Fast 3D ³¹P B₁ ⁺ Mapping Using Concentric Ring Trajectory MRSI at 7 T

<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup>P protocols, even at 7 T, are long, severely limiting the time available to collect flip angle maps needed for metabolite quantification across the heart. Here we aimed to evaluate the feasibility of accelerating <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup>P ${\text{B}}_1^ + $ mapping in the myocardium at 7 T. Using the BlochSiegert B<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> mapping technique, flip angle maps were estimated using Cartesian 2D-MRSI (FA<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CSI</inf>) and concentric ring trajectory-based 3D-MRSI (FA<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CRT</inf>) and compared in the thigh of 4 participants. FA<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CRT</inf> was also estimated in the myocardium of 3 participants. We have found a non-identity linear relationship between FA<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CSI</inf> and FA<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CRT</inf>, raising the need for a correction. This correction yielded homogeneous flip angle values in the myocardium. Our 3D ${\text{B}}_1^ + $ mapping approach, using half the acquisition time of a 2D Cartesian CSI-MRSI can significantly shorten the length of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">31</sup>P protocols at 7 T while allowing absolute quantification of myocardial energetics.