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Biomedical subjects

G Stroink

Publications and source records attributed to G Stroink.

13 recordsLinked to original sources
PubMed1992

Discrimination between myocardial infarct and ventricular tachycardia patients using magnetocardiographic trajectory plots and iso-integral maps.

Magnetocardiograms were recorded from 30 normal (N) subjects, 15 myocardial infarct (MI) patients, and 15 ventricular tachycardia (VT) patients. Discrimination between the groups was affected by iso-integral magnetic field mapping (MFM) and trajectory plotting of MFM extrema. Iso-integral MFM for the QRST, QRS, and ST-T intervals was created for each test group member. A polarity score, based on the number of extrema features present, was assigned to each iso-integral MFM. Differences in group mean integral of QRST map polarity scores were significant (p less than 0.05) between MI and N, between VT and N (p less than 0.005), and between MI and VT (p less than 0.05) subjects. integral of ST-T map polarity scores were significantly (p less than 0.0001) different between VT and N and between MI and VT (p less than 0.001) subjects. Discrimination between MI and VT patients, based on polarity score difference, was 56% accurate using integral of QRS maps and 73% accurate using integral of ST-T maps. For each subject, time-normalized MFM was used to construct trajectory plots of the maxima and minima in the QRS and ST-T intervals. Discrimination between MI and VT patients was based upon intergroup differences in fragmented trajectory plots. When the number of discrete trajectories and/or the total number (F) of trajectory points at which discrete trajectories coexist were considered, QRSmin trajectory plots were significantly (p less than 0.05) different for VT and N, but not for MI and N subjects. The significant (p less than 0.05) difference between MI and VT trajectory plots enabled 76% accuracy for MI and VT identification. ST-Tmax trajectory plots show significantly (p less than 0.0001) higher F values for VT patients facilitating accurate (87%) discrimination between MI and VT patients. These results suggest that the abnormalities of repolarization processes, displayed by MFM as multipolar integral of ST-T maps and/or as fragmented trajectory plots of ST-T extrema, may be useful indicators of the arrhythmia substrate/processes that characterize VT and vulnerable MI patients.

Diagnosis, Differential↗
PubMed1992

The effect of measurement conditions on MCG inverse solutions.

A magnetic inverse solution that uses a single current dipole in a homogeneous volume conductor with realistic torso shape was tested numerically to establish the effect of magnetic noise, number of measurement points, and torso size on the localization accuracy. Seven different sites of cardiological interest were selected as locations for the source dipole. The three components of the magnetic field were calculated as if measured by second order gradiometers, Gaussian noise was added, and Monte Carlo tests performed for inverse solutions using a single field component, or all three combined. It was found that for any of the single component solutions, and a signal-to-noise ratio of 100, 25 measuring points are sufficient for good accuracy; just 12 points are needed if all three components are used together. If, however, the torso size of the inverse solution is different from that of the field data by 10 or 20%, a larger error occurs, even for 56 measurement points and no noise. In this case, the field component orthogonal to the measurement grid, Bz, yields better results than the other two components, or even all three combined. We conclude that a multichannel system measuring the z component of the magnetic field in about 30 locations would be the best choice to locate a dipolar source, provided the torso of the field data is closely matched by the model used in the inverse solution. To this effect, scaling of the torso model can easily be included in the computation. Imaging techniques could be used to accommodate different torso shapes.

Bias↗
PubMed1991

Orthogonal expansions: their applicability to signal extraction in electrophysiological mapping data.

The applicability of orthogonal expansions (singular-value decomposition, Karhunen-Loève transform and principal-component analysis) for the purpose of identifying source distributions associated with definite electrophysiological events in the heart and brain is explored with a current dipole source model. By definition, the expansion eigenvectors are orthogonal, and as such will extract the features of one specific source only if all other secondary signals are orthogonal to that first source. The number of significant eigenvectors can be related to the number of original components forming a signal, but there is not a one-to-one correspondence between these eigenvectors and the individual components. Furthermore, many eigenvectors may be needed to faithfully represent even a single source, if that source is nonstationary. We conclude that generally it would be inappropriate to ascribe any physiological significance to the data resulting from such expansions.

Electroencephalography↗
PubMed1991

Magnetocardiographic localisation and modelling.

In our magnetocardiographic (MCG) localisation studies, two modelling approaches have been applied: (a) modelling the sources with dipole and quadrupole moments in a general multipole expansion and using a homogeneous, semi-infinite volume conductor, and (b) using a single current dipole source in a homogeneous, realistically shaped torso. Both approaches have been successfully applied in localising the premature ventricular excitation site in patients suffering from the Wolff-Parkinson-White syndrome. In addition, we have participated in developing a model of propagation of electrical activation in the ventricles. Anisotropic conductivity properties and spiral arrangement of myocardial fibres are included in the model.

