Molar axis estimation from computed tomography images.

Estimation of tooth axis is needed for some clinical dental treatment. Existing methods require to segment the tooth volume from Computed Tomography (CT) images, and then estimate the axis from the tooth volume. However, they may fail during estimating molar axis due to that the tooth segmentation from CT images is challenging and current segmentation methods may get poor segmentation results especially for these molars with angle which will result in the failure of axis estimation. To resolve this problem, this paper proposes a new method for molar axis estimation from CT images. The key innovation point is that: instead of estimating the 3D axis of each molar from the segmented volume, the method estimates the 3D axis from two projection images. The method includes three steps. (1) The 3D images of each molar are projected to two 2D image planes. (2) The molar contour are segmented and the contour's 2D axis are extracted in each 2D projection image. Principal Component Analysis (PCA) and a modified symmetry axis detection algorithm are employed to extract the 2D axis from the segmented molar contour. (3) A 3D molar axis is obtained by combining the two 2D axes. Experimental results verified that the proposed method was effective to estimate the axis of molar from CT images.

MRI findings and correlative study of MRI and visual evoked potentials in optic neuritis / 中华放射学杂志

Objective To investigate the effective MRI sequences and describe the correlation between MRI and visual evoked potential(VEP)in diagnosing optic neuritis.Methods One hundred and fifty-four eyes with visual impairment of 98 patients with diagnoses of optic neuritis,papillitis,multiple sclerosis and Devic's disease underwent MRI and VEP examination. The MRI findings were analyzed and correlated with VEP results and clinical presentation by using x2 test,wilcoxon test and Kappa test.Results Out of the 154 sick eyes.56 eyes presented thickened optic nerves.76 eyes had normal diameter of the optic nerve,and 22 eyes had thin optic nerves.A total of 132 optic nerves showed abnormally high signal in STIR sequences.including involvement of intraocular segment in 7,intraorbitsl segment in 135,intracanalicular segment in 109,intracranial segment in 97,optic chiasm in 56,and optic tract in 23.A total of 54 patients underwent postcontrast MRI. Seventy-four optic nerves of 87 eyes showed enhancement.Among the 196 eyes of 98 patients,132 eyes presented visual impairment and simultaneous abnormal MR signal of the optic nerve.and 26 eyes had both normal vision and normal MR signal of optic nerve.The consistency of MRI findings and vision status was 80.61%(Kappa=0.453,P＜0.01).Among the 175 eyes with VEP results.129 eyes had visual loss with simultaneous VEP abnormalities,and 30 eyes had both normal vision and normal VEP results.The consistency of VEP and vision status was 90.86%(Kappa=0.731,P＜0.01).Among the 175 eyes with VEP results,117 eyes had abnormal MR signal of the optic nerve and simultaneous abnormal VEP,and 24 eyes had both normal MR signal of the optic nerve and normal VEP.The consistency of MRI findings and VEP was 80.57%(Kappa=0.460,P＜0.01).Conclusion STIR sequence and gadolinium-enhanced T1-weighted MR sequence combined with fatsuppression are helpful in diagnosis of optic neuritis.VEP is helpful in diagnosing optic neuritis and in finding subclinical visual problem.The MRI combined with VEP could improve the diagnostic accuracy of optic neuritis.