Comparing the Variability Between Measurements for Sarcopenia Using Magnetic Resonance Imaging and Computed Tomography Imaging

The meta-analysis by van Vugt and colleagues highlights the independent prognostic value of computed tomography (CT) in evaluating sarcopenia as a predictor of pre- and posttransplant mortality in cirrhosis (1.van Vugt JL Levolger S de Bruin RW van Rosmalen J Metselaar HJ IJzermans JN Systematic review and meta-analysis of the impact of computed tomography assessed skeletal muscle mass on outcome in patients awaiting or undergoing liver transplantation.Am J Transplant. 2016; (doi: 10.1111/ajt.13732 [Epub ahead of print].)Abstract Full Text Full Text PDF Scopus (214) Google Scholar). These data provide strong evidence for using cross-sectional imaging–based surveillance as an objective diagnostic and prognostic tool in identifying sarcopenia in patients with cirrhosis. In clinical practice, both CT and magnetic resonance imaging (MRI) are used as cross-sectional imaging modalities for hepatocellular carcinoma surveillance. It is foreseeable that scans performed for routine clinical care may be used concurrently to quantify muscle mass. The studies included in the current meta-analysis were CT based. This focus on CT has several limitations including the significant risk of radiation and contrast exposure (2.Saab SM Bul V Sundaram V Cumulative radiation exposure in liver transplant candidates and patients transplanted with hepatocellular carcinoma.J Liver Disease Transplant. 2014; 3: 1-4Google Scholar) and the potential exclusion of a sizeable number of cirrhosis patients who underwent MRI for hepatocellular carcinoma surveillance. Given the emerging utility of cross-sectional imaging to measure body composition in cirrhosis, it is important for both clinical practice and research to evaluate the comparability of muscle mass assessments of the same patients measured using CT and MRI. If comparable, MRI scans could also be used for analysis without undue radiation exposure for the patient. Briefly, we retrospectively identified 61 living adults in the liver transplant donor program who had CT and MRI scans taken within a mean of 5.3 ± 18.5 days. Using SliceOmatic v4.3 (TomoVision, Magog, Canada), the skeletal muscle cross-sectional area at the third lumbar vertebra (L3) was normalized to stature by dividing the muscle cross-sectional area by the height squared. A blinded observer measured the CT and MRI scans and determined the skeletal muscle mass for each participant using our previously described methods (3.Tandon P Ney M Irwin I Severe muscle depletion in patients on the liver transplant wait list - its prevalence and independent prognostic value.Liver Transpl. 2012; 18 (et al): 1209-1216Crossref PubMed Scopus (388) Google Scholar). Variability between the imaging modalities was determined by the intraclass coefficient correlation (ICC). The ICC is based on the analysis of variance and was calculated using a two-way mixed-effects model with absolute agreement (4.Shrout PE Fleiss JL Intraclass correlations: Uses in assessing rater reliability.Psychol Bull. 1979; 86: 420-428Crossref PubMed Scopus (17076) Google Scholar). We found that the overall ICC for the skeletal muscle indices obtained for CT versus MRI scans was 0.98 (95% confidence interval [CI] 0.96–0.99; p = 0.001). The results were similar for both sexes (p = 0.001). Because an ICC of 1 represents no variance in the assessment of muscle mass, our results indicate that CT and MRI scans are comparable. Furthermore, the Bland Altman plot (Figure 1) demonstrates a difference in mean muscle mass between CT and MRI equivalent to only ≈1.1 g (95% CI 0.03–4.4 g) of muscle (5.Snyder WS Cooke MJ Manssett ES Larhansen LT Howells GP Tipton IH Report of the task group on reference man. Pergamon, Oxford, UK1975Google Scholar). After 3 mo, the same blinded observer repeated the measures and calculations using CT and MRI scans for five randomly selected participants. A second blinded observer repeated the same tasks. The intra- and interobserver ICC values using CT and MRI scans were ≥0.99 or 1.0, indicating very high agreement. In light of the evidence associating sarcopenia with mortality in cirrhosis, it is probable that routine monitoring of skeletal muscle mass will play a role in the clinical care of these patients. Recognizing the limitation of our modest sample size, our brief report indicates that MRI can be used interchangeably with CT to quantify L3 skeletal muscle cross-sectional area. The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation