Biomedical subjects

C Schulze

Publications and source records attributed to C Schulze.

At least 37 records · Page 2Linked to original sources

PubMed2000

Reduced myocardial cellular damage and lipid peroxidation in off-pump versus conventional coronary artery bypass grafting.

BACKGROUND: The development of new surgical devices and techniques allows off pump coronary artery bypass grafting (OPCAB) without the use of CPB and cardioplegia. This study tested whether OPCAB reduces myocardial cell damage, lipid peroxidation and systemic endothelin release when compared to conventional coronary artery bypass grafting. METHODS: Twenty-six patients were assigned to either the OPCAB procedure using a suction device and regular sternotomy (n = 13) or were treated conventionally using extracorporeal circulation, blood cardioplegia and hypothermic arrest (29-31 degrees C; n = 13). Troponin I and creatine kinase - MB were determined for cardiac specific cell damage. Myocardial and systemic malondialdhyde levels were measured to account for oxyradical mediated lipid peroxidation. Systemic big-endothelin levels were determined as a marker for endothelial cell activation. RESULTS: A significant reduction of the cardiac specific cell damage was observed in the OPCAB group vs. the CABG group over time in the absence of acute myocardial ischemia or infarction. In addition, systemic and myocardial lipid peroxidation as measured by the malondialdehyde (MDA) levels were lower in the OPCAB group when compared to CABG. Finally, plasma levels of big-Endothelin (big-ET) significantly rose in the CABG but not in the OPCAB group. CONCLUSIONS: The data of the present study indicate that OPCAB revascularization without the use of CPB and cardioplegic arrest reduces myocardial cell damage and lipid peroxidation. It is also associated with a reduced activation of the potent vasoconstrictor peptide endothelin. All of this may contribute to improved myocardial function and faster postoperative recovery from surgical revascularization procedures, particularly in critically ill patients.

Aged↗

PubMed2000

Effects of Celsior and University of Wisconsin preservation solutions on hemodynamics and endothelial function after cardiac transplantation in humans: a single-center, prospective, randomized trial.

Optimal preservation of the myocardium remains a major concern in clinical and experimental heart transplantation. The present study compared the efficacy of University of Wisconsin (UW) and Celsior preservation solution with respect to myocardial performance, epicardial and microvascular endothelial vasomotor function and myocardial expression of endothelin and nitric oxide synthases in humans. Forty-one cardiac transplant recipients received either UW (n = 20) or Celsior (n = 21) preserved hearts. Catecholamine and vasodilator requirements were assessed within the first 5 postoperative days. Left ventricular performance and endothelial function was assessed 1 month after transplantation. Endothelin and nitric oxide synthase gene expression were detected in myocardial biopsy samples. Celsior preserved hearts required significantly more catecholamines and vasodilators within the first 5 postoperative days. Myocardial performance and endothelial function were comparable 1 month after transplantation. Total ischemic time correlated with impaired endothelial function in the Celsior but not in the UW group. Endothelin and inducible nitric oxide synthase gene expression were significantly higher in the Celsior group. The results of the study show that both solutions provide myocardial protection with regard to left ventricular performance and endothelial function 1 month after cardiac transplantation. The necessity for higher vasodilator and catecholamine therapy in Celsior preserved hearts suggests post-ischemic myocardial stunning within the first 5 postoperative days. The positive correlation between impaired endothelial function and total ischemic time in the Celsior group requires longitudinal investigation in particular with regard to the development of allograft vasculopathy.

Adenosine↗

PubMed2000

An association between microvascular endothelial dysfunction, transcardiac nitric oxide production and pro-inflammatory cytokines after heart transplantation in humans.

