ABSTRACT
BACKGROUND: Finite element models (FEMs) of medical images can provide information about the underlying tissue that cannot be obtained from the original images. Preforming an accurate simulation requires the careful experimental calibration of boundary conditions. Here we describe a method for deriving a geometric mesh for soft biological materials using a magnetic resonance imaging (MRI) system, and an experimental workflow for calibrating the boundary conditions and optimizing the mesh density in these simulations. METHODS: A three-dimensional image stack of a ballistic sphere gel, a bovine caudal intervertebral disc (IVD), and a human lumbar IVD were generated using a positional MRI system. These images were then segmented using a semi-automated process, converted to a tetrahedral mesh, and then modeled as a linear elastic solid. The mesh density was optimized based on simulation time and convergence with the experimental results. The modulus of the ballistic gel was determined experimentally, while the material properties for the nucleus pulposus (NP) and the annulus fibrosus (AF) within the bovine and human IVDs were assigned from literature. The simulation for the spherical gel and the bovine IVD matched the reaction forces determined experimentally in compression. We then simulated a 0.3 MPa compressive load on the human lumbar IVD at the optimal mesh density and material properties determined from the bovine model and then examined the resultant internal strains. RESULTS: The scaled mesh density demonstrated excellent correspondence with the experimental results, confirming that accuracy was not compromised. Both the ballistic gel and the IVD samples exhibited a wide range of internal strains. The NP of the IVD underwent greater deformation than the AF under loading. CONCLUSIONS: This study validated a strategy for mesh optimization and FEM of soft biological materials from data generated from MRI scans. This calibrated approach allows for the rapid examination of internal strain distributions medical images that can be performed on the order of minutes.
ABSTRACT
The supergiant VX Sagittarii is a strong emitter of both H2O and SiO masers. However, previous VLBI observations have been performed separately, which makes it difficult to spatially trace the outward transfer of the material consecutively. Here we present the astrometrically registered, simultaneous maps of 22.2 GHz H2O and 43.1/42.8/86.2/129.3 GHz SiO masers toward VX Sagittarii. The H2O masers detected above the dust-forming layers have an asymmetric distribution. The multi-transition SiO masers are nearly circular ring, suggesting spherically symmetric wind within a few stellar radii. These results provide the clear evidence that the asymmetry in the outflow is enhanced after the smaller molecular gas clump transform into the inhomogeneous dust layers. The 129.3 GHz maser arises from the outermost region compared to that of 43.1/42.8/86.2 GHz SiO masers. The ring size of the 129.3 GHz maser is maximized around the optical maximum, suggesting that radiative pumping is dominant.
ABSTRACT
Giant cell tumor (GCT) is a relatively rare neoplasm. In GCT, the bone affection of the axial skeleton is extremely rare. Most GCT arises in the meta-epiphyseal ends of the long bones. Its peak incidence is between 30 to 40 years of age. GCT is usually classified as benign, but shows locally aggressive behavior and may occasionally undergo a malignant transformation. The patients with GCT in the spine often complain of the lower back pains, as the tumors primarily involve the sacrum. We report a case of an adolescent female complaining of the upper back pain with a sudden weakness of the lower extremities, later diagnosed with the GCT of the T2 vertebra. The present patient showed American Spinal Injury Association Impairment Scale (AIS) D before the surgery, which changed to AIS E after the treatments including the surgery, radiation therapy and rehabilitation.
