SU-E-J-101: Weighted Voting Method for Multi-Atlas Segmentation in CT Scans

PURPOSE

We investigate automating the task of segmenting structures in head and neck CT scans, to minimize time spent manually contouring. We focus on the brainstem and left and right parotids.

METHODS

To generate contours for an unlabeled image, we assume an atlas of labeled 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 targetimage. Our weighted voting method acts one structure at a time to determine for each voxel whether or not it exists in a structure. The weight for a voxel's vote from each atlas depends on the intensity difference of the target and the transformed atlas at that voxel, in addition to the distance of that voxel from the boundary of the structure.

RESULTS

We applied our method to sixteen labeled images, generating automatic segmentations foreach using the other fifteen images as the atlas. We compared the resulting Dice and Hausdorff metrics with a majority voting method using the same registrations and saw remarkable improvement. Mean Dice scores were around .7, with maximum Hausdorff of about 15mm, and mean Hausdorffs around 2 or 3mm.

CONCLUSIONS

Our method produces contours with boundaries usually only a few millimeters away from the manual contour, which could save physicians considerable time, because they only have to make small modifications to each slice instead of contouring from scratch.

Factors affecting outcome after traumatic limb amputation

BACKGROUND

Traumatic leg amputation commonly affects young, active people and leads to poor long-term outcomes. The aim of this review was to describe common causes of disability and highlight therapeutic interventions that may optimize outcome after traumatic leg amputation.

METHODS

A comprehensive search of MEDLINE, Embase and Cumulative Index to Nursing and Allied Health Literature databases was performed, using the terms 'leg injury', 'amputation' and 'outcome'. Articles reporting outcomes following traumatic leg amputation were included.

RESULTS

Studies demonstrated that pain, psychological illness, decreased physical and vocational function, and increased cardiovascular morbidity and mortality were common causes of disability after traumatic leg amputation. The evidence highlights that appropriate preoperative management and operative techniques, in conjunction with suitable rehabilitation and postoperative follow-up, can lead to improved treatment outcome and patient satisfaction.

CONCLUSION

Patients who undergo leg amputation after trauma are at risk of poor long-term physical and mental health. Clinicians involved in their care have many opportunities to improve their outcome using a variety of therapeutic variables. Copyright © 2011 British Journal of Surgery Society Ltd. Published by John Wiley & Sons, Ltd.

A fast double template convolution isocenter evaluation algorithm with subpixel accuracy

PURPOSE

To design a fast Winston Lutz (fWL) algorithm for accurate analysis of radiation isocenter from images without edge detection or center of mass calculations.

METHODS

An algorithm has been developed to implement the Winston Lutz test for mechanical/ radiation isocenter agreement using an electronic portal imaging device (EPID). The algorithm detects the position of the radiation shadow of a tungsten ball within a stereotactic cone. The fWL algorithm employs a double convolution to independently find the position of the sphere and cone centers. Subpixel estimation is used to achieve high accuracy. Results of the algorithm were compared to (1) a human observer with template guidance and (2) an edge detection/center of mass (edCOM) algorithm. Testing was performed with high resolution (0.05 mm/px, film) and low resolution (0.78 mm/px, EPID) image sets.

RESULTS

Sphere and cone center relative positions were calculated with the fWL algorithm for high resolution test images with an accuracy of 0.002 +/- 0.061 mm compared to 0.042 +/- 0.294 mm for the human observer, and 0.003 +/- 0.038 mm for the edCOM algorithm. The fWL algorithm required 0.01 s per image compared to 5 s for the edCOM algorithm and 20 s for the human observer. For lower resolution images the fWL algorithm localized the centers with an accuracy of 0.083 +/- 0.12 mm compared to 0.03 +/- 0.5514 mm for the edCOM algorithm.

CONCLUSIONS

A fast (subsecond) subpixel algorithm has been developed that can accurately determine the center locations of the ball and cone in Winston Lutz test images without edge detection or COM calculations.

International collaborative study to establish reference preparations to standardise haemagglutination testing for anti-A and anti-B in normal intravenous immunoglobulins by the direct method

A joint project (coded BSP089) was run by the European Directorate for the Quality of Medicines & HealthCare (EDQM) of the Council of Europe, the National Institute for Biological Standards and Control (NIBSC) on behalf of the World Health Organization (WHO) and the Center for Biologics Evaluation and Research (CBER) of the U.S. Food and Drug Administration (FDA) to evaluate, in an international collaborative study, 3 lyophilised intravenous immunoglobulin (IVIG) preparations for their suitability to serve as Reference Preparations to standardise and control the highly variable haemagglutination testing for anti-A and anti-B in IVIG products. 23 laboratories tested candidate IVIG reference preparations consisting of a Positive control, a Negative control and a specifically formulated Limit test reference preparation to define the maximum (e.g., pharmacopoeial) limits of anti-A and anti-B haemagglutinins in IVIG products, where limits are applicable. Laboratories performed direct haemagglutination using papain-treated erythrocytes and/or indirect anti-globulin tests. For both methods, there was up to 16-fold variation in anti-A and anti-B titres, although there was good agreement over a 2-fold titre range for anti-A and anti-B between laboratories using the direct method for both the Positive control and Limit reference preparations. Comparative titration data for the Positive control and Limit reference preparations indicated that the use of a 'Limit' test reference preparation would facilitate identification of higher titre batches when the direct haemagglutination method is used. The Positive control, Negative control and Limit test preparations were adopted in November 2008 by the Commission of the European Pharmacopoeia (Ph. Eur.) as Biological Reference Preparations. The same preparations have been established as reference reagents by the WHO and the U.S FDA, including the maximal specifications defined by the Limit test preparation. This will facilitate global standardisation of haemagglutination tests for anti-A and anti-B, ensure that such tests are sufficiently sensitive and specific, and facilitate identification of batches that exceed maximum recommended levels of anti-A and anti-B antibodies.