Detection of maturity and ligament injury using magic angle directional imaging

Abstract

Purpose:To investigate whether magnetic field-related anisotropies of collagen may be correlated with postmortem findings in animal models. Methods: Optimized scan planning and new MRI data-processing methods were proposed and analyzed using Monte Carlo simulations. Six caprine and 10 canine knees were scanned at various orientations to the main magnetic field. Image intensities in segmented voxels were used to compute the orientation vectors of the collagen fibers. Vector field and tractography plots were computed. The Alignment Index was defined as a measure of orientation distribution. The knees were subsequently assessed by a specialist orthopedic veterinarian, who gave a pathological diagnosis after having dissected and photographed the joints. Results: Using 50% less scans than reported previously can lead to robust calculation of fiber orientations in the presence of noise, with much higher accuracy. The 6 caprine knees were found to range from very immature (< 3 months) to very mature (> 3 years). Mature specimens exhibited significantly more aligned collagen fibers in their patella tendons compared with the immature ones. In 2 of the 10 canine knees scanned, partial cranial caudal ligament tears were identified from MRI and subsequently confirmed with encouragingly high consistency of tractography, Alignment Index, and dissection results. Conclusion: This method can be used to detect injury such as partial ligament tears, and to visualize maturity-related changes in the collagen structure of tendons. It can provide the basis for new, noninvasive diagnostic tools in combination with new scanner configurations that allow less-restricted field orientations. K E Y W O R D Scollagen, magic angle effect, musculoskeletal imaging

Moving Beyond the Limits of Detection: The Past, the Present, and the Future of Diagnostic Imaging in Canine Osteoarthritis

“…The hope is that these “pre-OA” biomarkers represent the ever-elusive biomarkers of early disease prior to irreversible joint demise, and will fuel development of interventions which are able to reverse OA progression. A further emerging area with MRI imaging, is using magic angle directional imaging to identify the dominant collagen fiber orientation ( 126 ). This application of MRI allows mapping of collagen bundles within soft-tissues which could provide other indicators of the structural derangements occurring in the cartilage ( Figure 11 ).…”