In ordered systems, where the molecular motion is anisotropic, quadrupolar and dipolar interactions are not averaged to zero. In such cases, double quantum (DQ) coherences can be formed. This review deals mainly with the effect of anisotropic motion of water molecules and sodium ions in intact biological tissues on ²H, ¹H and ²³Na NMR spectroscopy and its application to NMR imaging (MRI).

Double quantum filtered (DQF) spectra of water molecules and sodium ions were detected in a variety of ordered biological tissues. In collagen‐containing tissues such as ligaments, tendons, cartilage, skin, blood vessels and nerves, the DQ coherences are formed as a result of the interaction with the collagen fibers. In red blood cells and presumably also in nerve axons it stems from the interaction with the cytoskeleton.

For ²³Na, an I = 3/2 nucleus, the DQ coherences can also be formed in isotropic media. By a judicial choice of the pulse angle in the DQ pulse sequence only the DQ coherences arising from anisotropic motion are detected. For I = 1 nuclei such as ²H, DQF spectra can be observed only in ordered structures. Thus, the observation of ²H DQF spectra is an indication of order. The same is true for pairs of equivalent ¹H 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 resolved from different tissues by performing the measurements at different creation times. In this way, the ²H 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 perpendicular to the axon's long axis, a result from which the axon diameter could be deduced. In blood vessel walls, this characteristic enabled the different layers of the vessel to be viewed and studied under strain.

For ²H, a DQF spectroscopic imaging sequence was used to study the orientation of the collagen fibers in the different zones of articular cartilage and bone plug. The effect of pressure on the fibers and their return to equilibrium 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 ¹H DQF imaging technique was demonstrated on a phantom of rat tail where only the four tendons were detected at short creation times. ¹H DQF imaging and spectroscopy followed the healing of a rabbit's ruptured Achilles tendon and the results were far more sensitive to the process than conventional imaging. Finally, the method was implemented on a commercial whole body MRI spectrometer. Images of human wrist and ankle showed a positive contrast for the tendons and ligaments, indicating the potential of the method for clinical imaging. Copyright © 2001 John Wiley & Sons, Ltd.

AT

Achilles tendon

DQF

double quantum filter

DQF‐SQE

double quantum filtered‐single quantum quadrupolar echo

EDST

extensor digitorum superficialis tendon

FDPT

flexor digitorum profoundus tendon

FDST

flexor digitorum superficialis tendon

GRE

gradient echo

IP‐DQF

in‐phase double quantum filter

JB

Jeener–Broekaert

MQF

multiple quantum filter

PGSE

pulsed gradient spin echo

SEM

scanning electron microscopy

SQ

single quantum

TQF

triple quantum filter

TQF‐QE

triple quantum filtered‐quadrupolar echo

ZQF

zero quantum filter.