Biomedical subjects

G Weisser

Publications and source records attributed to G Weisser.

24 records · Page 2Linked to original sources

PubMed1994

[The color-coded duplex sonography and contrast-enhanced magnetic resonance tomography of scintigraphically cold thyroid nodules].

In order to establish diagnostic criteria, colour-coded duplex sonography was performed on 40 patients who had a total of 43 operatively confirmed thyroid lesions which were scintigraphically "cold" (28 adenomas, 8 carcinomas, 4 cases of thyroiditis and 3 cysts). 32 of these patients also had MRT with T2- and T1-weighted images before and after injection of Gd-DTPA (0.1 mmol/kg). Adenomatous nodules and adenomas showed a peripheral vascular halo on colour-coded duplex sonography with a sensitivity of 96% and a specificity of 93%. Malignant lesions showed marked central vascularisation and on B-images irregular marginal structures. Adenomas and adenomatous nodules showed hyperintense areas on T1-weighted unenhanced MR images and/or homogeneous uptake in the lesion (sensitivity 100%, specificity 77%). Malignant lesions typically showed an irregular margin with increased contrast uptake on MRT. If sonography and colour-coded duplex sonography is unable to classify a lesion with any degree of assurance then MRT with Gd-DTPA enhancement should be performed.

Adult↗

PubMed1994

[MR tomography of lung metastases with rapid gradient echo sequences. Initial results in diagnostic applications].

Rapid gradient echo sequences enable MR imaging (MRI) of pulmonary metastases with acquisition times of less than 1 s per slice. By optimization of this technique, density, T1- and T2-weighted images can be obtained (FLASH: TR 6.5 ms, TE2 = 3 ms, alpha = 10 degrees; T1w-Turbo-FLASH: TI 200 ms, TR 6.5 ms, TE2 = 3 ms, alpha = 10 degrees; T2w-Turbo-FLASH: TE1 = 50 ms, TR = 6.5 ms, TE2 = 3.5 ms; alpha = 10 degrees). In a prospective study 25 patients in whom pulmonary metastases were suspected were examined with three techniques in all three anatomical planes prior to surgery. All lung metastases revealed a high signal intensity on the FLASH as well as the T2w-Turbo-FLASH images, whereas vascular structures revealed a low signal intensity on the T2-weighted Turbo-FLASH images. Analysis regarding detection and correct number of lung metastases per patient with MRI compared with the histology revealed (n = 25): sensitivity of 82%, specificity 67%, positive predictive value of 95% and negative predictive value of 33%. While MRI does not currently have any diagnostic advantages over CT, the excellent differentiation of parenchymal lesions and vascular structures without the use of contrast medium and the variability of imaging planes are significant methodological advantages.

Adolescent↗

PubMed1989

[Escape of hydrogen peroxide and oxygen from the root canal].

In vitro investigations demonstrate that hydrogen peroxide, like the oxygen emitted from the root canal, escapes into the area around the root. The amount measurable was dependent on the concentration, the amount of time that the hydrogen peroxide was left in the root canal and the patency of the foramen apicale. The growth of the Staphylococcus aureus (SG 511) was restricted in the area around those roots whose root canal contained a 5% solution of hydrogen peroxide.

Dental Pulp Cavity↗

PubMed1981

[Neuroradiology of the normal and pathological anatomy of the rat brain.--III Morphology and growth behaviour of experimental brain tumours following radiation therapy (author's transl)].

Radiation induced (30 Gy) morphological changes of experimental malignant brain tumors, which were produced by chemical carcinogenesis, were investigated by microangiography and correlated with the histological findings in 62 BD-IX-rats. In randomized groups the investigations were performed 2, 3, 6 and 8 weeks after the radiation was finished. Morphologically different reactions could be differentiated: remissions or partial recovery of the tumors, rest or recurrent tumor and uninfluenced tumor growth. The characteristic findings, the reasons for different courses and possible conclusions concerning the radiotherapeutical effect are discussed.

Animals↗

PubMed1980

[Neuroradiology of the normal and pathological anatomy of the rat brain. II Microangiographic investigations of the vascularisation of transplanted malignant brain tumors (author's transl)].

70 BD-IX rats, in which chemically induced mixed gliomas have been transplanted intracerebrally, were investigated by microangiography. The pattern and the degree of tumor vascularisation of all animals was correlated with the histological findings. Depended on the type of the tumor different localisations of tumor growth could be found: G XII-gliomas preferred the juxtaventricular region and subarachnoid space whereas GL 2.2-gliomas mainly grew as solid intracerebral space occupying lesions. Microangiograms of all tumor stages from the 14th to 42nd day after transplantation revealed a typical vascular pattern consisting of lacunar, glomerulose and netlike vessels. Further, necrosis, bleedings into the tumor, and irregularities of the capillary network could be demonstrated. The volume, age and vascularisation of the tumors are correlated and the results are discussed with regard to the principles of tumor growth and malignancy.

Animals↗

PubMedDate not supplied

Quantitative characterization of color Doppler images: reproducibility, accuracy, and limitations.

A computer-based quantitative analysis for color Doppler images of complex vascular formations is presented. The red-green-blue-signal from an Acuson XP10 is frame-grabbed and digitized. By matching each image pixel with the color bar, color pixels are identified and assigned to the corresponding flow velocity (color value). Data analysis consists of delineation of a region of interest and calculation of the relative number of color pixels in this region (color pixel density) as well as the mean color value. The mean color value was compared to flow velocities in a flow phantom. The thyroid and carotid artery in a volunteer were repeatedly examined by a single examiner to assess intra-observer variability. The thyroids in five healthy controls were examined by three experienced physicians to assess the extent of inter-observer variability and observer bias. The correlation between the mean color value and flow velocity ranged from 0.94 to 0.96 for a range of velocities determined by pulse repetition frequency. The average deviation of the mean color value from the flow velocity was 22% to 41%, depending on the selected pulse repetition frequency (range of deviations, -46% to +66%). Flow velocity was underestimated with inadequately low pulse repetition frequency, or inadequately high reject threshold. An overestimation occurred with inadequately high pulse repetition frequency. The highest intra-observer variability was 22% (relative standard deviation) for the color pixel density, and 9.1% for the mean color value. The inter-observer variation was approximately 30% for the color pixel density, and 20% for the mean color value. In conclusion, computer assisted image analysis permits an objective description of color Doppler images. However, the user must be aware that image acquisition under in vivo conditions as well as physical and instrumental factors may considerably influence the results.

Algorithms↗