Endothelial dysfunction anticipates the development of transplant coronary artery disease (TxCAD) observed more than 1 year after transplantation (HTx). We investigated whether in patients early after HTx myocardial inducible and constitutive nitric oxide synthases (iNOS; cNOS) are expressed and cardiac nitric oxide production occurs. Moreover, a possible relationship to alterations in endothelium dependent and independent vasomotor function was assessed. Forty-two transplant recipients were studied 37 +/- 5 days after HTx. Microvascular coronary flow velocity reserve (CFVR) was tested endothelium dependent (acetylcholine; 30 microg/min x 5 min/i.c.) and independent (adenosine; 160 microg/min x 5 min/i.c.) by Doppler flow wire. Flow velocity increase by a factor greater than 2 was considered normal. Quantitative coronary angiography was used to assess epicardial vasomotor function in response to the same stimuli. Myocardial iNOS and cNOS gene expression were detected by semiquantitative reversed transcriptase polymerase chain reaction. Plasma nitrite levels (microM) were measured by spectrophotometry. Cytokines (TNF-alpha, IL-6; pg/ml) were measured by enzyme linked immunosorbent assay. In 26.1% of patients (n = 11; group A) an impaired endothelium dependent CFVR (1.65 +/- 0.23 increase) was observed; in 73.9% (n = 31, group B) a normal endothelium dependent CFVR (3.0 +/- 0.7 increase; P = 0.003) was observed. Myocardial iNOS and cNOS gene expression did not differ between the two groups. Transcardiac cytokine production was noted in 58.8% of patients for IL-6 and in 53.3% for TNF-alpha. Coronary sinus (CS) levels of TNF-alpha, IL-6 and nitrite were higher in group A. A significant increase in nitrite production was found only in patients with impaired endothelium dependent CFVR (aorta: 43.9 +/- 3.7 vs CS: 52.8 +/- 5.6, P = 0.05), suggesting transcardiac nitric oxide production. In addition, CS nitrite levels correlated with CS TNF-alpha levels in patients with impaired CFVR (r = 0.44, P = 0.003). Microvascular endothelium dependent CFVR is impaired in 26% of patients early after HTx. Activation of cytokines and the NO pathway seem to be involved in this vasomotor dysfunction The association between cardiac nitric oxide production and TNF-alpha in this group indicates a chronic high immunologic process, which may represent an early and important target for therapy and prevention of TxCAD.

Adenosine↗

PubMed2000

Three-dimensional video and robot-assisted port-access mitral valve operation.

BACKGROUND: In order to minimize surgical trauma, video-assisted mitral valve operation has been started using the Port-Access technique with the addition of a three-dimensional visualization system (Vista Cardiothoracic Systems Inc, Westborough, MA) and a voice-controlled camera-holding robotic arm (Aesop; Computer Motion Inc, Goleta, CA). METHODS: Port-Access mitral valve replacement or repair (PAMVR) was undertaken using an endovascular cardiopulmonary bypass (CPB) system. Fifty patients underwent Port-Access mitral valve replacement or repair. A three-dimensional thoracoscope was inserted allowing complete three-dimensional projection of the mitral valve (Vista). In the last 20 patients, the camera was attached to a robotic arm (Aesop), which allowed stabilization and voice-activated movement of the camera. Mitral valve repair was performed in 26 patients, and the valve was replaced in 24 patients with a mechanical valve prosthesis. RESULTS: Median time of operation was 4.2 hours, aortic cross-clamp time 83 minutes, CPB time 125 minutes, intensive care unit stay 1.5 days and hospitalization 9.0 days. Three months follow-up was complete in 40 patients, with 34 patients (85%) in New York Heart Association class I and 6 patients in class II. Mortality was 0% and rate of reoperation was 2%, with a follow-up time up to 1.5 years postoperatively. CONCLUSIONS: Using three-dimensional video and robotic assistance, it was possible to minimize the length of skin incision, but at the same time to optimally visualize the whole mitral valve apparatus in order to perform true Port-Access mitral valve operation, including various repair techniques.

Adult↗

PubMed2000

Reduced expression of systemic proinflammatory cytokines after off-pump versus conventional coronary artery bypass grafting.

