Synopsis

Keywords: Musculoskeletal: Muscular

The present educational lecture will provide an overview of the technical aspects of the most important quantitative skeletal muscle imaging techniques and will discuss recent applications and current trends. Special focus will be given to techniques to measure the proton density fat fraction and relaxation parameters of skeletal muscle and to the application of the techniques in the context of neuromuscular diseases and orthopedic imaging.

Objective

The present educational lecture aims to introduce the importance of quantitative imaging measures in skeletal muscle imaging, to provide an overview of the most frequently used techniques to measure skeletal muscle fat infiltration, inflammation and muscle architecture and to discuss the general application of the methods in neuromuscular disorders, orthopedics, metabolic diseases and aging.

Premise of quantitative imaging in skeletal muscle

Alterations of skeletal muscles have been traditionally characterized by qualitative assessment of muscle atrophy and qualitative grading of fatty infiltration and edematous changes. The need to follow small changes in skeletal muscle composition and function longitudinally under the progression of different diseases has increased the recent interest in reliably measuring quantitative muscle measures. In parallel, quantitative muscle imaging enables the monitoring of different therapies.

Quantitative skeletal MRI measures

Numerous techniques have been developed for skeletal muscle quantitative imaging. The most frequently used ones in the current research setting including techniques to measure the proton density fat fraction, relaxation properties and diffusion properties.Chemical shift encoding techniques constitute the state-of-the-art methods for imaging skeletal muscle fat fraction aiming to extract the proton density fat fraction as a standardized imaging marker of muscle fat infiltration. The most important confounding effects in the measurement of the skeletal muscle proton density fat fraction will be introduced.Relaxation mapping techniques and especially T2 mapping have been employed to assess edematous muscle changes. The need to measure the muscle water T2 will be specifically discussed. Alternative relaxation mapping techniques will be finally introduced, including T1 mapping techniques and multi-parametric techniques.Diffusion techniques have been also employed to measure muscle fiber orientation and microstructure. Skeletal muscle fiber tracking and extraction of diffusion tensor imaging parameters will be only very briefly discussed.

Lessons learned from application of quantitative muscle imaging

Quantitative muscle imaging has been compared to qualitative grading schemes used to characterize skeletal muscle fat infiltration and edema. The most prominent application of quantitative skeletal muscle imaging relates to the measurement of the muscle fat fraction primarily in the extremities as a metric of therapy outcome in patients with neuromuscular diseases. Additional examples include the application of quantitative imaging techniques in orthopedic research and especially in patients with rotator cuff tendon injuries, knee osteoarthritis and back pain. Lessons learned from the application of the technique in different scenarios will be discussed.

Perspectives

Perspectives and challenges regarding the broader adoption of the quantitative imaging methods in skeletal muscle research will be discussed. Specifically, the segmentation of the individual skeletal muscles on quantitative maps in order to report any quantitative muscle MRI metric remains a significant challenge in the analysis of such data and a significant hurdle in the broader expansion of the application of the techniques.

Acknowledgements

No acknowledgement found.

References

No reference found.