Dynamic MR imaging of a minipig's knee using a high-density multi-channel receive array and a movement device.

OBJECT: To construct an optimised, high-density receive array and a movement device to achieve dynamic imaging of the knee in orthopedic large animal models (e.g., minipigs) at 1.5 T. MATERIALS AND METHODS: A 13-channel RF receive array was constructed, and the crucial choice of the array element size (based on considerations like region of interest, geometry of the minipig's knee, achievable signal-to-noise ratio, applicability of parallel imaging, etc.) was determined using the Q factors of loops with different sizes. A special movement device was constructed to guide and produce a reproducible motion of the minipig's knee during acquisition. RESULTS: The constructed array was electrically characterised and the reproducibility of the cyclic motion was validated. Snapshots of dynamic in vivo images taken at a temporal resolution (308 ms) are presented. Some of the fine internal structures within the minipig's knee, like cruciate ligaments, are traced in the snapshots. CONCLUSION: This study is a step towards making dynamic imaging which can give additional information about joint injuries when static MRI is not able to give sufficient information, a routine clinical application. There, the combination of a high-density receive array and a movement device will be highly helpful in the diagnosis and therapy monitoring of knee injuries in the future.

Specific identification of iron oxide-labeled stem cells using magnetic field hyperthermia and MR thermometry.

Cell-based therapies represent important novel strategies for the improved treatment of various diseases. To monitor the progress of therapy and cell migration, noninvasive imaging methods are needed. MRI represents such a modality, allowing, for example, for the tracking of cells labeled with superparamagnetic iron oxide nanoparticles. Unfortunately, the labeled cells cannot always be identified nonambiguously in the MR images. In this article, we present the combination of two different types of MR experiment to identify iron oxide-labeled cells nonambiguously. The labeled cells appear as hypointense spots on standard T(2)*-weighted MR images. Furthermore, they can be heated magnetically and subsequently identified by MR thermometry as a result of their heat dissipation. Other hypointense regions in the MR images are not heated and do not show heat dissipation. A proof-of-principle study was successfully performed in vitro and in vivo. The positive identification of the iron oxide-labeled cells was demonstrated in collagen type I hydrogel phantoms and in living mice with high spatial and temporal accuracy. The motion of the in vitro samples was corrected in order to improve the specificity of the identification of labeled cells. Therefore, this method possesses the potential for cell tracking without prior knowledge about the cells, and thus allows the noninvasive monitoring of cell-based therapies, as long as the cells contain a sufficient amount of iron oxide for detection in MR thermometry and imaging.

BMP12 and BMP13 gene transfer induce ligamentogenic differentiation in mesenchymal progenitor and anterior cruciate ligament cells.

BACKGROUND AIMS: To date there are only very few data available on the ligamentogenic differentiation capacity of mesenchymal stromal/progenitor cells (MSC) and anterior cruciate ligament (ACL) fibroblasts. METHODS: We describe the in vitro potential of MSC and ACL cells to undergo ligamentogenic differentiation upon transduction with adenoviral vectors encoding the human cDNA for bone morphogenetic protein (BMP) 12 and BMP13, also known as growth and differentiation factors (GDF) 6 and 7, respectively. RESULTS: Transgene expression for at least 14 days was confirmed by Western blot analyzes. After 21 days of cell culture within collagen type I hydrogels, histochemical (hematoxylin/eosin (H&E), Azan and van Gieson), immunohistochemical and polymerase chain reaction (PCR) analyzes of the genetically modified constructs of both cell types revealed elongated, viable fibroblast-like cells embedded in a ligament-like matrix rich in collagens, vimentin, fibronectin, decorin, elastin, scleraxis, tenascin, and tenomodulin. CONCLUSIONS: It appears that both MSC and ACL fibroblasts are capable of ligamentogenic differentiation with these factors. This information may aid in the development of biologic approaches to repair and restore ACL after injury.