Adiabatic excitation for (31) P MR spectroscopy in the human heart at 7 T: A feasibility study.

Journal article

PURPOSE: Phosphorus magnetic resonance spectroscopy ((31) P-MRS) provides a unique tool for assessing cardiac energy metabolism, often quantified using the phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio. Surface coils are typically used for excitation for (31) P-MRS, but they create an inhomogeneous excitation field across the myocardium, producing undesirable, spatially varying partial saturation. Therefore, we implemented adiabatic excitation in a 3D chemical shift imaging (CSI) sequence for cardiac (31) P-MRS at 7 Tesla (T).
METHODS: We optimized an adiabatic half passage pulse with bandwidth sufficient to excite PCr and γ-ATP together. In addition, the CSI sequence was modified to allow interleaved excitation of PCr and γ-ATP, then 2,3-DPG, to enable PCr/ATP determination with blood correction. Nine volunteers were scanned at 2 transmit voltages to confirm that measured PCr/ATP was independent of B1+ (i.e. over the adiabatic threshold). Six septal voxels were evaluated for each volunteer.
RESULTS: Phantom experiments showed that adiabatic excitation can be reached at the depth of the heart using our pulse. The mean evaluated cardiac PCr/ATP ratio from all 9 volunteers corrected for blood signal was 2.14 ± 0.16. Comparing the two acquisitions with different voltages resulted in a minimal mean difference of -0.005.
CONCLUSION: Adiabatic excitation is possible in the human heart at 7 T, and gives consistent PCr/ATP ratios.

Authors: Valkovič, L; Clarke, W; Purvis, L; Schaller, B; Robson, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Wiley
• Journal: Magnetic Resonance in Medicine
• Publication date: 2016-12-21
• Acceptance date: 2016-11-18
• DOI: 10.1002/mrm.26576
• EISSN: 1522-2594
• ISSN: 0740-3194
• Language: English
• Keywords: 7T; high energy phosphate; 7 Tesla; 31P-MRS; ultra-high field; adiabatic; 31P; heart