The magnetic field dependence of water T₁ in tissues

Abstract

The magnetic field dependence of the composite 1H2O NMR signal T1 was measured for excised samples of rat liver, muscle, and kidney over the field range from 0.7 to 7 T (35 MHz to 300 MHz) with a NMR spectrometer using sample-shuttle methods. Based on extensive measurements on simpler component systems, the magnetic field dependence of T1 of all tissues studied are readily fitted at Larmor frequencies above 1 MHz with a simple relaxation equation consisting of three contributions: a power law, A*ω−0.60 related to the interaction of water with long-lived-protein binding sites, a logarithmic term B*τd*log(1+1/(ωτd)2) related to water diffusion at macromolecular interfacial regions, and a constant term associated with the high frequency limit of water-spin-lattice relaxation. The parameters A and B include the concentration and surface area dependences respectively. The logarithmic diffusion term becomes significant at high magnetic fields and is consistent with rapid translational dynamics at macromolecular surfaces. The data are fitted well with translational correlation times of approximately 15 ps for human brain white matter, but with a B value three times larger than gray matter tissues. This analysis suggests that the water-surface translational correlation time is approximately three times longer than gray matter.

NMR dispersion investigations of enzymatically degraded bovine articular cartilage

“…The frequency dependence of the proton longitudinal relaxation of different polypeptides, cells and live tissue as a function of water content has been investigated several decades ago . A recent approach to modeling this dispersion has been presented in Diakova et al but is beyond the range of this study.…”

Relationships between tissue microstructure and the diffusion tensor in simulated skeletal muscle

“…Intra‐ and extracellular particles were assigned different diffusion coefficients and magnetic relaxation (T 1 , T 2 ) rates based on literature values. Relaxation rates and diffusion coefficients of molecular species were taken from the literature: intracellular (T 1 /T 2 : 1,740/25 ms , D: 1.8*10 −3 mm 2 /s ); and extracellular (T 1 /T 2 : 2500/95 ms , D: 2.2*10 −3 mm 2 /s ). A total of 200,000 particles were simulated to accurately converge on an analytical solution based on the diffusion coefficients and b‐value chosen for this experiment .…”

Ultra-wide range field-dependent measurements of the relaxivity of Gd1−xEuxVO4 nanoparticle contrast agents using a mechanical sample-shuttling relaxometer

“…However, the extension of T 1 contrast to high fields is not straightforward. Although the measured T 1 in tissues and blood have been found to rise with increasing fields34, the difference in T 1 for different tissues becomes less pronounced at higher magnetic fields (B 0  > 2 T), leading to a reduction in imaging contrast. This points to the necessity for increasing the image contrast with appropriately designed contrast agents56.…”