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Biomedical subjects

H Lenzen

Publications and source records attributed to H Lenzen.

32 records · Page 2Linked to original sources
PubMed1995

[Exposure of personnel in interventional radiology].

The surface dose at five typical positions around the patient couch was measured during transjugular intrahepatic porto-systemic stent shunt (TIPSS) interventions for retrospective calculation of staff dose. Additionally, the surface dose was measured on three members of staff (two radiologists and one technician) by placing thermoluminescence (TL) dosimeters directly on the eyebrows, thyroid, sternum, gonads, hands, knees, and feet. The measured surface dose values and the TL dosimeter measurements are used for estimation of effective dose per examination received by personnel. The effective dose for the radiologists is calculated to 25-35 microSv. The maximum number of examinations allowed per year is calculated on the basis of a given yearly dose limit, by looking at organ dose and effective body dose.

Female↗
PubMed1994

[The value of the InSight HC asymmetric film-screen system in thoracic diagnosis].

The asymmetric film-screen system InSight HC represents a development to optimize chest imaging. The purpose of the study was to compare the exposure range and the image quality of this new system with a conventional film-screen system. The optical density of images in both techniques was measured and the image quality of 100 chest images from 50 intensive-care patients was evaluated. 4 observers graded the image quality of organic, non-organic and pathological structures. Statistical evaluation was performed by interobserver analysis. The asymmetric film-screen system shows a larger exposure range and a superior image quality in the mediastinal field. The image quality in the peripheral field must be judged critically and improved especially because of the poor recognizability of pneumothoraces.

Evaluation Studies as Topic↗
PubMed1994

Artificial bone erosions: detection with magnification radiography versus conventional high-resolution radiography.

PURPOSE: To compare the diagnostic performance of direct magnification radiography with computed radiography versus that of conventional radiography in detection of artificial bone erosions. MATERIALS AND METHODS: Thirty-one paws from German shepherd dogs were embedded in paraffin and examined with x6 magnification radiography and conventional radiography before and after creation of artificial bone erosions. A microfocal x-ray unit with a focal spot of 20-130 microns was used for magnification radiography. All 210 images were analyzed by five radiologists, and receiver operating characteristic (ROC) analysis was performed. Interobserver analysis in evaluation of anatomic structures was also performed. RESULTS: ROC analysis of pooled data from all readers showed a larger area under the ROC curve for magnification radiography (0.88) than for conventional radiography (0.72). Magnification radiography produced higher scores in interobserver analysis as well. CONCLUSION: Magnification radiography is superior to conventional radiography in detection of small bone erosions.

Animals↗
PubMed1993

[Postmortem high-resolution computed tomography of the lung. Radiologic-morphologic correlations].

To establish precise correlations between high-resolution computed tomography (CT) and normal pulmonary anatomy and pulmonary pathology, 49 lungs affected by different diseases were analysed. Post-mortem high-resolution CT scans were compared with the corresponding macroscopic and microscopic pathological findings. For scanning, lungs were inflated and fixed, which avoided any decrease in the structural resolution of pulmonary parenchyma and allowed a topographically exact correlation between CT appearances and morphological changes. After demonstration of the structural details relevant for CT in normal pulmonary parenchyma, an attempt is made to establish the morphological basis of the following CT phenomena: thickening of interlobular septae, increase in pulmonary translucency, consolidation of the non-nodular alveolar and of the nodular type, and changes in the pleural region. Although CT findings in pulmonary lesions are mainly non-specific, knowledge of the corresponding morphological basis is helpful in diagnostic evaluation.

Animals↗
PubMed1992

Gas exchange impairment and pulmonary densities after cardiac surgery.

In 11 patients with impaired respiratory function after coronary artery revascularization surgery, thoracic computed tomography (TCT) and cardiopulmonary profile were obtained. The patients were haemodynamically stable without clinical or radiological signs of lung oedema. Oxygenation was reduced in all patients (alveolo-arterial PO2-difference (PA-aO2) = 37.3 +/- 10.39 kPa, venous admixture (QVA/QT) = 26.4 +/- 4.4%) during mechanical ventilation with positive end-expiratory pressure (PEEP = 5 cmH2O) (0.5 kPa). TCT-scan analysis revealed considerable amounts of crest-shaped bilateral densities in dependent lung regions. There were no differences between the right and left hemithorax. Atelectatic lung tissues were defined as areas presenting with attenuation values of -200 to +20 Hounsfield Units. The magnitude of non-ventilated areas correlated with QVA/QT (r = 0.875, P < or = 0.01), but not with the duration of either extracorporeal circulation, surgical procedure or general anaesthesia. It is concluded that atelectasis in dependent lung areas contributes to impaired gas exchange after cardiac surgery.

