Dependencies of Multi-component T2 and T1ρ Relaxation on the Anisotropy of Collagen Fibrils in Bovine Nasal Cartilage

Both NMR spectroscopy and MRI were used to investigate the dependencies of multi-component T2 and T1ρ relaxation on the anisotropy of bovine nasal cartilage (BNC). The non-negative least square (NNLS) method and the multi-exponential fitting method were used to analyze all experimental data. When the collagen fibrils in nasal cartilage were oriented at the magic angle (55°) to the magnetic field B0, both T2 and T1ρ were single component, regardless of the spin-lock field strength or the echo spacing time in the pulse sequences. When the collagen fibrils in nasal cartilage were oriented at 0° to B0, both T2 and T1ρ at a spin-lock field of 500 Hz had two components. When the spin-lock field was increased to 1000 Hz or higher, T1ρ relaxation in nasal cartilage became a single component, even when the specimen orientation was 0°. These results demonstrate that the specimen orientation must be considered for any multi-component analysis, even for nasal cartilage that is commonly considered homogenously structured. Since the rapidly and slowly relaxing components can be attributed to different portions of the water population in tissue, the ability to resolve different relaxation components could be used to quantitatively examine individual molecular components in connective tissues.