Individualized and accurate SAR characterization method based on equivalent circuit model for MRI system

Abstract

Purpose To protect patients from RF heating in MRI scan, this work proposes an accurate and patient‐specific whole‐body specific absorption rate (SAR) characterization method based on an equivalent circuit model. Compared to the standard pulse energy method defined in NEMA MS 8‐2016, this method avoids the complexity of integrating flux loops and has the potential to be easily implemented in MRI scanners. Theory and Methods In this study, we use an equivalent parallel circuit to model the power distribution on the transmit coil and subject. The coil and subject equivalent resistances are fitted by the frequency response functions of reflection coefficient and are thereafter used to calculate the power ratio between them. To assess the accuracy of this method, we measured the subject absorbed power of 2 phantoms and 5 volunteers and compared it with the standard pulse energy method with flux loops. Results The resistances, resonant frequencies, and quality factors of the transmit coil are fitted with the equivalent circuit model in both unloaded and loaded conditions. Whole‐body SAR of 5 volunteers is measured at 2 different landmarks. In addition, the relationship between SAR and the working frequencies of the transmit coil is measured and analyzed. The subject absorbed power measured by the proposed method demonstrates good accuracy (RMS error and maximum error of 3.77% and 9.47%, respectively) relative to the flux loop method. Conclusion The equivalent circuit model‐based method enables individualized, accurate, and simplified SAR characterization for clinical applications and research with moderate implementation complexity.

An Early Breast Cancer Detection by Using Wearable Flexible Sensors and Artificial Intelligent

“…The monopole antenna's performance enables wearable integration, in contrast to previous research in the literature that used end-fire Vivaldi antennas for similar purposes [28]. Moreover, the suggested antenna-based sensors' specific absorption rate (SAR) is calculated and recorded [29]. In comparison to the conventional rated value, the suggested antenna-based sensor accomplished an enhanced low SAR, validating its safety as a single element or array in the suggested wearable system.…”

“…This will not allow sensors to be conformally positioned on breast or comfortably inserted in Wearables. In terms of utilized topologies for antennas, Vivaldi and Monopole antennas are used in [27][28][29]. Vivaldi are high gain antennas with an output beam perpendicular to the antenna axis.…”

Evaluation and Correction of $B_{1}^+$-Based Brain Subject-Specific SAR Maps Using Electrical Properties Tomography

“…While methods for calculating B − 1 have been proposed [25], the implementation in clinical settings can be challenging, leaving the estimation of subject-specific head SAR estimation with the B + 1 field as the only available method. Different methods have estimated subject-specific SAR maps during MRI exams, based on an equivalent circuit model [26], using hybrid simulation and data acquisition approaches [27], or like in this work, using B 1 fields [28], [29]. The B + 1 approaches, however, have not compared the SAR obtained with the whole B 1 to the SAR obtained with B + 1 only.…”