR scanner, we evaluated the effects of increasing concentrations of ferumoxytol and ferumoxytol aggregates on MR-derived mu-maps using an agarose phantom. In addition, we performed a baboon experiment evaluating the effects of a single i.v. ferumoxytol dose (10 mg/kg) on the liver, spleen, and pancreas 18F-FDG SUV at baseline (ferumoxytol-naïve), within the first hour and at 1, 3, 5, and 11 weeks.ResultsPhantom experiments showed mu-map artifacts starting at ferumoxytol aggregate concentrations of 10 to 20 mg/kg. The in vivo baboon data demonstrated a 53% decrease of observed 18F-FDG SUV compared to baseline within the first hour in the liver, persisting at least 11 weeks.ConclusionsA single ferumoxytol dose can affect measured SUV for at least 3 months, which should be taken into account when administrating ferumoxytol in patients needing sequential PET/MR scans.Advances in knowledge1. Ferumoxytol aggregates, but not ferumoxytol alone, produce significant artifacts in MR-derived attenuation correction maps at approximate clinical dose levels of 10 mg/kg.2. When performing simultaneous whole-body 18F-FDG PET/MR, a single dose of ferumoxytol can result in observed SUV decreases up to 53%, depending on the amount of ferumoxytol aggregates in the studied tissue.Implications for patient careAdministration of a single, clinically relevant, dose of ferumoxytol can potentially result in changes in observed SUV for a prolonged period of time in the setting of simultaneous PET/MR. These potential changes should be considered in particular when administering ferumoxytol to patients with expected future PET/MR studies, as ferumoxytol-induced SUV changes might interfere with therapy assessment.Electronic supplementary materialThe online version of this article (doi:10.1186/s40658-015-0109-0) contains supplementary material, which is available to authorized users.
Highlights
Simultaneous PET/MR imaging depends on MR-derived attenuation maps for accurate attenuation correction of PET data
When performing simultaneous whole-body 18F-FDG PET/MR, a single dose of ferumoxytol can result in observed standardized uptake values (SUV) decreases up to 53%, depending on the amount of ferumoxytol aggregates in the studied tissue
No significant artifacts were observed at ferumoxytol and ferumoxytol aggregate concentrations up to 10 mg/kg and below with minor differences in mu-map values at 10 mg/kg with the phantom with 10 mg/kg aggregates being incorrectly classified as soft tissue
Summary
Simultaneous PET/MR imaging depends on MR-derived attenuation maps (mu-maps) for accurate attenuation correction of PET data. The use of fully integrated PET/MR systems as a clinical imaging modality has increased significantly in recent years [1,2] This novel hybrid technique has many workflow advantages; one of the essential prerequisites for its clinical acceptance is that semi-quantitative PET measures such as standardized uptake values (SUV) are not altered by the endogenous administration of intravenous or oral contrast agents such as gadolinium-based contrast agents (GBCA) or iron oxide-based contrast agents. In order to obtain quantitative PET information, PET/MR imaging relies on MR information that is processed into an MR-derived attenuation map (mu-map), which in turn can be used for attenuation correction (AC) of PET data [3] This implies that, because both PET and MRI examinations can be performed simultaneously, there is the potential of MR-related temporal changes (such as injected GBCA) to affect the accuracy of PET measurements. Preliminary data on oral iron oxide-based MRCA in the same study did show a significant effect on the quality of MR-based attenuation correction maps
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