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 < 0.05. Likewise, ex vivo myocardial triglyceride concentrations correlated with the in vivo myocardial triglyceride content: n = 20, r = 0.50; P < 0.05. Data Conclusion: We validated the use of localized ¹H-MRS of the human heart at 3 T for quantitative assessments of in vivo myocardial tissue metabolite content by estimating the measurement precision and accuracy. Level of Evidence: 2. Technical Efficacy Stage: 2.