Search PubMed⌕ Search

Biomedical subjects

H Alfke

Publications and source records attributed to H Alfke.

At least 37 records · Page 2Linked to original sources
PubMed2000

Quantitative human in vivo evaluation of high resolution MRI for vessel wall morphometry after percutaneous transluminal angioplasty.

Visualization of the vessel wall after transluminal angioplasty is important to monitor the restenosis progress. Intravascular ultrasound proved its capabilities as an invasive procedure in many studies. The aim of this study was to evaluate the feasibility of high-resolution MRI as a non-invasive tool for follow-up after PTA. High-resolution magnetic resonance images (pixel size: 0.49 * 0.49 mm(2)) were acquired on a 1.0 T clinical scanner. Morphometry was conducted after conversion of DICOM images into TIFF format using ScionImage on a PC. In-vitro studies using a polyvinylchloride tube were evaluated by two independent investigators. Goldstandard was a caliper rule and direct radiography. Five patients were monitored before and 24 h, six weeks, three months and six months after PTA. In vivo measurements promised a good concordance for both investigators for area as well as for diameter measurements. Area measurements showed correlations up to r = 0.86 (p < 0.001) whereas the correlations of diameters were slightly inferior (r between 0.58 and 0.84; p < 0.005). Relocation of the same slice position in the follow up studies could be guaranteed using anatomic landmarks in the images. As a non-invasive tool to assess restenosis after PTA high-resolution MRI promises to be a reproducible technique. It is easy to identify the same vascular region in different studies due to neighboring anatomic landmarks. Progression of disease as well as success of pharmacologic treatment to prevent restenosis may be monitored.

Aged↗
PubMed2000

Comparison of C-arm CT fluoroscopy and conventional fluoroscopy for percutaneous biliary drainage procedures.

PURPOSE: To conduct a prospective randomized evaluation of C-arm computed tomography (CT) fluoroscopy for external biliary drainage procedures in comparison with conventional fluoroscopic guidance to reduce the number of transhepatic punctures as a primary endpoint. MATERIALS AND METHODS: In 18 patients with biliary obstructions, 20 external percutaneous biliary drainage procedures were prospectively performed with use of either C-arm CT fluoroscopy or conventional fluoroscopy alone. The number of hepatic punctures, procedure time, and fluoroscopy time, were analyzed separately for both methods. RESULTS: C-arm CT fluoroscopy resulted in a reduced number of transhepatic punctures, with decreased procedure and fluoroscopy times (P < .05; t test). When compared with conventional external biliary drainage procedures, a mean of 1.8+/-1 versus 4.8+/-2.8 hepatic punctures at a fluoroscopy time of 3.4+/-1.5 versus 11.4+/-7.4 minutes was required for C-arm CT fluoroscopy, while procedure times were 11+/-3.6 versus 16.2+/-9.3 minutes. CONCLUSIONS: C-arm CT fluoroscopy is associated with decreased procedure and fluoroscopy times, while fewer transhepatic punctures are required to establish external biliary drainage.

Adolescent↗
PubMed2000

Mid-term follow-up after percutaneous hydrodynamic thrombectomy in lower limb ischemia: initial experience with two-dimensional MR imaging and three-dimensional MR angiography.

