A Quantitative Comparison of 31P Magnetic Resonance Spectroscopy RF Coil Sensitivity and SNR between 7T and 10.5T Human MRI Scanners Using a Loop-Dipole 31P-1H Probe

In vivo phosphorus-31 (³¹P) magnetic resonance spectroscopy (MRS) imaging (MRSI) is an important non-invasive imaging tool for studying cerebral energy metabolism, intracellular nicotinamide adenine dinucleotide (NAD) and redox ratio, and mitochondrial function. However, it is challenging to achieve high signal-to-noise ratio (SNR) ³¹P MRS/MRSI results owing to low phosphorus metabolites concentration and low phosphorous gyromagnetic ratio (γ). Many works have demonstrated that ultrahigh field (UHF) could significantly improve the ³¹P-MRS SNR. However, there is a lack of studies of the ³¹P MRSI SNR in the 10.5 Tesla (T) human scanner. In this study, we designed and constructed a novel ³¹P-¹H dual-frequency loop-dipole probe that can operate at both 7T and 10.5T for a quantitative comparison of ³¹P MRSI SNR between the two magnetic fields, taking into account the RF coil B₁ fields (RF coil receive and transmit fields) and relaxation times. We found that the SNR of the ³¹P MRS signal is 1.5 times higher at 10.5T as compared to 7T, and the power dependence of SNR on magnetic field strength (B₀) is 1.9.