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Biomedical subjects

H M Klein

Publications and source records attributed to H M Klein.

At least 37 records · Page 2Linked to original sources
PubMed1994

[Effect of ambient lighting on the diagnostic efficiency of display screen workplaces].

The aim of our study was to determine the influence of ambient lighting conditions on the diagnostic performance when using digital reporting work-stations. We acquired 15 normal and 30 fractured porcine femurs using a storage phosphor system. All images were demonstrated on a high-quality image display under optimised (128 lx) and non-optimised (450 lx) ambient lighting conditions and on a conventional viewing-box under non-optimised conditions (450 lx). Results were analysed using ROC-statistics. The area under the ROC-curve was 0.895 for optimised conditions and 0.684 for non-optimised conditions using digital displays and 0.849 for the conventional viewing-box. The difference in diagnostic performance between optimised and non-optimised conditions using a digital display was highly significant (p < 0.001). Our results emphasise the importance of adequate surrounding lighting conditions for radiologic diagnostic performance, particularly for the use of digital reporting consoles.

Animals↗
PubMed1994

Intra-urethral ultrasound in women with stress incontinence.

OBJECTIVE: To investigate whether the sphincter area in women can be seen and quantified with intra-urethral ultrasound (IUUS). Currently, sphincter capacity in women is determined by clinical tests, vaginal palpation, urodynamics and urethral pressure profile. PATIENTS AND METHODS: A pilot study using IUUS was carried out in 32 stress incontinent and 12 healthy women to enable the urethra and para-urethral tissue to be visualized. Round-tipped miniature transducer-containing (20 MHz) catheters (6 and 9 F) were tested. Both provided 15 frames per second. Real-time 360 degrees cross-sectional ultrasound images were obtained by using a standard intraluminal ultrasound system. The external urethral sphincter was visualized and its circumference and area were measured. RESULTS: IUUS provided high resolution imaging of the urethra and surrounding tissues. The whole length of the urethra was visualized. The external sphincter was easily recognized as an oval-shaped, hypoechoic structure. Examination of 44 stress incontinent and healthy women revealed a negative correlation between the external urethral sphincter (area and circumference) and the grade of stress incontinence (P < 0.01). In no patient with normal urinary continence was the sphincter reduced in size (< 2.8 cm circumference). CONCLUSION: IUUS is a useful technique in the diagnosis of incontinence, as conventional methods provide little information on the sphincter itself. The evaluation of sphincter size and morphology could help in the choice of therapy.

Female↗
PubMed1993

[High-resolution CT of the dentate alveolar ridge in comparison with histological thin section preparations].

Human bone segments of the toothed jaw were scanned using high-resolution CT with axial and coronal contiguous 1 and 2 mm slices. The bone segments were sliced analogous to the performed CT image positions. Contact films and micro-sections were made from the cuttings. Length and width of the teeth, the thickness of the alveolar bone and the distance between bone and dental surface were measured. Comparison of the CT measurements with contact films and histological specimen yielded best results for axial slices with 1 mm slice thickness (mean error 0.3-0.5 mm). Coronary oriented slices showed an error of 0.3-1.6 mm. 3D-reformatting can improve spatial orientation for axially produced image series. For CT imaging of the toothed jaw concerning the dento-alveolar structures, contiguous axial scanning with 1 mm slice thickness appears to be the concept of choice.

Alveolar Process↗
PubMed1993

[The diagnosis of focal liver lesions by the texture analysis of dynamic computed tomograms].

Characterisation of focal liver lesions on computed tomography (CT) depends on correct interpretation of morphology and dynamic changes during bolus injection of contrast medium. The aim of this study was to develop a texture analysis concept for computer based interpretation of dynamic CT images. 148 focal liver lesions were investigated by serial CT. The study comprised 61 haemangiomas, 25 other benign lesions (FNH/adenomas) and 62 malignant lesions (primary or secondary). FNH, adenomas and malignant lesions were histologically proven. Diameter was 8-145 mm (mean 31 mm). Regions of interest were interactively defined. After extraction of characteristic textural features, a pattern classifier was trained. All CT series were evaluated using the "leaving-one-out" method. 134 of the 148 lesions were correctly classified (positive predictive value 0.9). Sensitivity for the presence of malignancy was 0.93 (80/86), specificity was 0.9 (56/62). False classification of a lesion was found to depend strongly on the quality of the examination (bolus intensity, positional change of the lesion due to respiratory movements).

