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Biomedical subjects

M Georgi

Publications and source records attributed to M Georgi.

At least 91 records · Page 5Linked to original sources
PubMed1995

Resolution of catecholic tetrahydroisoquinoline enantiomers and the determination of R- and S-salsolinol in biological samples by gas chromatography-mass spectrometry.

Tetrahydroisoquinolines (TIQs) might be formed endogenously and can act centrally to promote a mechanism governing alcohol drinking behaviour. The possibility that biosynthesis occurs through a stereospecific enzymatic reaction is considered. Several TIQs were transformed into diastereomers by a two-step derivation with N-methyl-N-trimethylsilyltrifluoracetamide and R-(-)-2-phenylbutyrylic acid and were analyzed by gas chromatography-mass spectrometry (GC-MS). High resolution of the TIQ enantiomers was achieved. This method was applied to the quantification of the enantiomers of salsolinol (SAL) in urine and plasma of healthy humans. Deuterated SAL was used as the internal standard. SAL was extracted from biological material using phenyl-boronic phase cartridges and transformed into diastereomers. The sensitivity and specificity of the assay permit the determination of the enantiomeric composition of SAL in plasma and urine. The limit of quantification was found to be 100 pg/ml for each enantiomer. The described method has the advantage that optimal resolution of the SAL enantiomers without peak overlapping between analyte and other compounds can be achieved. Contrary to other findings, our GC-MS studies have demonstrated that endogenously formed SAL is racemic in plasma as well as in urine of healthy subjects.

Deuterium↗
PubMed1995

[Noninvasive quantification of cerebral blood volume and blood flow with dynamic MR tomography. Studies of probands and patients with cerebrovascular insufficiency].

PURPOSE: A non-invasive MR-method for the quantification of regional cerebral blood flow (rCBF) and blood volume (rCBV) is used to examine healthy volunteers and patients with cerebrovascular disorders. MATERIALS AND METHODS: 20 healthy volunteers and 10 patients with severe cerebrovascular disorders were examined. MR imaging was performed on a 1.5 T imaging system. Before, during and following brief antecubital vein bolus injection of Gd-DTPA, a series of 32 rapid T2*-weighted gradient echo images of two different slices ere simultaneously acquired in order to measure th concentration-time-curves in the brain tissue and the arterial input function in the brain feeding arteries. From these series of images the concentration-time-curves were computed. Principles of indicator dilution analysis were applied to compute rCBF and rCBV. The volunteers underwent one examination each. All patients underwent two examinations, one before and the second after azetazolamide stimulation. RESULTS: In volunteers the measured rCBF and rCBV values are in good agreement with data from positron emission tomography studies. In patients with cerebrovascular disorders in the asymptomatic hemisphere a mean increase of rCBF of 43,45 +/- 18.04% was observed after azetazolamide stimulation. In the affected areas of the symptomatic hemisphere in 8 from 10 patients the acetazolamide test reveals a significantly reduced response to azetazolamide stimulation, indicating an exhausted cerebrovascular reserve capacity. CONCLUSION: Dynamic MR-Imaging can provide quantitative information about rCBF and rCBV. In patients with cerebrovascular disorders, this method can be applied to estimate the cerebrovascular reserve capacity.

Acetazolamide↗
PubMed1994

[CT diagnosis of acute mesenteric vein thrombosis with intestinal infarction].

Imaging methods provide an important diagnostic basis to clarify mesenteric ischemia. Angiography is the definitive method of investigation in such cases. Other noninvasive methods such as ultrasonography, computed tomography, and magnetic resonance imaging must still prove their importance. We describe three cases of unspecific abdominal pain where the CT shows a mesenteric venous thrombosis with an infarcted bowel. The venous infarcted bowel is clearly demonstrated by CT when other signs for MTV such as ascites, bowel wall thickening, bowel dilatation, and pneumatosis intestinalis are present. CT seems to be a good procedure in order to identify unspecific abdominal pain as being caused by a vascular insufficiency.

Adult↗
PubMed1994

Usefulness of bioelectric impedance and skinfold measurements in predicting fat-free mass derived from total body potassium in children.