PURPOSE: To assess noninvasively mid-term patency, reocclusion, and mid-term changes of the arterial wall after percutaneous hydrodynamic thrombectomy in patients with acute lower limb ischemia using magnetic resonance (MR) imaging/MR angiography (MRA). MATERIALS AND METHODS: Arterial wall and luminal changes were evaluated in 16 patients (10 men, six women; mean age, 70 years), with a minimum follow-up of 12 months after percutaneous thrombectomy with a hydrodynamic catheter for acute lower limb ischemia (embolic, n = 5; thrombotic, n = 11). Adjunctive PTA was performed in 44%. The mean follow-up was 23 months +/- 7.6 (range, 12-33 months). MR imaging and MRA were performed on a 1.0 T system using an extremity coil and two-dimensional (2D) time-of-flight, turbo spin echo, 2D gradient echo, and contrast enhanced three-dimensional (3D) gradient echo sequences. RESULTS: In one patient, a complete reocclusion was noted and, in two patients, a hemodynamically insignificant restenosis (< or = 50%) was identified with MR imaging. This was in accordance with color flow duplex sonography, physical examination, ankle/brachial index measurements, and the treadmill test. The MR morphometry documented an increase of the entire vessel area from 48.9 mm2 +/- 3.3 (control segments) to 55.5 mm2 +/- 2.8 at the treated segments (+13.3%; P < .05). The vessel wall area increased from 31.7 mm2 +/- 1.8 to 39.4 mm2 +/- 2.3 (+24.4%; P < .05). The mean area stenosis grade was 12%. CONCLUSION: MR imaging with use of morphometric analysis is a possible tool to noninvasively determine the mid-term patency and restenosis/reocclusion and remodeling process after percutaneous thrombectomy and other interventional procedures.

Aged↗
PubMed2000

Nitric oxide inhibits the basic fibroblast growth factor-stimulated migration of bovine vascular smooth muscle cells in vitro.

BACKGROUND: The purpose of this study was to evaluate the effect of nitric oxide (NO) on basic fibroblast growth factor (bFGF)-stimulated migration of bovine VSMC in vitro. METHODS: For the migration assay 50,000 cells from passages 4 to 8 were put into a migration chamber and stimulated with 10 ng bFGF/ml (control group). For another experiment, the NO donator sodium nitroprusside (SNP) (10(-6), 10(-8), 10(-10) M), the second messenger of NO 8-bromo-cGMP (10(-6), 10(-8), 10(-10) M) and 100 U of superoxide dismutase (SOD) were added. Migration of cells was quantified after fixing and staining of the cells by means of light microscopy. RESULTS: Cell migration was significantly inhibited by SNP in a dose dependent manner (p < 0.01 with t-test). This effect was mirrored by 8-bromo-cGMP and not significantly inhibited by SOD, confirming this to be an NO mediated effect and excluding side-effects of superoxide-derived oxidation products. CONCLUSION: Nitric oxide inhibits the basic fibroblast growth factor stimulated migration of bovine vascular smooth muscle cells in vitro.

Animals↗
PubMed2000

[A review of molecular radiology. I: Gene therapy].

The term molecular radiology intermediate region between radiological imaging and interventional radiology on the one side and molecular biology on the other. In the field of imaging methods are currently being developed by which molecular processes, i.e., gene expression and protein function, can be visualized in vivo. These techniques open new perspectives for research and clinical diagnosis and will be presented in the second part of this review. The present part provides a survey of current developments in gene therapy from a radiological point of view and highlights the part that our specialty may play in this field.

Animals↗
PubMed1999

Effects of nitinol Strecker stent placement on vascular response in normal and stenotic porcine iliac arteries.

PURPOSE: This experimental study was conducted to evaluate neointimal thickness, lumen diameters, and histologic changes in normal and stenotic porcine iliac arteries following placement of self-expanding nitinol Strecker stents. MATERIALS AND METHODS: Neointimal trauma causing slight vascular stenosis was induced unilaterally within external iliac arteries of 12 swines by means of endothelial abrasion and high cholesterol diet. Nitinol Strecker stents were placed within the stenotic and the normal contralateral vascular segments. For histopathologic evaluation, the pigs were killed 12 or 24 weeks after stent placement and luminal diamters were evaluated angiographically. RESULTS: Excluding one occlusion, 15% narrowing of the lumen diameter was induced unilaterally (P = .002). Initial luminal gain after stent placement was greater for stenotic than for normal arteries. The amount of neointima thickness was not different between stenotic and normal vessels (P > .05). Comparing vascular diameters before stent placement and at follow-up, luminal loss due to neointima proliferation was 22% within normal arteries (P = .0002), while a luminal gain by 15% was found within the stenotic arteries (P = .008). Maturation of neointima and endothelial coverage were complete after 24 weeks. CONCLUSIONS: Even though nitinol Strecker stents induce excessive neointimal proliferation, stenotic arteries seem to profit from great early luminal gain resulting in 15% of vascular expansion at follow-up while slight stenosis is induced within normal iliac arteries.

