[Digital volume tomography in ENT medicine]. / Die digitale Volumentomographie in der HNO-Heilkunde.

Digital volume tomography (DVT) is an advancement of panoramic tomography used in dentistry. DVT enables precise display of fine osseous structures without any disturbing artefacts. This makes its application interesting in the field of the lateral, anterior skull base and paranasal sinuses, as well as for the diagnosis of nasal bone fractures. The tomograms can be completed according to need by volume rendering or panoramic slices within a short time. Assuming they have the appropriate technical qualifications in radiation protection, ENT specialists are even able to perform tomography independently using DVT.

[Protection of eye lens in computed tomography--dose evaluation on an anthropomorphic phantom using thermo-luminescent dosimeters and Monte-Carlo simulations]. / Schutz der Augenlinse in der Computertomografie--Dosisevaluation an einem antropomorphen Phantom mittels Thermolumineszenzdosimetrie und Monte-Carlo-Simulationen.

PURPOSE: The lens of an eye is a particularly radiosensitive organ. This study investigates two different materials for eye shielding during CT scanning, i. e. a commercially available bismuth protector and a newly developed material for eye shielding, comprised of an alloy of Bi/Sb/Gd/W. MATERIALS AND METHODS: The radiation dose during head CT scanning was measured using thermoluminescence dosimeters and an anthropomorphic Alderson-RANDO phantom. A radiation dose reduction was compared to two shielding materials and to the condition without any eye shielding. The effect of gantry angulation that excludes the eyes from beam path was also investigated. Radiation dose measurements were validated using a Monte-Carlo simulation. For this simulation we used the EGSsnr code system, and a new application CTDOSPP was developed for simulation of the computed tomography examination. Eight radiologists evaluated the diagnostic quality of the images. RESULTS: Dose measurements and Monte-Carlo simulations are in good agreement. If the eye shields are placed in the primary beam path, bismuth eye shielding and the new material reduce the dose by up to 38 % and 48 %, respectively. Angling the gantry causes an 88 % reduction in radiation dose. All shielding materials generate beam hardening artifacts located close to the protector, but the artifacts do not spread into the brain. CONCLUSION: The application of eye shields during CT examination of a head causes a significant reduction in radiation dose. The new protector material shows a significantly higher dose reduction in contrast to the commercially available bismuth shield. The best protection from radiation dose can be attained using gantry angulation.

[Virtual organization in the digital age of radiology - principle and solution for radiologic research?]. / Virtuelle Organisation im digitalen Zeitalter der Radiologie - Prinzip und Lösung für die radiologische Forschung?

The research project "VICORA - Virtual Institute for Computer-Assisted Radiology", funded by the German Federal Ministry of Education and Research, was initiated in the year 2000. Its virtual organization brings together physical science, engineering, information technology, clinical radiology and the medical technology industry. In the German radiology research domain VICORA serves as a model for interdisciplinary collaboration for the changing radiology paradigm illustrated by a "radiologycube". The project does not only aim at scientific goals but also considers the infrastructure, components and human resource management within a virtual organization. The common rapid prototyping platform ILAB 4 ensures user-friendly and time-efficient software that assists with the routine radiology work-flow including full DICOM functionality. By offering a new work environment and collaborative culture based on telematics and knowledge exchange in radiology research, VICORA overcomes limitations of traditional research organization.

[Bone adaptation changes mechanical stress in the femur--a prospective two years follow up after Hüft-TEP implantation]. / Knöcherne Anpassung ändert mechanische Beanspruchung des Femurs--eine zweijährige prospektive Studie nach Hüft-TEP Implantation.

AIM: Periprosthetic adaptive bone remodeling after total hip arthroplasty (THA) has been frequently simulated in computer models, combining bone remodeling theory with finite element analysis. Unfortunately, there is still a lack of clinical validation data. The collection of prospective volumetric bone density data with a clinical computerized tomography study after THA was previously conducted. The objective of the study presented here is an additional evaluation of femoral strain. METHOD: In a prospective clinical trial with 7 female patients after THA computerized tomography (CT) and finite element (FE) modeling was patient specifically combined immediately after surgery, as well as at three and 24 months postoperatively. Mechanical strain was expressed by strain energy density. RESULTS: Corresponding to a bone density decrease, a decrease of the femoral strain energy density was observed during the two year follow-up after surgery (approximately 20 %). The predominant change occurred within the first three months and was found to be distally stronger than proximally. CONCLUSION: As far as we are aware, this is the first combination of fully prospective 3D CT density data in vivo with patient-specific finite element modeling. The assessment of mechanical strain data during a follow-up trial should be a new approach for analyzing hip stems in clinical biomechanics. A future confirmative study based on a statistical case number calculation would increase the evidence of the results presented here.

