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

Purpose: Phosphorus MRS (P MRS) enables noninvasive 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 TRs. In response to these challenges, we propose a novel short TR 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 7 T. Protocols were optimized using simulations and validated through phantom experiments. The method was validated in the human brain using a P 1Ch-trasmit/32Ch-receive coil and skeletal muscle using a birdcage H/P volume coil.

Results: The results of fDAM were compared with the classical DAM. A good correlation (r = 0.95) was obtained between the two maps. A 3D P mapping in the human calf muscle was achieved in about 10:50 min using a birdcage volume coil, with a 20% extended coverage (number of voxels with SNR > 3) relative to that of the classical DAM (24 min). fDAM also enabled the first full-brain coverage P 3D mapping in approximately 10:15 min using a 1Ch-transmit/32Ch-receive coil.

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