Investigating the effect of trigger delay on cardiac 31P MRS signals

Stefan Wampl,Michael Wolzt,Albrecht Ingo Schmid,Ladislav Valkovič,Tito Körner,Martin Meyerspeer,Siegfried Trattnig

doi:10.1038/s41598-021-87063-8

Abstract

The heart’s geometry and its metabolic activity vary over the cardiac cycle. The effect of these fluctuations on phosphorus (31P) magnetic resonance spectroscopy (MRS) data quality and metabolite ratios was investigated. 12 healthy volunteers were measured using a 7 T MR scanner and a cardiac 31P-1H loop coil. 31P chemical shift imaging data were acquired untriggered and at four different times during the cardiac cycle using acoustic triggering. Signals of adenosine-triphosphate (ATP), phosphocreatine (PCr), inorganic phosphate (Pi) and 2,3-diphosphoglycerate (2,3-DPG) and their fit quality as Cramér-Rao lower bounds (CRLB) were quantified including corrections for contamination by 31P signals from blood, flip angle, saturation and total acquisition time. The myocardial filling factor was estimated from cine short axis views. The corrected signals of PCr and gamma-ATP were higher during end-systole and lower during diastasis than in untriggered acquisitions (P<0.05). Signal intensities of untriggered scans were between those with triggering to end-systole and diastasis. Fit quality of PCr and gamma-ATP peaks was best during end-systole when blood contamination of ATP and Pi signals was lowest. While metabolite ratios and pH remained stable over the cardiac cycle, signal amplitudes correlated strongly with myocardial voxel filling. Triggering of cardiac 31P MRS acquisitions improves signal amplitudes and fit quality if the trigger delay is set to end-systole. We conclude that triggering to end-systole is superior to triggering to diastasis.

Highlights

The heart’s geometry and its metabolic activity vary over the cardiac cycle
Phosphorus (31P) magnetic resonance spectroscopy (MRS) directly measures the concentrations of the high-energy phosphates adenosine-triphosphate (ATP) and phosphocreatine (PCr) in vivo in the human myocardium
The signal amplitudes and Cramér-Rao lower bounds (CRLB) of PCr, γ-ATP and 2,3-DPG are shown in Fig. 2 for the voxels individually and all voxels pooled

Summary

Introduction

The heart’s geometry and its metabolic activity vary over the cardiac cycle. The effect of these fluctuations on phosphorus (31P) magnetic resonance spectroscopy (MRS) data quality and metabolite ratios was investigated. 12 healthy volunteers were measured using a 7 T MR scanner and a cardiac 31P-1H loop coil. 31P chemical shift imaging data were acquired untriggered and at four different times during the cardiac cycle using acoustic triggering. Reproducibility studies of human cardiac 31P MRS at 1.5 T, 3 T and 7 T7–9 have shown the difficulty of establishing reliable, predictive and reproducible PCr/ATP While these studies present various protocol optimizations and emphasize the importance of post-processing steps as saturation and blood correction, surprisingly, a systematic investigation of the effect of cardiac triggering on the quality of 31P MRS acquisitions has not been reported, yet. From cardiac 1H MRS studies on the m atter[21–23] it is known, that highest spectral quality, SNR, signal stability and repeatability are achievable when triggering to a short period around end-systole These recommendations, are not necessarily directly applicable to 31P measurements due to several important differences, e.g. voxel size compared to myocardial thickness, acquisition duration or spectral contamination. For the same reasons correction of respiratory motion, important in 1H MRS, is less relevant in 31P MRS

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Conclusion