Measurement and evaluation of specific absorption rate and temperature elevation caused by an artificial hip joint during MRI scanning

Youngseob Seo,Zhiyue J Wang

doi:10.1038/s41598-020-80828-7

Abstract

A primary safety concern in a magnetic resonance imaging environment is heating of metallic implants by absorbing radiofrequency (RF) energy during MRI scanning. Experimental measurement in conjunction with computational modeling was used to evaluate the risk of biological tissue injury from the RF heating of artificial hip joints by obtaining both specific absorption rate (SAR) and temperature elevation at 1.5 T and 3 T MRI systems. Simulation result showed that high SAR and high temperature appeared near both head and tail sections of the artificial hip joints. For five different 1.5 T and 3 T MRI systems, measured temperature location showed that high temperature rises occurred near both head and tail regions of the metallic hip joints. Measured SAR value of 24.6 W/kg and the high temperature rise (= 4.22 °C) occurred in the tail region of the hip joint at 1.5 T, which was higher than the limits for temperature required by the international electrotechnical commission 60601-2-33. We have demonstrated the feasibility of evaluating RF heating of metallic hip joints during MRI scans.

Highlights

It is important to measure the specific absorption rate (SAR) of the RF energy absorbed by the body accurately
Both high SAR and high temperature appear near both head and tail sections of the artificial hip joints
A previous phantom study has reported that temperature near metallic hip joint implants rose from 1 to 9 °C at six measured positions from the tip to the head of the hip implants[33]

Summary

Introduction

It is important to measure the specific absorption rate (SAR) of the RF energy absorbed by the body accurately. Commercial MRI scanners provide an estimated SAR level for each scan under an average condition without any implant; this level is calculated from the RF waveforms and sequence parameters, system calibration, coil factors, patient weight and height, etc. It has been known that SAR values indicated by clinical MRI scanners may not be r eliable[11,12,13,14,15], and much higher local SAR induced by the presence of a metal implant can cause damages to the tissue. We aimed to measure SAR levels of metallic hip implants and evaluate the risk of injury from RF-induced heating of the hip implants from different vendors during high-field MRI scanning. Computer simulation was performed for one case to examine the spatial distribution of the electric field (E-field) which causes heating

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Conclusion