BACKGROUND: Both cardiopulmonary bypass (CPB) and operative trauma are associated with increased expression of proinflammatory cytokines. We assessed the relative contribution of CPB on activation of various proinflammatory cytokines in patients undergoing coronary revascularization by comparing them with patients receiving coronary artery bypass grafts using off-pump (OPCAB) techniques. METHODS: Twenty-six patients were assigned to either the OPCAB procedure using a suction device and regular sternotomy (n = 13) or were treated conventionally using extracorporeal circulation, blood cardioplegia and hypothermic arrest (29-31 degrees C; n = 13). C-reactive protein and systemic levels of TNF-alpha, TNF specific receptors Rp1 and Rp2, Interleukin-6 (IL-6) and soluble IL-2 receptors (sIL-2r) were assayed by ELISA or EIA. To account for systemic nitric oxide production, total nitrate/nitrite (NOx) was measured using the Griess reaction. RESULTS: Coronary revascularization with CPB was associated with a significant expression increase in the TNF-system and sIL-2r when compared to the OPCAB patients. Although IL-6 expression did not differ between both groups, C-reactive protein levels were significantly lower in the OPCAB group. Moreover, systemic NOx levels as the stable end-product of nitric oxide were lower in the OPCAB group. CONCLUSIONS: The data of the present study indicate that, despite comparable surgical trauma, the OPCAB revascularization procedure without the use of CPB and cardioplegic arrest significantly reduces the systemic inflammatory response syndrome and early catecholamine requirement. This may contribute to improved organ function, subsequently resulting in improved postoperative recovery from surgical revascularization procedures, particularly in critically ill patients.

Aged↗

PubMed2000

Coronary vasomotor dysfunction in the cardiac allograft: impact of different immunosuppressive regimens.

Immunosuppression may have an important impact on early graft coronary endothelial injury. We investigated functional and morphologic coronary alterations, myocardial expression, and cardiac release of possible mediators of allograft vasculopathy within 6 months after cardiac transplantation with respect to different immunosuppressive regimens. Epicardial and microvascular endothelium-dependent and endothelium-independent vasomotor function and epicardial intimal thickening were measured in 8 transplant recipients treated with cyclosporin A (CyA), azathioprine, and prednisone (group 1), 9 transplant recipients treated with tacrolimus (TKL), azathioprine, and prednisone (group 2), and 14 patients treated with TKL, mycophenolate mofetil (MMF), and prednisone (group 3). The gene expressions of inducible and endothelial nitric oxide synthase (iNOS and eNOS), endothelin-1, prostacyclinsynthase, and thromboxansynthase were analyzed in endomyocardial biopsy specimens using semiquantitative reverse transcription polymerase chain reaction. Transcardiac cytokine release, endothelin-1, and nitrate-release were determined from plasma samples. Epicardial endothelial dysfunction (vasoconstriction to acetylcholine > 10%) and microvascular smooth muscle cell dysfunction (flow velocity increase to adenosine and nifedipine < 2.0) were enhanced in heart transplant recipients immunosuppressed with TKL, azathioprine, and prednisone. The prevalence of epicardial dysfunction was 78% in group 2 versus 44% and 46% in group 1 and 3 (p < 0.05), respectively. The prevalence of microvascular dysfunction was 56% in group 2 versus 13% and 7% in group 1 and 3 (p < 0.02), respectively. Coronary vasomotor dysfunction was associated with increased myocardial iNOS expression (p < 0.05), decreased eNOS expression (p < 0.05), and enhanced cardiac immunoreactive interleukin-6 (p < 0.01). Coronary intimal thickening was not different between the groups. The combination of TKL and MMF appears to be superior to TKL and azathioprine (and comparable to CyA and azathioprine) concerning preservation of early coronary vasomotor function, eNOS expression, iNOS suppression as well as cardiac interleukin-6 release. This may have an important impact on subsequent development of transplant coronary atherosclerosis.

Adult↗

PubMed2000

Extrahepatic biliary atresia in a border collie.

