Abstract
Purpose: The purpose of this study was to investigate the need for high-resolution detailed anatomical modeling to correctly estimate radio-frequency (RF) safety during magnetic resonance imaging (MRI). RF-induced heating near metallic implanted devices depends on the electric field tangential to the device (Etan). Etan and specific absorption rate (SAR) were analyzed in blood vessels of an anatomical model to understand if a standard gel phantom accurately represents the potential heating in tissues due to passive vascular implants such as stents.Methods: A numerical model of an RF birdcage body coil and an anatomically realistic virtual patient with a native spatial resolution of 1 mm3 were used to simulate the in vivo electric field at 64 MHz (1.5 T MRI system). Maximum values of SAR inside the blood vessels were calculated and compared with peaks in a numerical model of the ASTM gel phantom to see if the results from the simplified and homogeneous gel phantom were comparable to the results from the anatomical model. Etan values were also calculated in selected stent trajectories inside blood vessels and compared with the ASTM result.Results: Peak SAR values in blood vessels were up to ten times higher than those found in the ASTM standard gel phantom. Peaks were found in clinically significant anatomical locations, where stents are implanted as per intended use. Furthermore, Etan results showed that volume-averaged SAR values might not be sufficient to assess RF safety.Conclusion: Computational modeling with a high-resolution anatomical model indicated higher values of the incident electric field compared to the standard testing approach. Further investigation will help develop a robust safety testing method which reflects clinically realistic conditions.
Highlights
Magnetic resonance imaging (MRI) has become one of the most popular medical imaging modalities thanks to its noninvasive nature based on non-ionizing radiation
The standard provides indication on how to evaluate the whole-body averaged specific absorption rate (SAR), the local SAR, and the temperature rise caused by the device using a rectangular box filled with a saline gel (“ASTM phantom”)
The MRI RF exposure was modeled as a continuous wave, which is the typical approach used in literature
Summary
Magnetic resonance imaging (MRI) has become one of the most popular medical imaging modalities thanks to its noninvasive nature based on non-ionizing radiation. It is often used as the diagnostic tool of choice for various diseases and represents a safe imaging device, some risks still exist and need to be mitigated. RF Safety in Blood Vessels to elicit the magnetic resonance (MR) signal may induce a temperature increase inside the patient’s body. The standard provides indication on how to evaluate the whole-body averaged specific absorption rate (SAR), the local SAR, and the temperature rise caused by the device using a rectangular box filled with a saline gel (“ASTM phantom”)
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