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Biomedical subjects

E Nagel

Publications and source records attributed to E Nagel.

At least 55 records · Page 3Linked to original sources
PubMed2000

Noninvasive detection of myocardial ischemia from perfusion reserve based on cardiovascular magnetic resonance.

BACKGROUND: Myocardial perfusion reserve can be noninvasively assessed with cardiovascular MR. In this study, the diagnostic accuracy of this technique for the detection of significant coronary artery stenosis was evaluated. METHODS AND RESULTS: In 15 patients with single-vessel coronary artery disease and 5 patients without significant coronary artery disease, the signal intensity-time curves of the first pass of a gadolinium-DTPA bolus injected through a central vein catheter were evaluated before and after dipyridamole infusion to validate the technique. A linear fit was used to determine the upslope, and a cutoff value for the differentiation between the myocardium supplied by stenotic and nonstenotic coronary arteries was defined. The diagnostic accuracy was then examined prospectively in 34 patients with coronary artery disease and was compared with coronary angiography. A significant difference in myocardial perfusion reserve between ischemic and normal myocardial segments (1.08+/-0.23 and 2.33+/-0.41; P<0.001) was found that resulted in a cutoff value of 1.5 (mean minus 2 SD of normal segments). In the prospective analysis, sensitivity, specificity, and diagnostic accuracy for the detection of coronary artery stenosis (> or =75%) were 90%, 83%, and 87%, respectively. Interobserver and intraobserver variabilities for the linear fit were low (r=0.96 and 0.99). CONCLUSIONS: MR first-pass perfusion measurements yielded a high diagnostic accuracy for the detection of coronary artery disease. Myocardial perfusion reserve can be easily and reproducibly determined by a linear fit of the upslope of the signal intensity-time curves.

Coronary Angiography↗
PubMed2000

Assessment of prosthetic aortic valve performance by magnetic resonance velocity imaging.

OBJECTIVES: Magnetic resonance (MRI) velocity mapping was used to evaluate non-invasively the flow profiles of the ascending aorta in normal volunteers and in patients with an aortic (mechanical) valve prosthesis. BACKGROUND: In patients with artificial aortic valves the flow profile in the ascending aorta is severely altered. These changes have been associated with an increased risk of thrombus formation and mechanical hemolysis. METHODS: Velocity profiles were determined 30 mm distal to the aortic valve in six healthy volunteers and seven patients with aortic valve replacement (replacement within the last 2 years) using ECG triggered phase contrast MRI. Peak flow, mean flow and mean reverse flow were measured in intervals of 25 ms during the entire heart cycle. Systolic reverse flow, end-systolic closing and diastolic leakage volume were calculated for all subjects. RESULTS: Peak flow velocity during mid-systole was significantly higher in patients with valvular prosthesis than in normals (mean + SD, 1.9 +/- 0.4 m/s vs. 1.2 +/- 0.03 m/s, P < 0.001) with a double peak and a zone of reversed flow close to the inner (left lateral) wall of the ascending aorta of the patients. Closing volume was significantly larger in patients than in controls (-3.3 +/- 1.2 ml/beat vs. -0.9 +/- 0.5 ml/beat; P < 0.001). There was reverse flow during systole in valvular patients amounting to 15.7 +/- 6.7% of total cardiac output compared to 2.3 +/- 1.2% in controls (P < 0.001). Diastolic mean flow was negative in patients after valve replacement but not in controls (-11.0 +/- 15.2 ml/beat vs. 6.8 +/- 3.2 ml/beat; P < 0.01). CONCLUSIONS: The following three major quantitative observations have been made in the present study: (1) Mechanical valve prostheses have an increased peak flow velocity with a systolic reverse flow at the inner (left lateral) wall of the ascending aorta. (2) A double peak flow velocity pattern can be observed in patients with bileaflet (mechanical) prosthesis. (3) The blood volume required for leaflet closure and the diastolic leakage blood volume are significantly higher for the examined bileaflet valve than for native heart valves.

Adult↗
PubMed2000

Cardiovascular magnetic resonance: myocardial perfusion.