Despite the increasing use of tetrapolar whole-body bioelectric impedance (BI) analysis in the assessment of body composition, its usefulness in estimating fat-free mass (FFM) has not been evaluated in comparison with conventional skinfold anthropometry in children. We therefore compared 1) the intraobserver and interobserver reproducibility of BI and skinfold measurements and the derived FFM estimates, and 2) the predictability of FFM as calculated from measurements of total body potassium (TBK) using 40K spectrometry by equations based on either BI or skinfold measurements in 112 healthy children, adolescents, and young adults aged 3.9 to 19.3 y. A best-fitting equation to predict TBK-derived FFM from BI and other potential independent predictors was developed and cross validated in two randomly selected subgroups of the study population by stepwise multiple regression analysis. Although the technical error associated with BI measurements was much smaller than that of skinfold measurements, the reproducibility of BI-derived FFM estimates (intraobserver coefficient of variation [CV], 0.39%; interobserver CV, 1.23%) was only slightly better than that of FFM estimates obtained by use of weight and two skinfold measurements (0.62% and 1.39%, respectively). The cross validation procedure yielded the following best-fitting prediction equation: FFM = 0.65 x (height2/impedance) + 0.68 x age + 0.15 (R2 = 0.975, root mean square error = 1.98 kg, CV = 5.8%, 95% limits of agreement = -11.1% to +12.4%). Conventional anthropometry, using published equations to estimate FFM from skinfolds, slightly over-estimated TBK-derived FFM, but predicted FFM with precision similar to the best-fitting equation involving BI. Previously published FFM equations incorporating BI predicted TBK-drived FFM with variable predictive precision and accuracy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Digital fluoroscopic radiology: evaluation of the clinical impact.

The use of digital image intensifier radiography (DIIR) for examinations in projection radiography is becoming more common. Fluoroscopic controlled contrast studies (barium- or iodine-based), particularly of the gastrointestinal tract, can be performed quickly and easily with a considerable decrease in radiation exposure. A wide dynamic range permits a constant high image quality with fewer incorrect exposures. The limited spatial resolution of large image intensifier input screens is the major drawback of DIIR. Digital image acquisition enables post-processing, digital storage and transfer of images, thus allowing an integration into PACS-systems. Imaging capabilities and clinical applications are described here.

Contrast Media↗
PubMed1993

[Prevention of human birth trauma I. Computer-assisted simulation of delivery using magnetic resonance tomography and finite element analysis].

Imaging procedures suitable for diagnosis of cephalopelvic disproportion, such as radiological pelvimetry, computer- or magnetic resonance imaging (MRI) fail to reflect the dynamics of delivery, including deformations of the birth channel as well as of foetal structures. In order to validate findings of imaging procedures in this respect, a method has been developed to perform dynamic, biomechanical postprocessing of the static information obtained from MRI. Using a specially developed software MRI pixel, matrices of the maternal pelvis and the foetal head were colour-coded and--according to the principle of equal density--line data were created. After sectional attribution of the resulting polygones, a three-dimensional mesh of so called Finite Elements (FE) was created, which can then be used for deformation analysis. The foetal head was then moved through the birth channel by means of computed simulation. This allows not only ongoing deformations to be visualised, but also resulting forces can be calculated at any time of the delivery process for any point of the anatomical model. Furthermore, these calculations can be performed assuming various conditions such as different cephalopelvic dimensions and various labour forces or biomechanical properties of the tissues involved. This paper aims at presenting the method and its mode of working by means of one example of a computed birth simulation.

Adult↗
PubMed1993

[Computed tomography in a case of pseudomembranous colitis].

Pseudomembranous colitis (PMC) is an infectious colitis usually occurring as a complication of antibiotic therapy. The computed tomography (CT) findings of 10 patients with PMC are reviewed. All patients demonstrated an abnormal large bowel wall with an average thickness of 13 mm (range 7-31 mm). Additional, but less frequent findings included mesenteric inflammation, ascites, pleural effusions, and dilatation of the large or small bowel. Pancolonic involvement was seen in 7 cases, while three patients had focal colitis. Although the CT appearance of PMC is not specific, the diagnosis may be suggested in the proper clinical setting.