Alloys↗
PubMed1999

Differential gene expression of vascular smooth muscle cells. Detection by RNA arbitrarily primed polymerase chain reaction.

BACKGROUND: Vascular smooth muscle cells (VSMC) play an important role in the development of restenotic lesions. However, regulation of proliferation, migration, and matrix synthesis of these cells is still poorly understood. The aim of this study was to analyze gene expression of differently stimulated bovine VSMC. MATERIAL AND METHODS: RNA was isolated from stimulated bovine VSMC after different time periods. For stimulation we used growth factors (platelet-derived growth factors PDGF-AA, PDGF-BB, basic fibroblast growth factor) and a nitric oxide donating drug (sodium nitroprusside). Gene expression of stimulated and control cells was analyzed by non-radioactive RNA fingerprinting (RNA arbitrarily primed polymerase chain reaction, RAP-PCR) and standard gel electrophoresis. Polymorphic fragments were sequenced and further characterized. RESULTS: By RAP-PCR we detected changes in the RNA fingerprint pattern of stimulated cells compared with unstimulated cells. Sequences of five fragments out of 12 showed high homology to known human genes (serine-methyl-transferase, DUTT1, laminin B2, a newly cloned translational regulator (p97), and a human expressed sequence tag). For laminin B2 we could confirm an upregulation after stimulation with growth factors at 1 and 6 hours and after stimulation with SNP at 1 hour in comparison to controls. For p97 we could show a downregulation after stimulation with SNP, bFGF and PDGF-BB but not PDGF-AA. CONCLUSION: RAP-PCR is well suited for analysis of VSMC gene expression in vitro. The laminin B2 and p97 gene are differently expressed after growth factor stimulation in bovine VSMC.

Animals↗
PubMed1998

[Magnetic resonance phlebography (MRP) of the abdomen and pelvis].

PURPOSE: To evaluate the image quality of magnetic resonance venography (MRV) of pelvic and abdominal veins. METHODS: A retrospective analysis of all MRV between 1993 and 1996 was conducted. A 2D-FLASH-TOF without breath hold and with arterial presaturation was used. All venous segments have been assessed for the quality of visualisation and an overall image quality was determined. 43% of our patients had malignant disease and phlebothrombosis had already been diagnosed in 64%. RESULTS: 126 examinations and 1696 venous segments were analysed. The overall quality of the examination was good, however one examination was non diagnostic because of motion artefacts. Vessels along the vertical axis were good visualised in over 90%. Most important reasons for insufficient visualisation were breathing, motion and metal artefacts as well as compression and displacement of veins due to tumour disease. CONCLUSIONS: Magnetic resonance venography without breath hold TOF technique is practical and robust for routine clinical applications.

Abdomen↗
PubMed1998

[Postoperative imaging of synthetic coronary artery bypass graft patency by means of CT angiography].

PURPOSE: CT angiography was performed in 12 patients with insufficient autologous graft situations to evaluate postoperative patency and situation of the proximal, distal and coronary artery anastomoses of synthetic Perma-Flow coronary artery bypass grafts. METHODS: Bypass grafts were evaluated postoperatively with spiral CT of the mediastinum. At a flow rate of 3 ml/s, 120 ml of contrast material were applied over a cubital vein. Slice thickness was 3 mm, maximum pitch factor 2 and image reconstruction was performed at 2 mm increment. Shaded surface displays were analysed together with axial scans for bypass evaluation. RESULTS: 8 out of 12 synthetic bypasses proved to be patent. One bypass was completely occluded and in three patients the distal portions of the grafts were occluded. Coronary angiography performed in one case confirmed complete bypass occlusion. Due to the occlusions, 8 distal and 12 proximal anastomoses were visible. Only 8 out of 19 side-to-side coronary artery anastomoses could be sufficiently well imaged with this technique. CONCLUSIONS: CT angiography is suitable for postoperative screening of synthetic coronary bypasses to determine the patency and anastomotic situations. Coronary artery anastomoses however are not sufficiently imaged and coronary angiography continues to be required.

