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

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.