Milena L. Pachowsky MD, Presenter: Nothing to Disclose

Siegfried Trattnig MD, Abstract Co-Author: Nothing to Disclose

Kolja Gelse MD, Abstract Co-Author: Nothing to Disclose

Joachim Friske, Abstract Co-Author: Nothing to Disclose

Martin Brix, Abstract Co-Author: Nothing to Disclose

Goetz Hannes Welsch MD, Abstract Co-Author: Nothing to Disclose

T2 mapping at 7T might help to understand the development of osteoarthritis (OA) and of integration processes after cartilage repair procedures, i.e. autologous chondrocyte transplantation (ACT). Purpose of this study is to determine biochemical properties of cartilage in a sheep model, using biochemical MRI by means of quantitative T2-mapping and establish a histological validation.

Three groups of sheep (healthy cartilage, n=30, a model of osteoarthritis (post meniscectomy), n=30, and sheep with cartilage defects at the femoral condyle treated by ACT, n=15) were examined. MR scans were achieved at 7T MR whole body system (Magnetom, Siemens Healthcare, Erlanen, Germany) using a 28-channel transmit/receive knee array coil. T2 relaxation maps were measured by a sagittal multi-echo spin sequence. TR 5260ms; TE 12, 24, 36, 48, 60, and 72ms; FOV 145x145mm, 716x869 matrix size; BW 180 Hz/pixel, slice thickness 2mm; flip angle 145°. Semi-automatic region-of-interest analysis was performed. For stratification with regards to anatomical (collagen) structure, subregional analysis was done (deep - superficial cartilage layer). Results were compared to histological findings. Statistical analysis-of-variance was performed.  

In healthy cartilage, T2 values averaged 41,92ms (SD 11,7) in the superficial layer and 32,69ms (SD 9,74) in the deep layer. OA showed results of 60,90ms (SD 14,34) in the superficial layer and 47,28ms (SD 13,54) in the deep layer. After ACT results averaged at 58,41ms (SD 15,53) in the superficial and 45,66 (SD 20,81) in the deep layer. Increase of T2 values between deep and superficial zone was highly significant in the group with healthy cartilage, significant in the OA model and the ACT group. OA and ACT group showed significantly higher values compared to healthy cartilage. Comparison between histological scoring and MR findings showed a significant correlation.

The sheep model shows differences between healthy cartilage, OA and cartilage repair sites in T2 mapping. Our new approach at 7T gives additional information about the imaging techniques of the ultra-structure of cartilage and provides one of the very few histological validations of T2 mapping in vitro.

The presented study of T2 mapping in a sheep model and histological validation is an important approach towards establishing T2 mapping of articular cartilage in clinical appplication.

Pachowsky, M, Trattnig, S, Gelse, K, Friske, J, Brix, M, Welsch, G, Ultra-high Field Analysis of Knee Cartilage in a Sheep Model by Means of Quantitative T2 Mapping Using 7T MRI and Histological Validation.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045641.html