Depth and orientational dependencies of MRI T(2) and T(1ρ) sensitivities towards trypsin degradation and Gd-DTPA(2-) presence in articular cartilage at microscopic resolution.

Depth and orientational dependencies of microscopic magnetic resonance imaging (MRI) T(2) and T(1ρ) sensitivities were studied in native and trypsin-degraded articular cartilage before and after being soaked in 1 mM Gd-DTPA(2-) solution. When the cartilage surface was perpendicular to B(0), a typical laminar appearance was visible in T(2)-weighted images but not in T(1ρ)-weighted images, especially when the spin-lock field was high (2 kHz). At the magic angle (55°) orientation, neither T(2)- nor T(1ρ)-weighted image had a laminar appearance. Trypsin degradation caused a depth- and orientational-dependent T(2) increase (4%-64%) and a more uniform T(1ρ) increase at a sufficiently high spin-lock field (55%-81%). The presence of the Gd ions caused both T(2) and T(1ρ) to decrease significantly in the degraded tissue (6%-38% and 44%-49%, respectively) but less notably in the native tissue (5%-10% and 16%-28%, respectively). A quantity Sensitivity was introduced that combined both the percentage change and the absolute change in the relaxation analysis. An MRI experimental protocol based on two T(1ρ) measurements (without and with the presence of the Gd ions) was proposed to be a new imaging marker for cartilage degradation.