Layer-to-Layer Heart Electrical Image Based on
Magnetocardiography Data in Comparison with
Perfusion Image Based on PET

Michael Primin^a, Illya Chaikovsky^a, Caroline Berndt^b, Igor Nedayvoda^a, Jan Korfer^b

^aSQUID International AG, Essen, Germany
 ^bHeart and Diabetes Centerof NRW, Ruhr University, Bad-Oyenhausen, Germany

Correspondence: I Chaikovsky, SQUID Int. AG, 45145 Kruppstrasse 82-100 Essen, Germany
E-mail: ic@squid.de, phone +49 201 1059132, fax +49 201 1059140

1.    Introduction

The non-invasive diagnosis of cardiac ischemia remains a one of the most important tasks of the modern cardiology. Positron emission tomography, allowing analyse myocardial perfusion, is one of the most sensitive and well-established methods, which could be classified as the “gold standard” of non-invasive methods.

Magnetocardiography (MCG) is known as a new fully non-invasive method to measure electrical cardiac activity.

Aim of this study was to find the way to represent electrical image of the heart obtained from magnetocardiographic data in comparison with perfusion image obtained from PET based on a few cases of diagnostically problematic patients with the absence of signs of ischemia on stress and rest ECG and unchanged function of left ventricle on echocardiogram.

2.    Material and Methods

The study includes 3 patients (2 female, 1 male) and one healthy volunteer (male). All 3 patients underwent resting and stress ECG, EchoCG at rest, PET and coronaroangiography. Healthy volunteer had no history of any cardiovascular disease, normal ECG at rest and stress as well as a normal echocardiogram at rest.

PET was performed with Adenosine to recruit the coronary reserve; resting and stress recordings have been made with N-13-Ammoniak. MCG recordings were taken at 9 pre-thoracic sites using a four-channel SQUID-magnetometer (SQUID AG, Essen) in an unshielded setting within a 20 by 20 rectangular grid with a 4 cm pitch over the precordial area. Data were recorded at each registration point for 30 seconds with simultaneous registration of lead II of the surface ECG.

Further analysis was based on “inverse problem solution” i.e. reconstruction of the sources in the heart originating magnetic field measured. We use a model of the magnetic dipole as the source of biomagnetic signal in contrast to common approaches using the electric dipole as a source.

Based on this method source of biomagnetic signal can be represented in the form of N elementary magnetic dipoles. Knowing density, coordinates and magnetic moments of all elementary magnetic dipoles currents distribution as a current density vectors maps could be obtained for any r_z coordinate i.e. for any distance (layer) from the measurement plane [Primin and Nedayvoda, 1999].

The layer-by-layer reconstructions were used for further medical analysis. These reconstructions have been done for single time moment in the middle of ST-T interval.

3.    Results

Healthy volunteer M. (male, 47 year)

PET: Normal perfusion; MCG: The layer-by-layer representation (see Fig.1a) shows homogeneous current distribution with similar structure of maps at each layer. The layer with maximal density is located on the middle distance from the measurements plane.

Patient J. (male, 72 years)

PET: reduced myocardial perfusion in the all walls in particular in septoapical area; MCG: Two area of activity (see Fig.1b) - one of them is located on the anterior part of the cube of reconstruction with maximal intensity on 12 cm, another is shifted left- backwards with maximal activity on 18 cm.

Patient l. (male,74 years)

PET: reduced myocardial perfusion in the apical, septoapical and suproapical areas; MCG: Two areas of activity (see Fig.1c) which are located approximately on one layer - 11-12 cm.

Patient T (female, 42 year)

PET: Small local reducing of myocardial perfusion in the inferioapical area; MCG: single but non-compact, distributed area of activity with fuzzy contours (see 1d).

Figure 1. Layer-to-layer current reconstruction at the middle of ST-T interval. Axonometric projection of cube of current reconstruction (sagittal view). A)healthy volunteer M.;B)patient J.; C)patient L.;D)patient T.

4.    Discussion

Highly homogeneous type of layer-to-layer electrical image in the healthy volunteer examination as we consider reflects absence of myocardial zones with perfusion insufficiency i.e. absence of zones with different electrical properties. In contrast currents reconstruction of patients are nonhomogeneous. The degree of this nonhomogeneity correlates with degree of perfusion insufficiency detected by PET. Further investigations will be done to make this diagnostical approach useful in a clinical routine.

References

Primin,M.,Nedayvoda,I. Algorithm for Magnetic Data Processing. Engineering Simulation, 16: 111-122,1999.