Water proton NMR relaxation mechanisms in lung tissue

Abstract

The NMR relaxation times T'2, T2, and T1 were measured in isolated rat lungs as functions of external magnetic field B0, temperature, and lung inflation. The observed linear dependence on B0 of the tissue-induced free induction decay rate (T'2)-1 provides independent confirmation of the air/water interface model of the lung. Furthermore, measurements of the Larmor frequency dependence of T1 are consistent with a spin-lattice relaxation rate of the form 1/T1 = A omega -1/2 + B as expected for the case in which the relaxation arises from water-biopolymer cross-relaxation, which should be proportional to the surface area of the lung. This prediction was verified by observations of an approximately linear dependence of 1/T1 on transpulmonary pressure and thus on the lung surface area.

Multiexponential proton relaxation processes of compartmentalized water in gels

“…Proton relaxation times of compartmentalized water have been determined in tissues (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15), gels (22)(23)(24)(25), food materials ( 2 6 ) , and plants (27). In general, a monoexponential relaxation process of water in a closed compartment indicates fast exchange between free water and hydration water according to and h relate to free and hydration water.…”

“…More accurate measurements and a better analysis of relaxation processes (in vitro and in vivo) should be based on a large number of data points of a relaxation curve allowing the decomposition of multiexponential processes into monoexponential components. These monoexponential components may be more useful for the improved determination of TI and T 2 and allow the estimation of fractions of the relaxation components in each voxel, which correlate with the proton density of a particular water fraction (7)(8)(9)(10). However, it should not be withheld that it is difficult to obtain well-digitized relaxation curves employing routine imaging procedures and that one needs special techniques ( 12).…”

“…They are most important for the contrast behavior of soft tissues in images ( I , 2). In addition, relaxation time measurements have contributed to tissue characterization and differentiation in vitro (3)(4)(5)(6)(7)(8)(9)(10) and in vivo ( 1 I -15 ) . Water proton relaxation times reflect the specific environment of the water molecules in the tissues, due to dipolar interactions, chemical exchange processes between water molecules and the surrounding biological macromolecules, and the particular physicochemical state of the water in cellular compartments.…”

Sodium MRI with coated magnetite: Measurement of extravascular lung water in rats

“…Proton MRI studies have demonstrated correlation of the signal intensity from edematous lungs with the amount of lung water present (6)(7)(8)(9)(10). Proton lung water imaging, though, is complicated by magnetic susceptibility effects (11,12). Further, protons in all the fluid compartments of the edematous lungs-intracellular, alveolar, interstitial, and plasma-contribute to the total signal intensity.…”

In vivo magnetic resonance methods in pharmaceutical research: current status and perspectives

“…The resulting susceptibility gradients at the air/tissue interfaces are the cause of the short relaxation times, with T 2 * being of the order of 0.5-1 ms, while T 2 shows a biexponential decay with a short component of 1 ms and a longer one of 50-100 ms, respectively. 225,226 These factors largely prevent the detection of signals from lung parenchyma using conventional spin-echo or gradient-echo pulse sequences. Moreover, cardiac and respiratory motion as well as pulsatile blood flow in the thoracic vasculature render MRI of the lung difficult.…”