An assessment of the repeatability and sensitivity of T2 mapping in low-grade cartilage lesions at 3 and 7 Tesla
Vladimir Juras1,2, Laurent Didier3, Vladimir Mlynarik1, Pavol Szomolanyi1, Stefan Zbyn1, Nicole Getzmann3, Joerg Goldhahn3, Stefan Marlovits4, and Siegfried Trattnig1,5

1Department of Biomedical Imaging and Image-Guided Therapy, High Field MR Centre, Medical University of Vienna, Vienna, Austria, 2Department of Imaging Methods, Institute for Measurement Science, Bratislava, Slovakia, 3Novartis Institutes for Biomedical Research, Basel, Switzerland, 4Department of Traumatology, Medical University of Vienna, Vienna, Austria, 5Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna, Austria

Synopsis

An assessment of the reliability of T2 mapping was achieved with a 3D-TESS sequence in patients with cartilage lesions ICRS Grade I-II. Since low-grade cartilage lesions are not usually accompanied by collagen matrix remodeling, we tested the sensitivity of T2 to detect these lesions at 3 and 7T. It seems that the reproducibility of 3T T2 mapping is higher than that of 7T; however, the sensitivity of T2 mapping for the detection of low-grade cartilage lesions was greater at the ultra-high field. T2 mapping could be used in the future as a good alternative to cartilage biopsies in future clinical trials on new therapies aimed at cartilage regeneration.

INTRODUCTION

Cartilage degeneration or defective repair after an injury is typically associated with changes in the macromolecular composition and zonal organization of the cartilage. Thus, the roughening of the articular surface results from cartilage fibrillation, a process involving denaturation of the collagen fibril structure and fragmentation of the collagen network. A complex structure such as the articular cartilage makes any repair of a defect challenging to monitor, and a non-invasive approach could then be considered as a good alternative approach to cartilage biopsies. T2 mapping appears to be well adapted for the evaluation of the collagen network1; however, the application of this technique to early degeneration has not yet been validated. Here, we show preliminary results obtained from an observational study with T2 mapping; the aim was to assess the repeatability and sensitivity of T2 at different field strengths to detect low-grade cartilage lesions.

MATERIALS AND METHODS

Seven patients (mean age, 50.3/5.4 years; 2 males/5 females) were imaged, who had confirmed cartilage defect(s) in the knee joint (ICRS Grade I or II) in the femoral region. Cartilage T2 mapping was acquired for each of these patients on both a 3T and a 7T whole-body Siemens MR scanner and repeated after eight days as a follow-up. T2 relaxation times were 0.25x0.25x3.0 mm3 (3T) and 0.37x0.37x3mm3 (7T) using a 3D-Triple Echo Steady State sequence (3D-TESS)2 with the following parameters: TR/TE 11.14/5.06 ms; FA 15°; TA 3:48 min. For image analysis, regions of interest (ROIs) were defined in 2D-TSE (3T) and 3D-DESS (7T) morphological images in the region suspicious for a cartilage defect and in a region of normal-appearing cartilage. These ROIs were then transferred to T2 maps (both 3 T and 7 T). All measurements were repeated eight days later as a part of a test-retest variability assessment. To compare lesions with reference cartilage, a paired t-test was used. A P-value lower than 0.05 was considered statistically significant.

RESULTS

The mean intra-class correlation coefficient was 0.914 for 3T and 0.638 for 7T (Fig. 1). At 3T, mean T2 was 38.85±8.5ms in lesions, 34.66±4.2ms in non-weight bearing cartilage, and 31.21±6.8ms in weight-bearing cartilage. At 7T, mean T2 was 28.73±3.2ms in lesion, 23.26±2.1ms in non-weight bearing cartilage, and 28.1±3.8ms in weight-bearing cartilage. At both time-points in all subjects, the T2 of the lesions was higher compared to healthy cartilage; however, statistical significance was recorded only in case of 7T with eight days of follow-up (p=0.035; Figs. 2 and 3). There was a tendency toward corrupted zonal stratification in lesions, but this did not reach statistical significance (Fig. 4).

DISCUSSION

Preliminary results of this study showed that collagen network disorganization can be detected in patients with low-grade lesions, in our case, at 7T only. However, the T2 values acquired at 3T seem to be more robust and repeatable. Interestingly, the T2 in non-weight bearing zones was lower than the T2 in weight bearing zones at 7T. We attributed this to miscalculated pixels, which appeared mostly on 7T T2 maps (the reason is unknown at the moment). Zonal variation seems to be promising marker for the detection of low-grade lesions. This study is continuing, with more subjects (up to 20) and a three-month follow-up, which will prospectively validate these preliminary results

CONCLUSION

T2 mapping with 3D-TESS enables monitoring of the changes in low-grade cartilage lesions and prospective follow-up of patients over time. This might be a valuable marker for monitoring cartilage development after regenerative therapy, as it may allow differentiation of the early formation of hyaline from fibrotic cartilage without resorting to serial biopsies.

Acknowledgements

Funding support provided by Austrian Science Fund (FWF) P 25246 B24

References

1.TJ Mosher et al. Cartilage MRI T2 relaxation time mapping: overview and applications, Seminars in Musculoskeletal Radiology 2004; 8(4):355-368

2.Heule R. et al. Triple echo steady-state (TESS) relaxometry, Magnetic Resonance in Medicine 2004; 71(1) 230–237

Figures

Fig.1 An example of a patient with cartilage injury in the lateral femoral condyle (Grade II) examined at 7T. A) The morphological image acquired with 3D-DESS; B) 3D-TESS T2 map overlaid on the second echo. Arrows indicate the defective cartilage region. A color bar indicates T2 values in milliseconds.

Fig.2 The reproducibility of T2 mapping with 3D-TESS at different field strengths (3 and 7 T) in various regions (lesion, non-weight bearing cartilage, weight-bearing cartilage).

Fig.3 Differences of T2 observed between healthy and defective cartilage regions both at 7T and 3T scanned at the baseline

Fig.4 Differences of T2 observed between healthy and defective cartilage regions both at 7T and 3T scanned at eight days follow-up. The asterisk sign indicates statistical significance (Student’s t-test).

Zonal stratification (ratio of superficial and deep zone) of three investigated regions (cartilage lesion [lesion], weight-bearing [wbr], and non-weight bearing [nowbr] zones) and the p-values, calculated by paired t-test. No statistical significance was found; however, there was a tendency toward lower p-values at 7T at eight days follow-up, which suggests there might be processes of cartilage remodeling present after eight days.



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