Quantification of Myocardial Creatine and Triglyceride Content in the Human Heart: Precision and Accuracy of in vivo Proton Magnetic Resonance Spectroscopy

Background Proton magnetic resonance spectroscopy (1H‐MRS) of the human heart is deemed to be a quantitative method to investigate myocardial metabolite content, but thorough validations of in vivo measurements against invasive techniques are lacking. Purpose To determine measurement precision and accuracy for quantifications of myocardial total creatine and triglyceride content with localized 1H‐MRS. Study type Test–retest repeatability and measurement validation study. Subjects Sixteen volunteers and 22 patients scheduled for open‐heart aortic valve replacement or septal myectomy. Field Strength/Sequence Prospectively ECG‐triggered respiratory‐gated free‐breathing single‐voxel point‐resolved spectroscopy (PRESS) sequence at 3 T. Assessment Myocardial total creatine and triglyceride content were quantified relative to the total water content by fitting the 1H‐MR spectra. Precision was assessed with measurement repeatability. Accuracy was assessed by validating in vivo 1H‐MRS measurements against biochemical assays in myocardial tissue from the same subjects. Statistical Tests Intrasession and intersession repeatability was assessed using Bland–Altman analyses. Agreement between 1H‐MRS measurements and biochemical assay was tested with regression analyses. Results The intersession repeatability coefficient for myocardial total creatine content was 41.8% with a mean value of 0.083% ± 0.020% of the total water signal, and 36.7% for myocardial triglyceride content with a mean value of 0.35% ± 0.13% of the total water signal. Ex vivo myocardial total creatine concentrations in tissue samples correlated with the in vivo myocardial total creatine content measured with 1H‐MRS: n = 22, r = 0.44; P