Abstract
PurposeWe present a new Bloch‐Siegert four Angle Saturation Transfer (BOAST) method for measuring the creatine kinase (CK) first‐order effective rate constant kf in human myocardium at 7 tesla (T). BOAST combines a variant of the four‐angle saturation transfer (FAST) method using amplitude‐modulated radiofrequency pulses, phosphorus Bloch‐Siegert B1+‐mapping to determine the per‐voxel flip angles, and nonlinear fitting to Bloch simulations for postprocessing.MethodsOptimal flip angles and repetition time parameters were determined from Monte Carlo simulations. BOAST was validated in the calf muscle of two volunteers at 3T and 7T. The myocardial CK forward rate constant was then measured in 10 volunteers at 7T in 82 min (after 1H localization).ResultsBOAST kfCK values were 0.281 ± 0.002 s−1 in the calf and 0.35 ± 0.05 s−1 in myocardium. These are consistent with literature values from lower fields. Using a literature values for adenosine triphosphate concentration, we computed CK flux values of 4.55 ± 1.52 mmol kg−1 s−1. The sensitive volume for BOAST depends on the B1 inhomogeneity of the transmit coil.ConclusionBOAST enables measurement of the CK rate constant in the human heart at 7T, with spatial localization in three dimensions to 5.6 mL voxels, using a 10‐cm loop coil. Magn Reson Med 78:20–32, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Highlights
IntroductionPhosphocreatine (PCr) and the terminal (g-) phosphate group of adenosine triphosphate (ATP) undergo two-way chemical exchange in the creatine kinase (CK) shuttle in the mitochondria and in the myofibrils
Phosphocreatine (PCr) and the terminal (g-) phosphate group of adenosine triphosphate (ATP) undergo two-way chemical exchange in the creatine kinase (CK) shuttle in the mitochondria and in the myofibrils.Both PCr and ATP give prominent signals during cardiac phosphorus magnetic resonance spectroscopy (31PMRS)
The standard deviation (SD) of the distribution was scaled to be equal to the Cramer–Rao lower bound (CRLB) of cardiac 31P MR spectra, which was acquired with the hardware that we planned to employpfoffiffiffirffiffiffi Bloch-Siegert four Angle Saturation Transfer (BOAST) scans and scaled for the variable TRðCRLB= TRÞ [9]
Summary
Phosphocreatine (PCr) and the terminal (g-) phosphate group of ATP undergo two-way chemical exchange in the CK shuttle in the mitochondria and in the myofibrils. Both PCr and ATP give prominent signals during cardiac phosphorus magnetic resonance spectroscopy (31PMRS). Cardiac 31P-MRS is able to measure the pseudo first-order rate constant of the CK energy shuttle kfCK in the human myocardium [5]. Measurements of kfCK in the human heart have been made using pulse sequences without localization, with localization in one dimension, or with outer volume suppression (OVS) only (see Supporting Table S1)
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