title: Specific absorption rate reduction using nonlinear gradient fields.
abstract: The specific absorption rate is used as one of the main safety parameters in magnetic resonance imaging. The performance of imaging sequences is frequently hampered by the limitations imposed on the specific absorption rate that increase in severity at higher field strengths. The most well-known approach to reducing the specific absorption rate is presumably the variable rate selective excitation technique, which modifies the gradient waveforms in time. In this article, an alternative approach is introduced that uses gradient fields with nonlinear variations in space to reduce the specific absorption rate. The effect of such gradient fields on the relationship between the desired excitation profile and the corresponding radiofrequency pulse is shown. The feasibility of the method is demonstrated using three examples of radiofrequency pulse design. Finally, the proposed method is compared with and combined with the variable rate selective excitation technique.
authors.affiliation: National Magnetic Resonance Research Center (UMRAM), Bilkent University, Bilkent, Ankara, Turkey.
authors.forename: Emre
authors.initials: E
authors.lastname: Kopanoglu
authors.forename: Ugur
authors.initials: U
authors.lastname: Yilmaz
authors.forename: Yildiray
authors.initials: Y
authors.lastname: Gokhalk
authors.forename: Ergin
authors.initials: E
authors.lastname: Atalar
mesh_terms: D000465:Algorithms; D004574:Electromagnetic Fields; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D017711:Nonlinear Dynamics; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods*; D011874:Radiometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity