For many years, imaging of the musculoskeletal (MSK) system has focused on subjective and qualitative analysis. However, quantitative assessment of imaging data may provide precise and reproducible image-derived metrics, and through their use there is a promise of increased value of imaging. Specifically, these metrics, or biomarkers, may be used for improved diagnosis, determination of patient prognosis, and monitoring of treatment response. This issue of Seminars in Musculoskeletal Radiology is dedicated to quantitative MSK imaging.

Giraudo et al provide a comprehensive overview of the quantitative methods that can be applied to assess inflammatory rheumatologic diseases, considering not only different radiologic techniques but also hybrid imaging. In addition, they describe emerging technologies such as artificial intelligence and radiomics.

Burge and Jawetz discuss advanced magnetic resonance imaging (MRI) techniques in osteoarthritis that can comprehensively evaluate joint health, providing additional information regarding both cartilage status and the state of surrounding articular tissues. Gitto and colleagues discuss the currently available state-of-the-art quantitative ultrasound imaging tools available in MSK radiology including shear-wave elastography, perfusion with contrast-enhanced ultrasound and superb microvascular imaging, and quantitative ultrasound assessment of osteosarcopenia.

Hemke et al present an overview of quantitative imaging methods to assess the distribution of lean tissue, adipose tissue, and bone in the human body, and their relationship with various pathologies. They stress the importance of body composition imaging for predicting overall health and risk profiling of patients. Jerban and colleagues summarize the quantitative MRI techniques recently developed for cortical and trabecular bone evaluation. Compared with radiograph-based techniques that focus on measuring bone mineral density, the new quantitative MRI techniques can comprehensively evaluate all the components of bone including the organic matrix, bone minerals, water, and fat. Weber et al review the role of neuromuscular imaging in the diagnosis of inherited and acquired muscle diseases. They discuss whole-body imaging as well as more advanced MRI applications including nonproton MRI and multiparametric quantitative imaging that provides deeper insights into muscle pathophysiology.

Griffith describes the role of quantitative imaging for the assessment of spine abnormalities. These quantitative techniques have led to a greater understanding of spinal development, marrow physiology, and disease pathogenesis. In their article on quantitative musculoskeletal tumor imaging, Howe and colleagues highlight the emerging role of various quantitative MRI and positron emission tomography (PET) techniques for the characterization, staging, prognosis, and follow-up of bone and soft tissue tumors. They also touch on the role of computed tomography and MRI-based virtual surgical planning and three-dimensional printing as a means to optimize surgical treatment of MSK tumors.

Yoon et al review novel approaches to pinpoint MSK pain generators with the use of PET imaging. They also discuss the added value of new radiotracers and of combining information in one hybrid PET/MRI examination. Liu presents the concepts of deep learning and demonstrates how these methods applied to quantitative MRI may accelerate image acquisition and reconstruction, improve tissue segmentation, and aid in the detection of structural knee abnormalities. Finally, Visser and colleagues discuss the trend in medicine that is moving from volume- to value-based payments, and they review the role that quantitative imaging may play. They also discuss the influence of artificial intelligence on value-based health care.

The variety of applications across all imaging modalities presented in this issue exemplifies the significant effort being made in developing and validating quantitative imaging techniques applied to the MSK system. The fact that several novel applications are still at the stage of development and optimization while other, more established, methods are already being translated into the clinical applications, demonstrates the tremendous ongoing activity in the field of quantitative MSK imaging.

We thank all the authors for their outstanding contribution to this issue. We hope the readers will be as excited as we are to apply quantitative imaging biomarkers in their clinical practice.