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Biomedical subjects

A Oppelt

Publications and source records attributed to A Oppelt.

At least 19 recordsLinked to original sources
PubMed1990

In vivo magnetic resonance imaging and spectroscopy of humans with a 4 T whole-body magnet.

A research-type 4 T whole-body magnet, built by Siemens AG, Erlangen, FRG, was used to investigate magnetic resonance at high field strengths. Designs for head and body coils operating at 170 MHz are described. Proton images of the human head and body are degraded by dielectric resonances and penetration effects. The nature of the dielectric resonances was demonstrated in phantoms containing distilled and saline doped water. Radiation damping at 170 MHz generates secondary echoes after a spin echo sequence. This effect was observed in phantoms and with reduced amplitude in the human head. Hydrogen spectra of the human head were selected utilizing stimulated and spin echoes. The latter technique allows the volume size to be reduced to 1 cm3. Examples of brain tumors that have been routinely investigated with volumes of 8 cm3 are given. Natural abundance carbon and phosphorus spectra of muscle and liver demonstrate the expected increase in spectral resolution and signal to noise ratio. Carbon spectra from the liver show the glycogen signal. Fluorine spectroscopy was used to study the time course of the absorption and emptying of a fluorinated antibiotic from the human stomach.

Brain↗
PubMed1990

Multichannel biomagnetic system for study of electrical activity in the brain and heart.

The authors designed a multichannel system for noninvasive measurement of the extremely weak magnetic fields generated by the brain and the heart. It uses a flat array of 37 superconducting magnetic field-sensing coils connected to sophisticated superconducting quantum interference devices. To prevent interference from external electromagnetic fields, the system is operated inside a shielded room. Complete sets of coherent data, even from spontaneous events, can be recorded. System performance was evaluated with phantom measurements and evoked-response studies. A spatial resolution of a few millimeters and a temporal resolution of a millisecond were obtained. First results in patients with partial epilepsy and investigations of the cardiac conductive pathway indicate that biomagnetism is now ready for a systematic clinical evaluation. Interpretation of measurements was facilitated by highlighting biomagnetically localized electrical activity in three-dimensional digital magnetic resonance images.

Brain↗
PubMed1989

[Recanalization and dilatation in chronic occlusion of the renal artery: 2 case reports].

The authors describe their experience in two cases of mechanic desobliteration and subsequent percutaneous transluminal angioplasty in a chronically occluded renal artery. It has become obvious that although this surgery has been so far performed only rarely it is technically viable and may exert a favourable therapeutic effect on hypertension of renovascular etiology as well as angioplasty of stenosing lesion of kidney arteries. The paper also discusses a possibility of influencing renal function by this method. The authors arrive at the conclusion that recanalization of a chronic occlusion of renal artery extends the presently relatively stabilized indications for percutaneous transluminal angioplasty in this localization.

Adult↗
PubMed1986

Multiple-spin-echo imaging with a 2D Fourier method.

In 2D Fourier imaging the normal Carr-Purcell multiple-echo sequence generally leads to center line and mirror artifacts caused by imperfect rotations by the rf pulses. We describe a method to avoid these distortions using a phase alternating-phase shift (PHAPS) sequence which also allows multiple-slice and multiple-echo imaging at the same time. Measuring phantoms with calibrated T2 values, we have shown that the PHAPS imaging sequence leads to an accuracy of quantitative T2 determinations of better than 10%. Contrast-enhanced images are presented which we calculated from multiple-echo images and extrapolated to arbitrary echotimes, including negative ones. We believe that these improvements in T2 imaging will result in a significant reduction of patient investigation time in magnetic resonance imaging.

Fourier Analysis↗
PubMed1986

Magnetic resonance imaging of aneurysms and thrombi.

This is a report of the first systematic investigation of the qualitative and quantitative diagnosis of aneurysms in the regions of the left ventricle and thoracic and abdominal aorta plus proof of intracavitary thrombi in the heart and the aorta, as well as aneurysms in the superior and inferior vena cava. For diagnosis of the heart, ECG gating is an absolute necessity, but for the analysis of abdominal aortic aneurysms it only leads to a considerable improvement of the spatial resolution. For differential diagnosis of the blood flow and intracavitary clots in the heart and the aorta, use of a second or even multiple echoes is needed. Also, digital subtraction between the first and second echoes (magnetic resonance digital subtraction) can assist in assessing flow. When dissecting aortic aneurysm is suspected and in cases when risk of perforation of ventricular and aortic aneurysms is present. MR offers particular advantages, since it is noninvasive and few scans can provide all the information that is required.

Aged↗
PubMed1986

Equilibrium radionuclide right ventriculography at rest and during exercise in patients with pulmonary hypertension.

