IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 18, NO. 2, JUNE 2008 891 Characterization of Bougienage Electromagnetic Forces Makoto Takayasu, D. Bruce Montgomery, and Joseph V. Minervini Abstract—Infants born with esophageal atresia can be treated by an electromagnetic bougienage method to lengthen the esophageal segments. This method uses magnetic forces generated between magnetic bullets (bougies) by a background magnetic field. Two types of bougies, solid rounded rod and hollow cylinder bullets, have been characterized using a fabricated prototype bougienage magnet. Analytical methods have been developed to obtain the magnetic forces on bougienage bullets. The calculation results were confirmed to agree well with the experimental results. Index Terms—Electromagnetic forces, force measurement, mag- netic force, medical treatment. I. INTRODUCTION I N the condition of esophageal atresia the esophagus fails to bridge the connection from the mouth to the stomach. Over the past half century esophageal atresia has been treated by primary anastomoses, colon or gastric tube interposition graft, manual bougienage, or by electromagnetic bougienage. When the two esophageal segments are sufficiently close, they can be joined by anastomosis without tension. However, for approxi- mately 100 babies/year in the US, the two ends of the esophagus are too widely separated. For these cases, the most common procedure is to interpose a segment of colon to bridge the dis- tance. This is an extremely arduous procedure for the infant. As an alternative to the use of colonic graft, Howard and Myers [1] introduced mechanical bougienage into the lumen of the upper esophageal segment. They used a regimen of daily manual stretching of the esophageal tissue over a 30 day period. This alternating application of a tissue stretching force followed by relaxation promoted tissue growth to the point where surgery could be successfully performed. An electromagnetic bougienage method to lengthen esophageal segments was developed thirty years ago by Hendren and Hale [2]–[4]. Magnetic bougie bullets were placed in the two ends of the esophagus. A magnetic field was applied across the infant’s chest to attract the bougies in order to stretch the esophageal tissue for 1 minute, followed by one minute of relaxation, with the cycle typically repeated. When Manuscript received August 28, 2007. This work was supported by the US National Institute of Health, and Children’s Hospital Charitable Funds, Boston. M. Takayasu and J. V. Minervini are with Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, USA (e-mail: takayasu@psfc.mit.edu). D. B. Montgomery is with Magplane Technology, Inc., 380 Hanscom Drive, Bedford, MA 01730, USA. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TASC.2008.921236 Fig. 1. (a) Magnet with a force measurement setup; one bullet suspended on a load cell at the top. (b) Enlarged view of the magnet. Two bullets are placed on the magnet axis. The lower bullet is mounted under the magnet. the two esophageal segments were sufficiently close after one to two months of treatment, they could be surgically joined together. This approach has been performed successfully and confirmed to be feasible for infants. However, the technique was not further developed at that time. Recently Magplane Technology, Inc. has been developing a next generation device for electromagnetic bougienage that meets modern hospital standards for safety and ease of use. This paper presents char- acteristics of magnetic forces acting on two types of bougie bullets, rounded rod bullets and hollow cylinder bullets, in a prototype bougienage magnet along with discussion of an analytical method for calculating the forces on the bougie. II. MAGNET AND BOUGIE BULLETS The magnet is composed of six elliptical racetrack double pancakes with eight layers of a hollow conductor (9.0 mm square O.D. and 4.5 mm I.D.) The magnet dimension and shape were designed to fit the infant’s chest. The magnet was designed by Robert Weggel and fabricated by Stonite Coil Corporation. The magnet has a bore of major diameter 330.6 mm and a minor diameter of 238.6 mm, with a height of 114.8 mm. Electrical specifications of the magnet include: maximum current of 800 A with water cooling (11 L/min), maximum power of 20.7 kW, resistance of 32.3 , and an inductance of 2.7 mH. Fig. 1 shows the magnet with a bullet force measure- ment set up described later. The center field measured in Oe was approximated as a function of the current in amperes by . Each coil winding of an egg-shaped racetrack was approxi- mated by an elliptical single turn coil of the major diameter and the minor diameter . The center field on the axis of the elliptical coil is given at the current by , here and (where is the Elliptic Integral of the second kind). 1051-8223/$25.00 © 2008 IEEE