There is growing evidence that the noninvasive assessment of myocardial perfusion with cardiovascular magnetic resonance is a valid and accurate tool for the assessment of ischemic heart disease and its introduction into routine clinical evaluation of patients is rapidly expected. Magnetic resonance measurements allow the evaluation of reversible and irreversible myocardial ischemia, the assessment of acute myocardial infarction, as well as the recognition and detection of viable myocardium. Magnetic resonance perfusion measurements are mainly performed with T1-shortening contrast agents such as gadolinium-DTPA either by visual analysis or based on the analyses of signal intensity time curves. For the detection of myocardial ischemia the first pass kinetics of a gadolinium-DTPA bolus and for the detection of myocardial necrosis and the definition of viable myocardium steady state distribution kinetics are assessed. Quantitative analysis of myocardial perfusion can be performed but requires complex modeling due to the characteristics of gadolinium-DTPA. Thus, semi-quantitative parameters are preferred. There is accumulating evidence in the literature that magnetic resonance imaging can be used for the detection of coronary artery stenosis with high diagnostic accuracy both with semi-quantitative or visual analysis. Myocardial infarction can be reliably detected and the infarcted area determined. Non-reperfused infarcted myocardium can be differentiated from reperfused myocardium by different enhancement patterns that correlates with viability. Cardiac magnetic resonance is a promising technique that can combine different functional studies during one examination, such as the assessment of wall motion and perfusion at rest and stress. With further improvements in analysis software magnetic resonance perfusion measurement may rapidly become a routine tool for the assessment of patients with coronary artery disease.

Contrast Media↗
PubMed2000

[Dilatation of large retinal vessels after increased intraocular pressure].

PURPOSE: To measure dilation of large retinal branch vessels. METHODS: Diameters of a vessel section of a branch artery and vein were examined by the retinal vessel analyzer. Intraocular pressure (IOP) was increased briefly by an oculo-oscillo-dynamograph. The examination was repeated after 2 weeks. RESULTS: A vessel reaction was found in all volunteers. The mean venous diameter decreased 9.9 +/- 9.4% during the suprasystolic phase of intraocular pressure. A maximal dilation was found in arteries (7.0 +/- 6.2%) and veins (9.3 +/- 5.2%) 1 min after lowering of IOP. The results were reproduced in the second examination for veins in all phases of the examination and for arteries in the middle phase after lowering IOP (4 min). Various changes in mean systolic blood pressure did not significantly affect reproducibility of the vessel reaction. CONCLUSION: The vessel reaction caused by rise in IOP can be measured for single vessel sections. The venous reaction is well reproducible in healthy volunteers. Further research should examine the benefit of this method in the diagnosis and follow-up of glaucoma.

Adult↗
PubMed2000

Cardiac rotation and relaxation in patients with aortic valve stenosis.

BACKGROUND: Diastolic dysfunction with delayed relaxation and abnormal passive elastic properties has been described in patients with severe pressure overload hypertrophy. The purpose of this study was to evaluate the time course of rotational motion of the left ventricle in patients with aortic valve stenosis using myocardial tagging. METHODS: Myocardial tagging is a non-invasive method based on magnetic resonance which makes it possible to label ('tag') specific myocardial regions. From the motion of the tag's cardiac rotation, radial displacement and translational motion can be determined. In 12 controls and 13 patients with severe aortic valve stenosis systolic and diastolic wall motion was assessed in an apical and basal short axis plane. RESULTS: The normal left ventricle performs a systolic wringing motion around the ventricular long axis with clockwise rotation at the base (-4.4+/-1.6 degrees) and counter-clockwise rotation at the apex (+6.8+/-2.5 degrees) when viewed from the apex. During early diastole an untwisting motion can be observed which precedes diastolic filling. In patients with aortic valve stenosis systolic rotation is reduced at the base (-2.4+/-2.0 degrees; P<0.01) but increased at the apex (+12.0+/-6.0 degrees; P<0.05). Diastolic untwisting is delayed and prolonged with a decrease in normalized rotation velocity (-6.9+/-1.1 s(-1)) when compared to controls (-10.7+/-2.2 s(-1); P<0.001). Maximal systolic torsion is 8.0+/-2.1 degrees in controls and 14.1+/-6.4 degrees (P<0.01) in patients with aortic valve stenosis. CONCLUSIONS: Left ventricular pressure overload hypertrophy is associated with a reduction in basal and an increase in apical rotation resulting in increased torsion of the ventricle. Diastolic untwisting is delayed and prolonged. This may explain the occurrence of diastolic dysfunction in patients with severe pressure overload hypertrophy.

Adult↗
PubMed2000

Cardiac rotation and relaxation after anterolateral myocardial infarction.