Adult↗
PubMed1993

[Echomorphology of breast cancer].

Breast carcinoma presents with very heterogeneous histopathological pattern. According to the macroscopic growth pattern, we distinguish five different tumor types, each responsible for typical sonographic characteristics: intraductal, circumscribed, stellate, diffuse and intermediate/mixed pattern. The different echographic features of these malignancies will be analysed in relation to histomorphological parameters.

Breast Diseases↗
PubMed1993

[New imaging methods in thoracic diagnosis. A study to evaluate digital storage screen radiography, the slit technique ("AMBER"), asymmetric ("InSight") and conventional film-screen techniques].

New methods have been introduced in recent years in chest imaging to achieve high image quality simultaneously in the mediastinum and in the lung field. In this study the clinical value is assessed for four techniques: digital storage phosphor radiography, slit-technique ("AMBER"), asymmetrical film/screen ("InSight") and conventional film/screen. 43 patients were examined with these techniques within one day. Seven readers of four universities graded the image quality according to ten criteria of the mediastinum and the lung field. The slit-technique ("AMBER") showed the best image quality in both areas. Compared to conventional film/screen, storage phosphor radiography and asymmetrical film/screen ("InSight") yield better image quality only in the mediastinum.

Adult↗
PubMed1993

[New analog and digital imaging techniques for chest diagnosis--principles--clinical value--economics].

For chest imaging new analog and digital imaging techniques are now available. In this publication the imaging methods conventional film/screen, asymmetric film/screen("In-Sight"), slit(AMBER)-technique, spotfilm(100 mm)-technique, storage phosphor radiography and digital image intensifier radiography are compared. The clinical value is discussed by measured imaging capabilities and patient examinations. The highest image quality was demonstrated by the slit(AMBER)-technique. In comparison to conventional film/screen, storage phosphor radiography and asymmetric film/screen was graded higher only in the mediastinal field. Because of the low spatial resolution the image quality of digital image intensifier radiography was classified too poor for chest imaging.

Germany↗
PubMed1992

[MR angiography of the vertebrobasilar circulatory area: the potential uses of the saturation technic to determine the direction of the flow].

MR angiography (MRA) combined with selective saturation techniques has proved to be a reliable method for the determination of flow direction and vascular supply at the level of the circle of Willis. We describe its application to the vertebrobasilar system (VBS) in ten volunteers and five patients with abnormal findings. In one patient with postsurgical stenosis of the brachiocephalic artery, reverse flow of the vertebral artery (VA) was demonstrated. Collateral blood flow from the anterior circulation over the posterior communicating arteries was shown in three patients with bilateral vertebral or proximal basilar artery occlusion. Due to increase of pressure during contrast injection into the contralateral VA, DSA showed reverse flow of a dissected VA in one patient. MR flow determination as well as TCD proved antegrade flow. All results correlated with both DSA and transcranial Doppler (TCD). The technique is little time consuming and is a promising add-on examination to conventional and MRA imaging of the VBS.

Adult↗
PubMed1992

[MR tomographic studies of the cerebral circulation: the methodological principles and initial clinical experiences with T2*-weighted gradient-echo sequences and CM administration as a bolus].

Paramagnetic contrast agents produce local magnetic field inhomogeneity when they pass through the cerebrovascular system. This effect can be monitored with T2*-weighted gradient echo images, which show transient signal loss, while a bolus of GdDTPA is passing through the brain tissue. This signal loss is correlated to the local cerebral tissue perfusion and the local cerebral blood volume. In a prospective study 10 volunteers and 14 patients with cerebral infarcts and brain tumours were examined. After bolus application of GdDTPA a dynamic series of rapid T2*-weighted gradient echo images were recorded, and the local dynamics of contrast flow in brain tissue was examined. From the series of images, local changes in signal intensity were calculated pixel by pixel and presented as parameter images. By this method, infarcted areas and brain tumours can be distinguished from normal tissue by their contrast flow dynamics. The abnormal contrast dynamics depend on changes in local tissue perfusion and alterations in local blood volume. The separation of the influence of both parameters however is still an unsolved problem.

Adolescent↗