Faculty Bibliography

Objective: To investigate the feasibility of laxative-free bowel preparation to relieve the patient stress in colon cleansing for virtual colonoscopy. Materials and Methods: Three different bowel-preparation protocols were investigated by 60 study cases from 35 healthy male volunteers. All the protocols utilize low-residue diet for two days and differ in diet for the third day - the day just prior to image acquisition in the fourth day morning. Protocol Diet-1 utilizes fluid or liquid diet in the third day, Diet-2 utilizes a food kit, and Diet-3 remains the low-residue diet. Oral contrast of barium sulfate (2.1%, 250 ml) was added respectively to the dinner in the second day and the three meals in the third day. Two doses of MD-Gastroview (60 ml) were ingested each in the evening of the third day and in the morning before image acquisition. Images were acquired by a single-slice detector spiral CT (computed tomography) scanner with 5 mm collimation, 1 mm reconstruction, 1.5-2.0:1.0 pitch, 100- 150 mA, and 120 kVp after the colons were inflated by CO(2). The contrasted colonic residue materials were electronically removed from the CT images by specialized computer-segmentation algorithms. Results: By assumptions that the healthy young volunteers have no polyp and the image resolution is approximately 4 mm, a successful electronic cleansing is defined as '' no more than five false positives and no removal of a colon fold part greater than 4 mm '' for each study case. The successful rate is 100% for protocol Diet-1, 77% for Diet-2 and 57% for Diet-3. Conclusion: A laxative-free bowel preparation is feasible for virtual colonoscopy.

Objective: To investigate a less stressful bowel preparation for polyp screening by virtual colonoscopy (VC) withfollow-up biopsy on the positive findings by optical colonoscopy (OC). Materials and Methods: Fifty-eight volunteers of age older than 40 -- receiving low-residue diet and laxatives of magnesium citrate, bisacodyl tablets and suppository -- were divided into three groups. In Group 1, 16 volunteers took three 40cc oral doses of MD-Gastroview with the three meals respectively, the day prior to VC procedure. In Group 11, 18 volunteers ingested barium sulfate suspension (2 % w/v, 250 cc/dose) at bedtime and in the next day morning of VC. In Group 111, 24 volunteers received 60 cc of MD-Gastroview at bedtime and in the next day morning of VC. Following colon inflation with CO(2), computer tomography (CT) abdominal images were acquired by a standard single-slice detector-band VC protocol, i.e., 5 mm collimation, 1 mm reconstruction, 1.5-2.0:1.0 pitch, 120 kVp and 100-150 mA. The CT density of the tagged residual fluid was measured. An image segmentation algorithm was applied to remove electronically the residue fluid. Results: The average fluid density was 97 HU for Group 1, 221 HU for Group 112, and 599 HU for Group Ill. These three groups' density means are significantly different (p < 0.001 one-way ANOVA). After the electronic cleansing, the % of cleansed fluid regions was 5.5 %, 16.5 % and 93.1 % (p < 0.0001 Chi square) for these groups respectively. Conclusion: A less-stressful bowel preparation with low residue diet and MD-Gastroview oral contrast is feasible for VC screening with follow-up biopsy on the positive findings by OC.

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.

The insulin-sensitizing drugs thiazolidinediones (TZDs), such as rosiglitazone, improve insulin sensitivity and also promote adipocyte differentiation in vitro. The authors hypothesized that TZDs might be beneficial to patients with HIV disease to improve insulin sensitivity and the distribution of body fat by increasing peripheral fat. The ability of rosiglitazone (8 mg/d) to improve insulin sensitivity (from hyperinsulinemic-euglycemic clamp) and to improve body fat distribution (determined from computed tomography measurements of visceral adipose tissue [VAT] and subcutaneous adipose tissue [SAT]) was determined in 8 HIV-positive patients. Before treatment, the insulin sensitivity of the patients was reduced to approximately 34% of that in control subjects. The rate of glucose disposal during a hyperinsulinemic-euglycemic clamp (Rd) was 3.8 +/-.4 (SEM) mg glucose/kg lean body mass/min compared with 11.08 +/- 1.1 (p<.001) in healthy age- and body mass index (BMI)-matched control subjects. After rosiglitazone treatment of 6 to 12 weeks, Rd increased to 5.99 +/-.9 (p=.02), an improvement of 59 +/- 22%. SAT increased by 23 +/- 10% (p=.05), and, surprisingly, VAT was decreased by 21 +/- 8% (p=.04) with a trend for increased SAT/VAT that failed to reach statistical significance. There were no significant changes in blood counts, viral loads, or CD4 counts with rosiglitazone treatment. The study demonstrates that rosiglitazone therapy improves insulin resistance and body fat distribution in some patients with HIV disease.

We present the case of a 30-year-old man who developed a small bowel obstruction from an acute midgut volvulus 8 days after undergoing a laparoscopic appendectomy. There was no evidence of congenital malrotation or midgut volvulus on the initial computed tomography (CT) scan or at laparoscopy. Subsequently, a midgut volvulus developed in the absence of congenital malrotation.

We have developed a method that automatically displays, places in sized order and allows viewing of the areas of the colon surface not visualized during initial endoscopic navigational viewing. While complete surface visualization is possible, we demonstrate that all of these "missed patches" do not have to be reviewed to detect clinically significant colon polyps. CT scans are performed on 147 patients and volunteers after bowel preparation and colon distention with CO2. After automatic segmentation and electronic cleansing of the colon lumen, the medial axis (centerline) is extracted. Volume rendering fly-through alone, the centerline is performed and visualized surfaces are marked. To simulate optical colonoscopy, the virtual camera is passed in the antegrade direction. For virtual colonoscopy, the camera is passed both antegrade and retrograde, and the combined visible surface voxel count is recorded. After both fly-throughs, the total visualized surface is recorded and all "patches" of connected surface area not yet seen are identified, measured, sorted by size, and counted. Clinically significant patches, defined as smallest diameter being > 5mm, are sequentially visualized by stepping through the sorted list until reaching the patch diameter of 5 mm. for each. By enabling endoscopic navigation in both antegrade and retrograde directions, virtual colonoscopy is able to evaluate behind haustral folds and around sharp bends, thereby visualizing significantly more surface area than optical colonoscopy. Furthermore, automatic marking of the visualized surface area and identifying and viewing unseen patches allows examination of all clinically significant surfaces of the colon.

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.

The first important step in pre-processing data for 3D virtual colonoscopy requires careful segmentation of a complicated shaped colon. We describe all automatic colon segmentation method with a new patient-friendly bowel preparation scheme. This new bowel preparation makes the segmentation more appropriate for digitally removing undesirable remains in the colon. With the aim of segmenting the colon accurately, we propose two techniques which can solve the partial-volume-effect (PVE) problem on the boundaries between low and high intensity regions. Based on the features of the adverse PVE voxels on the gas and fluid boundary inside the colon, our vertical filter climinates these PVE voxels. By seriously considering the PVE on the colon boundary. our gradient-magnitude-based region growing algorithm improves the accuracy of the boundary. The result of the automatic colon segmentation method is illustrated with both extracted 2D images from the experimental volumetric abdominal CT datasets and a reconstructed 3D colon model.

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.

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.