Combining either paramagnetic (gadolinium chelates) or superparamagnetic (ferrite) contrast agents with polymers such as polyethylene glycol or cellulose, or with simple sugars such as dextrose, results in mixtures that exhibit improved T1 and/or T2 relaxivity compared with that of the contrast agent alone. It is suggested that the addition of such inexpensive and nontoxic polymers or saccharides may improve the effectiveness and decrease the cost of enteric contrast agents.

Cellulose↗

PubMedDate not supplied

Magnetic field dependence of 1/T1 of protons in tissue.

It is well established that the spin-lattice magnetic relaxation rate 1/T1 of solvent protons in homogeneous protein solutions increases dramatically as the magnetic field is reduced well below the traditional NMR range. For a 5% solution of protein of 10(5) Daltons, for example, 1/T1 increases from about 50% above the pure solvent rate at 20 MHz to five times the solvent rate at 0.01 MHz. At higher fields, the effect of protein on the relaxation rate decreases progressively toward zero. 1/T1 of solvent in erythrocyte suspension behaves similarly, indicating that extracellular water has ready access to intracellular protein. We now report analogous data for samples of various mammalian tissues: we find that the data can be accommodated within the conceptual framework developed earlier for analyzing homogeneous protein solutions. It appears that tissue water probes the macromolecular composition and structure in a tissue-specific fashion. The variation of 1/T1 with field differs for each tissue, and its magnitude at low fields varies by more than a factor of three, far more than does the water content of the tissues. The relevance to contrast in NMR imaging is discussed.

Adipose Tissue↗

PubMedDate not supplied

The importance of the motion of water for magnetic resonance imaging.

Since the water content of all soft tissues is about the same, contrast in magnetic resonance imaging depends principally on the parameters that govern nonequilibrium behavior of the nuclear spin system of the water protons of tissue, the longitudinal and transverse relaxation rates 1/T1 and 1/T2. A fundamental understanding of the determinants of both 1/T1 and 1/T2 at a cellular level, and ultimately at a molecular level (so that contrast can be optimized and perhaps manipulated), will require a model of the behavior of water that describes the dynamics of the motion of water molecules throughout tissue. A particular model is presented here, one in which tissue water is relatively free to diffuse randomly throughout the intracellular and extracellular regions of tissue, colliding with cellular and subcellular constituents along the way; this motion dominates 1/T1 at higher fields. When not in actual contact with interfaces, ie, within about 5 A of a macromolecular surface, the thermal motion of the water molecules is not influenced by the interfaces, but is altered slightly by the presence of solute macromolecules. However, this small difference is amplified 10(6)-fold, roughly the ratio of the macromolecular to solvent molecular weights, by a mechanism previously named the "slosh effect"; this effect dominates 1/T1 at low fields, and 1/T2 at all fields. It is shown how the foregoing view of tissue water follows quite naturally from NMRD profiles (measurements of the magnetic field dependence of 1/T1 of water protons) of a wide variety of protein solutions and samples of tissue, both native and containing added paramagnetic (Mn2+)ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