[Selection of subjects: a problem of clinical trials in traumatology. Selection effects and the problem of representation as exemplified by a prospective randomized trial on whiplash injuries]. / Selektionseffekte--Ein Problem unfallchirurgischer Studien? Stichprobenselektionseffekte und das Problem der Repräsentativität am Beispiel einer prospektiven randomisierten Studie zur HWS-Beschleunigungsverletzung.

INTRODUCTION: The internal and external validity of studies is endangered by many factors, such as selection of subjects for inclusion. Selection bias itself is a major problem, but remains unmentioned and probably unexamined in the majority of published clinical trials in traumatology. AIM OF THE STUDY: The aim of this investigation was to detect effects of subject selection which occurred during our own prospective intervention study. The clinical trial compared subjects with whiplash injury who were either treated by early mobilization or immobilization (soft collar). MATERIAL AND METHODS: Source population, eligible subjects, study participants and final study participants were compared for differences on various items like age, gender and further sociodemographic as well as crash related factors and clinical findings. RESULTS: Between 21.08.1997 and 30.04.1999 a total of 732 patients was examined and treated after whiplash in our trauma department. The options for inclusion were met by 453 patients. While 346 escaped from the study, 107 agreed to participate. Of these another 39 patients dropped out of the study. Selection effects were detected on two different levels, leading to distinct statistical procedures from those proposed in the study protocol. CONCLUSIONS: Uncontrolled selection effects could undermine the interpretability of the results of clinical trials. Awareness of selection effects is mandatory regarding the applicability of these results to subjects, other than those in the group of the final study participants.

[Effects of shaft length of finger joint prostheses on tension distribution in the bone]. / Auswirkung der Schaftlänge von Fingergelenkprothesen auf die Spannungsverteilung im Knochen.

In order to investigate the influence of stem length in finger joint prostheses on stress in the surrounding bone area, finite element (FEM) calculations of finger bones before and after prosthetic replacement of metacarpophalangeal joints with cementless implants of different stem length were performed. CT scans of the metacarpal bone and proximal phalanx before and after implantation of a prototype of a noncemented semiconstrained implant for the MP joint, which has been developed to replace metacarpophalangeal joints destroyed by rheumatoid arthritis, were analysed. The FEM calculations showed comparatively decreased differences of the von-Mises stress after implantation of intramedullary stems reaching the middle of the diaphysis. At the metaphysis of the metacarpal head we found an increase of the von-Mises stress of 1.3 MPa (Mega Pascal = 10(6) Pa), an increase of 18.9 MPa around the shortest prosthesis and a decrease of 21.4 MPa around the prosthesis with the longest stem.

[Thromboembolism complication in multiple trauma patients: an underestimated problem? Results of a clinical observational study of 50 patients]. / Thromboembolische Komplikationen bei mehrfachverletzten Patienten: ein unterschätztes Problem? Ergebnisse einer klinischen Beobachtungsstudie mit 50 Patienten.

INTRODUCTION: The incidence of thromboembolic complications in patients with severe polytrauma in the ICU is not well known. Only a few publications deal with this problem. Systematic investigations in this high-risk patient group are not routinely used. METHOD: From January 1996 to January 1998, 50 polytrauma patients with a mean ISS > 15 were included in a clinical study to evaluate the incidence of thromboembolism in this patient group. Further inclusion criteria were a minimum stay of 72 h in the ICU and mechanical ventilation for a minimum time of 72 h. All patients were examined with color-coded duplex sonography according to a standardized protocol. The duplex sonography was performed before the patients were first mobilized in the ICU (15 +/- 12.8 days). RESULTS: If not otherwise indicated all values are given as mean +/- SD. The age of the patients was 38 years (range 17-77 years), the severity of trauma was characterized by an ISS of 40 (range 16-70). Eight of the included patients died during their stay in the ICU after developing a multiple organ failure. According to autopsy data none of them had a deep venous thrombosis or pulmonary embolus. Eight patients (19%) developed deep venous thrombosis, and 4 patients with thrombosis developed pulmonary embolism. CONCLUSION: The incidence of deep venous thrombosis in polytrauma patients seems to be much higher than expected reviewing the results of other publications. The low detection rate of other authors results from using only clinical signs. The routine use of color-coded duplex sonography is effective in detecting unsuspected deep vein thrombosis.

