Scanning electron microscopy of collagen fibers. Image credit: Tom Deerinck and Mark Ellisman, NCMIR (CC BY-NC 2.0)
Magnetic resonance imaging (MRI) is a well-established clinical technique for examining the body non-invasively. It uses magnetic fields and radio waves to disturb hydrogen atoms in the body, which then emit signals as they return to a normal state. A computer analyses these signals to create detailed images of different tissues inside the body.
Because these signals have a limited lifetime, the duration of the imaging process is critical in determining which tissues can be detected. Conventional MRI primarily measures signals from bulk water in soft tissues, which decay over tens to hundreds of milliseconds. However, a substantial fraction of signals in the body decays on the microsecond timescale, making them inaccessible to standard MRI methods.
One important source of such rapidly decaying signals is collagen, the most abundant protein in the human body and a key structural component of tissues including skin, cartilage, tendons and bone. Because of its extremely short signal lifetime, collagen has traditionally been assessed only indirectly through MRI of the surrounding water.
Direct collagen MRI could offer greater specificity than indirect approaches and support both research and clinical applications. For example, it could improve understanding of tissue changes associated with disease and injury or enable bone density measurements without exposure to ionising radiation.
To find out if MRI could image collagen directly, van Schoor et al. used a combination of recently developed custom hardware and specialised imaging methodology designed to detect and spatially encode the extremely short-lived collagen signal. The approach was first validated in bovine tendon and bone samples and subsequently extended to imaging of the human forearm.
The images obtained not only visualised collagen directly but also captured the rapid decay of its signal over time. This demonstrates that direct MRI of collagen is indeed feasible.
Direct MRI of collagen could have important applications in fields such as musculoskeletal medicine, tissue engineering, and fibrosis research, where collagen content and organisation are central to tissue function and pathology. Although the current method still relies on custom-built hardware, these findings provide a foundation for developing clinical MRI systems capable of imaging rapidly decaying signals in a wider range of tissues, diseases and patient populations. With further refinement, this approach could complement existing imaging techniques, provide new non-invasive insights into tissue structure, and potentially enable direct MRI of other macromolecules.
