Multicomponent analysis of T₁ relaxation in bovine articular cartilage at low magnetic fields

Abstract

Purpose The multi‐exponential character of T 1 relaxation in bovine articular cartilage was investigated at low magnetic fields below 0.5 T. The ultimate aim was to identify a parameter based on the T 1 relaxation time distribution as a biomarker to biochemical features of osteoarthritis. Methods Osteoarthritis conditions were simulated by enzymatic digestion of cartilage with trypsin. Fast‐field cycling NMR relaxometry was carried out in the magnetic field range B 0 = 70 μT to 600 mT. The data were analyzed in terms of T 1 distributions on a log‐time scale using inverse Laplace transform, whereas integral properties such as mean T 1 s and distribution widths were obtained without data inversion from logarithmic moment analysis and a stretched‐exponential fit to the data. Attempts were also made to differentiate between water dynamic components through multi‐Lorentzian decomposition of average relaxation‐rate dispersions. Results T 1 distribution in bovine articular cartilage was found to be bimodal, with the dominating, long component shifting toward larger values following trypsin digestion. The effect is more prominent toward lower magnetic field strength. This shift leads to an overall increase of the distribution width and an equivalently more pronounced deviation from exponential behavior. Conclusion The logarithmic width of T 1 distribution functions at fields of 0.5 T and below, and the stretched‐exponential decay fit exponent β , show a significant trend after trypsin digestion of cartilage. These 2 parameters are suggested as possible biomarkers for osteoarthritis in humans and can be acquired entirely in vivo, with increasing significance for lower magnetic field strengths.

A whole-body Fast Field-Cycling scanner for clinical molecular imaging studies

“…Measurement of T 1 on a conventional (fixed-field) NMR or MRI device can only report on a single characteristic time of molecular motion, while FFC allows access to several decades 10 of motional dynamics, typically from tens of nanoseconds to several milliseconds. Such measurements of the T 1 dispersion with the magnetic field strength, the T 1 NMRD profiles, report quantitatively on the nature of molecular motion and are exploited to determine structural parameters [12][13][14] . In biological tissues, such time scales correspond to structures varying in size from tens of nanometres up to several micrometres, which is particularly relevant for the study of tissue remodelling in disease.…”

Dehydration assessment via a portable, single sided magnetic resonance sensor

“…Finally, the measurement can be performed in a few minutes suggesting potential for use as a real‐time measure of fluid volume status. Portable, single sided MR sensors have recently shown potential across a wide range of biomedical applications …”

Theory of fast field-cycling NMR relaxometry of liquid systems undergoing chemical exchange

“…Finally, recent theoretical developments in the analysis of multi-exponential relaxation data [22] should facilitate the precise determination of the physico-chemical parameters involved in systems of nuclear spins undergoing chemical exchange.…”

“…The columnsC 0 (s),C ± (s) are readily obtained from Equations (23) and (24). Using Equation(22), they yield the site magnetisationsM Az (τ + s) = χ A B a + [(p B χ A − p A χ B )e −R + a s + χ A e −R − a s ](B r − B a ) + [p B m Azr (0) − p A m Bzr (0)]e −R + a s e −R + r τ + p A [m Azr (0) + m Bzr (0)]e −R − a s e −R − r τ , M Bz (τ + s) = χ B B a + [−(p B χ A − p A χ B )e −R + a s + χ B e −R − a s ](B r − B a ) − [p B m Azr (0) − p A m Bzr (0)]e −R + a s e −R + r τ + p B [m Azr (0) + m Bzr (0)]e −R − a s e −R − r τ ,(52)and the total magnetisationM z (τ + s) = χ B a + χ e −R − a s (B r − B a ) + [m Azr (0) + m Bzr (0)]e −R − a s e −R − r τ . (53)…”