Progressive lameness and leg pain were the predominant clinical signs in a 17-week-old male border collie presented for examination. On clinical investigation, extrahepatic cholestasis in association with rickets due to inadequate vitamin D resorption was diagnosed. The dog was treated parenterally with vitamin D and a cholecystoduodenostomy was performed. At 25 days postsurgery the lameness had resolved and bone structure was radiographically normal. However, at six weeks postsurgery, the dog's condition deteriorated rapidly and euthanasia was finally performed at eight weeks postsurgery. At postmortem examination, Toxocara canis nematodes were found to have invaded the biliary system via the anastomosis between the gallbladder and duodenum, causing biliary and hepatic toxocariasis. The cause of the primary extrahepatic cholestasis was atresia of the common bile duct at the hepatic end. The liver tissue showed microscopic lesions of chronic extrahepatic cholestasis as well as acute inflammation associated with the nematode invasion. There was no postmortem evidence of bone lesions. Extrahepatic biliary atresia is extremely rare in animals and has not been described before in dogs. In contrast, it represents the most common cause of congenital cholestasis in children, occurring in approximately one per 10,000 to 15,000 live births.

Animals↗

PubMed1999

Modulation of coronary vasomotor tone by cytokines in cardiac transplant recipients.

BACKGROUND: Upon exposure to cytokines, endothelial cells may undergo profound alterations of vasomotor function. In this study, we characterized the relationship between coronary epicardial and microvascular vasomotor function and expression of specific cytokine patterns in human heart transplant recipients. METHODS: We studied 49 cardiac transplant recipients, without acute rejection or infection at an average of 6+/-3 months after transplantation. Coronary resistance vessel function was measured in an endothelium-dependent manner with acetylcholine (5 and 150 microg/5 min; intracoronary injection) and in an endothelium-independent manner with adenosine (400 and 800 microg/5 min; intracoronary injection) using an intracoronary Doppler flow wire. Simultaneous epicardial diameter changes were measured using quantitative coronary angiography. Coronary sinus and aortic serum levels of soluble interleukin (IL)-2 receptor and soluble tumor necrosis factor-a receptors (sTNF-R1 and sTNF-R2), TNF-alpha, and IL-6 were determined. Transcardiac cytokine release (coronary sinus minus aortic levels) was correlated with coronary vasomotor function. RESULTS: The highest amounts of cardiac cytokine release were observed for IL-6 (32+/-14% increase) and sTNF-R1 (26+/-13% increase). A significant inverse correlation between microvascular endothelial function and cardiac release of soluble IL-2 receptor (P=0.04) and IL-6 (P=0.03) was detected, whereas a positive correlation was observed to sTNF-R1 (P=0.004). Distal epicardial endothelial vasomotion was inversely correlated to transcardiac sTNF-R2 release (P=0.03). CONCLUSIONS: Cytokine production and activation, a common phenomenon early after heart transplantation, is related at least in part to endothelial vasomotor dysfunction of the epicardial and microvascular compartment. These results support the hypothesis that coronary endothelial dysfunction after cardiac transplantation is an immunologic phenomenon. Since endothelial dysfunction seems to be a crucial step in the pathogenesis of cardiac allograft vasculopathy, coronary cytokine suppression should be a therapeutic target of improved future immunosuppressive regimens.

Adult↗

PubMed1999

Inducible nitric oxide synthase activation after ischemia/reperfusion contributes to myocardial dysfunction and extent of infarct size in rabbits: evidence for a late phase of nitric oxide-mediated reperfusion injury.

