Fast 3D P B mapping with a weighted stack of spiral trajectory at 7 Tesla.

Purpose: Phosphorus Magnetic Resonance Spectroscopy (P 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 P mapping (fDAM).

Methods: 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 H/P volume coil.

Results: 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 P 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 P 3D mapping in approx. 10 min using a 1 Tx/ 32 Rx coil.

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