ABSTRACT
Objectlve To demonstrate the feasibility of three-dimensional(3D)spin-lattice relaxation time in the rotating frame(T1ρ)-weighted imaging of porcine patellar cartilage in vitro at 7.0 T and the measurement of T1ρ of agarose phantom and patellar cartilage.Methods All the MR Imaging experiments were performed on a 7.0 T Varian scanner using a 6.0-cm-diameter quadrature birdcage RF coil tuned to 300 MHz.A 3D spin-echo sequence with a self.compensating spin-lock pulse cluster was used to acquire 3D-T1ρ-weighted images.The time of spin-locking(TSL)was from 0 to 50 ms with an interval of 10 ms.Spin-lock power wag 440 Hz.3D-T1ρweighted imaging was done three times for 6 phantoms (concentration 1%t0 6%),as well as once for 8 porcine patellar cartilages in order to assess the reproducibility of this technique.Signal-to-noise ratio(SNR)was measured on the acquired images of both phantoms and patellar cartilages,which were tested for significance using Two-way ANOVA.The images were processed on Vnmr J workstation using home-built processing software to construct 3 D T1ρ maps.T1ρ values were calculated within manually drawn regions-of-interest(ROI),and differences between groups were tested for significance using analysis of variance(One-way ANOVA).Results T1ρ -weighted images with a shorter TSL had a higher SNR value,which measured between 48±8 and 95±8 in the global cartilage.Cartilage images had a higher SNR(TSL＜30 ms)compared to agarose phantoms and a lower SNR(TSL ＞30 ms)only compared to l%agarose phantorm T1ρ relaxation times in agarose phantoms increased as agarose concentrations decreased in global regions.The CV of T1ρ in agarose phantoms was less than 10%.Global and regional analyses of patellar cartilage T1ρ were 68.9±6.3 ms,80.7±12.8 ms,65.7±7.0 ms,82.4±7.7 ms,and 69.7±6.4 ms in the global cartilage,the superficial layer,the transitional layer,the deep layer,and the calcified layer,respectively.T1ρ in the superficial and deep layer was significantly higher than in the transitional,calcified layer and global cartilage(F=6.436,P＜0.05).Conclusions The present study demonstrates the feasibihty of 3D-T1ρ-weighted imaging of porcine patellar cartilage at 7.0 T with hish image quality.T1ρ maps can be used to quantify the laminar structures in 3D-T1ρ-weighted images of articular cartilage,which pave the way to evaluate early osteoarthritis and cartilage regeneration.