BACKGROUND: Both systolic and diastolic dysfunction have been observed in patients with anterolateral myocardial infarction. Diastolic dysfunction is related to disturbances in relaxation and diastolic filling. OBJECTIVE: To analyse cardiac rotation, regional shortening and diastolic relaxation in patients with anterolateral infarction. METHODS: Cardiac rotation and relaxation in controls and patients with chronic anterolateral infarction were assessed by myocardial tagging. Myocardial tagging is based on magnetic resonance imaging and allows us to label specific myocardial regions for imaging cardiac motion (rotation, translation and radial displacement). A rectangular grid was placed on the myocardium (basal, equatorial and apical short-axis plane) of each of 18 patients with chronic anterolateral infarction and 13 controls. Cardiac rotation, change in area and shortening of circumference were determined in each case. RESULTS: The left ventricle in controls performs a systolic wringing motion with a clockwise rotation at the base and a counterclockwise rotation at the apex when viewed from the apex. During relaxation a rotational motion in the opposite direction (namely untwisting) can be observed. In patients with anterolateral infarction, there is less systolic rotation at the apex and diastolic untwisting is delayed and prolonged in comparison with controls. In the presence of a left ventricular aneurysm (n = 4) apical rotation is completely lost. There is less shortening of circumference in infarcted and remote regions. CONCLUSIONS: The wringing motion of the myocardium might be an important mechanism involved in maintaining normal cardiac function with minimal expenditure of energy. This mechanism no longer operates in patients with left ventricular aneurysms and operates significantly less than normal in those with anterolateral hypokinaesia. Diastolic untwisting is significantly delayed and prolonged in patients with anterolateral infarction, which could explain the occurrence of diastolic dysfunction in these patients.

Aged↗
PubMed2000

Coronary arterial stents: safety and artifacts during MR imaging.

PURPOSE: To investigate the safety and imaging artifacts with different coronary arterial stents and magnetic resonance (MR) imaging sequences. MATERIALS AND METHODS: The heating, artifacts, and ferromagnetism with different stents were studied with a 1.5-T MR tomograph with ultrafast gradients by using turbo spin-echo, turbo gradient-echo, and echo-planar imaging sequences. Nineteen stents, which were 8-25 mm in length and 3.0-4.5 mm in diameter, were evaluated. Stent deviation induced by the magnetic field and during MR imaging, migration, and heating caused by the radio-frequency pulses were examined. The size of imaging artifacts was measured with all the stents under standardized conditions and with six stents after their implantation into the coronary arteries of freshly explanted pig hearts. RESULTS: All except two types of stents showed minimal ferromagnetism. No device migration or heating was induced. Turbo spin-echo images had minimal artifacts; larger artifacts were seen on the turbo gradient-echo and echo-planar images. With ultrafast gradients, the artifacts on the echo-planar images were substantially reduced. CONCLUSION: The studied coronary stents were not influenced by heating or motion during 1.5-T MR imaging. Artifact size differed according to the type and size of the stent and the MR imaging sequence used. Thus, patients with these stents can be safely examined.

Angioplasty, Balloon, Coronary↗
PubMed2000

Magnetic resonance real-time imaging for the evaluation of left ventricular function.

New ultrafast gradient systems and hybrid imaging sequences make it possible to acquire a complete image in real time, without the need for breathholding or electrocardiogram (ECG) triggering. In 21 patients, left ventricular function was assessed by the use of a turbo-gradient echo technique, an echo-planar imaging (EPI) technique, and a new real-time imaging technique. End-diastolic and end-systolic volumes, left ventricular muscle mass, and ejection fraction of the ultrafast techniques were compared with the turbo-gradient echo technique. Inter- and intraobserver variability was determined for each technique. Image quality was sufficient for automated contour detection in all but two patients in whom foldover occurred in the real-time images. Results of the ultrafast imaging techniques were comparable with conventional turbo-gradient echo techniques. There was a tendency to overestimate the end-diastolic volume by 3.9 and 1.3 ml with EPI real-time imaging, the end-systolic volume by 0.9 and 5.0 ml, and the left ventricular mass by 2.6 and 23.8 g. Ejection fraction showed a tendency to be overestimated by 1.1% with EPI and underestimated by 4.5% with real-time imaging. Correlation between EPI real-time imaging and turbo-gradient echo were 0.94 and O.95, respectively, for end-diastolic volumes, 0.98 and 0.96, respectively, for end-systolic volumes, and 0.96 and 0.89, respectively, for left ventricular mass. Inter- and intraobserver variability was low with all three techniques. Real-time imaging allows an accurate determination of left ventricular function without ECG triggering. Scan times can be reduced significantly with this new technique. Further studies will have to assess the value of real-time imaging for the detection of wall motion abnornmalities and the imaging of patients with atrial fibrillation.

Analysis of Variance↗
PubMed1999

Alterations in the local myocardial motion pattern in patients suffering from pressure overload due to aortic stenosis.

