Lipid-targeted echo-planar spectroscopic imaging technique for in vivo lipid composition measurement

Accurate in vivo assessment of lipid composition with high resolution and full abdominal coverage is essential for understanding lipid metabolism. This study aimed to develop and evaluate a novel lipid-targeted imaging technique, chemical shift-selective adiabatic refocusing spin-echo echo-planar spectroscopic imaging (EPSI) (Csar-EPSI), for rapid, precise, and reliable lipid composition measurements.

Csar-EPSI was designed with adiabatic pulses to selectively refocus lipid signals, suppress water, minimize chemical-shift displacement errors, and enable flexible voxel selection. Phantom and in vivo experiments were performed on a 7T Bruker MR system, comparing Csar-EPSI with conventional spin-echo EPSI (Con-EPSI) and point-resolved spectroscopy. Accuracy in lipid composition measurement was validated in phantoms, whereas test-retest reliability and sensitivity were assessed in the liver and subcutaneous white adipose tissue (WAT) of obese and healthy control mice.

Csar-EPSI demonstrated higher time efficiency, improved water suppression, and reduced chemical-shift displacement errors compared with traditional methods. It exhibited higher sensitivity for detecting low-concentration lipid biomarkers, particularly polyunsaturation indices (PUI and PUI_UFA), with lower test-retest variability and higher reliability. Csar-EPSI effectively differentiated lipid profiles between obese and healthy control mice, revealing significant reductions in polyunsaturated lipids in the liver and WAT of obese mice. Additionally, significantly higher polyunsaturated lipid markers in the liver compared with WAT in both groups were identified.

Csar-EPSI enables rapid, precise, and reliable in vivo lipid composition assessment with enhanced sensitivity over conventional methods. This novel technique facilitates detailed studies of unsaturated lipid metabolism in the liver and other abdominal organs, providing valuable insights into disease pathology and metabolic pathways.