title: The magnetic susceptibility effect of gadolinium-based contrast agents on PRFS-based MR thermometry during thermal interventions.
abstract: BACKGROUND
  Proton resonance frequency shift (PRFS) magnetic resonance (MR) thermometry exploits the local magnetic field changes induced by the temperature dependence of the electron screening constant of water protons. Any other local magnetic field changes will therefore translate into incorrect temperature readings and need to be considered accordingly. Here, we investigated the susceptibility changes induced by the inflow and presence of a paramagnetic MR contrast agent and their implications on PRFS thermometry.
  
  
  METHODS
  Phantom measurements were performed to demonstrate the effect of sudden gadopentetate dimeglumine (Gd-DTPA) inflow on the phase shift measured using a PRFS thermometry sequence on a clinical 3 T magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) system. By proton nuclear magnetic resonance spectroscopy, the temperature dependence of the Gd-DTPA susceptibility was measured, as well as the effect of liposomal encapsulation and release on the bulk magnetic susceptibility of Gd-DTPA. In vivo studies were carried out to measure the temperature error induced in a rat hind leg muscle upon intravenous Gd-DTPA injection.
  
  
  RESULTS
  The phantom study showed a significant phase shift inside the phantom of 0.6 ± 0.2 radians (mean ± standard deviation) upon Gd-DTPA injection (1.0 mM, clinically relevant amount). A Gd-DTPA-induced magnetic susceptibility shift of ΔχGd-DTPA = 0.109 ppm/mM was measured in a cylinder parallel to the main magnetic field at 37°C. The temperature dependence of the susceptibility shift showed dΔχGd-DTPA/dT = -0.00038 ± 0.00008 ppm/mM/°C. No additional susceptibility effect was measured upon Gd release from paramagnetic liposomes. In vivo, intravenous Gd-DTPA injection resulted in a perceived temperature change of 2.0°C ± 0.1°C at the center of the hind leg muscle.
  
  
  CONCLUSIONS
  The use of a paramagnetic MR contrast agent prior to MR-HIFU treatment may influence the accuracy of the PRFS MR thermometry. Depending on the treatment workflow, Gd-induced temperature errors ranging between -4°C and +3°C can be expected. Longer waiting time between contrast agent injection and treatment, as well as shortening the ablation duration by increasing the sonication power, will minimize the Gd influence. Compensation for the phase changes induced by the changing Gd presence is difficult as the magnetic field changes are arising nonlocally in the surroundings of the susceptibility change.
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, High Tech Campus 11.p 261, Eindhoven, 5656 AE, the Netherlands.
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Hijnen
authors.affiliation: Department of Minimally Invasive Healthcare, Philips Research Eindhoven, Eindhoven, 5656 AE, the Netherlands.
authors.forename: Aaldert
authors.initials: A
authors.lastname: Elevelt
authors.affiliation: Department of Minimally Invasive Healthcare, Philips Research Eindhoven, Eindhoven, 5656 AE, the Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Pikkemaat
authors.affiliation: Image Sciences Institute, Imaging Division, University Medical Center Utrecht, Utrecht, 3584 CX, the Netherlands.
authors.forename: Clemens
authors.initials: C
authors.lastname: Bos
authors.affiliation: Image Sciences Institute, Imaging Division, University Medical Center Utrecht, Utrecht, 3584 CX, the Netherlands.
authors.forename: Lambertus W
authors.initials: LW
authors.lastname: Bartels
authors.affiliation: Biomedical NMR, Department of Biomedical Engineering, Eindhoven University of Technology, High Tech Campus 11.p 261, Eindhoven, 5656 AE, the Netherlands.|Department of Minimally Invasive Healthcare, Philips Research Eindhoven, Eindhoven, 5656 AE, the Netherlands.
authors.forename: Holger
authors.initials: H
authors.lastname: Grüll
keywords: Gadolinium; Image-guided drug delivery; MR thermometry; MR-HIFU; Susceptibility