[Testing dental implants with an in vivo finite element model]. / Zahnimplantattestung am In-vivo-Finite-Elemente-Modell.

The finite element method (FEM) makes it possible to simulate biomechanical situations on a computer. In the present study the so-called voxel method [9, 14, 17, 18, 19] was used for the construction of the mandible model. For this, the relationship between the biological tissue (e.g. bone) and the corresponding attenuation coefficient of CT data (Hounsfield units = HU) were utilized. The CT data were obtained from an edentulous patient provided with a prosthesis borne on two titanium implants. In a parallel study, the bite forces of the same individual were measured. These were recorded digitally in three dimensions (cranio-caudal, anterior-posterior and left-right) The forces determined by a special program were then transferred to the FEM model implants. We were able to show that a bar joining the implants had a far greater effect on maximum equivalent stress than was expected from the measuring data alone. The highest stress at maximum occlusive force was lowered by 704% on using the connecting bar. On chewing, a stress reduction of 59.9% was observed. The reduction in stress achieved by the bar could, we believe, prolong the life of the implant.

[X-rays taken by radiologists! Influence on a continuous quality improvement process?]. / Röntgen durch Radiologen! Einfluss auf einen kontinuierlichen Qualitätsverbesserungsprozess?

PURPOSE: To evaluate how the training of radiology residents in taking radiographs influences the work of radiographers and the established quality standards. METHODS: A first year radiology resident was trained for 4 weeks in focusing and exposure techniques by radiographers. In a second period the resident took 582 radiograms, which were compared with those taken by technicians for error estimation on a daily basis. During a third period the radiographs were produced in a contest between the resident and a skilled radiographer. Errors were analyzed by two independent experts according to established guidelines of the German Medical Association. RESULTS: At the beginning of the second period the average error rate of the resident was 11.9% as compared to 8.9% in the technicians team, in the following month 9.2% versus 15.9%. In the third period no relevant difference in errors could be observed. Finally, unexpected quality improvements were implemented like an improved standardization of focusing and exposure techniques as well as dose reduction. CONCLUSIONS: Radiology residents easily learn focusing and exposure techniques and achieve comparable results as radiographers within a short period of time. The additionally achieved knowledge improves the technical process of taking radiographs. We recommend to include a two plane radiography training period in the curriculum of radiology residents. It reinforces the radiologist's role in continuous quality improvements of the diagnostic process.

Bone remodelling in humeral arthroplasty: follow-up using CT imaging and finite element modeling--an in vivo case study.

Little material is available in the literature about remodelling of the human humerus after implantation of a shoulder hemiarthroplasty. A 73-year-old patient was examined by CT 4 years after implantation of a right shoulder hemiarthroplasty, and the bone density as represented by Hounsfield values was compared with the contralateral side. Additionally, a three-dimensional finite-element model was generated from the image data and analysed. Bone density was reduced around the prosthesis when compared with the contralateral side. The stresses were transmitted through the prosthesis, while low bone stresses were found surrounding the prosthesis. Distally from the prosthesis, high stresses were found. On the control side, a more homogeneous stress distribution was noted. The results could be explained by bone resorption around the prosthesis caused by stress shielding; this hypothesis has to be confirmed by future studies.

Comparison of geometry-based and CT voxel-based finite element modelling and experimental validation.

The objectives of the paper presented here is the comparison of a geometry-based and voxel-based finite element (FE) method preprocessor of the human femur. The models were experimentally validated by strain gauge measurements (principal stress). The correlation coefficients (r) between the three methods (geometry-based FEM, voxel-based FEM, strain gauge measurements) were found to be in the range 0.91-0.94 (r2: 0.84-0.88). The relationships between the samples are highly significant (P = 0.001), where the strain gauge results are the independent variables. These results suggest that the validity with respect to the principal stress of a voxel-based modelling is similar to the validity of geometry-based modelling. In summary, therefore, we conclude that voxel-based meshing allows a straightforward interfacing with computerized tomography (CT) scans and might contribute to a clinically applicable FEM technology.