Adult↗
PubMed1997

[Teleteaching with CONRAD. From collected cases to interactive learning system].

Radiological teaching files on the Internet suffer from certain restrictions such as limited user interactivity. The Internet teaching project CONRAD (computer online network for radiological didactics) circumvents these restrictions by using a new database structure that also reflects the development of a diagnosis over time. The cases are presented in the internet with different HTML-based teaching programs. To support interactivity, CONRAD offers the building of online learning groups over the internet.

Computer Communication Networks↗
PubMed1997

[Venous compression syndrome: etiology, diagnosis and therapy from the radiologic viewpoint].

Venous compression is a clinical entity distinct from deep vein thrombosis although the clinical signs may be indistinguishable. Reasons for venous compression are tumors, scars, hematomas, postoperative changes and anatomic variations. The differential diagnosis between compression and thrombosis is important because therapy and prognosis differ markedly between the two patient groups. Ultrasound, computed tomography and magnetic resonance tomography are the diagnostic tools of choice because they offer not only information about the intraluminal situation but also about the extraluminal pathology.

Constriction, Pathologic↗
PubMed1996

L-arginine induces nitric oxide-dependent vasodilation in patients with critical limb ischemia. A randomized, controlled study.

BACKGROUND: L-Arginine is the precursor of endogenous nitric oxide (NO), which is a potent vasodilator acting via the intracellular second-messenger cGMP. In healthy humans, L-arginine induces peripheral vasodilation and inhibits platelet aggregation due to an increased NO production. Prostaglandin E1 (PGE1) induces peripheral vasodilation via stimulating prostacyclin receptors. METHODS AND RESULTS: We investigated the effects of one intravenous infusion of L-arginine (30 g, 60 minutes) or PGE1 (40 microgram, 60 minutes) versus those of placebo (150 mL 0.9% saline, 60 minutes) on blood pressure, peripheral hemodynamics, and urinary NO3- and cGMP excretion rates in patients with critical limb ischemia (peripheral arterial occlusive disease stages Fontaine III or IV). Blood flow in the femoral artery was significantly increased by L-arginine (+42.3 +/- 7.9%, P<.05) and by PGE1 (+31.0 +/- 10.2%, P<.05) but not by placebo (+4.3 +/- 13.0%, P=NS). Urinary NO3- excretion increased by 131.8 +/- 39.5% after L-arginine (P<.05) but only by 32.3 +/- 17.2% after PGE1 (P=NS). Urinary cGMP excretion increased by 198.7 +/- 84.9% after L-arginine (P<.05) and by 94.2 +/- 58.8% after PGE1 (P=NS). Both urinary index metabolites were unchanged by placebo. CONCLUSIONS: We conclude that intravenous L-arginine induces NO-dependent peripheral vasodilation in patients with critical limb ischemia. These effects are paralleled by increased urinary NO3- and cGMP excretion, indicating an enhanced systemic NO production. Increased urinary NO3- excretion may be a sum effect of NO synthase substrate provision (L-arginine) and increased shear stress (PGE1 and L-arginine).

Aged↗
PubMed1996

[Restenosis after percutaneous transluminal angioplasty: II. Possibilities for pharmacologic intervention].

