Abstract
BackgroundNon-destructive structural evaluation of the osteochondral unit is challenging. Here, the capability of high-field magnetic resonance imaging (μMRI) at 9.4 Tesla (T) was explored to examine osteochondral repair ex vivo in a preclinical large animal model. A specific aim of this study was to detect recently described alterations of the subchondral bone associated with cartilage repair.MethodsOsteochondral samples of medial femoral condyles from adult ewes containing full-thickness articular cartilage defects treated with marrow stimulation were obtained after 6 month in vivo and scanned in a 9.4 T μMRI. Ex vivo imaging of small osteochondral samples (typical volume: 1–2 cm3) at μMRI was optimised by variation of repetition time (TR), time echo (TE), flip angle (FA), spatial resolution and number of excitations (NEX) from standard MultiSliceMultiEcho (MSME) and three-dimensional (3D) spoiled GradientEcho (SGE) sequences.ResultsA 3D SGE sequence with the parameters: TR = 10 ms, TE = 3 ms, FA = 10 °, voxel size = 120 × 120 × 120 μm3 and NEX = 10 resulted in the best fitting for sample size, image quality, scanning time and artifacts. An isovolumetric voxel shape allowed for multiplanar reconstructions. Within the osteochondral unit articular cartilage, cartilaginous repair tissue and bone marrow could clearly be distinguished from the subchondral bone plate and subarticular spongiosa. Specific alterations of the osteochondral unit associated with cartilage repair such as persistent drill holes, subchondral bone cysts, sclerosis of the subchondral bone plate and of the subarticular spongiosa and intralesional osteophytes were precisely detected.ConclusionsHigh resolution, non-destructive ex vivo analysis of the entire osteochondral unit in a preclinical large animal model that is sufficient for further analyses is possible using μMRI at 9.4 T. In particular, 9.4 T is capable of accurately depicting alterations of the subchondral bone that are associated with osteochondral repair.
Highlights
Non-destructive structural evaluation of the osteochondral unit is challenging
The development of High-field magnetic resonance imaging (μMRI) scanners at 9.4 T allows for a detailed assessment of experimental cartilage repair, especially when dedicated transmit/receive coils for small samples are employed [18,19,20,21]
While μMRI offers a vast range of possible applications [13], higher radiofrequency (RF) energy deposition is applied resulting in warming of the samples and maintaining the field homogeneity is demanding [21,22,23,24,25,26]
Summary
The capability of high-field magnetic resonance imaging (μMRI) at 9.4 Tesla (T) was explored to examine osteochondral repair ex vivo in a preclinical large animal model. Non-destructive structural evaluation of the osteochondral repair tissue in experimental cartilage repair is challenging [1,2,3]. Goebel et al BMC Musculoskeletal Disorders (2015) 16:91 techniques In this regard, the development of novel non-invasive tools such as high-field magnetic resonance imaging (μMRI) has the potential to significantly broaden the armamentarium to precisely assess experimental osteochondral repair [9,10]. In contrast to conventional experimental methods for assessing osteochondral repair, MRI permits a non-destructive and direct evaluation of osteochondral specimen without the often time-consuming need for decalcification or other processing. A multiplanar assessment of the entire reconstructed specimen is possible
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