Quantifying skeletal muscle volume and shape in humans using MRI: A systematic review of validity and reliability

Abstract

AimsThe aim of this study was to report the metrological qualities of techniques currently used to quantify skeletal muscle volume and 3D shape in healthy and pathological muscles.MethodsA systematic review was conducted (Prospero CRD42018082708). PubMed, Web of Science, Cochrane and Scopus databases were searched using relevant keywords and inclusion/exclusion criteria. The quality of the articles was evaluated using a customized scale.ResultsThirty articles were included, 6 of which included pathological muscles. Most evaluated lower limb muscles. Partially or completely automatic and manual techniques were assessed in 10 and 24 articles, respectively. Manual slice-by-slice segmentation reliability was good-to-excellent (n = 8 articles) and validity against dissection was moderate to good(n = 1). Manual slice-by-slice segmentation was used as a gold-standard method in the other articles. Reduction of the number of manually segmented slices (n = 6) provided good to excellent validity if a sufficient number of appropriate slices was chosen. Segmentation on one slice (n = 11) increased volume errors. The Deformation of a Parametric Specific Object (DPSO) method (n = 5) decreased the number of manually-segmented slices required for any chosen level of error. Other automatic techniques combined with different statistical shape or atlas/images-based methods (n = 4) had good validity. Some particularities were highlighted for specific muscles. Except for manual slice by slice segmentation, reliability has rarely been reported.ConclusionsThe results of this systematic review help the choice of appropriate segmentation techniques, according to the purpose of the measurement. In healthy populations, techniques that greatly simplified the process of manual segmentation yielded greater errors in volume and shape estimations. Reduction of the number of manually segmented slices was possible with appropriately chosen segmented slices or with DPSO. Other automatic techniques showed promise, but data were insufficient for their validation. More data on the metrological quality of techniques used in the cases of muscle pathology are required.

Advancements in magnetic resonance imaging‐based biomarkers for muscular dystrophy

“…Among potentially hundreds of slices collected, only 1–5 slices of a muscle may be selected for segmentation and analysis . Although this may be sufficient for measurement (depending on the research question being asked), there may also be missed opportunities inherent in not analyzing all of the data that is obtained . Some investigators have sought to address this limitation by using semiquantitative scoring systems (which assess whole‐muscle volumes) together with quantitative techniques, similarly to the way that manual muscle testing is used along with quantitative muscle testing.…”

“…One of the more accessible methods involves segmenting individual muscles or defining regions of interest (ROI) within muscles and calculating the cross‐sectional area of a muscle in a single slice. If multiple slices of the muscle are similarly analyzed and added together, an estimate of total muscle volume can be made . In studies in which muscles are infiltrated by fat, investigators may take an additional step of subtracting the areas that correspond to fat signal from the total muscle volume to calculate the contractile muscle cross‐sectional area or volume .…”

“…There are no widely accepted values for healthy muscle size that take these factors into account in a clinically useful way. Second, segmentation of individual muscles must be performed through specialized programs that allow selection of areas of interest . Analyzing potentially hundreds of slices by using manual selection of individual muscles is generally too time consuming to be performed in a clinical setting .…”

“…If multiple slices of the muscle are similarly analyzed and added together, an estimate of total muscle volume can be made. 28 In studies in which muscles are infiltrated by fat, investigators may take an additional step of subtracting the areas that correspond to fat signal from the total muscle volume to calculate the contractile muscle cross-sectional area or volume. 29,30 This type of quantitative muscle imaging is rarely performed outside of a research context for multiple reasons.…”

“…Second, segmentation of individual muscles must be performed through specialized programs that allow selection of areas of interest. 28 Analyzing potentially hundreds of slices by using manual selection of individual muscles is generally too time consuming to be performed in a clinical setting. 32 In a research context, however, contractile muscle areas and volumes may serve as a relatively straightforward biomarker of overall muscle health.…”