I n t e l l i g e n t   D e s i g n   a n d   D e v e l o p m e n t      

Magnetic Location and Tracking Technology

Lucent's magnet tracking technology provides bedside, real-time confirmation of catheter or tube placement without the cost, time, and hazard of X-ray imaging.  The components of the Lucent  system are defined below:

Small Permanent Magnet

The locatable, indwelling medical device can contain one or more small, permanent magnets.  The magnets may be chemically composed of NdFeB (neodymium iron boron), SmCo (samarium cobalt), or AlNiCo (aluminum nickel cobalt), and choice of magnet type depends on manufacturing and cost issues.

Locatable (Indwelling) Device

Lucent locatable devices include catheters and other medical tubes, guidewires, probes, surgical tags, implantable valves and shunts, and any devices to which a magnet can be attached.

Locating and Tracking Algorithms

Lucent’s magnet locating and tracking technology relies upon a set of proprietary software algorithms that solve the problem of finding a dipole magnet in 3D space, which itself contains a background magnetic field (from the Earth).  Our software takes the data from an array of magnetic field sensors, and employs a neural net, a non-linear optimization routine, and various heuristics to determine both the location and orientation of the magnet while canceling out the Earth’s background field.

Magnetic Sensors and Signal Processing Hardware

Lucent’s magnet tracking and locating systems are constructed using an array of magnetic field sensors, one or more digital signal and microprocessors, and necessary support electronics.  For several of our detectors, we’ve used Honeywell magneto-resistive sensors arranged in groups to form four or more sets of 3D-vector sensors.

Detector and Display

Lucent’s hand-held detectors are fully self-contained, with either rechargeable or primary batteries, and graphics or segment-based LCD display screens.  They typically have a built-in data-port for optionally sending the magnet’s location and tracking information to a remote desktop or laptop computer.

Lucent System

A Lucent magnet tracking and locating system can be customized for a particular medical need and application.  We have built systems to track magnets as small as 0.030” in diameter, at distances up to 12 cm below the detector.  Larger magnets will have an increased detection range.  Location accuracy is typically better than +/- 5mm with orientation accuracy of +/- 2 degrees in pitch and yaw.

US patents covering Lucent’s technology are listed below:

Patent No.           Issue Date

5,879,297            March 9, 1999

6,129,668            Oct. 10, 2000

6,216,028            April10, 2001

6,263,230            July 17, 2001

Some Magnet Facts

Magnet Field Strength

“Magnetic field strength”, as used in this document, is synonymous with “magnetic flux density”, which has units of gauss in the cgs (centimeter-gram-second) system of measurement, and is commonly denoted by the symbol β.  The stronger the magnetic field strength at a point in space, the more effect it will have on a magnetic material, compass needle, or moving charged particle.

The Earth’s natural magnetic field has a strength that varies depending on location, and ranges from about 0.2 to 0.6 gauss (200 to 600 milligauss).  The magnetic field inside the bore of a typical diagnostic magnetic resonance imager (MRI) is 15,000 gauss, although there are clinical MRI magnets ranging from 3000 to 40,000 gauss.

The theoretical maximum magnetic field strength from a permanent magnet, which would be measured at zero distance from the center of one of the magnet’s poles (i.e. one end) depends on the “grade” of magnet material used.  A higher-grade magnet material can retain a greater magnetization and can generate a larger maximum field.  Lucent locatable devices have for the most part used magnets of NdFeB grade 45 or higher, with maximum theoretical field strengths of over 13,500 gauss.  However, the field strength due to the magnet decreases extremely rapidly with distance, and at typical distances from the magnet inside a patient to the Lucent detector, the field strength from the magnet can be as low as 10 milligauss.

Magnetic Field Direction

The magnetic field at a point in space is fully described as a vector, having both a direction and a magnitude.  The small permanent magnets used in Lucent locatable devices create a dipole magnetic field, in which the vectors change direction and magnitude in a known manner in the space surrounding the magnet.  By convention, the magnetic field vectors point perpendicularly out from the face of the magnet’s North pole, and into the magnet’s South pole, and make intermediate angles to the magnet’s axis as you travel from one pole to the other.

Magnetic Field Variability

The fields generated by permanent magnets, the Earth, and an MRI’s main magnet, are considered “static” magnetic fields, that is, they do not vary with time.   

Magnetic Field Biohazards

There are no known biological hazards from acute or chronic exposure to static magnetic fields with strengths on the order of the permanent magnets used in Lucent locatable devices.  By way of illustration, the most common magnetic resonance imagers routinely expose patients to whole-body, static, dipole magnetic fields stronger than the maximum theoretical field from the magnets we’ve used.

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