Abstract
Magnetic resonance imaging (MRI) has become an important diagnostic tool with an ongoing dynamic development towards application of increasing static magnetic flux densities and consequently, exposures to electromagnetic fields (EMF) of increasing radio frequencies (RF). This raises particular concern metallic implants could lead to excess tissue heating and consequently, to thermal tissue damage. In thorax surgery the intersected sternum is reconnected by metallic sutures (cerclages). To investigate whether patients with such implants can be accepted for MRI and whether there may be limitations with regard to static magnetic fields, by numerical anatomical and thermal modelling MRI induced tissue heating was assessed for magnetic flux densities 1.5 T, 3 T, 4 T and 7 T. Results show that overall tissue temperature increased with increasing RF EMF frequency. However, even for setting MRI exposure parameters at maximum permissible level partial body heating remained marginally affected and even at local level the additional contribution of the presence of the metallic cerclage remained below 1°C. This allows concluding that from a heating point of view metallic sutures as used to fix the sternum after thorax surgery are no contraindication for MRI with static magnetic flux densities up to 7 T.
Highlights
Magnetic resonance imaging (MRI) has become an important diagnostic tool with an ongoing dynamic development towards application of increasingly higher static magnetic flux densities
To investigate whether patients with such implants can be accepted for MRI and whether there may be limitations with regard to static magnetic fields, by numerical anatomical and thermal modelling MRI induced tissue heating was assessed for magnetic flux densities 1.5 T, 3 T, 4 T and 7 T
This paper quantitatively investigates potential health risks with regard to excess tissue heating
Summary
Magnetic resonance imaging (MRI) has become an important diagnostic tool with an ongoing dynamic development towards application of increasingly higher static magnetic flux densities. In addition to static magnetic fields and rapidly switched gradient magnetic fields, MRI exposes patients to radio frequency (RF) electromagnetic fields (EMF) which induce tissue heating. Due to physical laws the frequency of RF EMF proportionally increases with static magnetic flux densities by 42.6 MHz/Tesla. Tissue heating increases with increasing static field levels. Particular concern is raised about MR imaging of patients with metallic implants and the associated risk of excess tissue heating and subsequent thermal tissue damage. Studies concentrating on 1.5 T MRI showed that tissue heating critically depends on size, shape and orientation of metallic implants.
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More From: Journal of Electromagnetic Analysis and Applications
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