Room: Exhibit Hall | Forum 8
Purpose: Sensitivity of In vivo phosphorus metabolite measurements can be improved using the 1H-31P Nuclear Overhauser Effect (NOE). Aims: (i) compare NOE enhancement ratio of phosphorus metabolite in vastus lateralis and in external reference, (ii) investigate how decoupling flip angle affects NOE enhancement in vivo and (iii) confirm quantification of vastus lateralis (VL) metabolite concentrations in-vivo using our previously published quantitative 31P-MRS method.
Methods: A vial of methylene-diphosphonic acid (MDP), fixed to the surface coil, was used to calibrate coil sensitivity. Five subjects (4M/1F) were scanned using different NOE and WALTZ-4 sequences while varying decoupling flip angles (FA). Highest enhancements achieved in vivo were calibrated with a 15 cm diameter phantom (35 mM H3PO4, n=5). A slice-selective 31P-MRS sequence (TR/TE=9000/2.3 ms, NSA=12, thickness=25mm, BW=3000 Hz, FA=90o) was used. Consistency was evaluated using the coefficient of variation (CoV).
Results: The percent increase of NOE in leg phantoms was consistent: 22.19Â±2% (COV =15%) for FA=140Â° rectangle NOE pulse, 22.22Â±1.3% (COV =10%) for FA=180Â° rectangle NOE pulse, and 14.41Â±2.2% for FA=180Â° decoupling WALTZ pulse (COV =26%). In-vivo metabolite concentrations showed consistent increases in NOE enhancement under varying decoupling flip angles, especially phosphocreatine [PCr]: NOE rectangle: 5.83Â±2.1% at 60Â°, 5.96Â±0.71% at 90Â°, 4.27Â±2.1% at 140Â°, 10.18Â±3.0% at 180Â°; WALTZ: 7.01Â±2.3% at 60Â°, 8.67Â±2.3% at 90Â°, 8.95Â±2.8% at 140Â°, 9.21Â±2.8% at 180Â°, 9.60Â±1.5% at 270Â°, 12.14Â±3.75% at 360Â°. With calibration, rectangle pulse achieve enhancement of 8.70Â±1.5% (COV =25.3%) and WALTZ of 12.41Â±3.8 (COV =44.3%). Little NOE enhancement for MDP was found both in the subject (3.1Â±1.6%, COV =5.26%) and phantom (0.5Â±1.0%, COV=3.83%) studies, indicating its reliability for coil sensitivity correction.
Conclusion: NOE enhancement improves the sensitivity of quantitative 31P-MRS of different phosphorus metabolites, validating the use of NOE for absolute quantitative measurement in in vivo MRS studies.