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Dirk Hartmann

Publications and source records attributed to Dirk Hartmann.

14 recordsLinked to original sources
PubMed2006

Computer-assisted colonoscopy (the NeoGuide Endoscopy System): results of the first human clinical trial ("PACE study").

OBJECTIVES: Unsedated colonoscopy is an uncomfortable procedure for most patients. Discomfort during colonoscopy is largely related to looping of the colonoscope, which displaces the colon from its native configuration and stretches attachments to the mesentery. A novel computer-assisted colonoscope utilizes a fully articulated, computer-controlled insertion tube. On manual insertion of the colonoscope, the position and angle of the scope's tip are encoded into a computer algorithm. As the colonoscope is advanced, the computer directs each successive segment to take the same shape that the tip had at a given insertion depth. The insertion tube thus changes its shape at different insertion depths in a "follow-the-leader" manner. METHODS: This initial clinical trial with this novel colonoscopy system was designed as a prospective, nonrandomized, unblinded, feasibility study. Three physicians of varying levels of experience participated in the study. RESULTS: Eleven consecutive patients (seven men, four women, age range 19-80) meeting inclusion criteria for screening or diagnostic colonoscopy were enrolled in the study. The cecum was reached in 10 consecutive patients (100%). Findings included diverticular disease in two cases and multiple colonic polyps in two cases. Postprocedure assessment at discharge, 48 h, and 30 days revealed no complications or adverse effects. Physician satisfaction and patient acceptance of this new technique were high. CONCLUSIONS: In this limited, first of its kind feasibility study, the computer-assisted colonoscope was shown to perform colonoscopy safely and effectively. The colonoscope's unique design limited loop formation during colonoscopy. Large-scale clinical trials are indicated.

Adult↗
PubMed2006

Mathematical analysis of a free-boundary model for lung branching morphogenesis.

Lung branching morphogenesis has been widely studied in the field of developmental biology. Lung airway trees consist of relatively regular-sized distal branches, but how this regular branched pattern is formed is not well understood. In the present study, we undertake a detailed mathematical analysis of the model proposed in (Hartmann & Miura (2006), which numerically captures branching morphogenesis of the simplest possible experimental system in vitro. We investigate analytically the stability of 1D travelling waves with respect to periodic perturbations in two dimensions. This linear stability analysis leads to the so-called dispersion relations, predicting that a certain representative length dominates in this model. As the analytical analysis is restricted to travelling waves, we generalize the linear analysis to any 1D solution by numerical simulations. Both results predict how the representative lengths will change by experimentally changing specific parameters. Finally, we discuss the importance of the analytical results from a biological point of view and propose an experimental scheme for a quantitative comparison between experiments and theory.

Algorithms↗
PubMed2006

Limit behaviour of spatially growing cell cultures.

Growing cell cultures often exhibit branch patterns. The cultures are usually modelled as free boundary problems. Here, we review some of these models and investigate the appearance of branch patterns using methods from asymptotic analysis. Two extreme cases--large kinetics and small kinetics--are considered. For large kinetics the models reduce to the well-studied Stefan problem, which is known to exhibit a diffusive-instability and hence shows branch patterns. Considering small kinetics, small perturbations are smoothed out resulting in regular shapes of the cultures. The branching phenomenon in general can be understood as somewhere between these two extremes. Not relying on special assumptions, the presented analysis is very general.

Animals↗
PubMed2006

Modelling in vitro lung branching morphogenesis during development.

It has been shown experimentally that lung epithelial explants have an ability to undergo branching morphogenesis without mesenchyme. However, the mechanisms of this phenomenon remain to be elucidated. In the present study, we construct a mathematical model that can reproduce the dynamics of in vitro branching morphogenesis. We show that the system is essentially governed by three variables--c(0) which is the initial fibroblast growth factor (FGF) concentration, D which is the diffusion coefficient of FGF, and beta which describes the mechanical strength of the cytoskeleton. It is confirmed by numerical simulations that this model can reproduce the experimentally obtained patterns qualitatively. Finally, we experimentally verify two predictions from the model: effects of very high FGF concentration and effects of small mechanical contributions of the cytoskeleton. The theoretical predictions match well with the experimental results.

