title: On the potential for RF heating in MRI to affect metabolic rates and18FDG signal in PET/MR: simulations of long-duration, maximum normal mode heating.
abstract: OBJECTIVE
  To examine the possibility that MR-induced RF power deposition (SAR) and the resulting effects on temperature-dependent metabolic rates or perfusion rates might affect observed 18FDG signal in PET/MR.
  
  
  METHODS
  Using numerical simulations of the SAR, consequent temperature increase, effect on rates of metabolism or perfusion, and [18FDG] throughout the body, we simulated the potential effect of maximum-allowable whole-body SAR for the entire duration of an hour-long PET/MR scan on observed PET signal for two different 18FDG injection times: one hour before onset of imaging and concurrent with the beginning of imaging. This was all repeated three times with the head, the heart, and the abdomen (kidneys) at the center of the RF coil.
  
  
  RESULTS
  Qualitatively, little effect of MR-induced heating is observed on simulated PET images. Maximum relative increases in PET signal (26% and 31% increase, respectively, for the uptake models based on metabolism and the perfusion) occur in regions of low baseline metabolic rate (also associated with low perfusion and, thus, greater potential temperature increase due to high local SAR), such that PET signal in these areas remains comparatively low. Maximum relative increases in regions of high metabolic rate (and also high perfusion: heart, thyroid, brain, etc.) are affected mostly by the relatively small increase in core body temperature and thus are not affected greatly (10% maximum increase).
  
  
  CONCLUSIONS
  Even for worst-case heating, little effect of MR-induced heating is expected on 18FDG PET images during PET/MR for many clinically relevant applications. For quantitative, dynamic MR/PET studies requiring high SAR for extended periods, it is hoped that methods like those introduced here can help account for such potential effects in design of a given study, including selection of reference locations that should not experience notable increase in temperature.
authors.affiliation: Department of Radiology, New York University, New York, NY, 10016, USA.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Carluccio
authors.affiliation: Department of Radiology, New York University, New York, NY, 10016, USA.
authors.forename: Yu-Shin
authors.initials: YS
authors.lastname: Ding
authors.affiliation: Department of Radiology, New York University, New York, NY, 10016, USA.
authors.forename: Jean
authors.initials: J
authors.lastname: Logan
authors.affiliation: Department of Radiology, New York University, New York, NY, 10016, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Collins
mesh_terms: D065638:Absorption, Radiation; D016477:Artifacts; D001921:Brain / Q000378:metabolism / Q000528:radiation effects; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation*; D008954:Models, Biological; D064847:Multimodal Imaging; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D011846:Radio Waves; D013997:Time Factors
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: MRPET; SAR; metabolism; perfusion; simulations; temperature