Data Format

The raw data are retained and can be reviewed at any time. The filtered and averaged data described in the procedure above are available as temporal traces of the magnetic field intensity in a plane above the heart where the magnetic field SQUID sensors are located. The distance of this plane is approximately 6 cm above the epicardium in a typical patient. The appearance of the data is similar to conventional EKG tracings. Raw data are always available to the physician and technician for review. The software allows the operator to examine all MCG traces and from the hundreds recorded select any QRS complex as a template. Once having created a QRS template the operator can decide which signals will be used for subsequent data averaging by selecting the confidence level of pattern matching for all recorded signals relative to the template. This automatic procedure and final manual override allows the operator to remove external artifacts from data manipulation and analysis. Figure 2 shows the filtered signals from all 9 sensors measuring a subject in a typical hospital environment without magnetic room shielding.

Fig. 2. Filtered temporal MCG traces over several cardiac cycles collected in 9 channels simultaneously at one position over the subject torso. Data were collected in an unshielded environment at Boston Medical Center. The blue line with the red flag marks the user-selected QRS template; blue lines with clear flags are QRS complexes selected automatically by the software according to user-defined acceptance criteria. Accordingly, blue lines without flags are rejected automatically. An absence of a line (through a QRS complex) indicates a cardiac cycle not accepted by the user (for subsequent data manipulation).