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Biomedical subjects

K Barth

Publications and source records attributed to K Barth.

At least 19 recordsLinked to original sources
PubMed2002

Establishment of the telencephalon during gastrulation by local antagonism of Wnt signaling.

Cells at the anterior boundary of the neural plate (ANB) can induce telencephalic gene expression when transplanted to more posterior regions. Here, we identify a secreted Frizzled-related Wnt antagonist, Tlc, that is expressed in ANB cells and can cell nonautonomously promote telencephalic gene expression in a concentration-dependent manner. Moreover, abrogation of Tlc function compromises telencephalic development. We also identify Wnt8b as a locally acting modulator of regional fate in the anterior neural plate and a likely target for antagonism by Tlc. Finally, we show that tlc expression is regulated by signals that establish early antero-posterior and dorso-ventral ectodermal pattern. From these studies, we propose that local antagonism of Wnt activity within the anterior ectoderm is required to establish the telencephalon.

Animals↗
PubMed2000

Enhanced 3-D-reconstruction algorithm for C-arm systems suitable for interventional procedures.

Increasingly, three-dimensional (3-D) imaging technologies are used in medical diagnosis, for therapy planning, and during interventional procedures. We describe the possibilities of fast 3-D-reconstruction of high-contrast objects with high spatial resolution from only a small series of two-dimensional (2-D) planar radiographs. The special problems arising from the intended use of an open, mechanically unstable C-arm system are discussed. For the description of the irregular sampling geometry, homogeneous coordinates are used thoroughly. The well-known Feldkamp algorithm is modified to incorporate corresponding projection matrices without any decomposition into intrinsic and extrinsic parameters. Some approximations to speed up the whole reconstruction procedure and the tradeoff between image quality and computation time are also considered. Using standard hardware the reconstruction of a 256(3) cube is now possible within a few minutes, a time that is acceptable during interventions. Examples for cranial vessel imaging from some clinical test installations will be shown as well as promising results for bone imaging with a laboratory C-arm system.

Algorithms↗
PubMed1996

On-line evaluation of systolic performance by densitometry in digital left ventriculography.

The angiocardiographic evaluation of left ventricular end-diastolic (LVEDV) and end-systolic (LVESV) volumes and ejection fraction (EF) is routinely performed by the area-length method (ALM) but may lead to erroneous results. Digital imaging in real time allows densitometric procedures of determining left ventricular (LV) performance to be applied alternatively. In this study, we present densitometric algorithms for the analysis of LVEDV, LVESV, and EF from digital image data, establish accuracy and reproducibility, and determine value and limitations in comparison with ALM in single-plane 30 degrees right anterior oblique (RAO) projection. A linear relationship between iodine depth and measured densities is mainly burdened with scatter radiation and beam hardening which reduce primary radiation and suppress iodine depth. However, facilities such as deconvolution and correction algorithms are capable of reducing these sources of error. In the present study, computer-analyzed contrast images of iodine-filled wedges and spheres showed a near-linear relationship between iodine depth between 50-100 mg/cm2 and measured densities. Contrast images of heart casts and LV angio-grams of 54 patients were obtained with a digital image acquisition and processing system, and evaluated by two independent observers. The phantom study resulted in significantly (p < or = 0.01) better densitometric standard errors of estimate for volumes [3.3 ml densitometry (DENS) vs. 8.9 ml (ALM)] and simulated EF [4.3% (DENS) vs. 7.8% (ALM)] than ALM. The standard error of estimate for the comparison between both methods was 8.4 ml for volumes and 7.5% for EF. Densitometric volumes tended to underestimate volumes calculated by ALM. The angiographic study of patients demonstrated significant correlations between both methods (LVEDV r = 0.78, LVESV r = 0.83, total volumes: r = 0.89; EF r = 0.88). The standard errors of estimate can be ascribed to systematic, method-related errors of both DENS and ALM (LVEDV +/- 28.9 ml, LVESV +/- 23.4 ml, total volumes (EDV and ESV) +/- 27.1 ml; EF +/- 8.1%). The intra- and interobserver variability, respectively, exhibited significantly smaller (p < or = 0.01 and p < or = 0.05, respectively) standard errors of estimate for densitometric EF [4.6% (DENS) vs. 8.5% (ALM) and 7.1% (DENS) vs. 10.3% (ALM), respectively]. Inclined but not significant differences were found for LVEDV and LVESV. In conclusion, the data presented indicate that the calculation of LV volumes and EF in digital left ventriculography may be performed accurately by densitometric calculation in single-plane 30 degrees RAO projection. Minor underestimations in densitometric volume determination may be anticipated in the evaluation of LV geometry.

