Biomedical subjects

A Stargardt

Publications and source records attributed to A Stargardt.

At least 19 recordsLinked to original sources

PubMed1999

Errors of computer-assisted migration analysis in conventional radiographs of femoral hip implants--an experimental study.

Several methods have been described in the literature in order to analyze migration of femoral hip implants in conventional radiographs. However, no measurements were done regarding the potential errors inherent in such unstandardized radiographs of daily routine. In order to quantify this lack of reproducibility, we carried out experimental examinations with radiographs of a hip revision prosthesis, where different variables of technical X-ray conditions and femoral positions were changed. All radiographs were analyzed with a computer-assisted processing system by different procedures. At first, the radiographs were calibrated geometrically. Then, particular reference distances between defined points of the implant and cortical bone structures were analyzed quantitatively. The error of the axial migration analysis was up to 11.11 mm concerning different femoral positions, up to 8.29 mm in the case of different source-to-film distances and up to 2.21 mm due to different lateral localizations of the central X-ray focus. Significant errors for the migration analysis in the transverse and rotational planes were only found under conditions of varying the femoral position, and not under different technical X-ray conditions. From these experimental results, we derived the following criteria to minimize failure in a quantitative radiographic migration analysis: (1) the patient's leg has to be placed into an antirotation device to ensure identical object position; (2) the same source-to-film distance has to be used; (3) the central X-ray focus has to be localized on the center of the film-cassette; (4) film-screen systems should be of the same type and size; (5) the object has to be placed in the same position as in previous radiographs. As a conclusion, only if these standardization criteria are respected in the daily routine of conventional radiographs will an effective and meaningful use of migration analysis systems be possible to prove or to exclude mechanical failure of femoral hip implants in prospective longitudinal follow-up series.

Cadaver↗

PubMed1998

[New TIPS placement in pregnancy in recurrent esophageal varices hemorrhage--assessment of fetal radiation exposure].

Recurrent variceal bleeding due to liver cirrhosis led to treatment with a transjugular intrahepatic portosystemic shunt (TIPS) in a pregnant woman at 20 weeks' gestation. Fetal radiation exposure was estimated to be less than 10 mSv. The use of a graduated catheter allowed measurement of field size and reliable determination of the patient's entrance dose. Radiation exposure of an approximated fetal dosage of 5.2 mSv did not justify abortion for medical reasons. Therefore, TIPS procedure is not generally contraindicated during pregnancy itself. TIPS placement may be a therapeutic option related to the severity of the underlying maternal disease, after radiation exposure of the fetus has been estimated.

Adult↗

PubMed1997

Interventional magnetic resonance. Initial clinical experience with a 1.5-tesla magnetic resonance system combined with c-arm fluoroscopy.

RATIONALE AND OBJECTIVES: The authors evaluate the feasibility of performing magnetic resonance (MR) procedures on a 1.5-tesla (T) system combined with conventional c-arm fluoroscopy. METHODS: A 1.5-T MR imaging system was combined with a conventional c-arm fluoroscopy unit in one room. The two systems were connected via a floating table top. Twenty-six interventional procedures (biopsies, MR-portography, percutaneous alcohol injection, laser ablation, fluid aspiration, and breast marking) were performed in 22 patients under MR, fluoroscopic control, or both. For MR guidance, fast gradient echo sequences were used, initiated from a panel at the front of the magnet. Images were displayed on an liquid crystal display screen positioned on the magnet. RESULTS: All MR-guided procedures were performed successfully without complications. The addition of c-arm fluoroscopy was useful for bone interventions and MR-portography. All diagnostic biopsies yielded sufficient amounts of tissue for histologic diagnosis. In breast lesions, the target identified on dynamic MR imaging was marked correctly in each case. In interstitial laser thermotherapy the laser effect could be visualized, and in percutaneous ethanol injection the distribution of the alcohol could be seen. Both imaging systems worked without image distortions and high-quality MR images were obtained. CONCLUSIONS: The combination of a 1.5-T MR imager with a c-arm fluoroscopy system seems to be a promising technical solution for performing interventional MR procedures.

Adult↗

PubMed1996

Quality control of bioprosthetic heart valves by means of holographic interferometry.

