Tobias Bergen

Segmentation of leukocytes and erythrocytes in blood smear images

Differential blood count is a standard method in hematological laboratory diagnosis. In the course of developing a computer-assisted microscopy system for the generation of differential blood counts, the detection and segmentation of white and red blood cells forms an essential step and its exactness is a fundamental prerequisite for the effectiveness of the subsequent classification step. We propose a method for the exact segmentation of leukocytes and erythrocytes in a simultaneous and cooperative way. We combine pixel-wise classification with template matching to locate erythrocytes and use a level-set approach in order to get the exact cell contours of leukocyte nucleus and plasma regions as well as erythrocyte regions. An evaluation comparing the performance of the algorithm to the manual segmentation performed by several persons yielded good results.

Stitching and Surface Reconstruction From Endoscopic Image Sequences: A Review of Applications and Methods

Endoscopic procedures form part of routine clinical practice for minimally invasive examinations and interventions. While they are beneficial for the patient, reducing surgical trauma and making convalescence times shorter, they make orientation and manipulation more challenging for the physician, due to the limited field of view through the endoscope. However, this drawback can be reduced by means of medical image processing and computer vision, using image stitching and surface reconstruction methods to expand the field of view. This paper provides a comprehensive overview of the current state of the art in endoscopic image stitching and surface reconstruction. The literature in the relevant fields of application and algorithmic approaches is surveyed. The technological maturity of the methods and current challenges and trends are analyzed.

Feature-based real-time endoscopic mosaicking

In the field of minimally invasive surgery one barrier in clinical practice is the limited field of view provided by endoscopic cameras. We propose an image mosaicking approach to extend the field of view for real-time visualization by stitching several video frames. The approach is based on feature tracking and a robust estimation of the image-to-image transformations. We compare its performance to that of a state-of-the-art approach. Our method shows superior accuracy at frame rates of 6.8 to 8.1 frames per second, which allows for real-time visualization of the extended field of view.

Efficient large scale image stitching for virtual microscopy

We describe a weighted least squares based global registration method for creating virtual slides. In microscopy a large number of fields of view is required to capture a complete slide. These fields of view are aligned in such a way that a globally consistent virtual slide is formed. The positioning accuracy of the presented algorithm is evaluated using a new method based on synthetic virtual slides. Using these synthetic virtual slides it is now possible to give a ground truth about the positioning accuracy of stitching algorithm for virtual microscopy. Our algorithm has been evaluated on these synthetic slides and it can be shown that on average, each image exhibits a mean deviation of 0.8 pixel with respect to the correct position. Additionally the presented algorithm has been evaluated on several real world examples.

A graph-based approach for local and global panorama imaging in cystoscopy

Inspection of the urinary bladder with an endoscope (cystoscope) is the usual procedure for early detection of bladder cancer. The very limited field of view provided by the endoscope makes it challenging to ensure, that the interior bladder wall has been examined completely. Panorama imaging techniques can be used to assist the surgeon and provide a larger view field. Different approaches have been proposed, but generating a panorama image of the entire bladder from real patient data is still a challenging research topic. We propose a graph-based and hierarchical approach to assess this problem to first generate several local panorama images, followed by a global textured three-dimensional reconstruction of the organ. In this contribution, we address details of the first level of the approach including a graph-based algorithm to deal with the challenging condition of in-vivo data. This graph strategy gives rise to a robust relocalization strategy in case of tracking failure, an effective keyframe selection process as well as the concept of building locally optimized sub-maps, which lay the ground for a global optimization process. Our results show the successful application of the method to four in-vivo data sets.

