Vincent Schlageter

Noninvasive Verification of Nasogastric Tube Placement Using a Magnet-Tracking System: A Pilot Study in Healthy Subjects

BACKGROUND Fluoroscopic verification of nasogastric (NG) feeding tube placement is inconvenient and involves radiation exposure. We tested whether the position of an NG tube can be assessed reliably by a recently introduced magnet-tracking system. METHODS A small permanent magnet was attached at the end of an NG tube and its position was monitored using an external sensor array connected to a computer. NG tube trajectory, spontaneous movements of the magnet, and its position relative to the lower esophageal sphincter (LES) and xiphisternum were assessed in 22 healthy subjects and compared with esophageal manometry. In 12 subjects, localization of the magnet was also compared with fluoroscopy. RESULTS Magnet-tracking displayed NG tube tip movement reproducibly as it moved vertically in the esophagus and then laterally into the stomach. Compared with manometry, the accuracy and sensitivity of magnet tracking for localization of the NG tube tip, above or below the diaphragm, were 100%. Compared with fluoroscopy, the accuracy of NG tube localization by magnet tracking was 100%. With the magnet in the stomach, but not in the esophagus or LES, low amplitude displacements at a frequency of 3 per minute, consistent with gastric slow wave activity, were observed. CONCLUSIONS Magnet tracking allows accurate, real-time, 3-dimensional localization of an NG tube with respect to anatomic landmarks. Recorded motor patterns are indicative of the position of the NG tube. Magnet tracking may be a useful tool for bedside placement of nasogastric and enteral feeding tubes.

Understanding gastric forces calculated from high-resolution pill tracking

Although other methods exist for monitoring gastrointestinal motility and contractility, this study exclusively provides direct and quantitative measurements of the forces experienced by an orally ingested pill. We report motive forces and torques calculated from real-time, in vivo measurements of the movement of a magnetic pill in the stomachs of fasted and fed humans. Three-dimensional net force and two-dimensional net torque vectors as a function of time data during gastric residence are evaluated using instantaneous translational and rotational position data. Additionally, the net force calculations described can be applied to high-resolution pill tracking acquired by any modality. The fraction of time pills experience ranges of forces and torques are analyzed and correlate with the physiological phases of gastric digestion. We also report the maximum forces and torques experienced in vivo by pills as a quantitative measure of the amount of force pills experience during the muscular contractions leading to gastric emptying. Results calculated from human data are compared with small and large animal models with a translational research focus. The reported magnitude and direction of gastric forces experienced by pills in healthy stomachs serves as a baseline for comparison with pathophysiological states. Of clinical significance, the directionality associated with force vector data may be useful in determining the muscle groups associated with gastrointestinal dysmotility. Additionally, the quantitative comparison between human and animal models improves insight into comparative gastric contractility that will aid rational pill design and provide a quantitative framework for interpreting gastroretentive oral formulation test results.

High Sensitivity Hall Magnetic Sensors Using Planar Micro and Macro Flux Concentrators

We have studied the sensitivity of Hall devices using planar magnetic flux concentrators of various lengths. By placing magneto-concentrators (MCs) on Hall device, we obtained sensitivity up to 100 V/T for a bias current of 1 mA and for a length of the MCs of 50 mm. This value is about 1000 times better then that of a conventional silicon Hall devices, without adding significant amount of noise. The magnetic gain is achieved using a combination of micro-integrated and macroscopic magnetic flux concentrators.