Sub-voxel Estimation of Fat Infiltration in Degenerative Muscle Disorders using Multi-T2 Analysis – a Quantitative Disease Biomarker

Background: T2 relaxation is an effective biomarker for muscle pathologies.One of the hallmarks of muscle disorders is infiltration of subcutaneous fat and a loss of muscle volume,causing a mixture of two T2-components in each image voxel.Quantification of T2 values is hampered due to the bias of fast multi-echo-spin-echo (MESE) protocols by stimulated echoes.The echo-modulation-curve (EMC) algorithm overcomes this problem and provides accurate T2’s,stable across scanners,scan-settings. Here, we present an extension of the EMC-algorithm alongside two quantitative biomarkers of disease-state, estimating fat-water fractions within a single voxel, and the T2 and proton-density values of each component.This is demonstrated on calf muscle of a patient with Dysferlinopathy and compared to conventional Dixon analysis.

Methods: The patient was scanned on a 3T scanner using standard MESE protocol.Bloch simulations were performed using the exact pulse-sequence scheme. Maps of the patient’s calf were segmented to exclude subcutaneous fat, tibia and fibula bones. Biomarker1: voxels whose fat-fraction was >50% were labelled as ‘fat’(diseased muscle),and the rest were labelled as ‘muscle’(healthy muscle).The % fraction of healthy-to-whole muscle was then calculated. Biomarker2: the average fat fraction across all voxels in the healthy muscle area, yielding a “fat infiltration index”.

Results: Quantitative fat-water fraction maps of healthy and diseased muscle segments based on the EMC-algorithm and conventional-Dixon showed good agreement;similar fat-infiltration indices were produced (15.7±10.8% and 11.4±11% respectively). Moreover,the EMC-algorithm produces the tissue’s global and component-only T2’s – information not given by Dixon.

Conclusion: Using an extension of the EMC-algorithm, we can quantify water-fat fraction maps,and water and fat T2’s, indicative of underlying inflammatory processes, leading to improved diagnosis and treatment in muscle pathologies.