Method of making a miniaturized positional assembly

A method of producing a miniaturized set of inductive coils set mutually orthogonally inside a tube. In the method a positional template made of a sheet of substantially rigid material that defines a set of guide apertures, each of which is in the shape of one of the set of inductive coils. The guide apertures are disposed so that when an inductive coil is fitted into each one of the guide apertures the coils will be substantially orthogonal to one another.

BACKGROUND OF THE INVENTION

The ability to accurately determine the position of a device within the body currently yields a considerable benefit for at least one medical procedure. This is the electrophysiological mapping of the heart. Such mapping frequently permits the location and treatment of the neurological disorder that has given rise to a heart arrhythmia. In order to accurately perform this mapping a transceiver head must be introduced into the heart by way (in part) of the femoral artery. The position and orientation of this transceiver head must be accurately monitored.

In order to perform this monitoring a set of orthogonally positioned inductive coils are fixed at the transceiver head and conductively connected through the catheter to the outside of the body, where the current in each of the inductive coils can be read. Cooperating with these coils, powerful magnets are arrayed about the imaging station, so that the current through each coil is dependent on its orientation relative to the magnetic field created.

Heretofore, the manufacture of the unit in which the coils reside has been a challenging and expensive operation. Each coil was soldered to a pair of wires and adjusted so that its position was generally correct. Next the coils and attached wires are gently placed into a polymer tube, which is then filled with epoxy to retain the coils in their generally mutual orthogonal positions and to retain the tube in its protective position.

Performing this method resulted in many problems. First, there was the difficulty in maintaining the mutually orthogonal orientation of the inductive coils during their insertion into the tube and the filling of the tube with epoxy. Also, air pockets would sometimes form as the epoxy was being introduced into the tube.

Another difficulty in the manufacture of a device bearing orthogonally oriented inductive coils is the achievement of true orthogonal orientations. At the fraction of a millimeter scales required to create a device that can be moved through small blood vessels, it is not easy to ensure that each inductive coil is placed within 89.9° and 90.1° of the orientation of the others.

SUMMARY

The present invention is a method of producing a miniaturized set of inductive coils set mutually orthogonally inside a tube. In the method a positional template made of a sheet of substantially rigid material that defines a set of guide apertures, each of which is in the shape of one of the set of inductive coils. The guide apertures are disposed so that when an inductive coil is fitted into each one of the guide apertures the coils will be substantially orthogonal to one another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIGS. 1–3, in a first preferred embodiment of a method of manufacturing a miniaturized positional assembly8(FIG. 3), a piece of flex-circuit10is provided that is sized to accommodate a set of inductive coils12,14and16when folded into a square tube. The flex circuit has a set of six traces18, each of which extends from an area adapted to connect to a set of wires22, to a position adapted to permit the attachment of a terminal17of one of the inductive coils12,14and16. In an alternative preferred embodiment the terminal wires of coils12,14and16are extended to attach directly to the ends of wires22, which are far greater in diameter.

Each of the three coils12,14and16may be placed by a robot onto the flex circuit, which preferably has been readied for each with a drop of epoxy to hold the coil in place during further operations. The termini (not shown) of each coil are then soldered to the appropriate flex circuit trace18. A cable20is composed of a set of six wires22. Each wire22is soldered to a circuit trace18. Although more soldering operations are required than would be necessary if wires22were directly soldered to the terminals of the inductive coils12,14and16, the soldering operations are made far more repeatable and therefore may be automated.

At this point a positional template50is lowered into place about said inductive coils12,14and16. Template50defines a first guide aperture52adapted to fit closely about inductive coil12, a second guide aperture54adapted to fit closely about aperture inductive coil14and a third guide aperture56adapted to fit closely about inductive coil16. When coils12,14and16are all fitted into their respective guide apertures52,54and56, they should be oriented orthogonally to each other in a highly accurate manner.

In an alternative preferred embodiment (not shown) positional template is a flex circuit and inductive coils12,14and16are electrically connected to positional template50.

After the electrical and physical attachment of the inductive coils12,14and16to the flex circuit10, it is curled up in a piecewise manner about a set of laser created score lines58to form a tube that is rectangular in cross-section. Epoxy resin may be placed on flex-circuit10prior to curling it up into a tube, or epoxy resin could be added at either of a pair of tube openings62.

The wires used in inductive coils12,14and16, each has a diameter of from AWG 58 (10 microns) to AWG 50 (25 microns). Each inductive coil12,14and16has a diameter of 1 millimeter or smaller. The entire positional assembly8is only slightly than the diameter of each individual coil12,14and16. Accordingly, assembly can also be less than 1 millimeter thick and is approximately 5 millimeters long.