Multiquantum filters and order in tissues

G. Navon et al., Multiquantum filters and order in tissues, NMR BIOMED, 14(2), 2001, pp. 112-132
Citations number
Categorie Soggetti
Medical Research Diagnosis & Treatment
Journal title
ISSN journal
0952-3480 → ACNP
Year of publication
112 - 132
SICI code
In ordered systems, where the molecular motion is anisotropic, quadrupolar and dipolar interactions are not averaged to zero. In such cases, double qu antum (DQ) coherences can be formed. This review deals mainly with the effe ct of anisotropic motion of water molecules and sodium ions in intact biolo gical tissues on H-2, H-1 and Na-23 NMR spectroscopy and its application to NMR imaging (MRI). Double quantum filtered (DQF) spectra of water molecules and sodium ions we re detected in a variety of ordered biological tissues. In collagen-contain ing tissues such as ligaments, tendons, cartilage, skin, blood vessels and nerves, the DQ coherences are formed as a result of the interaction with th e collagen fibers. In red blood cells and presumably also in nerve axons it stems from the interaction with the cytoskeleton. For Na-23, an I = 3/2 nucleus, the DQ coherences can also be formed in isot ropic media. By a judicial choice of the pulse angle in the DQ pulse sequen ce only the DQ coherences arising from anisotropic motion are detected. For 1 = 1 nuclei such as 2H, DQF spectra can be observed only in ordered struc tures. Thus, the observation of H-2 DQF spectra is an indication of order. The same is true for pairs of equivalent H-1 nuclei. The dependence of the DQF signal on the creation time of the double quantum coherences is characteristic to each tissue and allows signals to be resol ved from different tissues by performing the measurements at different crea tion times. In this way, the H-2 DQF signals of the different compartments of sciatic nerve were resolved and water diffusion in each compartment was studied independently. In the axon, the diffusion was heavily restricted pe rpendicular to the axon's long axis, a result from which the axon diameter could be deduced. In blood vessel walls, this characteristic enabled the di fferent layers of the vessel to be viewed and studied under strain. For H-2, a DQF spectroscopic imaging sequence was used to study the orienta tion of the collagen fibers in the different zones of articular cartilage a nd bone plug. The effect of pressure on the fibers and their return to equi librium was studied as well. In blood vessels, a DQF image was obtained and strain maps of the different layers were calculated. The efficiency of the H-1 DQF imaging technique was demonstrated on a phant om of rat tail where only the four tendons were detected at short creation times. 'H DQF imaging and spectroscopy followed the healing of a rabbit's r uptured Achilles tendon and the results were far more sensitive to the proc ess than conventional imaging. Finally, the method was implemented on a com mercial whole body MRI spectrometer. Images of human wrist and ankle showed a positive contrast for the tendons and ligaments, indicating the potentia l of the method fur clinical imaging. Copyright (C) 2001 John Wiley sr Sons , Ltd.