BACKGROUND: MR tissue tagging allows the noninvasive assessment of the locally and temporally resolved motion pattern of the left ventricle. Alterations in cardiac torsion and diastolic relaxation of the left ventricle were studied in patients with aortic stenosis and were compared with those of healthy control subjects and championship rowers with physiological volume-overload hypertrophy. METHODS AND RESULTS: Twelve aortic stenosis patients, 11 healthy control subjects with normal left ventricular function, and 11 world-championship rowers were investigated for systolic and diastolic heart wall motion on a basal and an apical level of the myocardium. Systolic torsion and untwisting during diastole were examined by use of a novel tagging technique (CSPAMM) that provides access to systolic and diastolic motion data. In the healthy heart, the left ventricle performs a systolic wringing motion, with a counterclockwise rotation at the apex and a clockwise rotation at the base. Apical untwisting precedes diastolic filling. In the athlete's heart, torsion and untwisting remain unchanged compared with those of the control subjects. In aortic stenosis patients, torsion is significantly increased and diastolic apical untwisting is prolonged compared with those of control subjects or athletes. CONCLUSIONS: Torsional behavior as observed in pressure- and volume-overloaded hearts is consistent with current theoretical findings. A delayed diastolic untwisting in the pressure-overloaded hearts of the patients may contribute to a tendency toward diastolic dysfunction.

Adult↗
PubMed1999

Noninvasive diagnosis of ischemia-induced wall motion abnormalities with the use of high-dose dobutamine stress MRI: comparison with dobutamine stress echocardiography.

BACKGROUND: The analysis of wall motion abnormalities with dobutamine stress echocardiography (DSE) is an established method for the detection of myocardial ischemia. With ultrafast magnetic resonance tomography, identical stress protocols as used for echocardiography can be applied. METHODS AND RESULTS: In 208 consecutive patients (147 men, 61 women) with suspected coronary artery disease, DSE with harmonic imaging and dobutamine stress magnetic resonance (DSMR) (1.5 T) were performed before cardiac catheterization. DSMR images were acquired during short breath-holds in 3 short-axis views and a 4- and a 2-chamber view (gradient echo technique). Patients were examined at rest and during a standard dobutamine-atropine scheme until submaximal heart rate was reached. Regional wall motion was assessed in a 16-segment model. Significant coronary heart disease was defined as >/=50% diameter stenosis. Eighteen patients could not be examined by DSMR (claustrophobia 11 and adipositas 6) and 18 patients by DSE (poor image quality). Four patients did not reach target heart rate. In 107 patients, coronary artery disease was found. With DSMR, sensitivity was increased from 74.3% to 86.2% and specificity from 69.8% to 85.7% (both P<0.05) compared with DSE. Analysis for women yielded similar results. CONCLUSIONS: High-dose dobutamine magnetic resonance tomography can be performed with a standard dobutamine/atropine stress protocol. Detection of wall motion abnormalities by DSMR yields a significantly higher diagnostic accuracy in comparison to DSE.

Aged↗
PubMed1999

Functional MRI in ischemic heart disease based on detection of contraction abnormalities.

Even though several non-invasive techniques are available for the assessment of coronary artery disease and the detection of myocardial ischemia, many coronary angiograms yield negative results, thus, warranting higher accuracy for non-invasive tests. The detection of obstructive coronary artery disease is only possible during physical or pharmacological stress. Currently, the assessment of wall motion abnormalities by echocardiography is clinically the most widely used method. However, a significant number of patients yield suboptimal or non-diagnostic images despite improvements with harmonic imaging. Cardiovascular magnetic resonance (CMR) imaging allows a non-invasive visualization of the heart with high spatial and temporal resolution. Gradient echo CMR images permit an exact and reproducible determination of global and regional left ventricular function, wall thickness and wall thickening and identical pharmacological stress protocols, as currently used for dobutamine stress echocardiography, can be implemented for CMR imaging. A review of the literature on dobutamine stress CMR for the detection of stress induced wall motion abnormalities is presented and the safety of CMR stress examinations is discussed. The results show, that especially in those patients with suboptimal echocardiographic image quality dobutamine stress CMR is superior in comparison with dobutamine stress echocardiography and may replace echocardiography in these patients. Further possibilities by the use of myocardial tagging or intravascular contrast agents are outlined.

Cardiotonic Agents↗
PubMed1999

Noninvasive determination of coronary blood flow velocity with magnetic resonance imaging: comparison of breath-hold and navigator techniques with intravascular ultrasound.

