title: B₁ mapping with selective pulses.
abstract: Knowledge of B₁⁺ distribution is crucial for many applications, such as quantitative MRI. A novel method has been developed to improve the accuracy of the conventionally applied double-angle method for B₁⁺ mapping. It solves the remaining issues raised by the use of selective pulses for slice selection to accelerate the acquisition process. A general approach for reconstructing B₁⁺ maps is presented first. It takes B₁⁺-induced slice profile distortions over off-resonance frequencies into account. It is then shown how the ratio between the prescribed flip angles can be adjusted to reach a compromise between the level of noise propagated onto B₁⁺ maps and the width of the range in which the field can be mapped. Lastly, several solutions are proposed for reducing the B₁⁺-dependent pollution of regions distal to the image slice which participates significantly in the inaccuracy of B₁⁺ mapping. These methods were experimentally tested by comparison with gold standard B₁⁺ maps obtained on a phantom using a non-selective and thus much slower technique. As they are independent and lead to significant improvements, these solutions can be combined to achieve high precision and fast B₁⁺ mapping using spin-echo DAM.
authors.affiliation: UR370 QuaPA, INRA, F-63122 Saint Genès Champanelle, France.
authors.forename: Mustapha
authors.initials: M
authors.lastname: Bouhrara
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Bonny
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods / Q000592:standards; D007089:Image Enhancement / Q000379:methods* / Q000592:standards; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods* / Q000592:standards; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity