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Purpose: Phosphorus saturation-transfer experiments can quantify metabolicfluxes non-invasively. Typically, the forward flux through the creatine-kinasereaction is investigated by observing the decrease in phosphocreatine (PCr)after saturation of $\gamma$-ATP. The quantification of total ATP utilisationis currently under-explored, as it requires simultaneous saturation ofinorganic phosphate (Pi) and PCr. This is challenging, as currently availablesaturation pulses reduce the already-low $\gamma$-ATP signal present.  Methods: Using a hybrid optimal-control and Shinnar-Le-Roux method, aquasi-adiabatic RF pulse was designed for the dual-saturation of PCr and Pi toenable determination of total ATP utilisation. The pulses were evaluated inBloch equation simulations, compared with a conventional hard-cosine DANTEsaturation sequence, before application to perfused rat hearts at 11.7 Tesla.  Results: The quasi-adiabatic pulse was insensitive to a $>2.5$-fold variationin $B_1$, producing equivalent saturation with a 53% reduction in deliveredpulse power and a 33-fold reduction in spillover at the minimum effective$B_1$. This enabled the complete quantification of the synthesis anddegradation fluxes for ATP in 30-45 minutes in the perfused rat heart. Whilethe net synthesis flux ($4.24\pm0.8$ mM/s, SEM) was not significantly differentfrom degradation flux ($6.88\pm2$ mM/s, $p=0.06$) and both measures areconsistent with prior work, nonlinear error analysis highlights uncertaintiesin the Pi-to-ATP measurement that may explain a trend suggesting a possibleimbalance.  Conclusion: This work demonstrates a novel quasi-adiabatic dual-saturation RFpulse with significantly improved performance that can be used to measure ATPturnover in the heart in vivo.

Rapid, $B_1$-insensitive, dual-band quasi-adiabatic saturation transfer with optimal control for complete quantification of myocardial ATP flux