Fiber-Optic Probe at the Heart of MRI-Safe Pacemaker

Originally Published MPMN November 2002

PROFILE

Fiber-Optic Probe at the Heart of MRI-Safe Pacemaker

Probe tip is similar in size to pacemaker leads that it replaces

In 1997, FDA published a draft document recommending that individuals with implanted pacemakers should not enter magnetic resonance imaging (MRI) procedure rooms or come within the 5-G line around the scanner. The agency was responding to incidents in which the magnetic field generated by MRI equipment produced torque and displacement forces affecting pacemakers and other implantables, resulting in the tearing of soft tissue and device malfunctions. To enable patients with implanted pacemakers to take advantage of MRI procedures, Biophan Technologies Inc. (West Henrietta, NY) developed an MRI-compatible implantable device. To address materials and miniaturization issues, the firm enlisted the assistance of Valtronic (Solon, OH), a company that develops and manufactures miniature electronic components to customer specifications.

In traditional pacemaker designs, a metallic wire lead connects the pacemaker to the heart. In proximity to MRI equipment, the lead can get very hot and cause an adverse event. Biophan replaced the metal lead with a fiber-optic cable, thus eliminating this potential hazard. Having resolved the device performance issues, Biophan turned to Valtronic for help on miniaturization of the electronic components. In particular, company engineers asked their peers at Valtronic to make a miniature probe for the MRI-safe pacemaker. The major challenge, according to Valtronic director of sales and marketing Gary Pinkerton, resided in making "the probe tip small enough so that it would be superior in size to standard pacemaker leads."

The probe tip comprises an optical-fiber termination, electrode, LED, photodiode, and microprocessor. "That's where a lot of the magic happens," says Pinkerton. It's also where Valtronic worked its own magic . . . on a very small scale.

Flip Chips and Beyond

Gold-on-gold flip chips and 3-D chip-scale packaging (3D-CSP) are Valtronic's signature miniaturization strategies, according to Pinkerton. Flip-chip technology involves mounting raw integrated circuits facedown on a PC board, thus reclaiming the space surrounding the chips that was normally consumed by conventional packaging and leads. As initially developed by IBM, flip-chip technology was a solder-based process. Valtronic uses low-impedance gold contacts on the chips and circuit boards, bonding them by means of a proprietary nonconductive adhesive.

By combining flip chips with flexible PC board substrates, Valtronic produces 3-D chip-scale packaging, the smallest possible volume for electronic assemblies available to industry, according to the firm. 3D-CSP uses a combination of open and proprietary techniques to produce printed circuit boards that can be folded into dense electronic modules. These components achieve up to 80% size reductions compared to conventional assemblies. The technology has been used to design the electronics for a 4.5 x 4 x 3-mm, completely in-the-ear hearing aid, reportedly the world's smallest such device.

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