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

Area of Science:

• Magnetic Resonance Imaging
• Spectroscopy
• Metabolic Imaging

Background:

• ³¹P MRS is crucial for non-invasive energy metabolism assessment.
• Sensitivity limitations often necessitate high magnetic fields, causing spatial inhomogeneity.
• Accurate flip angle determination is vital for accelerated, short repetition time acquisitions.

Purpose of the Study:

• To introduce a novel, rapid 3D ³¹P Magnetic Resonance Spectroscopy (MRS) mapping technique.
• To address challenges of spatial inhomogeneity and flip angle accuracy in accelerated acquisitions.
• To develop a fast Double-Angle Method (fDAM) using a look-up table for 3D ³¹P MRS.

Main Methods:

• Employed 3D weighted stack of spiral gradient echo acquisitions with a frequency-selective pulse.
• Utilized phosphocreatine signal at 7 Tesla for efficient flip angle mapping.
• Optimized protocols via simulations and validated with phantom and skeletal muscle experiments using a birdcage ¹H/³¹P coil.

Main Results:

• Achieved good correlation (r=0.94) between fDAM and classical DAM (cDAM).
• Enabled 3D ³¹P mapping in human calf muscle in ~10 minutes with 20% greater coverage than cDAM.
• Demonstrated the first full brain 3D ³¹P mapping in ~10 minutes using a 1 Tx/ 32 Rx coil.

Conclusions:

• fDAM is an efficient method for 3D ³¹P MRS mapping.
• The technique shows significant promise for rapid ³¹P MR Spectroscopic Imaging (MRSI).
• fDAM enhances non-invasive assessment of energy metabolism.