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SAR comparison between CASL and pCASL at high magnetic field and evaluation of the benefit of a dedicated labeling coil
Author(s) -
Hirschler Lydiane,
Collomb Nora,
Voiron Jérôme,
Köhler Sascha,
Barbier Emmanuel L.,
Warnking Jan M.
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.27931
Subject(s) - electromagnetic coil , materials science , nuclear magnetic resonance , radiofrequency coil , decoupling (probability) , nuclear medicine , physics , medicine , quantum mechanics , engineering , control engineering
Purpose To investigate the heating induced by (pseudo)‐continuous arterial spin labeling ((p)CASL) sequences in vivo at 9.4T and to evaluate the benefit of a dedicated labeling coil. Methods Temperature was measured continuously in the brain, neck, and rectum of 9 rats with fiber‐optic temperature probes while running pCASL‐EPI and CASL‐EPI sequences, with labeling B 1 amplitudes (B 1ave ) of 3, 5, and 7 μT and using a dedicated labeling RF coil or a volume coil. From the temperature time courses, the corresponding specific absorption rate (SAR) was computed. A trade‐off between SAR and labeling quality was determined based on measured inversion efficiencies. Results ASL experiments with standard parameters (B 1ave = 5 µT, T acq = 4 min, labeling with volume coil) lead to a brain temperature increase due to RF of 0.72 ± 0.46 K for pCASL and 0.25 ± 0.17 K for CASL. Using a dedicated labeling coil reduced the RF‐induced SAR by a factor of 10 in the brain and a factor of 2 in the neck. Besides SAR due to RF, heat from the coil decoupling circuits produced significant temperature increases. When labeling with a dedicated coil, this mechanism was the dominant source of brain heating. At equivalent RF‐SAR, CASL provided slightly superior label efficiency to pCASL and is therefore the preferred sequence when an ASL coil is available. Conclusion B 1ave = 4–5 µT provided a good compromise between label efficiency and SAR, both for pCASL and CASL. The sensitivity of animals to heating should be taken into account when optimizing preclinical ASL protocols and may require reducing scan duration or lowering B 1ave .