Study of the Influence of Implant Material on Magnetocardiography Measurements Using SQUID Sensors

TL;DR

This study assesses whether implant materials influence magnetocardiography measurements obtained with a 96-channel SQUID-based system in a magnetically shielded environment. By using a Ti-6Al-4V ELI sample significantly larger than typical implants, the authors maximize potential magnetic interaction and quantify noise as a function of distance to the sensor array. They establish acceptance criteria based on heart-field magnitudes and SQUID sensitivity, and demonstrate that the Ti-6Al-4V ELI material produces negligible noise impact, with reproducibility confirmed via normality and t-test analyses. The work suggests implants with magnetic susceptibility at or below that of Ti-6Al-4V ELI are unlikely to distort MCG results in clinical settings, though in vivo micromotion effects and other materials remain to be explored.

Abstract

Magnetocardiography system is a medical device that diagnoses cardiac disease by measuring magnetic fields generated from electric currents flowing through the myocardium. However, the accuracy of measurement data can be degraded if strong magnetic materials are present or magnetic field changes occur near the MCG system. With the widespread use of implants, the number of patients with metallic implants is increasing, but there is a lack of in-depth research on the potential impact of implant materials on the results of the MCG examination. This study aims to analyze the effect of implant materials on MCG measurements and establish relevant criteria. In this study, a 96-channel MCG system employing Superconducting Quantum Interference Device sensors, specifically first-order gradiometers based on the Double Relaxation Oscillation SQUID method, and a Magnetically Shielded Room were utilized. Ti6Al4V ELI was selected as the representative implant material sample. Experiments were conducted under extreme conditions, where a sample significantly larger than an actual implant was placed as close as possible to the sensors. As a result, when the implant material was at the minimum distance to the sensor, the noise increase was approximately 0.7 fT/$\sqrt{\mathrm{Hz}}$, which satisfies the sensitivity criteria for MCG. Furthermore, since these results were obtained under severely adverse conditions designed to maximize the noise impact, it is anticipated that the effect would be even more negligible in actual clinical settings. In conclusion, it was confirmed that common implant materials have little to no effect on MCG measurements. However, as the experiments were not conducted with the material inserted into the human body, unlike actual clinical environments, the generation of magnetic fields due to micromotion has not been verified, thus requiring further experimentation.

Figures (9)

• Figure 1: Magnetocardiography system
• Figure 2: Magnetic susceptibilities of biomaterials used for medical devices.EffectsofphaseconstitutionofZrNballoysontheirmagneticsusceptibilities
• Figure 3: Positioning of test article
• Figure 4: Comparison of the 10-time averaged noise in the frequency domain based on the distance between the Dewar and material, (Inset) variation in baseline height near 100 Hz for each distance.
• Figure 5: Comparison of the 10-time average noise at 100 Hz for each distance between the Dewar and material (brown) - First trial, (blue) Second trial