Correlation and comparison of magnetic and electric detection of small intestinal electrical activity

The small intestinal basic electrical rhythm (BER) was detected simultaneously with serosal electrodes and a transabdominal superconducting quantum interference device (SQUID) magnetometer in anesthetized rabbits. We induced mesenteric ischemia to correlate serosal electrode recording of changes in BER with the SQUID magnetometer. The BER frequency was obtained by spectral analysis of the data using Fourier and autoregressive techniques. There was a high degree of correlation (r = 0.96) between the BER frequency determined using the serosal electrodes and the BER frequency ascertained from SQUID data. Additionally, the effects of an electrical insulator on the external electric and magnetic fields were studied in the rabbit model. The presence of an insulator profoundly attenuates external electric potentials recorded by cutaneous electrodes but does not significantly affect external magnetic fields or serosal potentials. We conclude that SQUID magnetometers could noninvasively record small intestinal BER that was highly correlated with the activity recorded by invasive serosal electrodes. The advantages of magnetic field measurements have encouraged us to investigate clinical applications.

Superconducting quantum interference device magnetometer for diagnosis of ischemia caused by mesenteric venous thrombosis

Although mesenteric venous thrombosis carries a better prognosis than arterial thrombosis, mortality and morbidity are still high. Previous studies have shown that the basic electrical rhythm (BER) of the bowel decreases early after induction of arterial ischemia. Furthermore, our studies have shown that these changes occur prior to pathologic changes and that they can be recorded noninvasively using a superconducting quantum interference device (SQUID). SQUIDs measure magnetic fields that are created by the electrical activity of the gastrointestinal smooth muscle and have been used to measure the BER of the small intestine in human volunteers. This study was conducted to determine if a SQUID could be used for early noninvasive detection of mesenteric venous ischemia in an animal model. Simultaneous recordings from serosal electrodes and a SQUID outside the abdomen were taken from anesthetized New Zealand rabbits. Recordings were made for 15 minutes before and 90 minutes after injection of thrombin into the superior mesenteric vein. The basic electrical rhythm of the small bowel dropped from 16.42 +/- 0.69 to 8.80 +/- 0.74 cycles per minute at 30 minutes and to 6.82 +/- 0.722 after 90 minutes (p < 0.0001, paired t-test). The correlation coefficient between the SQUID and electrical recordings was 0.954 (p < 0.0001). These data suggest that the ischemia caused by mesenteric venous thrombosis results in changes in the bioelectrical activity, which can be noninvasively detected using a SQUID.

Noninvasive diagnosis of mesenteric ischemia using a SQUID magnetometer

OBJECTIVE

The authors assessed the ability of a Superconducting Quantum Interference Device (SQUID) magnetometer to noninvasively detect mesenteric ischemia in a rabbit model.

SUMMARY BACKGROUND DATA

Superconducting Quantum Interference Device magnetometers have been used to detect magnetic fields created by the basic electrical rhythm (BER) and to detect changes in BER of exteriorized bowel of anesthetized rabbits during mesenteric ischemia.

METHODS

The BER of rabbit ileum was noninvasively measured transabdominally using a SQUID magnetometer and compared with the electrical activity recorded with surgically implanted serosal electrodes before, during, and after snare occlusion of the superior mesenteric artery.

RESULTS

Transabdominal SQUID recording of BER frequency was highly correlated to the measurements obtained with electrodes (R = 0.91). Basic electrical rhythm frequency decreased from 16.4 +/- 0.8 to 8.3 +/- 0.3 cpm (p < 0.001) after 25 minutes of ischemia. Reperfusion of ischemic bowel resulted in recovery of BER frequency to 14.3 +/- 0.4 cpm 10 minutes after blood flow was restored.

CONCLUSIONS

A SQUID magnetometer is capable of noninvasively detecting mesenteric ischemia reliably and at an early stage by detecting a significant drop in BER frequency. These positive findings have encouraged the authors to continue development of clinically useful, noninvasive, detection of intestinal magnetic fields using SQUID magnetometers.