Biomedical subjects

Karsten Alfke

Publications and source records attributed to Karsten Alfke.

5 recordsLinked to original sources

PubMed2005

Aggressive therapy with intravenous abciximab and intra-arterial rtPA and additional PTA/stenting improves clinical outcome in acute vertebrobasilar occlusion: combined local fibrinolysis and intravenous abciximab in acute vertebrobasilar stroke treatment (FAST): results of a multicenter study.

BACKGROUND AND PURPOSE: A combined therapy of local recombinant tissue plasminogen activator (rtPA) fibrinolysis and intravenous Abciximab platelet inhibition with additional percutaneous transluminal angioplasty (PTA)/stenting may improve recanalization and neurological outcome in patients with acute vertebrobasilar occlusion. METHODS: Combined FAST therapy consisted on intravenous bolus of Abciximab (0.25 mg/kg) followed by a 12-hour infusion therapy (0.125 microg/kg per minute) and low-dose intra-arterial rtPA (median dosage: 20 mg, FAST cohort: N=47). The results were compared with a retrospective cohort, treated by intraarterial rtPA monotherapy (median dosage: 40 mg, rtPA cohort, N=41). Additional PTA/stenting was performed in case of severe residual stenosis. Recanalization success was classified according to the Trials in Myocardial Infarction (TIMI) criteria: TIMI0/1, failed recanalization; TIMI2/3, successful recanalization. Bleeding complications were evaluated according to severe extracerebral hemorrhage (ECH), asymptomatic intracerebral hemorrhage (AIH), and symptomatic intracerebral hemorrhage (SIH). RESULTS: Overall bleeding rate was higher under the combined therapy, but the SIH rate did not differ (FAST versus rtPA: ECH, 3% versus 0%; AIH, 32% versus 22%; SIH 13% versus 12%). Additional PTA/stenting was performed in 14 (FAST) versus 5 (rtPA) patients. TIMI2/3 recanalization rate was similar (FAST, 72%; rtPA, 68%), but TIMI3 rate was remarkably higher under combined therapy (FAST, 45%; rtPA, N=22%). Neurologic outcome appeared better under combined therapy (FAST versus rtPA: favorable outcome rate: 34% versus 17%) with a significantly lower mortality rate (FAST versus rtPA: 38% versus 68%; P=0.006). These results were consistent for embolic and atherothrombotic occlusions. CONCLUSIONS: Combined therapy of intravenous Abciximab and half dose intra-arterial rtPA with additional PTA/stenting appears to improve neurologic outcome in acute vertebrobasilar occlusion despite an increase of overall bleeding complications.

Abciximab↗

PubMed2005

Improving the amplitude-modulated control experiment for multislice continuous arterial spin labeling.

The use of an amplitude-modulated radiofrequency (RF) pulse for a control experiment is a proven method to control for off-resonance effects in multislice continuous arterial spin labeling (CASL) experiments. This method is also known as double adiabatic inversion. The adiabaticity factor of a single half-pulse, beta(1/2), and a new dimensionless parameter alpha, which is obtained from the labeling parameters and the flow velocity, are introduced. This makes it possible to distinguish three distinct cases: 1) With low alpha, a double inversion occurs. 2) With alpha > or = approximately 4, the efficiency with which the longitudinal magnetization is returned to the z-axis depends on the phase of the amplitude modulation at the time the spins cross the center of the labeling plane. 3) In the intermediate region, the efficiency shows undesirable fluctuations. In a Bloch equation simulation, three optimized parameter sets are determined. Near ideal performance should always be achieved by combinations of parameters for which beta(1/2) > or = approximately 2 and alpha approximately pi/beta(1/2). The efficiency increases were realized in a volunteer study, showing the practical application of the suggested optimization.

Adult↗

PubMed2005

Continuous artery-selective spin labeling (CASSL).

A new technique for selective spin labeling of individual arteries is presented. It is based on continuous arterial spin labeling (CASL) with an amplitude-modulated control experiment. Precessionary motion of the labeling gradient about the axis of the artery, combined with an appropriate frequency modulation of the labeling RF pulse, restricts the adiabatic inversion to the desired artery. In phantom studies, it was found that the level of selectivity could be controlled by the sequence parameters, and that the achievable labeling efficiency was at a level of approximately 80% compared to a regular, nonselective CASL experiment. In a volunteer study we acquired high-quality images of the perfusion territories of the internal carotid artery (ICA), the basilar artery (BA), the middle cerebral artery (MCA), and both anterior cerebral arteries (ACAs). The results show the method's flexibility for different geometries and flow velocities. Potential applications include perfusion territory imaging of smaller cerebral arteries, and selective angiography techniques.

Adult↗

PubMed2004

Brain perfusion territory imaging applying oblique-plane arterial spin labeling with a standard send/receive head coil.

A new method for the selective spin labeling of left- or right-sided supplying arteries of the brain without the need for additional RF coils is demonstrated. A clinical 1.5 T scanner was used. The spatial selectivity of the labeling process is based on the limited coverage of the excitation field of a standard send/receive head coil together with an oblique positioning of the labeling plane. A computer simulation was used to optimize key labeling parameters under the condition of laminar flow. The validity of the computer model results was confirmed by MRI measurements with a flow model. For human studies, a double-inversion continuous arterial spin labeling (CASL) sequence was modified to allow for arbitrary positioning of the labeling plane. The obtained perfusion-weighted images showed a clear delineation of the perfusion territories of the selected arteries in the anterior circulation of the brain and good gray/white matter contrast.

Brain Mapping↗

PubMed2004

Treatment of intracranial broad-neck aneurysms with a new self-expanding stent and coil embolization.

BACKGROUND AND PURPOSE: Endovascular treatment of broad-neck intracranial aneurysms with detachable coils requires special techniques. Placement of a stent over the aneurysm neck and secondary coil embolization prevents coil migration and allows attenuated packing of the coils. However, access for the stent-delivery system can be technically limited in tortuous anatomy. We present six cases of broad-neck aneurysms treated with a new self-expanding stent and coil embolization. METHODS: Three aneurysms of the supraophthalmic internal carotid artery and three aneurysms of the basilar tip with extension to the origin of a posterior cerebral artery were treated. The stent was a new self-expanding stent with a 3F over-the-wire microcatheter delivery system. Coil embolization was performed with electrolytically detachable coils. Time-of-flight MR angiography was performed after treatment in five cases. Three other patients could not be treated with the stent because deployment was not possible after correct positioning of the delivery system. RESULTS: Access with the stent-delivery system was easy, and the aneurysm neck was covered sufficiently. After stent placement, total coil embolization was achieved in four and subtotal coil embolization was achieved in two. Parent arteries remained open, and no secondary coil migration was seen. On follow-up MR imaging, the stent was clearly visible and patency of the parent vessel and emerging branches was assessable. CONCLUSION: This new stent is a safe and efficient tool for the endovascular treatment of intracranial broad-neck aneurysms. Access to smaller vessels was easy, but the mechanism of deployment had to be improved. Follow-up MR imaging was sufficient.

Adult↗