Aged↗
PubMed1992

[Evaluation of different methods of control of film processing].

In addition to the official control method (DIN 6868), alternative test methods have been developed in the last few years: the "visuelle Methode" by Eder and the "Stuttgarter Modell." The aim of both methods is mainly to increase practicability and economy. The DIN method, however, demonstrates clear benefits, precision, practicability and economy, and it is the only method that allows a trend analysis at small intervals, which is the basis for possible preventive action.

Germany↗
PubMed1992

[Sources of error in the quality assurance of x-ray equipment].

With the introduction of the German industrial protocol for quality assurance of X-ray equipment, everybody using X-ray machines fell into some sort of trap or found some of the procedures misleading. Vigorous discussions were held on every conceivable aspect of this and other protocols, and are still in progress. This paper points out some of the common traps and considers a new type dosimeter, which allows a definite separation of quality assurance of X-ray equipment and of processing and which can also be used in future for quality assurance of digital radiography equipment.

Germany↗
PubMed1991

[Experimental results of the "visual technique"].

This is a study on the applicability of the visual method as an alternative to the present film processing control method according to German DIN standards. It was found that the results are greatly dependent of the kV values. This makes it doubtful whether the method is feasible in its present form. Furthermore, the validity of this method is also limited by the fact that fog and contrast are no longer used as criteria for assessing the development process.

Germany↗
PubMed1991

[A method of estimating doses in digital luminescent radiography].

Digital storage phosphor radiography can produce images of a constant optical density over a wide range of exposure dose by adjusting reading sensitivity. Since overexposed images are not as readily recognized as with the conventional film-screen technique, a formula was designed, which calculates the radiation dose in the film plane from image sensitivity (S factor), latitude (L factor) and average grey value of the region of interest. To verify the formula, 168 measurements with variation of dose, kVp, L factor, S factor and the readout algorithm were performed using the DIGISCAN storage phosphor system (Siemens). The experiments confirmed the validity of the formula for an S factor of below 5000 (values during routine use 50-400). Correlation between dosimetrically measured radiation dose and the calculated dose was 0.997.

Humans↗
PubMed1989

[CT studies of the lung in opportunistic infections].

Immunosuppressive patients are at high risk of opportunistic infections whose main site of manifestation is the lung. The prognosis depends largely on starting therapy in time. Thorax CT supplies an important contribution especially in diagnosis and monitoring of pneumomycoses, which are particularly relevant among the problem infections on account of their frequently lethal course: compared with conventional thorax imaging, CT detects infiltrates much earlier; in addition, it presents a characteristic course of pulmonary changes enabling at least in part some conclusions regarding the pathoanatomical substrate. The article reports on the prerequisites for an infection justified indication for thoracic CT, on its execution and on the findings as for example in pneumomycoses.

Aspergillosis↗
PubMed1988

[Quality assurance in x-ray diagnosis as specified in DIN 6868].

Regular quality control and safety assurance in diagnostic radiological systems are included in the new radiation protection regulations. The monitoring program for both the equipment and the film processor can enable the user to recognize loss of quality early. Variables in the film processing unit can be differentiated from faults in the X-ray equipment more easily, including its use. The cost and time spent in setting up a safety assurance program are justified by the increase in quality.

Germany, West↗
PubMedDate not supplied

[Clinical use of magnification radiography in rheumatologic differential diagnosis].

Rheumatologic joint disorders were examined with high-definition microfocal magnification radiography. The magnification technique was compared to conventional radiographs (mammographic film-screen combinations). The microfocal x-ray unit had a spot size of 20-130 microns. Fourty patients with early arthritis (history of less than 18 months) were examined; x5 magnification was used. Digital luminescence radiography was employed to minimize radiation dose. Digital image processing included simulation of conventional technique and edge enhancement. Magnification radiographs and conventional technique were evaluated. In 20/40 patients articular lesions were detected. Magnification radiography gave additional information in 14/20 patients: in 5/14 patients lesions were seen only with magnification radiography (erosions n = 3, loss of the cortical white line n = 2), in 9/14 patients the extent of the lesions could be evaluated better. Hence, magnification radiography proved a valuable mean in early diagnosing and evaluating rheumatic disease.

Adolescent↗