Animals↗
PubMed2006

Diagnosis of obscure gastrointestinal bleeding by intra-operative enteroscopy in 81 consecutive patients.

AIM: To analyze the results and complications of intra-operative enteroscopy (IOE) by investigating a series of selected patients with bleeding suspected to originate from the small intestine. METHODS: Eighty-one patients (mean age: 65 years) including 40 males (49.4%) and 41 females (50.6%) with obscure gastrointestinal bleeding underwent IOE between 1990 and 2004. The patients were identified from a database and data were selected from the patients' charts retrospectively. All the patients had undergone at least one non-diagnostic esophagogastroduodenoscopy, colonoscopy, standard enteroscopy and a negative abdominal ultrasound scan before IOE. RESULTS: The median minimal hemoglobin level in the patients was 59 + 15 g/L and 72.8% of the patients required transfusion of packed erythrocytes previously. A bleeding source was detected in 68 (84%) of the patients during IOE. Angiodysplasiae were found in 44 patients (54.3%) and 9 patients (11.1%) were affected by ulcers in the small intestine. A tumor in the small intestine was detected in another 6 patients. The treatment consisted of argon-plasma-coagulation, surgical suture or limited resection in most of the patients. CONCLUSION: Intra-operative enteroscopy is still used for the diagnosis of suspected small bowel bleeding. Recent developments such as wireless capsule endoscopy and double balloon enteroscopy, may lead to the replacement of IOE in the future.

Adult↗
PubMed2006

Risk factors for symptomatic stone recurrence after transpapillary laser lithotripsy for difficult bile duct stones using a laser with a stone recognition system.

BACKGROUND: Laser-induced shock-wave lithotripsy (LISL) is successfully used for the treatment of difficult bile duct stones. The aim of this study was to assess the long-term risk for a symptomatic bile duct stone recurrence after LISL and to detect risk factors predicting recurrence. METHODS: Between 1993 and 2001, 80 patients with difficult bile duct stones were successfully treated by intracorporeal LISL through the papilla of Vater. Seventy-one of these patients [median age, 65.8 years; 51 women (71.8%)] were followed for a median (range) period of 58 (1-114) months. RESULTS: Eleven patients (15.5%) had a symptomatic stone recurrence. The median (range) period between laser lithotripsy and recurrence was 40 (5-85) months. The presence of a bile duct stenosis (P=0.032) and a body-mass index below 25 (P=0.025) were significantly associated with an increased risk for stone recurrence. A gallbladder in situ, the presence of gallbladder stones, dilation of the bile duct, or a peripapillary diverticulum was not associated with stone recurrence. CONCLUSIONS: The presence of a bile duct stenosis is significantly related to bile duct stone recurrence after treatment with LISL. The impact of the body mass index on stone recurrence is interesting. The gallbladder status did not predict stone recurrence in our study.

Aged↗
PubMed2005

Colorectal polyps: detection with dark-lumen MR colonography versus conventional colonoscopy.

PURPOSE: To prospectively compare dark-lumen magnetic resonance (MR) colonography with conventional colonoscopy in the detection of colorectal polyps. MATERIALS AND METHODS: Local ethical committee approval and informed consent were obtained. One hundred consecutive patients (56 men, 44 women; mean age +/- standard deviation, 67.7 years +/- 14.7; range, 25-82 years) who were referred for conventional colonoscopy from January 2003 to January 2004 underwent MR colonography and conventional colonoscopy after standard precolonoscopic bowel cleansing. Colonoscopy was performed immediately after MR colonography. For MR colonography, the colon was filled with approximately 2000 mL of tap water. Imaging was performed with a 1.5-T MR unit with patients in the prone position. A T1-weighted three-dimensional volumetric interpolated breath-hold sequence was performed before and 75 seconds after intravenous administration of 0.2 mmol gadobenate dimeglumine per kilogram of body weight. Results of MR colonography were analyzed on a per-polyp and per-patient basis. Findings at colonoscopy were used as the reference for determining accuracy, sensitivity, specificity, and positive and negative predictive values of MR colonography. RESULTS: Of 100 patients recruited for study, 92 (52 men, 40 women; mean age, 61.5 years +/- 14.5; range, 25-82 years) underwent complete MR and conventional colonoscopy examinations. Forty-three of the 92 patients (47%) had normal findings at conventional colonoscopy. In the other 49 patients (53%), conventional colonoscopy depicted 107 polyps (82 adenomas, 25 hyperplastic polyps) and seven carcinomas. At per-polyp analysis, sensitivity of MR colonography in the detection of adenomatous polyps was 100% for polyps at least 10 mm in diameter and 84.2% for polyps 6-9 mm in diameter. At per-patient analysis, the accuracy of MR colonography was 93.1% (sensitivity, 89%; specificity, 96%) if detection of adenomatous polyps of all sizes was considered. CONCLUSION: Dark-lumen MR colonography is a promising modality with high accuracy for detecting colorectal polyps larger than 5 mm in diameter.

