Quantifying the effect of dobutamine stress on myocardial Pi and pH in healthy volunteers: A 31P MRS study at 7T

• Published in: Magnetic resonance in medicine Vol. 85; no. 3; pp. 1147 - 1159
• Main Authors: Apps, Andrew, Valkovič, Ladislav, Peterzan, Mark, Lau, Justin Y. C., Hundertmark, Moritz, Clarke, William, Tunnicliffe, Elizabeth M., Ellis, Jane, Tyler, Damian J., Neubauer, Stefan, Rider, Oliver J., Rodgers, Christopher T., Schmid, Albrecht Ingo
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2021; John Wiley and Sons Inc
• Subjects: 31P MRS; Adenosine triphosphate; cardiac energetics; Cardiomyopathy; Catecholamine; Catecholamines; Chemical equilibrium; Feasibility studies; Full Papers—Spectroscopic Methodology; Heart; myocardial pH; pH effects; Phosphocreatine; Phosphorus; Spectroscopy; STEAM
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.28494

Purpose Phosphorus spectroscopy (31P‐MRS) is a proven method to probe cardiac energetics. Studies typically report the phosphocreatine (PCr) to adenosine triphosphate (ATP) ratio. We focus on another 31P signal: inorganic phosphate (Pi), whose chemical shift allows computation of myocardial pH, with Pi/PCr providing additional insight into cardiac energetics. Pi is often obscured by signals from blood 2,3‐diphosphoglycerate (2,3‐DPG). We introduce a method to quantify Pi in 14 min without hindrance from 2,3‐DPG. Methods Using a 31P stimulated echo acquisition mode (STEAM) sequence at 7 Tesla that inherently suppresses signal from 2,3‐DPG, the Pi peak was cleanly resolved. Resting state UTE‐chemical shift imaging (PCr/ATP) and STEAM 31P‐MRS (Pi/PCr, pH) were undertaken in 23 healthy controls; pH and Pi/PCr were subsequently recorded during dobutamine infusion. Results We achieved a clean Pi signal both at rest and stress with good 2,3‐DPG suppression. Repeatability coefficient (8 subjects) for Pi/PCr was 0.036 and 0.12 for pH. We report myocardial Pi/PCr and pH at rest and during catecholamine stress in healthy controls. Pi/PCr was maintained during stress (0.098 ± 0.031 [rest] vs. 0.098 ± 0.031 [stress] P = .95); similarly, pH did not change (7.09 ± 0.07 [rest] vs. 7.08 ± 0.11 [stress] P = .81). Feasibility for patient studies was subsequently successfully demonstrated in a patient with cardiomyopathy. Conclusion We introduced a method that can resolve Pi using 7 Tesla STEAM 31P‐MRS. We demonstrate the stability of Pi/PCr and myocardial pH in volunteers at rest and during catecholamine stress. This protocol is feasible in patients and potentially of use for studying pathological myocardial energetics.