[Radiation exposure during thoracic radiography at the intensive care unit. Dose accumulation and risk of radiation-induced cancer in long-term therapy]. / Strahlenexposition durch Röntgenthoraxaufnahmen auf der Intensivstation. Dosiskumulation und Strahlenkrebsrisiko bei Langzeittherapie.

PURPOSE: Assessment of the additional morbidity risk due to repeated bedside chest radiography according to ICRP 60 during intensive care. MATERIAL AND METHODS: Ventral surface doses were recorded by thermoluminescence dosimetry in 2 man and 7 women, mean age 36 +/- 12 years, mean height 169 +/- 5 cm, mean weight 74 +/- 8 kg, receiving long-term ventilation therapy due to Adult Respiratory Distress Syndrome (ARDS). RESULTS: From 18 to 126 days duration of therapy 9 patients received a total of 348 bedside chest radiographs, mean 39 +/- 22 radiographs per patient. 217 chest radiographs yielded 217 surface doses and 217 gonadal doses. Patient's mean surface dose varies between at least 0.31 +/- 0.12 mGy and at most 0.56 +/- 0.09 mGy. The surface dose representing gonadal exposure is less than 0.03 mGy per exposure. The mean effective dose is about 0.15 mSv per exposure. The cumulative effective dose Heff ranges between 2.49 mSv and 14.09 mSv, thus estimating the additional individual cancer risk ranges between 0.01% and 0.07%. CONCLUSION: In comparison with the decreased prognosis of severely ill long-term ventilated patients the additional morbidity risk due to chest radiographs is a negligible quantity.

[Standardized enteroclysis. Monitoring of intra-lumen pressure in 3 different patient groups]. / Standardisierte Enteroklyse. Registrierung des intraluminalen Drucks in drei unterschiedlichen Patientenkollektiven.

PURPOSE: Monitoring of intraluminal pressure in standardized enteroclysis. MATERIAL AND METHODS: Pressure monitoring with a double-lumen tube during fluoroscopy-guided adjustment of contrast media instillation rate due to small bowel motility and contrast media transport of 67 patients. Stratification according to patient data and findings in enteroclysis: Crohn's disease (n = 12), non-inflammatory disease (n = 35) and irritable bowel syndrome (n = 20). RESULTS: The amount, instillation period and rate of contrast media and distension media were not statistically different within the study population. Crohn's disease patients showed elevated intraluminal pressure at the end of the distension phase (47.94 +/- 10.42 cm H2O versus 38.03 +/- 10.08 and 39.55 +/- 9.74 cm H2O, respectively, P = 0.0099), as well as at the end of the examination (48.59 +/- 10.42 cm H2O versus 39.66 +/- 6.52 and 35.67 +/- 8.28 cm H2O, P = 0.0002). In comparison with both other patient groups, maximum intraluminal pressure in Crohn's disease is higher and totals 51.75 +/- 9.94 cm H2O versus 43.00 +/- 6.20 and 39.55 +/- 9.74 cm H2O, P = 0.0010. Patients with Crohn's disease require a longer instillation period of distension media (28.05 +/- 12.82 min, not statistically significant). CONCLUSION: Intraluminal pressure differs in standardized enteroclysis with fluoroscopy-guided instillation rate adjustment. Irrespective of stenosis or acute inflammation, patients with Crohn's disease show a higher intraluminal pressure compared to patients with non-inflammatory disease or irritable bowel syndrome.

[Fully automated generation of hip prosthesis voxel models of the femur for finite element analysis. Comparison of direct and subsequent prosthesis implantation]. / Die vollautomatische Erstellung implantatbestückter Voxelmodelle des Femurs zur FE-Analyse, Vergleich von direkter und nachträglicher Prothesenimplantation.

