Methodological and physiological test-retest reliability of 13C-MRS glycogen measurements in liver and in skeletal muscle of patients with type 1 diabetes and matched healthy controls

Glycogen is a major substrate in energy metabolism and particularly important to prevent hypoglycemia in pathologies of glucose homeostasis such as type 1 diabetes mellitus (T1DM). 13C‐MRS is increasingly used to determine glycogen in skeletal muscle and liver non‐invasively; however, the low signal‐to‐noise ratio leads to long acquisition times, particularly when glycogen levels are determined before and after interventions. In order to ease the requirements for the subjects and to avoid systematic effects of the lengthy examination, we evaluated if a standardized preparation period would allow us to shift the baseline (pre‐intervention) experiments to a preceding day. Based on natural abundance 13C‐MRS on a clinical 3 T MR system the present study investigated the test–retest reliability of glycogen measurements in patients with T1DM and matched controls (n = 10 each group) in quadriceps muscle and liver. Prior to the MR examination, participants followed a standardized diet and avoided strenuous exercise for two days. The average coefficient of variation (CV) of myocellular glycogen levels was 9.7% in patients with T1DM compared with 6.6% in controls after a 2 week period, while hepatic glycogen variability was 13.3% in patients with T1DM and 14.6% in controls. For comparison, a single‐session test–retest variability in four healthy volunteers resulted in 9.5% for skeletal muscle and 14.3% for liver. Glycogen levels in muscle and liver were not statistically different between test and retest, except for hepatic glycogen, which decreased in T1DM patients in the retest examination, but without an increase of the group distribution. Since the CVs of glycogen levels determined in a “single session” versus “within weeks” are comparable, we conclude that the major source of uncertainty is the methodological error and that physiological variations can be minimized by a pre‐study standardization. For hepatic glycogen examinations, familiarization sessions (MR and potentially strenuous interventions) are recommended. Copyright © 2016 John Wiley & Sons, Ltd. Determination of glycogen levels by means of 13C‐MR spectroscopy is attractive yet very time consuming, such that interventional studies with a lengthy MRS–intervention–MRS sequence are often not feasible or could introduce systematic bias due to fatigue, hormonal changes or other variations. This study found in healthy volunteers and type 1 diabetes patients that physiological standardization can lead to suf