High resolution (HR) multi-electrode mapping is increasingly being used to evaluate gastrointestinal slow wave behaviors. To create the HR-activation maps from gastric serosal electrode recordings that quantify slow wave propagation, it is first necessary to identify the activation time (AT) of each individual slow wave event. Identifying these ATs has been a time consuming task, because there has previously been no reliable automated detection method. We have developed an automated AT detection method termed falling-edge, variable threshold (FEVT) detection. It computes a detection signal transform to accentuate the high 'energy' content of the falling edges in the serosal recording, and uses a running median estimator of the noise to set the time-varying detection threshold. The FEVT method was optimized, validated, and compared to other potential algorithms using in-vivo HR recordings from a porcine model. FEVT properly detects ATs in a wide range of waveforms, making its performance substantially superior to the other methods, especially for low signal-to-noise ratio (SNR) recordings. The algorithm offered a substantial time savings (>100 times) over manual-marking whilst achieving a highly satisfactory sensitivity (0.92) and positive-prediction value (0.89).

superconducting quantum interference device magnetometer; basic electrical rhythm; spectral analysis; volume conductor; small intestine; electrical control activity; electrical recordings SMOOTH MUSCLE in the gastrointestinal tract displays two types of electrical activities. A high-frequency spiking activity known as the electrical response activity is associated with muscle contraction, whereas an oscillating slow wave, known as the electrical control activity or basic electrical rhythm (BER), is present continuously (8, 9, 24). The BER has typically been detected with invasive serosal electrodes that measure the local potential difference of a section of bowel. Recently, Chen et al. (6) reported detecting the human small bowel BER using cutaneous electrodes. To record small bowel BER, a band-pass filter was used to filter out all other biologically active tissues (stomach, heart, and colon). The results indicate that the small bowel potentials result in low-amplitude cutaneous potentials that give a low signal-to-noise ratio. Moreover, the studies by Chen et al. (6) involved subjects in whom the jejunum had been attached to the abdominal wall, providing for increased electrical contact between the bowel and the cutaneous electrode. Presumably, even lower signal-to-noise ratios than Chen et al. (6) reported would be obtained if the direct electrical contact between the bowel and the cutaneous electrode, provided by attaching the bowel segment to the abdominal wall, were broken.Because magnetic fields are not attenuated by lowconductivity layers such as those found in the abdominal wall, another option is to measure the magnetic field produced by small bowel electrical activity (27). Biomagnetic fields are typically several orders of magnitude smaller than the magnetic field of the Earth, so a sensitive detection device is necessary. Superconducting quantum interference device (SQUID) magnetometers are able to detect the weak magnetic fields of biological origin. Previous studies have shown that SQUIDS can detect small intestine BER in vitro (25) and in vivo (11). Magnetoencephalography researchers routinely measure the magnetic field of the brain (27), which is at least an order of magnitude smaller than the magnetic field of the small intestine (21).We present an experiment to examine the effect of a nonconducting layer placed between the small bowel and the abdominal wall on the transabdominal magnetic field, the serosal potential, and the cutaneous potential. We hypothesized that the magnetic fields of small bowel electrical activity recorded with the SQUID would correlate with the potentials measured with invasive electrodes and would not be attenuated by the placement of a nonconducting layer between the bowel and the abdominal wall. Transabdominal magnetic measurements are not expected to suffer from the same problems (attenuation and smoothing by electrically insulating layers) as cutaneous electrical recordings. A previous study utilizing a mathematical model for the magnetic fields and electric poten...

An analysis of the relative capabilities of methods for magnetic and electric detection of gastrointestinal electrical activity is presented. The model employed is the first volume conductor model for magnetic fields from GEA to appear in the literature. A mathematical model is introduced for the electric potential and magnetic field from intestinal electrical activity in terms of the spatial filters that relate the bioelectric sources with the external magnetic fields and potentials. The forward spatial filters are low-pass functions of spatial frequency, so more superficial external fields and potentials contain less spatial information than fields and potentials near the source. Inverse spatial filters, which are reciprocals of the forward filters, are high-pass functions and must be regularised by windowing. Because of the conductivity discontinuities introduced by low-conductivity fat layers in the abdomen, the electric potentials recorded outside these layers required more regularisation than the magnetic fields, and thus, the spatial resolution of the magnetic fields from intestinal electrical activity is higher than the spatial resolution of the external potentials. In this study, two smooth muscle sources separated by 5cm were adequately resolved magnetically, but not resolved electrically. Thus, sources are more accurately localized and imaged using magnetic measurements than using measurements of electric potential.