BACKGROUND: Ischemia/reperfusion (I/R) leads to the induction of inducible nitric oxide synthase. The present study investigated the effects of selective and continuous inhibition of iNOS on myocardial performance, infarct size and histomorphological changes after I/R in rabbits. METHODS AND RESULTS: Ischemia/reperfusion (I/R) was induced by occlusion of the circumflex coronary artery for 30 min followed by 48 h of reperfusion. Sham animals (group A) served as control. Three groups were subjected to I/R: (B) placebo; (C) aminoguanidine (AMG; 10 mg/kg bolus) given prior to and 48 h after I/R to test its acute effects; (D) AMG (300 mg/kg/day s.c.) to test effects of continuous treatment. Hemodynamics, myocardial blood flow, infarct size, iNOS activity, cGMP levels, immunohistochemical analysis of iNOS expression and AMG tissue levels were determined. Continuous AMG treatment improved myocardial performance (hemodynamics and blood flow) compared to placebo group. iNOS was highest in placebo-treated animals. AMG tissue levels were highest in tissues affected by I/R. Infarct size (% of the circumflex region) was significantly smaller in group D when compared to group B. CONCLUSIONS: This is the first study showing that activation of myocardial iNOS isozyme during 48 h of reperfusion contributes to a late phase of I/R-induced injury in rabbits. Selective and continuous modulation of iNOS by AMG over this time period exerts protective effects with respect to myocardial performance, coronary blood flow, cellular infiltration and reduction of infarct size; this may be a novel therapeutic approach in the clinical situation to limit irreversible myocardial injury associated with ischemia and reperfusion.

Adrenergic beta-Agonists↗

PubMed1999

Protective capacity of a IgM/IgA-enriched polyclonal immunoglobulin-G preparation in endotoxemia.

Animal experiments were carried out to investigate whether a protective effect can be achieved in endotoxemia by intravenous (i.v.) application of a polyclonal immunoglobulin preparation (IVIG-IgG/A/M) enriched with 12% IgM and 12% IgA. Following administration of IVIG-IgG/A/M (500 mg/kg), endotoxemia was induced by intraperitoneal inoculation of a sublethal dose (5x10(8) CFU/kg) of Escherichia coli (E. coli) and subsequent i.v. administration of an antimicrobial agent (Imipenem). Plasma endotoxin activity, IL-6 activity, mean arterial pressure, and skeletal muscle oxygen pressure (tpO2) were measured at regular intervals over a total observation period of 7 h. Prophylactic administration of IVIG-IgG/A/M was found to significantly attenuate (P<0.01) the antibiotic-induced increase in endotoxin activity as compared to the albumin control group. Limited endotoxemia in the IgG/A/M group was associated with reduced levels of circulating IL-6 (P<0.01). Both lipopolysaccharide-induced hypotension and depression of tissue oxygenation were attenuated (P<0.01) by pre-treatment with IVIG-IgG/A/M. The experimental results suggest that in endotoxemia the polyclonal immunoglobulin preparation has a prophylactic protective effect on the acute phase responses and reduces the cardiodepressant effects of E. coli septicaemia.

Animals↗

PubMed1999

Leaflet escape in Omnicarbon monoleaflet valve.

In almost every type of artificial valve, mechanical disruption has been described. We present the first case of leaflet fracture with aortic embolization in an Omnicarbon monoleaflet valve 42 months after implantation. The 22-year-old male patient suffered of acute respiratory insufficiency and was referred to our hospital as an emergency case. Until a few days before presentation, he was in good condition without clinical complaints. By means of transesophageal echocardiography (TEE) and abdominal sonography the diagnosis of leaflet fracture with embolization to the abdominal aorta could be made. The patient underwent consecutive operative valve replacement and foreign body extraction that resulted in a complete recovery.

Adult↗

PubMed1999

Endothelin in coronary endothelial dysfunction early after human heart transplantation.