Adult↗
PubMed1996

Digital ventriculography: valid on-line calculation of cardiac volumes by corrected computer densitometry in coronary artery disease.

Cardiac catheterization facilitates the assessment of left ventricular function in coronary artery disease (CAD). Digital left ventriculography offers the potential for an on-line quantitative determination of left ventricular end-diastolic volume (LVEDV) and left ventricular end-systolic volume (LVESV). These are routinely evaluated by the area-length method (ALM), which is considered as a standard. Densitometry (DENS) is an alternative method but may lead to calculated underestimations. The purpose of this study was to investigate the accuracy of corrected DENS for LVEDV and LVESV in comparison with ALM in single-plane 30 degrees right anterior oblique (RAO) projection. The computer densitometric correction equation was adapted from the linear regression analysis (y = 0.86x + 2.73) in cardiac models and applied to the analysis of digital left ventriculograms in patients suffering from CAD. The study of cardiac models yielded highly significant correlations (r > or = 0.9; P < or = 0.001) between true volumes and both DENS and ALM. DENS and ALM correlated highly significantly (r > or = 0.9; P < or = 0.001) with a low standard error of estimate (SEE) of +/-9.5 mL. The comparison of DENS and ALM in 44 patients' digital ventriculograms exhibited highly significant (r = 0.74; P < or = 0.001) correlations for noncorrected and corrected LVEDV. Systematic underestimation by DENS of LVEDV disappeared after correction and SEE decreased from +/-23.7 to +/-19.2 mL. DENS and ALM correlated highly significantly for LVESV (r = 0.78; P < or = 0.001; SEE +/- 15.6 mL +/- 13.5 mL, respectively) after correction. Following correction, mean values for DENS increased from 116 +/- 32 to 132 +/- 37 mL (LVEDV) and 50 +/- 22 to 55 +/- 25 mL (LVESV). For ALM, mean values decreased from 159 +/- 35 to 127 +/- 28 mL (LVEDV) and 55 +/- 25 to 46 +/- 21 mL (LVESV). This study shows that LVEDV and LVESV can be reliably analyzed on-line by corrected computer densitometry. Method-related errors of both DENS and ALM are present and account for minor volume deviations.

Aged↗
PubMed1996

Improved densitometric analysis of ventricular volumes in on-line digital cardiac imaging.

In digital angiocardiography left ventricular volumes are routinely calculated by the area-length-method (ALM) which is considered to be a standard and with which other techniques are compared. Densitometric analysis (DENS) is an alternative method and can be performed on-line but may lead to erroneous results. A novel technique of densitometric calculation of left ventricular enddiastolic and endsystolic volume (LVEDV resp. LVESV) is presented. Digital images were analyzed by measuring densities of iodine signals and transforming these into calculated volumes by applying appropriate computer algorithms. The evaluation of volumes in cardiac models demonstrated significant correlations between true volumes and both DENS and ALM. An algorithmic approach to volume correction in patient evaluation of left ventricular volumes was drawn from the linear regression analysis of DENS and true volumes in the cardiac models. LVEDV and LVESV calculated by DENS correlated significantly with volumes determined by ALM in patients (r=0.78 resp. r=0.83) but showed a systematic underestimation for volumes > or =45 ml without densitometric correction. Following correction for DENS, an improvement in calculation was observed for volumes < or =200 ml without systematic deviations. In conclusion, our study demonstrates that corrected densitometric volumetry offers the potential for a reliable on-line analysis of enddiastolic and endsystolic volumes. Modest, but no systematic deviations for densitometric analysis may be anticipated in myogene dilatation with volumes larger than 200 ml. However, when comparing both DENS and ALM, method-related errors of both techniques are present and account for volume deviations.