The aim of this study was to evaluate two different magnetic resonance (MR) techniques for the noninvasive assessment of intracoronary blood flow. Coronary blood flow velocities were measured invasively in 26 angiographically normal segments of 12 patients. Noninvasive measurements were performed in identical segments with two MR techniques using a 1.5 T MR tomograph (ACS NT, Philips). A single breath-hold technique (temporal resolution: 140 msec) and a similar non-breath-hold technique with prospective navigator correction and improved temporal resolution (45 msec) were used. Maximal coronary flow velocities determined by MR correlated closely with invasive measurements (breath-hold: r = 0.70; navigator: r = 0.86); however, a significant underestimation of the MR measurements was found (slope = 0.33 and 0.37). The relative difference from the invasive method was lower for the navigator technique compared with the breath-hold technique (P<0.02). Both MR techniques allow the determination of coronary blood flow velocities. The higher temporal resolution and shorter acquisition window of navigator-corrected non-breath-hold techniques lead to increased accuracy. This approach is a further step toward the diagnostic use of MR flow measurements in coronary artery disease.

Aged↗
PubMed1999

Optimization of realtime adaptive navigator correction for 3D magnetic resonance coronary angiography.

Breathing motion artifacts reduce the quality of MR coronary artery images. Real-time adaptive navigator correction with different correction factors (0%, 30%, 60%, 80% of diaphragmatic displacement) was used to correct for respiratory motion in 3D coronary artery imaging. Significant improvements of image quality were achieved by adaptive motion correction in comparison with conventional navigator gating. A close correlation between the correction factor, which yielded optimal image quality, and cardiac displacement relative to diaphragmatic displacement was found. The quality of coronary artery imaging can be improved using real-time adaptive navigator correction. Correction factors have to be adjusted for each segment of the coronary arteries and for each patient. Magn Reson Med 42:408-411, 1999.

Adult↗
PubMed1999

[Changes in the quality of life after organ transplantations].

138 patients with end-stage kidney disease and 118 patients with end-stage liver disease were included in an observational cohort study regarding their quality of life. Instruments used were the Nottingham Health Profile (NHP), a scale for Activities of Daily Life (ADL), a Symptom Check List (SCL-90-R), and the Center of Epidemiology and Statistics Depression Scale (CES-D), all for self rating, as well as the indices of Spitzer and Karnofsky for foreign rating of life quality. Apart from the early postoperative period in both groups there was significant and persistent improvement in quality of life already three months after transplantation. In some dimensions, patients after kidney transplantation presented even lower trouble scores than a population sample. In addition, semistructured interviews showed clearly the need for psychotherapeutic support to guarantee the success for specific cases. The present investigation demonstrates, that systematic registration of the patients perception of illness and treatment is possible even in extreme situations and leads to a differentiated evaluation of medical procedures. Thereby the study also contributes to the development of modern evaluation research according to the spirit of evidence based medicine.

Activities of Daily Living↗
PubMed1999

[Influence of image quality on the diagnostic accuracy of dobutamine stress magnetic resonance imaging in comparison with dobutamine stress echocardiography for the noninvasive detection of myocardial ischemia].

The analysis of wall motion abnormalities with dobutamine stress echocardiography is an established method for the detection of myocardial ischemia. With ultrafast magnetic resonance tomography, the application of identical stress protocols as used for echocardiography is possible. In 208 consecutive patients (147 M, 61 F) with suspected coronary artery disease, dobutamine stress echocardiography partially using harmonic imaging and dobutamine stress magnetic resonance tomography (DSMR) were performed prior to cardiac catheterization. DSMR images were acquired during short breath holds in 3 short axis-, a 4-, and a 2-chamber view using a turbo gradient echo technique. Patients were examined at rest and during a standard dobutamine-atropine scheme until submaximal heart rate was reached. Regional wall motion was assessed in a 16 segment model. Significant coronary heart disease was defined as angiographic >/=50% diameter stenosis. With DSMR, significantly more patients yielded very good (69%) or good (13%) image quality in comparison with dobutamine stress echocardiography (20% and 31%, p<0. 05). Moderate image quality occurred in 16% with MR and 41% with dobutamine stress echocardiography (p<0.05), 2% and 8% were non-diagnostic. With each technique 18 patients could not be examined (DSE: emphysema: 10, adipositas: 8, DSMR: claustrophobia: 11, adipositas: 6, contraindication: 1). Four patients did not reach target heart rate. In 107 patients, significant coronary artery disease was found. With DSMR sensitivity was 88.7% (dobutamine stress echocardiography: 74.3%; p<0.05) and specificity 85.7% (dobutamine stress echocardiography: 69.8%; p <0.05). This difference was most pronounced in the group with moderate echocardiographic image quality. High dose DSMR is superior to dobutamine stress echocardiography and can replace this technique especially in patients with moderate echocardiographic image quality.

Adult↗