Diagnosis, Differential↗
PubMed1993

Digital radiography versus conventional radiography for the detection of a skull fracture under varying exposure parameters.

RATIONALE AND OBJECTIVES: The effect of varying exposure parameters on the detectability of a fracture with digital and conventional radiography were examined. METHODS: A macerated fractured skull was imaged by film-screen radiography (FSR) and digital storage phosphor radiography (DR) with various exposure values. Five radiologists traced the course of a fracture line. The length of the fracture was reported and the results were analyzed by Student's t test for paired samples. RESULTS: At 35% of the conventional radiation dose, the standard DR screen displayed an average of 48% of the fracture length. The difference from the conventional image (45%) was not significant in this case. An increase of the dose to ten times the conventional dose (250 mAs) yielded no significant improvement in the detectability of the length of the fracture (51%). CONCLUSIONS: This experiment shows that with use of the DR with the standard screen, a dose reduction of approximately 35% appears to be possible without any resulting loss of image quality compared to FSR. Use of the high resolution screens should be avoided, since they require a higher incident image dose than standard screens without offering any diagnostic advantages. The image dose of digital radiographs can be roughly estimated based on the digital device sensitivity value. As a rule, the sensitivity value should range between 100 and 200.

In Vitro Techniques↗
PubMed1993

Double contrast small bowel follow-through with an acid-resistant effervescent agent.

RATIONALE AND OBJECTIVES: A new technique was developed to achieve double contrast examinations in the small bowel without intubation. METHODS: Effervescent granules and tablets were coated with an acid-resistant acrylic lacquer to provide selective enteric gas release. The coating thickness was 15% of dry weight for the granules and 1 to 4.5 mg/cm2 for the tablets. Fifty patients were examined using the method in a controlled study. All examinations were reviewed by two radiologists using a three-step quality score. The results were compared to 20 enteroclysis examinations. RESULTS: Image quality was better for the coated tablets compared with the granules (P < .01). The double-contrast small bowel follow-through (DC-SBFT) provided a better quality examination in the terminal small bowel than in the jejunum. Enteroclysis yielded better results for the jejunum, but was not superior in the terminal ileum. Average time of fluoroscopy was 477 seconds for the DC-SBFT (n = 50) compared with 952 seconds for patients receiving enteroclysis (n = 528). No side effects or adverse reactions occurred due to contrast media application. CONCLUSIONS: The results of this new method are preliminary, yet promising. For young patients and certain indications it may provide a less invasive alternative to enteroclysis.

Abdominal Pain↗
PubMed1993

Comparative evaluation of digital radiography versus conventional radiography of fractured skulls.

OBJECTIVES: The authors assessed the relative efficacy of conventional and digital storage-phosphor radiographs for the detection of skull fractures. METHODS: Fifty conventional film-screen radiographs (FSR) and 50 digital storage-phosphor radiographs (DR) with 66 fractures were compared. Five radiologists evaluated image quality and fracture detectability. The results were analyzed by receiver operating characteristic (ROC) curve analysis. RESULTS: With a standard exposure, the ability to evaluate skull fractures was equally good with either technique (ROC area for DR, 0.8954; for FSR, 0.8870). Digital radiography was superior in evaluating nasal bone. For petrosal bone, the DR image simulates an underexposure. This disadvantage compared with FSR can be compensated by image postprocessing. CONCLUSION: In evaluation of skull fractures, radiologists performance with DR is equivalent to FSR.

Adolescent↗
PubMed1993

Assessment of incontinence with intraurethral US: preliminary results.

