Mark R. Wax

3D virtual colonoscopy

The authors present here a method called 3D virtual colonoscopy, which is an alternative method to existing procedures of imaging the mucosal surface of the colon. Using 3D reconstruction of helical CT data and volume visualization techniques, the authors generate images of the inner surface of the colon as if the viewers eyes were inside the colon. They also create interactive flythroughs and off-line automatically-produced animations through the inside of the colon. The visualization is accomplished with VolVis, which is a comprehensive system for interactive volume visualization. The authors are specifically interested in visualizing colonic polyps larger than one cm since these have a high probability of containing carcinoma. The authors present testing results of their method as applied to two plastic pipe simulations and to the Visible Human data set.

A novel approach to extract colon lumen from CT images for virtual colonoscopy

An automatic method has been developed for segmentation of abdominal computed tomography (CT) images for virtual colonoscopy obtained after a bowel preparation of a low-residue diet with ingested contrast solutions to enhance the image intensities of residual colonic materials. Removal of the enhanced materials was performed electronically by a computer algorithm. The method is a multistage approach that employs a modified self-adaptive on-line, vector quantization technique for a low-level image classification and utilizes a region-growing strategy for a high-level feature extraction. The low-level classification labels each voxel based on statistical analysis of its three-dimensional intensity vectors consisting of nearby voxels. The high-level processing extracts the labeled stool, fluid and air voxels within the colon, and eliminates bone and lung voxels which have similar image intensities as the enhanced materials and air, but are physically separated from the colon. This method was evaluated by volunteer studies based on both objective and subjective criteria. The validation demonstrated that the method has a high reproducibility and repeatability and a small error due to partial volume effect. As a result of this electronic colon cleansing, routine physical bowel cleansing prior to virtual colonoscopy may not be necessary.

Interactive volume rendering for virtual colonoscopy

3D virtual colonoscopy has recently been proposed as a non-invasive alternative procedure for the visualization of the human colon. Surface rendering is sufficient for implementing such a procedure to obtain an overview of the interior surface of the colon at interactive rendering speeds. Unfortunately, physicians can not use it to explore tissues beneath the surface to differentiate between benign and malignant structures. In this paper, we present a direct volume rendering approach based on perspective ray casting, as a supplement to the surface navigation. To accelerate the rendering speed, surface-assistant techniques are used to adapt the resampling rates by skipping the empty space inside the colon. In addition, a parallel version of the algorithm has been implemented on a shared-memory multiprocessing architecture. Experiments have been conducted on both simulation and patient data sets.

Inclusion of a priori information in segmentation of colon lumen for 3D virtual colonoscopy

Segmentation of colon lumen from computed tomography (CT) is necessary for 3D virtual colonoscopy. Identifying the residual fluid retained inside the colon after colon-cleansing procedure is one of the major tasks for the segmentation. This work developed a computer algorithm to segment out the residual fluid after the image intensity of the fluid has been enhanced by ingesting an adequate amount of contrasting solution of Diatrizoate Meglumine and Diatrizoate Sodium. The algorithm models the image-intensity statistics across the field-of-view (FOV) as a mixture of Gaussian functionals and assumes a Markov random field (MRF) for the labels of the underling tissue distribution. The model parameters of the mixture are fitted to the image data by the maximum-likelihood estimator. In the fitting, the a priori known attenuation coefficients of air (inside the colon), soft tissue (fat) and muscle are included as the initial estimate. As iteration progresses, the initial estimate is tuned to fit into the image data. The optimal number of tissue types is determined by an information criterion. With the determined number of tissue types and the fitted model parameters of the mixture, each image pixel is classified obeying the assumption of MRF across the FOV. The algorithm was tested by acquired CT abdomen images. Its performance was very encouraging. The computing efficiency was significantly improved when the histogram of the image data was used.

