1. Rapid, ‐insensitive, dual‐band quasi‐adiabatic saturation transfer with optimal control for complete quantification of myocardial ATP flux
- Author
-
A Tyler, Jack J. Miller, Paul A. Bottomley, Ladislav Valkovič, Christopher T. Rodgers, William Watson, Lisa C. Heather, Damian J. Tyler, Kerstin N. Timm, Matthew Kerr, and Lau Jyc.
- Subjects
Work (thermodynamics) ,Materials science ,biology ,Pulse (signal processing) ,Analytical chemistry ,Signal ,030218 nuclear medicine & medical imaging ,Phosphocreatine ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,chemistry ,Bloch equations ,biology.protein ,Degradation (geology) ,Radiology, Nuclear Medicine and imaging ,Creatine kinase ,Saturation (chemistry) ,030217 neurology & neurosurgery - Abstract
PURPOSE Phosphorus saturation-transfer experiments can quantify metabolic fluxes noninvasively. Typically, the forward flux through the creatine kinase reaction is investigated by observing the decrease in phosphocreatine (PCr) after saturation of γ-ATP. The quantification of total ATP utilization is currently underexplored, as it requires simultaneous saturation of inorganic phosphate ( Pi ) and PCr. This is challenging, as currently available saturation pulses reduce the already-low γ-ATP signal present. METHODS Using a hybrid optimal-control and Shinnar-Le Roux method, a quasi-adiabatic RF pulse was designed for the dual saturation of PCr and Pi to enable determination of total ATP utilization. The pulses were evaluated in Bloch equation simulations, compared with a conventional hard-cosine DANTE saturation sequence, before being applied to perfused rat hearts at 11.7 T. RESULTS The quasi-adiabatic pulse was insensitive to a >2.5-fold variation in B1 , producing equivalent saturation with a 53% reduction in delivered pulse power and a 33-fold reduction in spillover at the minimum effective B1 . This enabled the complete quantification of the synthesis and degradation fluxes for ATP in 30-45 minutes in the perfused rat heart. While the net synthesis flux (4.24 ± 0.8 mM/s, SEM) was not significantly different from degradation flux (6.88 ± 2 mM/s, P = .06) and both measures are consistent with prior work, nonlinear error analysis highlights uncertainties in the Pi -to-ATP measurement that may explain a trend suggesting a possible imbalance. CONCLUSIONS This work demonstrates a novel quasi-adiabatic dual-saturation RF pulse with significantly improved performance that can be used to measure ATP turnover in the heart in vivo.
- Published
- 2021