To explore the usefulness of intraluminal ultrasound (US) for diagnostic imaging of the female urethra, 22 female patients with different degrees of urinary incontinence and 10 female patients with normal continence underwent examination by means of a 20-MHz intravascular US system. Contiguous sections were used for three-dimensional reconstructions on a personal computer-based system in two patients. The circumference and area of the internal urethral sphincter were measured in all patients; the measurements were obtained by means of manual delineation of the inner and outer contours of the sphincter. A correlation was found between (a) area and circumference and (b) the degree of incontinence (P < .01). No patient with normal urinary continence showed a reduced sphincter size (a circumference smaller than 2.8 cm). Intraurethral US, which yields images of the urethra and surrounding tissues, may become an important adjunct to urethrography and functional methods (assessment of urodynamics) for the diagnostic evaluation of incontinence.

Female↗
PubMed1993

Computed tomographic cholangiography using spiral scanning and 3D image processing.

Volumetric computed tomography (CT) scans ("spiral CT") were performed after intravenous (i.v.) cholangiography followed by additional 3D surface reconstructions of gallbladder and biliary ducts. 34 patients were investigated prior to cholecystectomy. No allergic adverse reactions were observed. The scan time was 24 s. Contrast enhancement in the extrahepatic bile duct and gallbladder were measured. All CT image series were reviewed independently by four experienced physicians (two radiologists, two surgeons) and compared for quality with conventional cholangiography on a three-point scale. The average rating for the demonstration of the biliary tract was significantly better for spiral CT than for conventional cholangiography (p < 0.01). In all cases sufficient contrast was found in the common bile duct (mean 315 HU). 3D imaging was considered to be helpful for intraoperative orientation during laparoscopic surgery.

Adult↗
PubMed1993

Stereolithographic modelling for reconstructive head surgery.

Until now, bounds of model creation of medical objects had to be set because of the limited capabilities of available manufacturing equipment. Recently, stereolithography was developed as an alternative to current milling operations. In this process the surface of a photohardening liquid plastic compound is traced by a laser beam and hardened in layers. The models thus produced are extremely accurate and retain excellent detail. Specific implants can be designed and prepared as is illustrated in a case report. If tissue-compatible plastics are used, custom-made implants could soon be manufactured directly with the technique described.

Child↗
PubMed1993

[Computed tomographic imaging of the dentoalveolar-maxillary sinus lacuna of the dentate jaw].

A human bone segment of the lateral maxilla was scanned using high-resolution computed tomography (CT) in contiguous parallel axis slices in order to image the topographical relationship between upper molars and the maxillary sinus. The bone segment was dissected analogously in 1 mm thick sections. After exposing contact films from these jaw cuttings, microsections were made for histological interpretation. The radiological-histological comparison between the CT-scans, contact films and the histologic specimens revealed absolute differences of 0.2-0.6 mm. The high resolution CT allowed an interpretation of details located between teeth and bone when the minimum bone thickness was 0.5 mm or more. First experiences with the CT-technique in orthodontic patients were promising, especially for the differential diagnosis of the dentoalveolar maxillary sinus relation.

Adult↗
PubMed1992

Pediatric craniofacial surgery: comparison of milling and stereolithography for 3D model manufacturing.

To improve the planning phase for pediatric craniofacial surgery, 3D reconstructions of CT image series were performed on a personal computer. For construction of true models of the surgical site, two concepts were pursued. CT image data of six patients were used for model manufacturing by a conventional 2 1/2 axis milling system. The material used was polyurethane foam. Alternatively, in one patient a stereolithography was produced on the basis of the 3D reconstructed CT data. This new manufacturing device uses a photocurable monomer, hardened by a UV-laser. The spatial resolution of the system is about 0.1 mm. 3D-reconstructions were performed on a personal computer. Data were then transferred into a surface oriented structure to control a stereolithographic modeling device. Time for transfer was 70 min. The production of the modelled cranium took a total time of 59 h. Accuracy was found to be much higher in stereolithography than in milled models. The model served for surgical planning. The long time for production was caused by inadequate computer capacities, which are configured for much less complex objects in computer aided design. Furthermore the programs for the machine control are optimized for technical purposes. If these conditions are improved, stereolithography could be an attractive alternative to milling of medical models.

