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

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 $$\gamma$$ γ -ATP were higher during end-systole and lower during diastasis than in untriggered acquisitions ($$P<0.05$$ P < 0.05 ). Signal intensities of untriggered scans were between those with triggering to end-systole and diastasis. Fit quality of PCr and $$\gamma$$ γ -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.

Three‐dimensional, 2.5‐minute, 7T phosphorus magnetic resonance spectroscopic imaging of the human heart using concentric rings

“…Consistent acquisition within the end systolic phase through gating has shown improved reproducibility and SNR. 32 Implementation on hardware permitting interleaved 1 H navigator images would allow tracking of the myocardial position through all cardiorespiratory phases. 33 Further dedicated study is needed to assess the effect of different motion-correction strategies, given the subtle findings to date.…”

“…Nevertheless, the increased flexibility of the sequence acquisition timings and kt‐space acquisition speed may permit development‐integrated motion‐correction methods into the sequence. Consistent acquisition within the end systolic phase through gating has shown improved reproducibility and SNR 32 . Implementation on hardware permitting interleaved 1 H navigator images would allow tracking of the myocardial position through all cardiorespiratory phases 33 .…”

Increased cardiac Pi/PCr in the diabetic heart observed using phosphorus magnetic resonance spectroscopy at 7T

“…No respiratory triggering was used for 31 P-MRS. Following previous work, cardiac gating was used for Pi/PCr measurements [ 17 ], but not for PCr/ATP measurements to save scan time [ 16 , 19 ].…”

“…7T. Unlike the energy absorption-heavy decoupling applied at 1.5T [ 14 ], long TR acquisition can be used, exploiting the relaxation properties of Pi at 7T [ 15 , 16 ]. Alternatively, black-blood properties of the stimulated echo single-voxel MRS (STEAM) with longer mixing time (TM) can be used at 7T to acquire cardiac spectra free of blood pool contamination [ 17 ].…”

Novel Small-Molecule Troponin Activator Increases Cardiac Contractile Function Without Negative Impact on Energetics

“…Reproduction of our findings in clinical investigation is limited by availability of cutting-edge technology to measure |ΔG ~ATP | in patients. 49 The 31 P NMR signal from 2,3-diphosphoglycerate in red blood cells interferes with the assessment of chemical shift (indicative of intracellular pH) and concentration of Pi in vivo. These values, along with the total creatine concentration that we measure from frozen tissue by high-performance liquid chromatography, are needed for the calculation of |ΔG ~ATP |.…”