BACKGROUND: Cytokines and growth factors released as part of the immune response to alloantigenic stimuli are capable of regulating endothelin-1 expression in the allograft. Endothelin plays a significant role as a modulator of coronary vascular reactivity in the early stages of atherosclerosis and may be important as a participant in and marker for cardiac allograft vasculopathy. METHODS: We characterized a possible relationship between morphological and functional coronary changes, transcardiac plasma endothelin level and myocardial endothelin-mRNA expression in 33 cardiac transplant recipients in the early, stable phase 5+/-3 months after orthotopic heart transplantation. Coronary microvascular function was determined as endothelium-dependent with acetylcholine and endothelium-independent with adenosine using intracoronary Doppler-FloWire. The percentage of the epicardial diameter changes was measured using quantitative coronary angiography. Intravascular ultrasound was performed to quantify intimal hyperplasia. Cardiac endothelin uptake or release was determined by measuring plasma endothelin levels in the coronary sinus and aorta. Myocardial endothelin-gene expression was determined using semiquantitative RT-PCR. RESULTS: The aortic endothelin levels were significantly increased in transplant recipients compared to nontransplanted patients (11.8+/-2.2 vs 7.2+/-0.9 fmol/mL; P < 0.001). Endothelin uptake was noticed in the majority of patients, and the amount of endothelin uptake was correlated to microvascular (r = 0.37; P < 0.05) and epicardial (r = 0.41; P < 0.03) endothelium-dependent vasodilatation. High mRNA signal intensity was associated with significantly reduced coronary flow response to acetylcholine compared to patients with low myocardial gene expression (coronary flow reserve 2.4+/-0.9 vs 3.4+/-0.8, respectively; P < 0.005). Morphological coronary changes early after transplantation were not correlated to endothelin plasma levels or myocardial gene expression. CONCLUSION: Coronary endothelial vasomotor dysfunction after cardiac transplantation is associated with an increased myocardial endothelin mRNA expression and decreased endothelin-uptake by the heart. We postulate that early activation in the endothelin system may have a pivotal role in the acceleration of the atherosclerotic process in transplant patients.

Adult↗

PubMed1999

Aminoguanidine inhibits inducible NOS and reverses cardiac dysfunction late after ischemia and reperfusion--implications for iNOS-mediated myocardial stunning.

BACKGROUND: The functional significance of inducible nitric oxide synthase (iNOS) activation in response to myocardial ischemia and reperfusion (I/R) was investigated. METHODS: New Zealand rabbits were randomly treated with either placebo, aminoguanidine (AMG; selective iNOS inhibitor), or L-arginine. Left-ventricular hemodynamics and myocardial blood flow were measured before coronary occlusion and 30 minutes and 48 h after initiation of reperfusion. RESULTS: I/R resulted in left-ventricular dysfunction and increased myocardial iNOS activity. Placebo treatment had no effects on myocardial function. However, AMG significantly inhibited iNOS activity, significantly improved left-ventricular maximum + dP/dt and decreased LVEDP, whereas administration of L-arginine reduced + dP/dt and slightly increased LVEDP, compared to AMG-treated animals. Myocardial blood flow in the affected myocardium significantly increased after both AMG and L-arginine. CONCLUSIONS: The present data indicate that induction of myocardial iNOS after 48 h I/R contributes to the development of reversible left-ventricular dysfunction, suggesting the involvement of iNOS in myocardial stunning. Whereas L-arginine is associated with further reduction of left-ventricular contractility, continuous inhibition of iNOS activation by AMG improves left-ventricular performance; this may be a novel and clinically important therapeutic modality in certain disease states associated with I/R, including cardiac operations using extracorporeal circulation and coronary angioplastic procedures.

Animals↗

PubMed1998

Crosslinking the EcoRV restriction endonuclease across the DNA-binding site reveals transient intermediates and conformational changes of the enzyme during DNA binding and catalytic turnover.

EcoRV completely encircles bound DNA with two loops, forming the entry and exit gate for the DNA substrate. These loops were crosslinked generating CL-EcoRV which binds and releases linear DNA only slowly, because threading linear DNA into and out of the DNA-binding 'tunnel' of CL-EcoRV is not very effective. If the crosslinking reaction is carried out with a circular bound DNA, CL-EcoRV is hyperactive towards the trapped substrate which is cleaved very quickly but not very accurately. CL-EcoRV also binds to, but does not cleave, circular DNA when added from the outside, because it cannot enter the active site. Based on these results a two-step binding model is proposed for EcoRV: initial DNA binding occurs at the outer side of the loops before the gate opens and then the DNA is transferred to the catalytic center.

