This issue of Seminars in Musculoskeletal Radiology discusses the role of biomarkers in musculoskeletal (MSK) imaging. Biomarkers are defined as quantifiable indicators of biological processes or responses. Imaging biomarkers provide valuable anatomical, pathologic, and functional information using imaging modalities such as radiographs, ultrasonography (US), magnetic resonance imaging (MRI), and computed tomography (CT). Imaging biomarkers can be used to aid disease diagnosis, provide valuable information about disease progression and patient survival, and identify patients who are likely to respond favorably to specific therapies. This issue offers eight comprehensive review articles that describe the role of imaging biomarkers in a wide variety of MSK applications, including the evaluation of cartilage, tumors, bone, body composition, and peripheral nerves.

As an introduction to the issue, Ronnie Sebro surveys the role of biomarkers in radiology. Through an exploration of various biomarker types, such as imaging biomarkers, molecular biomarkers, and genetic markers, the review outlines their roles in disease detection, prognosis, prediction, and therapeutic monitoring. The article also discusses the significance of robust study designs, blinding, power and sample size calculations, performance metrics, and statistical methodologies in imaging biomarker research.

Frank Roemer and associates discuss the role of imaging biomarkers in osteoarthritis research. The current role of radiography, as well as advances in MRI-based quantitative three-dimensional morphological cartilage assessment and semiquantitative whole-organ joint assessment of osteoarthritis, are reviewed. Although MRI has evolved as the leading imaging method in osteoarthritis research, developments in CT imaging are also described. Finally, experiences from the foundations of the National Institutes of Health Biomarker Working Group consortium biomarker qualification study are described.

Maximilian Löffler et al survey the technical advances and current applications in the field of MRI-based biomarkers of cartilage composition. Compositional MRI can detect disease-related and treatment-related changes in articular cartilage through assessment of tissue composition and ultrastructure. Various techniques of compositional MRI are reviewed including T2 mapping, sodium imaging, T1rho mapping, ultrashort echo time imaging with T2*, gadolinium-enhanced T1 mapping, chemical exchange-dependent saturation transfer imaging, and diffusion-weighted imaging. The article also discusses standardization efforts by the Quantitative Imaging Biomarkers Alliance that aims to make compositional MRI of cartilage clinically feasible and comparable.

Ali Ghasemi and associates discuss MRI biomarkers for evaluating bone and soft tissue tumors. The article describes conventional imaging methods such as T1-weighted, fluid-sensitive, postcontrast, and chemical shift gradient-echo sequences that are useful for delineating the anatomical extent of tumors, defining their character and assessing the region of prior treatment. Various functional MRI methods are also reviewed, such as diffusion-weighted imaging that assesses tumor cellularity, dynamic contrast-enhanced MRI that can offer valuable information about the temporal pattern of tumor enhancement, and MRI spectroscopy that evaluates tumor chemical composition.

Daniel Brandenberger and Lawrence White examine the role of radiomics for evaluating MSK tumors. In radiomics, images are converted to higher dimensional image features that are subsequently extracted, or “mined,” for analysis and lesional characterization. Radiomics offers the potential for discovering novel imaging diagnostic and predictive biomarkers using standard-of-care medical imaging. The article details the core concepts of radiomics and the application of radiomics to date in MSK sarcoma research. Specific challenges related to radiomic studies, viewpoints on clinical adoption, and future perspectives in the field are also reviewed.

Saeed Jerban et al discuss the role of MRI biomarkers for characterizing the organic, water, fat, and mineral components of bone. The article describes the use of ultrashort echo time sequences for anatomical assessment of bone and for evaluating the total water, bone water, and pore water of bone. Additional ultrashort echo time applications of bone are also reviewed including tricomponent T2* analysis that can distinguish between bound water and pore water signals and fractions, magnetic transfer methods that can assess fat fraction and quantify the organic matrix, and quantitative susceptibility mapping techniques that provide a surrogate measure of bone mineral density.

Connie Chang and associates present the relevant clinical and imaging terminology needed to understand the clinical and research applications of body composition. Imaging biomarkers of bone, muscle, and fat tissues obtained with dual-energy X-ray absorptiometry, CT, MRI, and US are described. The article examines the rationale for imaging of body composition, presents the strengths and weaknesses of currently used methods, and reviews the most relevant clinical applications. Secondary analysis of tissue health “opportunistically” on imaging studies obtained for routine clinical care is also discussed.

Alireza Eajazi and colleagues discuss the role of MRI and US for evaluating peripheral nerves. The article describes conventional MRI and US methods that can quantify measures of nerve and fascicular size and signal and detect edema-like signal changes in nerves and fatty and fibrous changes in nerves and muscle. Functional biomarkers are also reviewed, such as apparent diffusion coefficient from diffusion-weighted imaging and fractional anisotropy and tractography from diffusion tensor imaging, that are useful for assessing nerve microstructure and integrity and dynamic contrast-enhanced MRI that estimates perfusion parameters to detect edema, inflammation, demyelination, and microvascular alterations in nerves.

I would like to thank all the authors of this issue for providing excellent comprehensive review articles that describe the role of imaging biomarkers in a wide variety of MSK applications. I would also like to express my gratitude to the editors for giving me the opportunity to act as guest editor.

Article published online:
08 February 2024

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