Multi-atlas segmentation in head and neck CT scans

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 45-46).We investigate automating the task of segmenting structures in head and neck CT scans, to minimize time spent on manual contouring of structures of interest. We focus on the brainstem and left and right parotids. To generate contours for an unlabeled image, we employ an atlas of labeled training images. We register each of these images to the unlabeled target image, transform their structures, and then use a weighted voting method for label fusion. Our registration method starts with multi-resolution translational alignment, then applies a relatively higher resolution affine alignment. We then employ a diffeomorphic demons registration to deform each atlas to the space of the target image. Our weighted voting method considers one structure at a time to determine for each voxel whether or not it belongs to the structure. The weight for a voxel's vote from each atlas depends on the intensity difference of the target and the transformed gray scale atlas image at that voxel, in addition to the distance of that voxel from the boundary of the structure. We evaluate the method on a dataset of sixteen labeled images, generating automatic segmentations for each using the other fifteen images as the atlas. We evaluated the weighted voting method and a majority voting method by comparing the resulting segmentations to the manual segmentations using a volume overlap metric and the distances between contours. Both methods produce accurate segmentations, our method producing contours with boundaries usually only a few millimeters away from the manual contour. This could save physicians considerable time, because they only have to make small modifications to the outline instead of contouring the entire structure.by Amelia M. Arbisser.M.Eng

Intraoperative fracture of phacoemulsification sleeve

<p>Abstract</p> <p>Background</p> <p>We describe a case of intraoperative fracture of phacoemulsification sleeve during phacoemulsification surgery.</p> <p>Case presentation</p> <p>Phacoemulsification surgery was performed in the left eye of a 58-year-old lady with grade II nuclear sclerosis & grade I cortical cataract. Towards the end of quadrant removal, there was anterior chamber instability with impaired followability of nuclear fragments. The distal part of the fractured sleeve remained inside the anterior chamber upon removal of the phacoemulsification probe. The retained sleeve was retrieved with a pair of forceps through the corneal incision site, which did not require widening. There was no missing fragments retained intraocularly and the patient had an uneventful recovery with vision of 20/25 at three months post-operatively.</p> <p>Conclusion</p> <p>Phacoemulsification sleeve fracture is an uncommon complication. With early identification of this condition and proper management, major complications can be avoided.</p

Do variations in the theatre team have an impact on the incidence of complications?

BACKGROUND: To examine whether variations in non-medical personnel influence the incidence of complications in a cataract theatre. METHODS: A retrospective Case-Control study was undertaken in a single-site, designated cataract theatre. Staffing variations within theatre were examined and the incidence of cataract complications was assessed. RESULTS: 100 complicated lists and 200 uncomplicated control lists were chosen. At least 7 nurses were present for every list. Mean experience of the nurses was 6.4 years for case lists and 6.5 years for control lists. Average scrub nurse experience in years was 7.6 years for complicated lists and 8.0 years for controls. 26% of complicated case lists were affected by unplanned leave and 17% in control lists. Odds ratio 1.7 (1.0 to 3.1) 95% CI. CONCLUSION: Unplanned leave can have a detrimental effect on the operating list. The impact of this may be modifiable with careful planning