[CT angiography in carotid stenosis. Diagnostic value compared to color-coded duplex ultrasonography and MR angiography]. / CT-Angiographie bei Karotisstenosen. Diagnostischer Wert im Vergleich zur farbkodierten Duplexsonographie und MR-Angiographie.

PURPOSE: To evaluate the accuracy of different diagnostic methods for the visualization of the carotid arteries and their pathological changes in order to avoid invasive angiography whenever surgery was considered. MATERIAL AND METHODS: 24 patients with clinically suspected stenosis or occlusion of the carotid arteries were prospectively examined via CT angiography. MR angiography and colour-coded duplex sonography (ccds) to evaluate the degree of stenosis and the extent of calcification. RESULTS: In 36 cases stenoses of different extent could be documented with CT angiography, 33 cases were found using colour-coded duplex sonography and MRA. Sonography could not prove mild stenoses (< 30%), and in two patients with sonographically suspected total occlusion vessel perfusion was documented via CT angiography. MR angiography led to a overestimation in patients with high-grade stenosis compared to the degree of stenosis obtained via ccds and CTA. With regard to the diagnosis of calcification MIP, reconstructions after CT examination showed best correlation to the plain CT slices referring to length (94.6%) and thickness (89.2%). CONCLUSION: CTA with MIP reconstructions is an excellent screening method and, in combination with ccds, CT angiography may replace DSA before surgery or intervention.

[Multiple slab MR angiography of the A. carotis interna: a preoperative comparative study]. / Mehrvolumen-MR-Angiographie der A. carotis interna: Eine präoperative Vergleichsstudie.

PURPOSE: With the introduction of MR angiography (MRA) into clinical routine, arteriosclerotic lesions of the supraaortic vessels may be well demonstrated. MATERIAL AND METHODS: The comparison between Multislab MRA (gradient echo, TOF) and X-ray angiography (XRA) as reference in 70 patients suspicious of stenotic lesions in the internal carotid artery proved the high reliability of these methods. RESULTS: In determining the degree of stenosis, according to the NASCET study (North American Symptomatic Endarterectomy Trial), a correlation between MRA and XRA of 92.3% could be calculated. The principal problem of MRA is the overestimation of high-grade stenoses; we observed 5 false-positive results in severe stenosis. Sensitivity and specificity were 95.6 and 92.6%, respectively, for detection of severe (> 60%) stenosis. CONCLUSION: Despite its limitations, MRA is a clinically important noninvasive technique for preoperative evaluation of patients undergoing carotid endarterectomy.

Ion transport through gramicidin A. Water structure and functionality.

Molecular Dynamics (MD) simulations were performed on a gramicidin A dimer model representing a transmembrane channel. Different from previous simulations the peptide was in contact with bulk water at both ends of the dimer to guarantee a realistic description of the hydration of the biomolecule. The flexible BJH model for water was employed in the simulations and the gramicidin-water, gramicidin-ion and ion-water potentials used are based on molecular orbital calculations. The water structure near the gramicidin was investigated first by a simulation without ions, while for the energy profiles of the ion transport through the channel a potassium or a sodium ion was added. These investigations provide a detailed and conclusive picture on a molecular level of the role of water in the ion transport through a gramicidin A channel and can explain the experimental results on the selectivity between alkali ions, their double or even triple occupancy, the exclusion or permeability of anions depending upon cation concentration and the consequences of differences in the ionic charge. The investigation demonstrate that the water molecules around the gramicidin behave as an integral part of the peptide and the functionality is the result of the whole complex biomolecule-water.