Adult↗
PubMed2005

[MRI in gastrointestinal diseases].

Magnetic resonance imaging (MRI) has been called the most important development in medical diagnosis since the discovery of the X-ray more than 100 years ago. The effectiveness of MRI has been expanded to a variety of gastrointestinal disorders. The gastroenterologist's attention is currently focused on biliopancreatic and bowel diseases. Magnetic resonance cholangiopancreatography (MRCP) has become a competitive replacement for diagnostic endoscopic retrograde cholangiopancreatography (ERCP) in a variety of hepatobiliary and pancreatic diseases. MR enteroscopy has the potential to become the preferred method for evaluating the entire small bowel, while on the other hand virtual colonoscopy is far from being promoted as a tool for general screening purposes in suspected colon diseases. In summary, whether or not the survival of endoscopy is under debate, MRI could mark a historic turning point in gastroenterology. So, MRI hardware might interdisciplinarily be used by, e. g., radiologists and gastroenterologists.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed2005

A prospective two-center study comparing wireless capsule endoscopy with intraoperative enteroscopy in patients with obscure GI bleeding.

BACKGROUND: Capsule endoscopy enables noninvasive diagnostic examination of the entire small intestine. However, sensitivity and specificity of capsule endoscopy have not been adequately defined. We, therefore, compared capsule endoscopy by using intraoperative enteroscopy as a criterion standard in patients with obscure GI bleeding. METHODS: Forty-seven consecutive patients with obscure GI bleeding (11 with ongoing overt bleeding, 24 with previous overt bleeding, and 12 with obscure-occult bleeding) from two German gastroenterologic centers were included. All patients who had a prior nondiagnostic evaluation, including upper endoscopy, colonoscopy with a retrograde examination of the distal ileum, and push enteroscopy, underwent capsule endoscopy followed by intraoperative enteroscopy. RESULTS: Capsule endoscopy identified lesions in 100% of the patients with ongoing overt bleeding, 67% of the patients with previous overt bleeding, and 67% of the patients with obscure-occult bleeding. Angiectasias were the most common source of bleeding (n = 22). Capsule endoscopy showed the source of bleeding in 74.4% of all patients. The method was more effective in patients with ongoing bleeding. Compared with intraoperative enteroscopy sensitivity, specificity, and positive and negative predictive values of capsule endoscopy were 95%, 75%, 95%, and 86%, respectively. CONCLUSIONS: Capsule endoscopy has high sensitivity and specificity to detect a bleeding source in patients with obscure GI bleeding. Thus, wireless capsule endoscopy can be recommended as part of the routine work-up in patients with obscure GI bleeding.

Adolescent↗
PubMed2005

A prospective study of the diagnostic accuracy of PillCam ESO esophageal capsule endoscopy versus conventional upper endoscopy in patients with chronic gastroesophageal reflux diseases.