BACKGROUND AND AIMS OF THE STUDY: Limited durability of porcine bioprostheses is mainly caused by the progressive development of calcification. We tested the hypothesis that hidden tissue anomalies or unfavorable stress concentrations of commercially available bioprostheses may lead to later calcification and dysfunction. Application of holographic interferometry for non-destructive testing of biological heart valves enables a full-field analysis of heart valves and reveals deformation irregularities of valve tissue. MATERIAL AND METHODS: We developed an accelerated calcification protocol for bioprosthetic heart valves including an accelerated pulsatile valve tester for simultaneous testing of 10 heart valves under identical conditions and a rapid synthetic calcification fluid containing a final Ca x P of 130 (mg/dl)2 in barbital buffer solution. Ten porcine bioprostheses (St. Jude Medical, Bioimplant) were assessed by holographic interferometry and subjected to the pulsatile accelerated calcification process. Distribution and amount of calcification was evaluated by microradiography after 12 x 10(6) and 19 x 10(6) cycles, respectively. Areas of irregular fringe patterns detected by holography as well as areas of calcification were calculated and compared using a personal computer. RESULTS: All tested bioprostheses had localized or extended areas with holographic irregularities and the accelerated valve testing protocol resulted in even macroscopically visible calcifications at various sites. Comparative analysis of the obtained microradiographs revealed that 74.2% +/- 6.0% of calcified leaflet areas lay within the previously detected holographic anomalies. CONCLUSIONS: Our first results show a strong correlation between holographic anomalies and calcification of porcine bioprostheses. We conclude that suitable methods for evaluation and quality control of bioprosthetic heart valves are available and seem to be predictive with regard to valve calcification.

Aortic Valve↗

PubMed1995

[The potentials of digital image-intensifier radiography exemplified by digital spot imaging (DSI)].

PURPOSE: We performed a comparative study of digitally and conventionally acquired images in gastrointestinal examinations. MATERIAL AND METHODS: Radiation dose and spatial resolution were determined in a water phantom. In 676 examinations with either conventional or digital imaging (system: Diagnost 76, DSI) the number of images and the duration of the fluoroscopy time were compared. 101 examinations with digital as well as conventional documentation were evaluated by using 5 criteria describing the diagnostic performance. RESULTS: The entrance dose of the DSI is 12% to 36% of the film/screen system and the spatial resolution of the DSI may be better than that of a film/screen system with a speed of 200. The fluoroscopy time shows no significant difference between DSI and the film/screen technique. In 2 of 4 examination modes significantly more images were produced by the DSI. With exception of the criterion of edge sharpness, DSI yields a significantly inferior assessment compared with the film/screen technique. CONCLUSION: The DSI system was well integrated in the daily routine of gastrointestinal examinations. Low dose imaging, direct availability of images and dynamic studies with a frame rate up to 8 images per second are the advantages of the DSI. The lower spatial resolution in some cases is a diagnostic disadvantage that can reduce the diagnostic information.

Contrast Media↗

PubMed1995

[A new concept for rational emergency diagnosis of polytrauma patients].

To optimize the emergency care of patients with multiple injuries, a special emergency room with integrated radiological equipment has been developed. It consists of a linear array of a computed tomography system, a mobile C-arm with an integrated scattered radiation grid for conventional films and a C-arm fluorographic system. The intent is to avoid delay caused by transport and repositioning of the patient. It enables all necessary diagnostic procedures to be performed within a minimal amount of time. If there are no emergency patients, the room can be divided by a sliding door and the equipment can be used separately.

Emergency Service, Hospital↗

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↗

PubMed1993

[Computer-assisted speech recognition and display of x-ray findings].

A voice recognition system, called Tangora, has been designed for the German language; its prototype has been tested to assess its clinical usefulness for radiological reporting. Its technical vocabulary consists of 20,000 words. The system recognises words spoken provided short pauses are inserted. The Tangora system was compared with conventional methods of dictation, using 68 radiological reports. The work necessary for each system was analysed. The average time taken by the Tangora system per report was 671 seconds compared with 182 seconds for conventional dictation but improvements in the speed of the new system for radiological reporting is to be expected.

Computer Terminals↗

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

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↗

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↗

PubMed1991

[The renaissance of simultaneous tomography with the fluorescent-film storage system].

The handling, technical and exposure details of digital simultaneous tomography are explained, while particular emphasis is placed on image quality. Selected case reports demonstrate the application of this technique by using the digital storage fluorescent system (Fa. Siemens, Erlangen). Simultaneous tomography with storage fluorescent screens is particularly suitable to demonstrate or exclude osseous findings at the skull, the column and large joints.

Adult↗

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↗

PubMed1989

[Digital radiography: a new approach in roentgen diagnosis].

Digital electronics now play a role in every branch of diagnostic imaging. One of the most recent methods, digital radiography (DR) makes it possible to store and view radiographs in the form of a matrix of discrete values. The present review describes the components needed for DR imaging and archiving as well as the advantages and disadvantages of the system. The use of storage phosphor is hereby of special interest. By enableing the viewer to process the images, it is hoped that DR will open up new possibilities for projection radiography and strengthen its position as a routine method in comparison to other digital imaging systems, e.g. CT. It remains to be seen whether or not DR, as an isolated system, will be widely used. But in any case it represents the missing link in the chain of digital imaging methods and opens new ways of imaging archiving and administration.

Bone Diseases↗

PubMed1986