Digital Mapping of the Urinary Bladder: Potential for Standardized Cystoscopy Reports

OBJECTIVE To develop a standardized digital reporting tool for cystoscopy of the urinary bladder using panoramic imaging. MATERIALS AND METHODS An image processing and stitching software (Endorama) was developed to generate panoramic images from cystoscopy data. In a processing phase, algorithms were modulated and refined by reference to cystoscopy sequences (n = 30). Subsequently, standard systematic cystoscopies (n = 12) were recorded in patients undergoing transurethral resection of a bladder tumor to create panoramic images. RESULTS All sequences were applicable for the development and refinements of the software. Processing increasingly allowed the creation of images illustrating large parts of the bladder and relevant anatomic landmarks in different locations. The pathway covered by the endoscope during the intervention was illustrated as a route in the respective digital image. During the application phase, panoramic images were successfully created in 10 out of 12 cases. The resolution of the images was 4096 × 2048 pixels and the images required a median digital memory of 3.9 MB (3.4-5.7). The panoramic images illustrated 22 relevant findings of which 7 were papillary tumors. CONCLUSION High-quality digital panoramic maps of the urinary bladder were created using specifically processed data of videocystoscopy. In this preliminary series, relevant findings were illustrated in the respective image. Our tool may help improve standardization of cystoscopy reports and reduce interobserver variability.

Laryngoscopic Image Stitching for View Enhancement and Documentation – First Experiences

One known problem within laryngoscopy is the spatially limited view onto the hypopharynx and the larynx through the endoscope. To examine the complete larynx and hypopharynx, the laryngoscope can be rotated about its main axis, and hence the physician obtains a complete view. If such examinations are captured using endoscopic video, the examination can be reviewed in detail at a later time. Nevertheless, in order to document the examination with a single representative image, a panorama image can be computed for archiving and enhanced documentation. Twenty patients with various clinical findings were examined with a 70 rigid laryngoscope, and the video sequences were digitally stored. The image sequence for each patient was then post-processed using an image stitching tool based on SIFT features, the RANSAC approach and blending. As a result, endoscopic panorama images of the larynx and pharynx were obtained for each video sequence. The proposed approach of image stitching for laryngoscopic video sequences offers a new tool for enhanced visual examination and documentation of morphologic characteristics of the larynx and the hypopharynx.

Shading correction for endoscopic images using principal color components.

PurposeInhomogeneous illumination often causes significant shading and vignetting effects in images captured by an endoscope. Most of the established shading correction methods are designed for gray-level images. Only few papers have been published about how to compensate for shading in color images. For endoscopic images with a distinct red coloring, these methods tend to produce color artifacts.MethodA color shading correction algorithm for endoscopic images is proposed. Principal component analysis is used to calculate an appropriate estimate of the shading effect so that a one-channel shading correction can be applied without producing undesired artifacts.ResultsThe proposed method is compared to established YUV and HSV color-conversion-based approaches. It produces superior results both on simulated and on real endoscopic images. Example images of using the proposed shading correction for endoscopic image mosaicking are presented.ConclusionA new method for shading correction is presented which is tailored to images with distinct coloring. It is beneficial for the visual impression and further image analysis tasks.

HemaCAM – A Computer Assisted Microscopy System for Hematology

Cost and competition force modern hematology laboratories to further automate their processes. To that respect the examination and analysis of the peripheral blood is of central importance as it is relevant to a large variety of diseases while on the other hand financial reimbursement is low. Over the past eight years, the HemaCAM system has been developed by the Fraunhofer IIS, which supports the assessment of peripheral blood samples and the so-called white blood differential. Since 2010, HemaCAM has been available on the market as a certified medical product, to be more specific as an in vitro diagnostic device. This contribution provides an overview of the key components of the HemaCAM system.

Panorama Mapping of the Esophagus from Gastroscopic Video

For the examination and clinical assessment of the esophagus, video endoscopy is applied. Video clips and still images are generated along these procedures which are then used for routine documentation. Due to the tight tubular geometry of the esophagus and the constrained field of view of endoscope devices, the provided insight into the esophagus and the relation to contextual information are limited. In this contribution, a shape-from-shading approach for the computation of panorama images of the esophagus wall from gastroscopic video is presented. Furthermore, the content of these panorama images can be mapped back to the original video data which gives the advantages of both panorama-view for improved contextual information and unaltered detail-views for improved examinations.