Absorptiometry, Photon↗
PubMed1993

[Digital subtraction angiocardiography: reliability of densitometric determination of left ventricular volume and ejection fraction].

The angiographic assessment of left ventricular volume (LV) and ejection fraction (EF) by means of the area-length method (ALM) is based upon geometric assumptions, which might lead to erroneous results. With the development of digital subtraction angiocardiography in real-time, densitometric procedures of calculating left ventricular parameters can be used on-line. This study examines both reliability and accuracy of a densitometric technique for evaluating LV and EF in comparison to the single-plane ALM. Contrast images of heart casts and left ventricular angiograms of 54 patients suffering from different cardiac diseases were obtained by the image acquisition and processing system Polytron 1000 VR (Siemens AG, Erlangen, FRG). Digital images of both heart casts and patients were evaluated densitometrically and geometrically by two independent observers. In the phantom study the densitometric method exhibited a significantly (p < 0.01) better agreement with the true values than the ALM. The evaluation of left ventricular angiograms in patients comparing densitometry with the ALM demonstrated a relatively high residual deviation (enddiastolic volume Syx = +/- 27 ml, endsystolic volume Syx = +/- 19.4 ml). This is mainly due to systematic, method-related errors of densitometry and the morphometric technique. The intra- and interobserver variability in calculating EF showed a significantly (p < 0.05) smaller residual deviation for densitometry than for ALM; no significant differences were found for the calculation of LV. In conclusion, we demonstrated that the presented densitometric technique offers an objective and simple means of determining LV and EF with comparable reliability and validity to the area-length method.

Absorptiometry, Photon↗
PubMed1991

Dieting and pain sensitivity: a validation of clinical findings.

To validate findings of a reduced pain sensitivity in anorexia and bulimia nervosa, the effects of dieting on somatosensation (especially pain sensitivity) were investigated in healthy young women. One group of subjects (n = 11) received a calorically reduced balanced diet for 21 days, while the other group (n = 14) continued to eat normally. The fasting state induced in the dieting subjects was comparable to that of eating disorder patients, since the dieters showed a reduction of the body mass index, a decrease in triiodothyronine and an increase in beta-hydroxybutyric acid plasma levels. However, neither the thresholds of pain, warmth, cold and vibration sensitivity nor the peripheral skin temperature changed systematically under the diet. Therefore, the reduced pain sensitivity in eating disorder patients is apparently not a mere effect of fasting, but a true pathological feature.

3-Hydroxybutyric Acid↗
PubMed1988

Factor analysis of the evaluation form for selecting patients for short-term anxiety-provoking psychotherapy. The Bergen project on brief dynamic psychotherapy.

The selection criteria of Sifneos' short-term anxiety-provoking psychotherapy has been assumed to consist of two separate dimensions, resources and motivation. A factor analysis revealed three factors: ego-resources, motivation for psychotherapy and motivation or desire to change. The resource items on the evaluation form constitute one factor as assumed, it is the items on the motivation section that are split into two independent factors. The evaluation form might become more useful if the motivation items are reorganized according to the two different dimensions of the concept.

Adult↗
PubMed1988

Assessment for three different forms of short-term dynamic psychotherapy. Findings from the Bergen Project.

Forty-four patients were assessed for three different short-term dynamic therapies, with an evaluation form based on Sifneos' criteria for Short-Term Anxiety-Provoking Psychotherapy (STAPP). Ten patients were ascribed to STAPP, 22 patients to Malan's Brief Psychotherapy (BP), and 12 patients to a more eclectic/integrative form of brief psychotherapy in this project called the FIAT model. 78% of the patients completed their treatment in agreement with the original ascription to therapy, with good results for all three therapies. The evaluation form seems to be a reliable and valid instrument offering a good and systematic basis for designing a tailor-made treatment format for different types of patients.

