Spin-spin relaxation and apparent diffusion coefficient of magnetically oriented collagen gels

This paper describes a study on the effect of structural differences in collagen fibers on the spin-spin (T₂) relaxation and the apparent diffusion coefficient (ADC) of water molecules. Two collagen gels were polymerized from a type-I collagen solution with and without a 4.7-T magnetic field. The T₂ relaxation time was measured by the Carr-Purcell-Meiboom-Gill sequence. The ADCs were measured using a stimulated echo sequence with motion probing gradient (MPG) pulses. The temperature in the bore was 15°C. The T₂ relaxation times of water molecules in the collagen gels with magnetically oriented fibers and randomly oriented fibers were T₂=0.52 s and T₂=1.32 s, respectively. The ADCs of water molecules measured with MPG directions parallel and perpendicular to the collagen fibers were ADC=2.08×10^-9 m²/s and ADC=1.92×10^-9 m²/s, respectively. These differences are attributed to a change of collagen fiber structures due to the magnetic orientation.