Interleaved Whole Brain 23Na-MRI and 31P-MRSI Acquisitions at 7 Tesla

Abstract

Non-¹H nuclei magnetic resonance spectroscopy (MRS) offers insights into metabolism, which may aid for example early stages of disease diagnosis, tissue characterization or therapy response evaluation. Sodium MRI can provide valuable information about tissue health and cellular function. When combined with ³¹P MR spectroscopic imaging (MRSI), complementary metabolic information on energy metabolism and cell proliferation can be obtained. However, sensitivity challenges stemming from low natural abundances and low gyromagnetic ratios of different nuclei have hindered progress. Besides, due to hardware constraints, different nuclei are often studied separately, and the need for dedicated hardware for x-nuclei imaging hampers clinical efficiency and patient-friendly assessments. This work introduces an interleaved acquisition scheme for 3D ³¹P-MRSI and 3D radial ²³Na-MR imaging (²³Na-MRI) at 7 Tesla (7T) and demonstrates the feasibility of interleaving these two nuclei acquisitions. The interleaved protocol effectively merged ³¹P-MRSI with ²³Na-MRI, while remaining within specific absorption rate (SAR) limits. Results revealed comparable signal-to-noise ratios (SNRs) and spectral quality between interleaved and non-interleaved scans, highlighting the approach's efficiency without compromising data quality.

Keywords: 23Na‐MRI; 31P‐MRSI; SAR limits; interleaved x‐nuclei scan; scan efficiency; ultra‐high field.