Study of order and dynamic processes in tendon by NMR and MRI

Abstract

Tendons are composed of a parallel arrangement of densely packed collagen fibrils that results in unique biomechanical properties of strength and flexibility. In the present review we discuss several advanced magnetic resonance spectroscopy (MRS) and imaging (MRI) techniques that have allowed us to better understand the biophysical properties of tendons and ligaments. The methods include multiple quantum and T 2 filtering combined with NMR and MRI techniques. It is shown in detail how these techniques can be used to extract a number of useful parameters: 1) the 1 H-1 H and 1 H-2 H dipolar interactions; 2) the proton exchange rates between water and collagen, and between water molecules; 3) the distribution of fibril orientations; and 4) the anisotropy of diffusion. It is shown that relaxation data as a function of angular dependence can be obtained in vivo using mobile NMR sensors. Finally, this article describes how double quantum filtered (DQF) MRI can be used to image and monitor the healing process in injured tendons. TENDONS ARE THE FIBROUS CONNECTIVE TISSUE that joins muscle to bone. For example, the Achilles tendon connects the heel to the muscles of the calf (Fig. 1). Ligaments are similar to tendons, except that they join one bone to another. Tendons and ligaments are unique in that they possess biomechanical properties of exceptional strength and flexibility due to the parallel arrangement of densely packed type-I collagen fibrils (see Fig. 2). In addition to collagen, these tissues contain a small amount of proteoglycans and cells called tenocytes. Injuries of the tendons and ligaments are very common issues in geriatric and sports medicine, so the adaptation of medical imaging techniques to these tissues is a subject of considerable interest. These important tissues are difficult to image by MRI due to their short and anisotropic T 2 resulting from the residual dipolar interactions of the water molecules. In this article we review advanced MR spectroscopy (MRS) and MRI techniques that can be applied to the tendons and ligaments. These methods have already allowed us to better understand the biophysical properties of tendons, and to suggest new directions for imaging. MEASUREMENT OF DIPOLAR INTERACTIONS IN TENDON BY DOUBLE QUANTUM FILTERED (DQF) NMR SPECTROSCOPYThe interaction of water molecules with collagen fibers induces an anisotropy in their motions (3,4). Thus, the intramolecular dipolar interaction does not average to zero, and a smaller (residual) dipolar splitting remains. While water molecules that interact directly with the highly ordered fibers may exhibit a large dipolar splitting, a fast exchange process with adjacent isotropically moving water molecules will reduce the splitting (Fig. 3). It follows that the resulting residual dipolar splitting depends on the ratio of bound to free water molecules, and therefore on the hydration level of the sample. Splitting of the water 1 H and 2 H NMR signals due to residual dipolar or quadrupolar interactions has been observed (4,5) in partially hy...

Mobile single-sided NMR

“…The different orientations of B 0 parallel and perpendicular to the sensor surface may be important in the analysis of objects with preferential orientational order in that plane such as a tendon [192][193][194][195] or a sample of strained rubber [196,197]. If the direction n of preferential order is parallel to the sensor surface, the angle between B 0 and n varies with rotation of the u-shaped magnet, while it remains at a value of 90°with the bar-magnet sensor.…”

The Agfa Mayneord lecture: MRI of short and ultrashortT2andT2* components of tissues, fluids and materials using clinical systems

“…For example, 90 u , 180 u , fat saturation and magnetisation transfer pulses can all be used to suppress unwanted long T 2 signals and to produce T 2 contrast in the short T 2 range. There are some fairly new potential mechanisms (as far as clinical imaging is concerned) that involve reductions in dipolar coupling [39,40] and double quantum filters [41]. These techniques are usually used in conjunction with one of the acquisition methods previously described.…”

Qualification of automated low-field NMR relaxometry for quality control of polymers in a production setting

“…[14,15] Additional efforts have been made in the areas of multiple quantum NMR, [16,17] low-power selective excitation, [18,19] and numerous magnetic resonance imaging (MRI) applications. [20][21][22] Recent incorporation of a 1D adjustable magnet stage using the Profile NMR-MOUSE ® has allowed for depth profiling within a sample. Modifications to the magnet system as well as the ability to make minute changes in the distance between the magnet surface and the sample has afforded very high resolution depth profiles on the order of ~2 µm.…”