Three-dimensionalspin-lattice relaxation time in the rotating frame imaging and quantitation of articularcartilage at 7.0 T MR

Abstract

：Objectlve To demonstratethe feasibility of three-dimensional(3D)spin-lattice relaxation time in the rotatingframe(T1ρ)-weighted imaging of porcine patellar cartilage in vitro at 7.0 Tand the measurement of T1ρ of agarose phantom andpatellar cartilage.Methods All the MR Imaging experiments were performed on a 7.0 T Varianscanner using a 6.0-cm-diameter quadrature birdcage RF coil tuned to 300 MHz.A 3Dspin-echo sequence with a self.compensating spin-lock pulse cluster was used to acquire3D-T1ρ-weighted images.The time of spin-locking(TSL)was from 0 to 50 mswith an interval of 10 ms.Spin-lock power wag 440 Hz.3D-T1ρweighted imaging was donethree times for 6 phantoms (concentration 1%t0 6%),as well as once for 8 porcine patellarcartilages in order to assess the reproducibility of this technique.Signal-to-noiseratio(SNR)was measured on the acquired images of both phantoms and patellarcartilages,which were tested for significance using Two-way ANOVA.The images wereprocessed on Vnmr J workstation using home-built processing software to construct 3 D T1ρ maps.T1ρ values were calculated withinmanually drawn regions-of-interest(ROI),and differences between groups were tested forsignificance using analysis of variance(One-way ANOVA).Results T1ρ -weighted images with a shorter TSL had a higher SNR value,whichmeasured between 48±8 and 95±8 in the global cartilage.Cartilage images had a higherSNR(TSL＜30 ms)compared to agarose phantoms and a lower SNR(TSL ＞30ms)only compared to l%agarose phantorm T1ρrelaxation timesin agarose phantoms increased as agarose concentrations decreased in global regions.The CVof T1ρ in agarose phantoms was lessthan 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 theglobal cartilage,the superficial layer,the transitional layer,the deep layer,and thecalcified layer,respectively.T1ρ in the superficial and deeplayer was significantly higher than in the transitional,calcified layer and globalcartilage(F=6.436,P＜0.05).Conclusions The present study demonstrates thefeasibihty of 3D-T1ρ-weighted imaging of porcine patellar cartilage at7.0 T with hish image quality.T1ρ maps can be used to quantifythe laminar structures in 3D-T1ρ-weighted images of articular cartilage,which pave the wayto evaluate early osteoarthritis and cartilage regeneration. Key words: Spin-lock imaging; Magnetic resonanceimaging; Phantom,imaging; Cartilage,articular; Porcine