Amino Acid Substitution↗

PubMed1998

A scattering filter for energy-dispersive optics.

A filtering technique to remove parasitic scattering from X-ray absorption spectra that are acquired in energy-dispersive mode has been developed and tested at the European Synchrotron Radiation Facility. The improved set-up removes small-angle scattering of the sample or the windows of sample cells which may spoil the energy resolution or reduce the intensity of prominent features in the absorption spectrum, such as the white line at the Pt L(III) edge. The sample is placed behind the curved monochromator and between two plane perfect crystals in the Bonse-Hart configuration. The dispersion of the Bonse-Hart double-crystal camera is matched to the dispersion of the curved monochromator by inclining the scattering planes of the two optical elements against each other.

Journal Article↗

PubMed1998

A bent Laue analyser crystal for Rayleigh-to-Compton computed tomography.

A new optical system to perform tomography based on the Rayleigh-to-Compton (RC) method with high spatial and spectral resolution is presented. The RC technique allows the effective atomic number of a sample to be measured and finds application in bone mineral densitometry in medicine. It is particularly useful for the characterization of the distribution of biological materials which do not exhibit distinctive diffraction peaks. The system is based on the separation of the elastic line from the spectrum that is scattered by the sample by means of a bent Laue analyser crystal, and the subsequent independent detection of the elastic and inelastic parts of the spectrum with two large-area scintillation counters. The high energy resolution permits operation at low momentum transfer, where the RC method has its best contrast-to-noise ratio for low-Z materials. The geometrical and spectral requirements in terms of the incident beam and the conical analyser crystal are discussed. A first-generation tomographic imaging system (pencil beam, scanned sample) as implemented at the ESRF Compton-Scattering Station ID15B is described. A high-resolution tomographic reconstruction of a bone sample is presented.

Journal Article↗

PubMed1998

Focusing Optics for High-Energy X-ray Diffraction.

Novel focusing optical devices have been developed for synchrotron radiation in the energy range 40-100 keV. Firstly, a narrow-band-pass focusing energy-tuneable fixed-exit monochromator was constructed by combining meridionally bent Laue and Bragg crystals. Dispersion compensation was applied to retain the high momentum resolution despite the beam divergence caused by the focusing. Next, microfocusing was achieved by a bent multilayer arranged behind the crystal monochromator and alternatively by a bent Laue crystal. A 1.2 micro m-high line focus was obtained at 90 keV. The properties of the different set-ups are described and potential applications are discussed. First experiments were performed, investigating with high spatial resolution the residual strain gradients in layered polycrystalline materials. The results underline that focused high-energy synchrotron radiation can provide unique information on the mesoscopic scale to the materials scientist, complementary to existing techniques based on conventional X-ray sources, neutron scattering or electron microscopy.

Journal Article↗

PubMed1998

Microfocusing of hard X-rays with cylindrically bent crystal monochromators.

High-energy X-ray focusing with bent-crystal monochromators is known to be hampered by so-called depth or crystal-thickness aberrations. A theoretical model of focus broadening based on the geometrical theory of X-ray diffraction in slightly deformed crystals is presented and compared with experimental data. First, it is shown that depth broadening can be avoided in the Laue geometry by an appropriate choice of asymmetry angle. Based on this finding, a monochromator for high-pressure diffraction experiments has been designed and a source-size-limited focal spot below 10 microns is observed. As a consequence of the box-shaped rocking curve of bent Laue crystals, the focus is free of long-ranging tails. Diffraction patterns of standard powder samples were recorded on imaging plates and a theoretical description of the energy-dispersion-related peak broadening is given. Finally, diffraction patterns of N2 at 180 kbar demonstrate the excellent data quality achievable with this monochromator.

Journal Article↗