Tier‐based formalism for safety assessment of custom‐built radio‐frequency transmit coils
The purpose of this work is to propose a tier‐based formalism for safety assessment of custom‐built radio‐frequency (RF) coils that balances validation effort with the effort put in determinating the safety factor. The formalism has three tier levels. Higher tiers require increased effort when valid...
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Veröffentlicht in: | NMR in biomedicine 2023-05, Vol.36 (5), p.e4874-n/a |
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Zusammenfassung: | The purpose of this work is to propose a tier‐based formalism for safety assessment of custom‐built radio‐frequency (RF) coils that balances validation effort with the effort put in determinating the safety factor. The formalism has three tier levels. Higher tiers require increased effort when validating electromagnetic simulation results but allow for less conservative safety factors. In addition, we propose a new method to calculate modeling uncertainty between simulations and measurements and a new method to propagate uncertainties in the simulation into a safety factor that minimizes the risk of underestimating the peak specific absorption rate (SAR). The new safety assessment procedure was completed for all tier levels for an eight‐channel dipole array for prostate imaging at 7 T and an eight‐channel dipole array for head imaging at 10.5 T, using data from two different research sites. For the 7 T body array, the validation procedure resulted in a modeling uncertainty of 77% between measured and simulated local SAR distributions. For a situation where RF shimming is performed on the prostate, average power limits of 2.4 and 4.5 W/channel were found for tiers 2 and 3, respectively. When the worst‐case peak SAR among all phase settings was calculated, power limits of 1.4 and 2.7 W/channel were found for tiers 2 and 3, respectively. For the 10.5 T head array, a modeling uncertainty of 21% was found based on B1+ mapping. For the tier 2 validation, a power limit of 2.6 W/channel was calculated. The demonstrated tier system provides a strategy for evaluating modeling inaccuracy, allowing for the rapid translation of novel coil designs with conservative safety factors and the implementation of less conservative safety factors for frequently used coil arrays at the expense of increased validation effort.
We propose a tier‐based formalism that stratifies the amount of effort put in validating EM simulations for custom built transmit coils. For increasing tier levels, more validation effort is required, which provides higher confidence in the EM simulations and allows for less conservative power limits. |
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ISSN: | 0952-3480 1099-1492 1099-1492 |
DOI: | 10.1002/nbm.4874 |