Child↗
PubMed1992

[The computer-assisted processing of CT data in planning endosseous implantation interventions].

The success of dental implantologic measures depends considerably on the correct positioning of the endosseous implants. A sufficient amount of bony substance is mandatory to provide overall covering of the implant with at least 1 mm of cortical bone. By the aid of a custom-developed software system, computed tomography image data can be handled on a conventional MS-DOS personal computer. The user is enabled to simulate size and positioning of the implant by interactive graphic animation. Quick and exact presentation is achieved by optimizing the computation algorithms. Storage needs are minimized by a segmentation procedure and additional compression of the image. Integrated patient data management and user friendly self-documenting program surfaces provide easy application.

Computer Graphics↗
PubMed1992

[Stereolithographic model construction based on 3-dimensional reconstructed CT sectional image sequences].

Techniques for 3D reconstruction of medical objects and production of models by CAM have been markedly improved. Milling tools have limited abilities to reproduce complex anatomical structures. Even if 5-axis milling systems are used, the problem of collisions between tool and object is not yet under control. An alternative is offered here by stereolithography. We performed a computed tomography (Somatom DRH, Siemens/Erlangen) of a child with extensive maxillary bone defect after surgical treatment of a congenital tumour. The bone defect was covered by an alloplastic implant. 3D reconstructions were performed by the aid of a conventional personal computer. Generated 3D volume data sets were transferred to a stereolithography system (3D Systems GmbH, Darmstadt/FRG). The produced model revealed high accuracy of the anatomical structures. Intraoperatively, the alloplastic prosthesis was removed and the shape of the new implant could be designed using the stereolithographic model.

Child↗
PubMed1992

Efficiency of a lead-containing tie for radiation protection of the thyroid gland.

During fluoroscopy the examiner is usually protected by a radiation-reducing body shield, leaving the thyroid unprotected. The fact that the thyroid is located in a region of the neck usually covered by the shirt collar led to the idea of designing a tie with lead core, providing easy and "decorative" reduction of the radiation dose. Sonographic examinations were carried out in 20 volunteers (10 men, 10 women) to determine the size of the gland and its coverage by such a tie. The reduction of the surface and organ dose was assessed using film dosimetry with scattered radiation, the body of the examiner being simulated by an Alderson phantom. On average 88% of the thyroid gland surface area was covered. Surface dose was reduced to 1%, and organ dose to 10% of the value without the protection tie.

Equipment Design↗
PubMed1992

[Methods for simulation of surgical interventions in head and neck surgery].

Preoperative evaluation of the operating site is essential in planning surgical procedures. The relationship of pathology to adjacent tissues and vital anatomical structures needs to be analyzed to determine the intraoperative procedures required. For this the surgeon mentally simulates the procedure planned. For complicated conditions or reconstructive surgery in extensive bony defects, surgery can be simulated with three-dimensional reconstruction on either a monitor screen or on an individually manufactured plastic model of the patient. For this purpose different procedures for 3 D representation and manipulation of tomographic image data have been developed in our departments and the technique of stereolithography used experimentally to create custom-made plastic model of patients. A computerized video image manipulator was also developed for simulation of aesthetic plastic surgical procedures.

Computer Graphics↗
PubMed1991

[Fracture diagnosis with digital luminescence radiography].

Conventional screen-film radiographs were compared with storage phosphorus images concerning diagnostic performance in traumatologic radiography. We used an image pool of 106 radiographs including 50 conventionally and 56 digitally recorded images. The images were reviewed by four experienced radiologists. Detectability of fractures was coded in a five-point scale of confidence and analysed by ROC statistics. Furthermore the image quality and the optical density was compared. Digital images are superior under difficult exposure conditions and offer advantages by additional image processing and documentation. For some indications (follow-up, functional examination), reduced x-ray exposure is tolerable. The detectability of subtle lesions, which is essential for the primary diagnosis of fractures was significantly better by conventional radiography.

Evaluation Studies as Topic↗