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Bioelectric Analyses of an Osseointegrated Intelligent Implant Design System for Amputees

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Parameters Affecting Worst-Case Gradient-Field Heating of Passive Conductive Implants.

Howard Bassen¹, Tayeb Zaidi¹

¹Division of Biomedical Physics, Center for Devices and Radiological Health, US Food and Drug Administration, Maryland, USA.

Journal of Magnetic Resonance Imaging : JMRI

|July 1, 2022

Summary

This study adapted ISO 10974 methods to test MRI gradient-induced heating in passive hip implants. Uniform gradient fields revealed worst-case heating, crucial for medical device safety assessments.

Keywords:

MRI safety computational modeling gradient field heating hip implant temperature measurement

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Area of Science:

Biomedical Engineering
Medical Physics
Materials Science

Background:

Regulatory testing of MRI gradient-induced heating for implanted medical devices is critical.
This study adapted ISO 10974 Technical Specification (TS) methods for passive hip implants.
Previous studies used non-uniform fields, necessitating worst-case heating identification with uniform fields.

Purpose of the Study:

To identify gradient-field parameters influencing maximum in vitro heating of a hip implant.
To evaluate heating in a cylindrical titanium disk as a comparative model.
To address the need for worst-case heating assessment in passive implants.

Main Methods:

Computational simulations and experimental validation were employed to assess induced heating.
Uniform gradient fields (up to 42 T/s RMS) were used, simulating ISO 10974 TS.
Heating was analyzed in a tissue-simulating gel phantom at various frequencies (1-10 kHz) and time points.

Main Results:

Maximum simulated temperature rise was 10 °C at 1 kHz and 0.66 °C at 10 kHz (10-minute exposure).
Heating was proportional to the square of the B-field's slew rate (dB/dt RMS).
Computational and experimental results showed no significant difference (p < 0.05).

Conclusions:

Implant heating is dependent on B-field frequency, cross-sectional area, and thickness relative to skin depth.
Testing with lower dB/dt RMS enables prediction of heating at higher values, per ISO TS.
This method provides a reliable approach for worst-case heating assessment of passive implants.