Heart Function Tests↗
PubMed1991

Moving dipole inverse solutions using realistic torso models.

A noniterative numerical solution for the potentials on the surfaces of a piecewise homogeneous volume conductor due to a current dipole is described. This forward solution has been used in electric and magnetic single moving dipole (SMD) inverse solutions that employ a torso volume conductor model whose boundaries are specified numerically. Thus, the volume conductor model used by the inverse solutions need not be limited to simple geometric shapes; torso models of realistic shape can be used.

Electric Conductivity↗
PubMed1991

Magnetocardiographic functional localization using a current dipole in a realistic torso.

We describe a fast and numerically effective biomagnetic inverse solution using a moving dipole in a realistic homogeneous torso. We applied the localization model and high-resolution magnetocardiographic mapping to localize noninvasively the ventricular preexcitation site in ten patients suffering from Wolff-Parkinson-White syndrome. In all cases, the computed localization results were compared to the results obtained by invasive catheter technique. Using a standard-size torso model in all cases, the average 3-D distance between the computed noninvasive locations and the invasively obtained results was 2.8 +/- 1.4 cm. When the torso was rescaled to better match the true shape of the subject in five cases, the 3-D average was improved to 2.2 +/- 1.0 cm. This accuracy is very satisfactory, suggesting that the method would be clinically useful.

Adult↗
PubMed1990

Complementary nature of electrocardiographic and magnetocardiographic data in patients with ischemic heart disease.

High resolution body surface potential maps (BSPM) and magnetic field maps (MFM) for study groups consisting of 11 Q wave and 11 non Q wave myocardial infarct (MI) patients as well as 9 normal subjects, were recorded in a magnetically and electrically shielded room. A control group of 22 normal subjects provided group mean normal time integral maps for selected QRST time intervals. The difference between magnitudes of extrema in each map defined the normal mean data range R for that time interval. The root mean square sum of the differences between the time integral map of a study subject and the normal group-mean map provided an estimate of individual map variability, V. Subsequent calculation of group-mean map variability, V, and group-mean normalized variability, V/R, for specific time intervals of the cardiac cycle, were used to test the abilities of BSPM and MFM techniques to distinguish between the normal and MI study groups. Results indicate that BSPM V/R differences between MI and normal groups are most pronounced during Q wave and Q zone activity; between inferior MI's and normals (p less than 0.05) and between anterior MI's and normal (p less than 0.01). Significant differences in MFM V/R occur during repolarization; between inferior MI's and non Q wave MI's (p less than 0.05), between anterior MI's and normals (p less than 0.05), between non Q wave MI's and normals (p less than 0.05) and between all MI's and normals (p less than 0.01). It is concluded that high resolution BSPM and MFM provide complementary means of discriminating between normal subjects and MI patients.

Coronary Disease↗
PubMed1987

Inverse problem solution in magnetisation studies.

Magnetic measurements of the remanent field produced by dust particles in the lungs of industrial workers have increased our knowledge of the total amount of dust, the clearance rate of this dust, and the progression of phagocytosis of the particles in the lungs. To estimate the dust load from the magnetic field measurements one has to calculate the dipole moment of the magnetised lung. We conclude from a theoretical model study that an analysis of the data that uses the dipole and quadrupole coefficients to find the origin of a multipole expansion of the field gives the most accurate results.

Dust↗
PubMed1987

The effect of torso geometry on magnetocardiographic isofield maps.

Using a computer model of a realistically shaped human torso with lungs and intraventricular blood masses, we have assessed how torso geometry and composition affect the extracorporal magnetic field produced by a current dipole in the centre of the ventricular mass. The magnetic induction vector B arising from the dipole has been calculated at points of a precordial measuring grid and the influence of boundaries has been assessed qualitatively, by comparing contour maps of the B component normal to the torso's frontal plane. We found that the maps reflected relatively faithfully the underlying dipolar source for the homogeneous torso and even for the torso with lungs. However, the intraventricular blood masses caused a noticeable rotation of the maps' extrema. Both lungs and blood masses tended to swing the distribution towards the distribution that would have been caused by a dipole oriented along the anatomical axis of the heart.

Computer Simulation↗
PubMed1987

A Mössbauer-effect study of autopsied lung tissue of asbestos workers.

A 57Fe Mössbauer-effect study of autopsied lung tissue from Canadian asbestos mine workers is presented. The spectra typically show large quantities of iron storage protein. This exhibits a quadrupole-split doublet at room temperature and both a doublet and a Zeeman-split sextet at 4.2 K, due to a distribution of particle sizes. A comparison is made with Mössbauer spectra of lung tissue from an individual not occupationally exposed to respirable asbestos, and with spectra of respirable chrysotile asbestos taken from Canadian mines.

Asbestos↗