INTRODUCTION: Endoscopy is commonly performed to evaluate for suspected or established esophageal diseases including gastroesophageal reflux disease (GERD) and its complications. The newly developed PillCam ESO Esophageal Capsule offers an alternative approach to visualize the esophagus and to evaluate patients with suspected esophageal disease. AIM: Compare the accuracy (specificity, sensitivity, positive predictive value [PPV], and negative predictive value [NPV]) of esophageal capsule endoscopy (ECE) compared with esophagogastroduodenoscopy (EGD) in evaluating patients with GERD. METHODS: A multicenter pivotal trial was conducted at seven sites. The PillCam ESO esophageal capsule is similar to the standard capsule endoscope used for the small bowel but acquires video images from both ends of the device at 2 frames/second/end. A total of 106 patients (93 GERD; 13 Barrett) underwent ECE followed by EGD. ECE videos were evaluated by an investigator blinded to EGD findings. A blinded adjudication committee reviewed all discrepant findings between ECE and EGD. RESULTS: Sixty-six of 106 patients had positive esophageal findings, ECE identified esophageal abnormalities in 61 (sensitivity, 92%; specificity, 95%). The per-protocol sensitivity, specificity, PPV, and NPV of ECE for Barrett esophagus were 97%, 99%, 97%, and 99%, respectively, and for esophagitis 89%, 99%, 97%, and 94%, respectively. ECE was preferred over EGD by all patients. There were no adverse events related to ECE. CONCLUSIONS: ECE is a convenient and sensitive method for visualization of esophageal mucosal pathology and may provide an effective method to evaluate patients for esophageal disease.

Endoscopy, Gastrointestinal↗
PubMed2004

Capsule endoscopy, technical impact, benefits and limitations.

BACKGROUND: The small bowel is the most difficult part of the bowel to examine owing to the distance from the mouth to anus. Conventional endoscopic techniques for examining the small bowel are limited by its length and its multiple, complex, looped configurations. However, for a wide variety of specific lesions, the diagnostic value of other tests for imaging the small bowel is low. For the first time wireless capsule endoscopy has made non-invasive imaging of the entire small bowel possible. A number of peer-reviewed studies has been published that compare the method with push-enteroscopy in patients with obscure gastrointestinal bleeding and have shown superior diagnostic results. CONCLUSION: Capsule endoscopy has opened up new horizons for the diagnosis of small-bowel disease. All published studies show a higher diagnostic yield of capsule endoscopy compared with push-enteroscopy and standard radiographic investigations.

Abdominal Pain↗
PubMed2004

ERCP and MRCP in the differentiation of pancreatic tumors.

The introduction of endoscopic retrograde cholangiopancreatography (ERCP) in the early 1970s provided gastroenterologists with a number of diagnostic as well as therapeutic possibilities for examining biliopancreatic systems. In the meantime, magnetic resonance cholangiopancreatography presents a non-invasive alternative to diagnostic ECRP providing the advantage of a lower rate of possible complications. This article addresses the two methods presently available for differentiating pancreatic tumors. The objective of this article is to describe the advantages and disadvantages as well as the possibilities inherent in both methods.

Adenoma, Islet Cell↗
PubMedDate not supplied

Self-expanding metal stents versus plastic prostheses in the palliation of malignant dysphagia: long-term outcome of 153 consecutive patients.

BACKGROUND: Malignant dysphagia due to esophagogastric cancer is associated with poor overall prognosis. Placements of self-expandable metal stents or plastic tubes are established methods as palliative treatment options. As an alternative and/or complementary therapy, radiologic techniques (external beam radiation/brachytherapy) and locally endoscopic techniques (laser, APC-beamer, PDT) are often used. STUDY AND GOALS: Retrospective trial of 153 patients treated in our department between 1993 and 2001. Forty-five patients received a plastic tube (Group A) and 108 patients were treated with metal stents (Group B). Both groups were compared for improvement of dysphagia score, survival, recurrent dysphagia and complications. RESULTS: Stent placement was successful in 41 of 45 (93%) patients of Group A and 107 of 108 (99%) of Group B. The median dysphagia score improved significantly in Group A (from 3.03 to 1.55, P = 0.010) and Group B (from 2.77 to 1.44, P = 0.009). Recurrent dysphagia was noted in 12 of 45 (27%) patients of Group A and 27 of 108 (25%) patients of Group B. Median survival time after stent insertion was 78 days (Group A) and 113 days (Group B). Overall complications occurred in 15 of 45 (33%) patients of Group A and 28 of 108 (26%) patients of Group B. However, significantly (P = 0.05) more major complications were seen in Group A than in Group B (22% vs. 9%). CONCLUSIONS: Our results indicate a marginal clinical benefit for metal stents versus plastic tubes in malignant dysphagia in the long run. However, metal stents seem to be safer and associated with a prolonged improvement of dysphagia score.

Adenocarcinoma↗