Reocclusion after percutaneous transluminal angioplasty is a major mechanism contributing to morbidity of patients after catheterization. Until now, pharmacological approaches to the prevention of restenosis were mostly disappointing, as only the early phase of thrombotic reocclusion, in which platelet activation is a major patho-physiological mechanism, could be treated with inhibitors of platelet aggregation and coagulation. Recently, several new approaches to the pharmacotherapy of restenosis have been introduced, for example thromboxane receptor antagonists or synthase inhibitors, GPIIb/IIa antagonists and hirudin as new inhibitors of platelet aggregation and coagulation, PDGF antagonists as inhibitors of intimal proliferation, and modulators of endothelial cell function, some of which may be effective in the late phase of myointimal proliferation. However, many substances that had been promising in experimental restenosis have proven ineffective in the first clinical trials. More recently, molecular biological techniques are increasingly used in experimental angioplasty. The role of these different approaches for the prevention of restenosis still has to be proven in clinical trials.

Angioplasty, Balloon↗
PubMed1993

[The premedication of PTA. A double-blind and randomized comparison of midazolam/tramadol versus placebo/tramadol].

A prospective, randomised and double blind comparative study of Midazolam/Tramadol or placebo/Tramadol for premedication before PTA was carried out on 40 patients (12 female and 28 male, average age 66.1 +/- 12). The anxiolytic, analgesic and general findings were quantified by means of a visual analogue score. Pre- and peri-interventional blood gas, blood pressure and pulse rates were determined. The complications of the two schemes were compared. 19 patients received Midazolam/Tramadol and 21 placebo/Tramadol. Patient anxiety was reduced significantly from 25.8 +/- 25 to 4.3 +/- 6 by premedication. Significant increase in the pain score during PTA was observed only in the placebo group (4.3 +/- 12.6 to 27.4 +/- 20.9). There was no difference in the incidence of complications and respiratory depression due to the Midazolam/Tramadol combination was not observed.

Aged↗
PubMed1993

[Conventional local intra-arterial fibrinolysis, spray lysis and mechanically accelerated fibrinolysis. An assessment of their position in the spectrum of angioplasty technics].

Intra-arterial local fibrinolysis was performed in 72 patients (51 men, 21 women, mean age 66.8 years) during the course of 78 angioplasties. 11.1% were stage IIa (Fontaine), 38.9% were stage II b, 27.8% were stage III and 22.2% were stage IV. The methods used were conventional fibrinolysis (15.4%), spray lysis (47.4%) and mechanically accelerated fibrinolysis (37.2%). In 66.7% the urokinase dose was < 600,000 I.U., in 17.9% it was > 1,000,000 I.U. Additional balloon dilatation was performed in 72 cases, percutaneous aspiration of thrombo-embolic material in 41 cases and stent implantation in 7 cases. Angiographically the procedure was successful in 90.7%; the Doppler index rose from 0.47 +/- 0.27 to 0.85 +/- 0.3 (p < 0.001). At discharge, staging was: I = 38.9%, IIa = 38.9%, IIb = 5.6%, III = 1.4%, IV = 15.3%. There were no systemic bleeding complications. In 5.1%, complications had to be treated surgically.

Adult↗
PubMed1992

[A prospective study to determine the recanalization time with a guide wire/recanalization catheter system in arterial occlusions].

The success rate and time taken for recanalization was determined in a prospective study of 82 consecutive unselected patients (53 men, 29 women; mean age 65.7 +/- 13, from 28 to 88 years). There were 106 complete occlusions of infrarenal arteries and a hydrophilic guide wire with a special 5-F recanalization catheter was used. Mean occlusion length was 12.97 +/- 10 cm (from 1 cm-45 cm). 79.3% of occlusions were in the femoro-popliteal territory, 6.6% were iliac and 14.1% tibial. 101 of the 106 occlusions were recanalized (95.3%). Mean recanalization time was 120.8 +/- 228.1 s (from 1 s-1440 s), mean recanalization velocity was 0.11 cm/s. The majority of obstructions could be recanalized in less than one minute. The five occlusions which could not be recanalized were distal lesions in the superficial femoral artery and which were longer than 10 cm; two were calcified. There were no complications resulting from the recanalization apart from three perforations which were clinically not apparent. Consequent angioplasty proved successful in 78.1% of these patients.

Adult↗