Two means of generating implant-bearing FE voxel models of the human femur are described and compared. The first method consists in the fully automatic production of a femur model from CT data and subsequent implantation of a prosthesis stem on the basis of a redefinition of existing voxel elements using geometrical data control. The second method processes the CT data of a femur already bearing a prosthesis. Here, the prosthesis elements are generated separately from the surrounding bony elements on the basis of the differing CT density thresholds. Although the two implantation algorithms produce comparable results, they have different fields of application. The method of numerical stress analysis involving automatic generation of voxel models can be applied to implant-bearing femurs. Clinical follow-up observations of patients with prostheses made of titanium can be supported by FE calculations.

[Blunt thoracic trauma with aortic rupture and lung contusion caused by hoof kick in a 15-year-old girl. Diagnostic and therapeutic management]. / Stumpfes Thoraxtrauma mit Aortenruptur und Lungenkontusion durch Hufschlag bei einem 15jährigen Mädchen. Diagnostisches und therapeutisches Management.

The number of published cases of adolescents surviving thoracic aortic injuries with accompanying severe thoracic injuries is small. Only 20-30% of all these patients reach the trauma center alive. In the present case we demonstrate the diagnostic, operative and intensive care management in a 15-year-old girl. The exact interpretation of the AP thoracic X-ray in connection with a typical mechanism of injury led to the detection of a haemomediastinum. This is very important in the further development of diagnostics, because the conventional X-ray picture does not show significant signs in the case of an incomplete aortic rupture. Diagnostic hints have to be derived from the detection of the haemomediastinum. The girl was operated on under left heart bypass. Spinal ischaemia was absent after surgery, and renal failure also did not occur. The adjacent severe lung confusion healed under kinetic therapy with a kinetic treatment table without pulmonary complications.

Prospective evaluation of different diagnostic techniques for the detection of liver metastases at the time of primary resection of colorectal carcinoma.

OBJECTIVE: To evaluate preoperative and operative methods of detecting liver metastases in patients undergoing primary resection for colorectal carcinoma. DESIGN: Prospective, open study. SETTING: Teaching hospital, Germany. SUBJECTS: 51 Patients with confirmed primary colorectal carcinoma. INTERVENTIONS: Computed tomography during arterial portography (CT-AP), percutaneous ultrasonography (US), operative palpation and examination of the liver, operative US, and computed tomography (CT) follow-up 6-12 months postoperatively. MAIN OUTCOME MEASURES: Sensitivity, specificity, positive and negative predictive value, and accuracy. RESULTS: Overall accuracy was worst for CT during portography, because of the diagnosis of many false positive lesions. Exploration and palpation of the liver had the highest sensitivity (83%) and specificity (100%), and operative US did not give any useful additional information. CONCLUSIONS: Preoperative percutaneous US is recommended as the best non-invasive screening test; otherwise careful inspection and palpation during operation are sufficient for the evaluation of the liver during primary resection for colorectal carcinoma.

[Windmill principle versus clockwork principle--tradition and interaction in academic lectures. A. N. S. A. Radiologica]. / Windmühlenprinzip versus Uhrwerkprinzip--Tradition und Interaktion in der akademischen Vorlesung. A. N. S. A. Radiologica.

In reply to depersonalization of teaching, students hiding behind anonymity and their decreasing effective presence in campus life, academic teaching has to become practice-oriented, attractive and at least more effective. The traditional teacher-based lecture competes with student-centered and issue-related academic events like problem-based learning, thus, concerning student-teacher interaction. The model of a clockwork represents the components of a traditional lecture. The model of a windmill is suitable for explaining synergistic effects in scope and experience during an interaction concerned lecture. An example of student-teacher interaction and students' activation even in a preclinical course of lectures on anatomy and radiology is given. A high response and acceptance of the lecture is assured by structure-and process-oriented features.

[Status of radiation protection courses for physicians--plea for a change in paradigm]. / Zur Situation der Strahlenschutzkurse für Arzte--Plädoyer für einen Paradigmenwechsel.

The purpose of this study was to evaluate the acceptance of the statutory course of radiation protection, which is attended by physicians. As a first step towards problem based quality management, an anonymous questionnaire was used to assess the participants' opinions. The present methods in teaching, practice-orientation of the educational objectives, the prize and efficiency of the course were judged poor. Neither valid indicators of quality nor a quality management of the course exists. Facing the status quo and future demands within the medical community and society there is a serious need for reshaping radiology. It is emphasized that instead of marginal corrections only a strategic and fundamental approach to a paradigmatic reorganization will meet success.