Improve the Detection of Cartilage Degradation by Dividing the Tissue Unequally – A Comparative Study of Two Methods
Farid Badar1, Ji Hyun Lee1, and Yang Xia1

1Department of Physics and Center for Biomedical Research, Oakland University, Rochester, MI, United States

Synopsis

The consequences of two different zone-division methods in MRI T2 of articular cartilage were studied, using an animal model of early osteoarthritis (OA). By dividing the cartilage thickness unequally, significant improvement in OA detection can be achieved – both in the deeper cartilage as well as between the contralateral and normal tissue. This improved detection may become important in the clinical diagnostics of early OA.

Purpose

This study was performed to compare the consequences of different zone-divisions in MRI T2 of articular cartilage using an animal model of early osteoarthritis (OA).

Material and Methods

The progression of osteoarthritis was studied using eighteen mature canines, which was approved by the institutional review committee. Six animals were the non-operated normal controls (Normal) and twelve animals underwent anterior cruciate ligament (ACL) transection on one of their knees. The operated animals were sacrificed 8 week and 12 weeks post-surgery (8wk-OA, 12wk-OA). The non-transected contralateral knees in these animals were also studied (8wk-C, 12wk-C). Within 24 hours of sacrifice, the intact knee joints were first imaged using a Varian 7T/20cm macro-MRI. T2 experiments were carried out using a multi-slice multi-echo (MSME) pulse sequence. The ten echo times were 10, 20, 30, ... 100ms, with TR set at 3 seconds. The FOV was 5cm with a matrix size at 256 x 256. The imaging matrix was reconstructed in post-acquisition to 512 x 512 using Varian’s Fourier reconstruction. Ten interleaved image slices were selected, approx. 2.5mm apart from each other. To determine the sub-tissue zonal division accurately, the joint capsules were opened after macro-MRI. Each medial tibial plateau was cut into five cartilage-bone blocks, which were T2 imaged on a Bruker 7T/9cm µMRI, at 17µm pixel resolution. Both macro-MRI and µMRI images were approximately at the same tissue locations in the knee. The data in this report were entirely from the macro-MRI experiments; the µMRI data, which would be presently in a separate report, only provided the criteria for the sub-tissue zone division 1 in this report.

Results

Fig 1a shows the quantitative T2 maps by macro-MRI, with the medial tibial location highlighted in Fig 1b (the cropped ROI) and the equivalent µMRI T2 map from the similar location in Fig 1c. Two methods of image analysis were used in macro-MRI T2 data analysis: (1) an equal division of the entire cartilage from the surface to the cartilage-bone interface (Fig 2), and (2) an unequal division of the same cartilage based on the knowledge from µMRI zones (Fig 3). With the equal division (Fig 2), significant difference can be detected statistically in Zone I between Normal and both OA groups; however, there were no statistical significance between Normal and Contralateral cartilage, or among any comparison in Zone II and Zone III. With the zonal knowledge from µMRI, the unequal division of the same T2 profiles from macro-MRI enabled the significant differences to be detected statistically in the superficial zone (SZ) between the Normal and OA, and between the Normal and Contralateral cartilage. In addition, significant differences can also be detected statistically in two sub-tissue zones (the transitional zone TZ and the upper radial zone RZ1).

Discussion

T2 in cartilage increases due to the progression of OA. This comparative project studies the intermediate-resolution macro-MRI T2 data, which shows the critical role of the zonal division in the detection of OA by MRI. The use of the equal division of cartilage thickness, which is common in clinical MRI of human cartilage 2, can detect cartilage degradation, but only in the surface tissue, and only between the directly lesioned tissue and the healthy tissue. This equal division has failed to detect the smaller differences in T2 between the normal and contralateral cartilage. In contrast, an unequal zonal division can significantly improve the detection of cartilage degradation – in the deeper tissues as well as between the contralateral and normal tissue. This improved detection may become important in the clinical diagnostics of early OA. We are completing a topographical analysis of this data at multiple resolutions, which could provide further insight into the complications of both depth-dependent and topographically distributed OA degradation on the medial tibial plateau.

Conclusion

In this study, we utilized the knowledge from the high-resolution µMRI zonal division to divide the T2 profiles at the intermediate resolution macro-MRI both equally and non-equally. We show significant differences between the two image analysis methods in the detection of small changes in T2 due to OA progression. A similar approach 3 could be developed and implemented in the image analysis in clinical MRI of human OA, to improve the detection sensitivity towards the early signs of cartilage degeneration in clinical MRI of human.

Acknowledgements

Y Xia thanks NIH for the R01 grant (AR052353). The authors are grateful to Dr. James R Ewing and Dr. Gary Ding (Henry Ford Hospital Neurology Dept.) for accessing to the 7T/20cm Varian MRI.

References

1 Lee JH, Xia Y. Quantitative zonal differentiation of articular cartilage by microscopic magnetic resonance imaging, polarized light microscopy, and Fourier-transform infrared imaging. Microsc Res Tech 2013, 76(6):625-632.

2 Wei B, Zong M, Yan C, Mao F, Guo Y, Yao Q, Xu Y, Wang L. Use of quantitative MRI for the detection of progressive cartilage degeneration in a mini-pig model of osteoarthritis caused by anterior cruciate ligament transection. J Magn Reson Imaging 2015, 42(4):1032-1038.

3 Xia Y. Resolution ‘Scaling Law’ in MRI of Articular Cartilage. Osteoarthritis Cartilage 2007, 15(4):363–365.

Figures

Quantitative Macro-MRI T2 Map of Medial Tibia. a) low-resolution T2 map of entire tibia imaged using the 7T/20cm bore magnet. b) The selected region of interest of the comparable tissue block. c) The µMRI representative of the same block.

Statistics of T2 comparisons when the tissue is divided into three equal partitions from the surface to the bone interface. (Zone I is surface cartilage; Zone III is cartilage just above the cartilage-bone interface. *** donates p <0.0001 in statistical analysis.)

Statistics of T2 comparisons when the tissue is divided into four unequal zones, based on the µMRI morphological zonal thickness. (SZ is the superficial zone; TZ is the transitional zone; RZI and RZII are the two equal halves of the radial zone.)



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
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