Biomedical subjects

R Graumann

Publications and source records attributed to R Graumann.

5 recordsLinked to original sources

PubMed1995

Localisation of myocardial ischaemia from the magnetocardiogram using current density reconstruction method: computer simulation study.

A computer simulation study is performed to investigate the method of current density reconstruction to localise myocardial ischaemia. A computer model of the entire human heart is used to simulate the excitation and repolarisation process in eight topographically different cases of myocardial ischaemia. The associated magnetocardiogram is calculated at 37 positions of the KRENIKON biomagnetic measurement equipment. The method of current density reconstruction is applied at the S-point (the last discernible deviation from the ST-segment at the end of the QRS-complex) of the MCG to find characteristics of the myocardial ischaemia simulated by the model. The results show that it is possible to determine the location of the ischaemia. The current density distribution may be interpreted physiologically in terms of the so-called 'injury-current'. This indicates that magnetocardiography might be a suitable method for noninvasive ischaemia diagnosis, and further investigations of the current density reconstruction method for the injury current should be performed on patients with ischaemic heart disease.

Computer Simulation↗

PubMed1991

Experiences in data analysis and modelling with a multichannel biomagnetic system.

Evaluation of MEG/MCG data, measured with the Siemens biomagnetic multichannel system KRENIKON, in patients with epilepsy, infarction, Wolff-Parkinson-White (WPW) syndrome or extra systoles are in good agreement with the results of different investigation techniques. The evaluations have been performed using an equivalent current dipole model within a sphere or a half-space with homogeneous conductivity. In cases where the current dipole model is not adequate, multiple dipoles or complete distributions of current sources have to be considered. Results from simulations and applications to in vivo data and the influence of geometries better adjusted to realistic geometries are discussed.

Brain↗

PubMed1988

A new steady-state imaging sequence for simultaneous acquisition of two MR images with clearly different contrasts.

We present a new steady-state imaging sequence, which simultaneously allows in a single acquisition the formation of two MR images with clearly different contrasts. The contrast of the first image is FISP-like, whereas the second image is strongly T2-weighted. In principle the T2 values in the image can be calculated from the combination of the first and second images. We also show calculated T2 images.

Head↗

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↗

PubMedDate not supplied

A new pulse sequence for determining T1 and T2 simultaneously.

Determination of the relaxation times T1 and T2 which are important for tissue characterization generally requires the use of different pulse sequences in magnetic resonance imaging. In this study, a new pulse sequence which facilitates simultaneous determination of the T1 and T2 times is presented. Determination takes place in this case pixel by pixel from the measured images. The measuring time corresponds in this case approximately to that of a normal spin-echo sequence with long repetition time and two data acquisitions. The functional dependence of the accuracy of the T1 and T2 determination upon external errors, e.g., angle of rotation errors, is discussed. The tissue contrast behavior of the individual echoes is shown and its dependence on pulse parameters is explained.

Biophysical Phenomena↗