The Impact of Coupling on Estimation of Local and Global SAR with Transmit Arrays

TL;DR

This paper investigates how coil coupling affects the accuracy of local and global SAR estimations in pTx MRI systems, revealing that neglecting coupling can significantly underestimate safety limits.

Contribution

It demonstrates the importance of accurately modeling inductive coupling in electromagnetic simulations to improve SAR prediction accuracy in transmit array systems.

Findings

Incorrect coupling modeling leads to 19-40% underestimation of local SAR.

Proper coupling consideration improves SAR prediction accuracy.

Neglecting coupling affects safety assessments in pTx MRI.

Abstract

In pTx MRI systems, the prediction of local SAR is based on numerical electromagnetic (EM) simulations and used to scale RF power to ensure FDA SAR limits are not exceeded. This prediction becomes more complex when superposition of E-fields from multiple coupled coils are employed in parallel transmission, each affected by dielectric and conductive properties of the human body. It was demonstrated that incorrect inductive coupling used in simulations of transmit array coil spatial excitation and SAR, leads to poor accuracy of predicted excitation and SAR, and more importantly from a safety perspective, underestimated local SAR by 19-40%.