Fast 3D ³¹P B₁ ⁺ mapping with a weighted stack of spiral trajectory at 7 Tesla

Phosphorus Magnetic Resonance Spectroscopy (³¹P MRS) enables non-invasive assessment of energy metabolism, yet its application is hindered by sensitivity limitations. To overcome this, often high magnetic fields are used, leading to challenges such as spatial $$ inhomogeneity and therefore the need for accurate flip angle determination in accelerated acquisitions with short repetition times $$ . In response to these challenges, we propose a novel short $$ and look-up table-based Double-Angle Method for fast 3D ³¹P $$ mapping (fDAM).

Our method incorporates 3D weighted stack of spiral gradient echo acquisitions and a frequency-selective pulse to enable efficient $$ mapping based on the phosphocreatine signal at 7T. Protocols were optimised using simulations and validated through phantom experiments. The method was validated in phantom experiments and skeletal muscle applications using a birdcage ¹H/³¹P volume coil.

The results of fDAM were compared to the classical DAM (cDAM). A good correlation (r=0.94) was obtained between the two $$ maps. A 3D ³¹P $$ mapping in the human calf muscle was achieved in about 10 min using a birdcage volume coil, with a 20% extended coverage relative to that of the cDAM (24 min). fDAM also enabled the first full brain coverage ³¹P 3D $$ mapping in approx. 10 min using a 1 Tx/ 32 Rx coil.

fDAM is an efficient method for ³¹P 3D $$ mapping, showing promise for future applications in rapid ³¹P MRSI.