In Vivo Compositional 7T MRI of the Achilles Tendon at 7 Tesla

The Achilles tendon is among the most frequently injured tendons of the body with a variety of types of traumatic and overuse conditions affecting it. These conditions are common, often come to clinical attention, and are frequently imaged. Tendons are mechanically responsible for transmitting muscle forces to bone, and in doing so, permit locomotion and enhance joint stability. Moreover, tendons are a living tissue and respond to mechanical forces by changing their metabolism as well as their structural and mechanical properties. Different tendons exhibit similar features in pathology. These involve an increase in glycosaminoglycan including hyaluronan and water content, collagen degeneration, disorientation and thinning and an increased cellularity and vascularity. Changes in composition are likely to precede signs of morphological alteration. With conventional MRI (Magnetic Resonance Imaging) techniques, the tendons give no signal. MRI has a great potential to quantify the biochemical composition of the tendon. Recently, several MRI methods have been investigating to indirectly visualize even a small change in biochemical composition of highly organized tissues such as cartilage and menisci. It was shown that the transversal relaxation time reflects the mobility of the water and the collagen orientation and composition. The contrast enhanced longitudinal relaxation time (T1) is dependent on proteoglycan concentration and distribution; however contrast media application is usually necessary. Apparent diffusion coefficient is also possible to quantify in highly oriented tissues using MRI. In the last years, hardware development allows one to acquire sodium signal acceptable resolution. Normalized sodium signal correlates with the proteoglycan concentration in the tissue since the sodium ion is a counter-ion to negatively charged chains of glycosaminoglycans. Within this project, the non- invasive assessment of biochemical information in addition to high-resolution morphology of the Achilles tendon by MRI will be investigated and will prospectively help to understand the function of the normal tendon and improve the diagnosis of early stages of tendon degeneration before MR morphological changes occur. Furthermore, the MRI monitoring of the tendon disease treatment will help to define the normal healthy process over time and may help to detect abnormal healing. The project will be solved in three phases: 1. in vitro testing of multiple Achilles tendons from cadaver ankles by the application of multi-parametric MR protocols at micro- imaging system at 7T and comparison with immunohistological analysis; 2. in-vivo application of the validated techniques and protocol optimization on volunteers; 3. application of the advanced Achilles tendon MR techniques on patients pre- and post-operatively to monitor the healing process after surgery.

[2] Juras et al, Multiparametric MR Imaging Depicts Glycosaminoglycan Change in the Achilles Tendon during Ciprofloxacin Administration in Healthy Men, Radiology (2015) In Press