Adult↗
PubMed1988

Brief dynamic psychotherapy for patients presenting physical symptoms.

Ten outpatients who complained of physical symptoms, without organic pathology, were treated with brief dynamic psychotherapy. Outcome ratings were provided by independent assessors at the end of therapy and 2 years post treatment. Improvement criteria included symptoms, adaptive functioning, and specific internal predispositions. The results showed that most of the patients gained substantially from their therapy experiences. Change did not only occur with regard to psychological difficulties, but also in their particular physical symptoms. Therapy gains at termination were maintained, and had even increased, at follow-up. Clinical improvement was confirmed by psychological test findings. In several patients marked positive change was also observed in their general body response patterns.

Adult↗
PubMed1988

Comprehensive assessment of change in patients treated with short-term dynamic psychotherapy: an overview. A 2-year follow-up study of 34 cases.

Change was assessed in 34 patients at the end of short-term dynamic psychotherapy (STDP), and at 2 follow-ups (1 year and 2 years subsequent to treatment). The assessment was made from different perspectives and according to multiple criteria and methods of measurement. The results indicate that, when a particular form of STDP is selected according to each patient's ego resources, motivation for therapy, and motivation for change, approximately 90% of the patients will attain substantial symptom relief. The majority of the patients in this study also gave evidence of positive change in adaptive functioning, while one-third attained some dynamic/structural change as well. Clinically rated improvement was confirmed by changes in the patients' self-reported distress level (SCL-90), and from psychological test findings (MMPI). Improvement observed at the end of therapy was sustained throughout the 2-year follow-up period.

Adaptation, Psychological↗
PubMed1986

Description of flow phenomena in magnetic resonance imaging.

The magnetic resonance (MR) signal from the hydrogen nuclei of blood is not only determined by the MR parameters T1, T2 and proton density, but is strongly dependent on the movement of the protons. Magnetic resonance imaging (MRI) offers therefore the possibility to visualize the distribution of moving spins, especially blood flow, noninvasively and without contrast agents; moreover, the velocity of the moving spins can be quantified. Flow phenomena in MRI are a pretentious field because the complicated hydrodynamics of the living system is coded in the MR signal; therefore, an understanding of the underlying physical principle of the MR signal is required to interpret and extract flow information from the image. However, rather simple theoretical and experimental models of fluid transport in vessels allow to explain the main features of various effects observed in images.

Blood Circulation↗
PubMed1977

Hepatic venography and wedge hepatic vein pressure measurements in diffuse liver disease.

Ninety patients with chronic diffuse liver disease were evaluated with free hepatic venography, wedge hepatic venography, hepatic vein pressure measurements, and liver biopsy. Free hepatic venograms were normal and minimally pruned in patients with hepatic sarcoidosis and fatty liver due to alcohol, and their biopsies showed little or no fibrosis. Pruning of hepatic vein branches on free hepatic venography correlated well with the corrected wedged hepatic vein pressure and with the degree of fibrosis in patients with alcoholic hepatitis, alcoholic cirrhosis, and postnecrotic cirrhosis. Free hepatic venography correlated better with hemodynamic measurements and fibrosis than did wedge hepatic venography. Free hepatic venography is a reliable predictor of the presence and degree of hepatic fibrosis and may be a useful alternative to liver biopsy in patients with clotting disorders.

Alcoholism↗
PubMed1976

Giant idiopathic thymomegaly.

Apart from the anterior mediastinal position and the usual size of the normal thymus, aberrant locations and extreme size variations may occur. This is illustrated by an eight month old boy whose histologically normal thymus presented as a large mass in the right hemithorax. It is the largest normal thymus on record in an infant. Thus, idiopathic thymomegaly should also be considered in the differential diagnosis of peripheral intrathoracic mass lesions.

Choristoma↗