Fast 3D ³¹P B 1 + mapping with a weighted stack of spiral trajectory at 7 T

Area of Science:

• Biophysics
• Biomedical Engineering
• Neuroimaging

Background:

• Phosphorus-31 Magnetic Resonance Spectroscopy (³¹P MRS) is crucial for noninvasive assessment of cellular energy metabolism.
• Sensitivity limitations of ³¹P MRS often necessitate high magnetic fields, which introduce challenges like spatial inhomogeneity.
• Accurate flip-angle determination is essential for accelerated ³¹P MRS acquisitions with short repetition times (TRs).

Purpose of the Study:

• To introduce a novel, fast 3D ³¹P Magnetic Resonance Spectroscopy (MRS) mapping method using a short TR and look-up table-based double-angle approach (fDAM).
• To address sensitivity limitations and spatial inhomogeneity challenges in high-field ³¹P MRS.
• To enable rapid and accurate flip-angle determination for accelerated ³¹P MRS acquisitions.

Main Methods:

• Developed fDAM incorporating 3D weighted stack-of-spiral gradient-echo acquisitions and a frequency-selective pulse.
• Utilized the phosphocreatine signal for efficient flip-angle (B1) mapping at 7 Tesla.
• Optimized protocols via simulations and validated with phantom experiments, human brain (1Ch-transmit/32Ch-receive coil), and skeletal muscle (birdcage coil).

Main Results:

• fDAM demonstrated a strong correlation (r=0.95) with the classical double-angle method (DAM).
• Achieved 3D ³¹P B1 mapping in human calf muscle in ~10:50 min, with 20% extended coverage compared to classical DAM (~24 min).
• Enabled the first full-brain 3D ³¹P B1 mapping in ~10:15 min using a 1Ch-transmit/32Ch-receive coil.

Conclusions:

• fDAM is an efficient and fast method for 3D ³¹P B1 mapping.
• The method shows significant promise for accelerating future applications in 3D ³¹P Magnetic Resonance Spectroscopic Imaging (MRSI).
• fDAM overcomes sensitivity and speed limitations, enhancing the utility of ³¹P MRS in clinical and research settings.