Vector analysis of gastrointestinal biomagnetic fields

Vector measurements of the magnetic field from gastrointestinal smooth muscle consist of three orthogonal components. These three components may be projected into arbitrary directions that affect the signal-to-noise ratio and emphasize particular aspects of interest in the biomagnetic signal. We describe two techniques for projection of magnetic field vectors that are suitable for analysis of gastric and intestinal biomagnetic fields. The technique known as vector projection technique-external reference correlation (VPT-ERC) allows us to obtain strong correlations with external reference signals. Another technique, vector projection technique-frequency correlation (VPT-FC), enables the discrimination of biomagnetic signals from different sources of bioelectric activity. Each of these methods produces information that is not attainable through the measurement of any individual magnetic field component.