Measurement of T₁ relaxation time of osteochondral specimens using VFA-SWIFT

Purpose To evaluate the feasibility of SWIFT with variable flip angle (VFA) for measurement of T₁ relaxation time in Gd-agarose-phantoms and osteochondral specimens, including regions of very short T₂∗, and compare with T₁ measured using standard methods Methods T₁s of agarose phantoms with variable concentration of Gd-DTPA^2- and nine pairs of native and trypsin-treated bovine cartilage-bone specimens were measured. For specimens, VFA-SWIFT, inversion recovery (IR) fast spin echo (FSE) and saturation recovery FSE were used. For phantoms, additionally spectroscopic IR was used. Differences and agreement between the methods were assessed using nonparametric Wilcoxon and Kruskal-Wallis tests and intraclass correlation. Results The different T₁ mapping methods agreed well in the phantoms. VFA-SWIFT allowed reliable measurement of T₁ in the osteochondral specimens, including regions where FSE-based methods failed. The T₁s measured by VFA-SWIFT were shifted toward shorter values in specimens. However, the measurements correlated significantly (highest correlation VFA-SWIFT versus FSE was r = 0.966). SNR efficiency was generally highest for SWIFT, especially in the subchondral bone. Conclusion Feasibility of measuring T₁ relaxation time using VFA-SWIFT in osteochondral specimens and phantoms was demonstrated. A shift toward shorter T₁s was observed for VFA-SWIFT in specimens, reflecting the higher sensitivity of SWIFT to short T₂∗ spins. Magn Reson Med 74:175-184, 2015.