Abstract
We aimed to investigate whether different transmission settings of the dual-transmit technology may influence the amount of heat induction around an implant material dependent on its location within the magnetic field. Metallic hip implants were positioned in the magnet of a 3-T scanner at various lateral offset positions in relation to the magnetic axis in a body-phantom tank filled with polyacrylic acid gel. The temperature increase close to the implants was measured during turbo spin-echo scanning using dual-channel parallel radiofrequency (RF) transmission with circular in comparison to elliptic RF polarization. Circularly polarized transmission (CPT) induced higher temperature increases (maximum 6.2 °C) than elliptically polarized transmission (EPT) (maximum 1.5 °C). The heat induction was dependent on the distance to the isocenter with increased heating by increased distance to the isocenter. EPT showed lower heating around implants compared to the CPT as commonly used in single-transmission system; further, less heating was observed for both transmission settings closer to the magnet isocenter.
Highlights
Recent implementations of metal-artifact reduction sequences in magnetic resonance imaging (MRI) have allowed the evaluation of anatomical structures close to metallic implants [1,2,3]
In the 2-min baseline experiment without any implant in the phantom, a maximal temperature increase of 0.5 °C was measured with Circularly polarized transmission (CPT), with a whole-body averaged specific absorption rate of 1.042 W/kg, while with the elliptically polarized transmission (EPT) no relevant temperature increase was observed
The temperature increase on the left side was higher compared to the right side (4.3 °C versus 1 °C; whole-body averaged specific absorption rate (wbSAR) 1.042 W/kg) using CPT
Summary
Recent implementations of metal-artifact reduction sequences in magnetic resonance imaging (MRI) have allowed the evaluation of anatomical structures close to metallic implants [1,2,3]. These sequences steadily become more important in daily clinical use given the strongly. There are safety issues associated with the examination of patients with metallic implants [5]. The trend towards MRI scanning at high field (≥ 3 T), beyond challenges of optimizing image contrast and minimizing artifacts, accentuates the problem of guaranteeing patient safety [8]. Attempts were made to optimize the RF transmitting field by using
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