Image segmentation approach to extract colon lumen through colonic material tagging and hidden Markov random field model for virtual colonoscopy

Virtual colonoscopy provides a safe, minimal-invasive approach to detect colonic polyps using medical imaging and computer graphics technologies. Residual stool and fluid are problematic for optimal viewing of the colonic mucosa. Electronic cleansing techniques combining bowel preparation, oral contrast agents, and image segmentation were developed to extract the colon lumen from computed tomography (CT) images of the colon. In this paper, we present a new electronic colon cleansing technology, which employs a hidden Markov random filed (MRF) model to integrate the neighborhood information for overcoming the non-uniformity problems within the tagged stool/fluid region. Prior to obtaining CT images, the patient undergoes a bowel preparation. A statistical method for maximum a posterior probability (MAP) was developed to identify the enhanced regions of residual stool/fluid. The method utilizes a hidden MRF Gibbs model to integrate the spatial information into the Expectation Maximization (EM) model-fitting MAP algorithm. The algorithm estimates the model parameters and segments the voxels iteratively in an interleaved manner, converging to a solution where the model parameters and voxel labels are stabilized within a specified criterion. Experimental results are promising.

Lemierre syndrome : a complication of acute pharyngitis

Lemierre syndrome, otherwise known as postanginal sepsis or necrobacillosis, is an illness that originates as an acute pharyngitis or tonsillitis which progresses to sepsis, usually fusobacterial, due to suppurative thrombophlebitis of the internal jugular vein. Septic thromboemboli then seed various organs, resulting in multiple organ system pathology, most commonly affecting pulmonary and hepatic systems and joints. Although rare in the age of antibiotics, this disease typically affects previously healthy adolescents with varied clinical manifestations depending upon organ system involvement (A. Lemierre, Lancet March (1936) 701-703; J. Barker, H.T. Winer-Muram, S. Grey, Southern Med. J. 89 (1996) 1021-1023). Prompt diagnosis based on clinical presentation, radiologic findings, particularly CT scanning with contrast and a high index of suspicion, is necessary in order to institute often life saving therapy (J. Barker, H.T. Winer-Muram, S. Grey, Southern Med. J. 89 (1996) 1021-1023). We will present two cases of Lemierre syndrome, review its clinical presentation, anatomic considerations, particularly its relationship to the parapharyngeal space, radiographic findings, potential life threatening complications and finally, a unique approach to therapy.

Segmentation of colon lumen for virtual colonoscopy

Residual stool and fluid and wall collapses are problematic for virtual colonoscopy. Electronic colon cleansing techniques combining both bowel preparation and image processing were developed to segment the colon lumen from the abdominal computed tomographic (CT) images. This paper describes our bowel preparation and image segmentation techniques and presents some preliminary results. A feasibility study using magnetic resonance imaging (MRI) is also reported.

Interactive electronic biopsy for 3D virtual colonscopy

We propose an interactive electronic biopsy technique for more accurate colon cancer diagnoses by using advanced volume rendering technologies. The volume rendering technique defines a transfer function to map different ranges of sample values of the original volume data to different colors and opacities, so that the interior structure of the polyps can be clearly recognized by human eyes. Specifically, we provide a user- friendly interface for physicians to modify various parameters in the transfer function, so that the physician can interactively change the transfer function to observe the interior structures inside the abnormalities. Furthermore, to speed up the volume rendering procedure, we propose an efficient space-leaping technique by observing that the virtual camera parameters are often fixed when the physician modifies the transfer function. In addition, we provide an important tool to display the original 2D CT image at the current 3D camera position, so that the physician is able to double check the interior structure of a polyp with the density variation in the corresponding CT image for confirmation. Compared with the traditional biopsy in the procedure of optical colonoscopy, our method is more flexible, noninvasive, and therefore without risk.

Robust colon residue detection using vector-quantization-based classification for virtual colonoscopy

We present an automatic and robust tagged-residue detection technique using vector quantization based classification. This technique enables electronic cleansing even on poorly tagged datasets, leading to more effective virtual colonoscopy. In order to reduce the sensitivity towards intensity variation among the tagged residual material, we use a multi-step technique. First, we apply classification using an unsupervised and self-adapting vector quantization algorithm. Then, we sort the resultant classes by their average intensities. We apply thresholding on these classes based on a conservative threshold. This helps us in differentiating soft tissue inside tagged material from poorly tagged region or noise.

Interactive navigation for PC-based virtual colonscopy

Virtual colonoscopy on powerful workstations has the distinct advantage of interactive navigation, as opposed to passive viewing of cine loops or pre-computed movies. Because of the prohibitive cost of hardware, only passive displays have been feasible for the wide-scale deployment required for mass screening. The purpose of our work is to compare low-cost commodity hardware as an effective tool for interactive colonographic navigation versus the expensive workstations.