Using the method of equilibrium radionuclide ventriculography (RNV), the right ventricular ejection fraction (RVEF) at rest and at a standard workload of 250 kpm per min was determined in 25 control subjects and in 30 patients with pulmonary hypertension (8 patients with chronic obstructive bronchopulmonary disease, 12 with recurrent pulmonary embolism and 10 with pure mitral stenosis). In the same week as RNV, pulmonary artery pressure was registered in patients with pulmonary hypertension at rest and at standard workload. RVEF was significantly higher (45 +/- 5%) in normal subjects than in patients with pulmonary hypertension (33 +/- 5%) and during exercise increased, whereas in patients with pulmonary hypertension it did not markedly change or decreased. The RVEF correlated at rest (r = -0.6293, p less than 0.001) and during exercise (r = 0.6980, p less than 0.05) with the degree of pulmonary hypertension at rest and during exercise. The results show a good correlation between the RVEF and the degree of pulmonary hypertension in patients with pulmonary hypertension at rest and during exercise.

Adult↗
PubMed1985

[ECG-triggered NMR-tomography of the heart. Pathological findings].

Initial systematic examinations of the heart by ECG-triggered NMR are reported. Twenty-three abnormal findings were observed amongst 46 patients examined. Special indications are the search for cardiac aneurysms, intracardiac thrombi and changes from pressure and volume stress.

Coronary Disease↗
PubMed1984

Evaluation of the effect of nifedipine in men after myocardial infarction.

The acute effect of nifedipine (Adalat, Bayer) was evaluated in 54 men with a history of transmural myocardial infarction. Haemodynamic changes (in 20 patients) and/or changes in left ventricular radionuclide ejection fraction (LVREF) (41 patients) were studied. 20 to 30 min after sublingual administration of 1 Adalat capsule (10 mg nifedipine) a decrease in arterial pressure and systemic resistance, and an increase in heart rate and cardiac output were observed already at rest. During exercise (50 W) there moreover occurred a decrease in pulmonary artery pressure and in arterial oxygen tension. LVREF was pathologically reduced already at rest, and in most patients exercise led to its further decrease. LVEF increased after Adalat administration only during exercise. In men with a history of myocardial infarction without clinical manifestations of heart failure, Adalat acted predominantly as a peripheral vasodilator; a negative inotropic effect was not demonstrable. The decrease in arterial oxygen tension, observed during exercise, was not clinically important.

Adult↗
PubMed1983

Equilibrium radionuclide ventriculography in men after transmural myocardial infarction.

Using equilibrium radionuclide ventriculography, the authors investigated left ventricular ejection fraction in 10 healthy men and in 57 men who had undergone their first transmural myocardial infarction (MI) 4 to 7 months earlier, were below 65 years of age and did not present signs of heart failure at the time of examination. Resting ejection fraction in healthy men amounted to 63 +/- 5%, in patients with uncomplicated MI to 54 +/- 7%, and in patients with clinical manifestations of heart failure in the acute phase to 37 +/- 8%. Patients with anteroseptal MI showed a negative correlation between the ejection fraction, on the one hand, and the sum of Q wave voltages in the precordial ECG map and the maximum value of serum creatine kinase in the acute phase of MI, on the other hand. The ejection fraction correlated with the degree of pulmonary hypertension during exercise. At work load of 50 W the ejection fraction measured in 31 patients was not significantly different shortly before discharge from hospital and 6 months after the onset of MI.

Adult↗
PubMed1982

[Assessment of regional ventilation using the inhalation of a radioactive and an aerosol of a 113mIn-labelled colloid solution].

Two methods of assessing regional ventilation distribution-dynamic scintigraphy with 133Xe-labelled gas inhalation, and pulmonary scanning following the inhalation of 113mIn-labelled colloid aerosol-were subjected to critical review. A total of 10 normal controls, 5 cardiac patients and 12 patients with pulmonary diseases were examined using both techniques. The subjective imaged of the lungs converged only in 24% of the cases. A considerable discrepancy in the results of the two investigation procedures was noted in 76%, primarily due to the sedimentation of inhaled colloid along the air passages. It is suggested that radio-aerosol scanning cannot visualize actual distribution of ventilation throughout the lungs; however, the method can be useful in the diagnosis of minor bronchial patency disorders before dynamic investigation using 133Xe can detect any changes, or where gamma-counter and analyzer facility is not available. To provide an accurate assessment of regional ventilation, the gas inhalation method should be combined with the dynamic analysis using a gamma-counter and analyzer facility, and perhaps a computer.

Aerosols↗
PubMed1981

[Nuclear magnetic resonance tomography].

Imaging methods based on nuclear magnetic resonance allow the production of sectional images of the human body without ionizing radiation. It is possible to measure the density and relaxation times of the water protons in body fluids or tissue. This allows not only to obtain morphological information but also to get some insight into the spatial distribution of physiological data. Starting with a review of the principles of nuclear magnetic resonance it is explained how the measured signal can be associated with an image point; it is also explained what type of apparatus is necessary and what the physical limitations are. Possible risks the patient may be exposed to in an examination using nuclear magnetic resonance are discussed. The present state of the technical development enables the production of whole-body sectional images of a living person within about one minute. By means of some typical examples the nature and properties of these images are explained. Although extensive clinical studies will be necessary before a more general assessment can be made of this method, an outlook is provided on expected further developments and possible future fields of application.

Humans↗