Local specific absorption rate in high‐pass birdcage and transverse electromagnetic body coils for multiple human body models in clinical landmark positions at 3T

Abstract

Purpose: To use electromagnetic (EM) simulations to study the effects of body type, landmark position, and radiofrequency (RF) body coil type on peak local specific absorption rate (SAR) in 3T magnetic resonance imaging (MRI).Materials and Methods: Numerically computed peak local SAR for four human body models (HBMs) in three landmark positions (head, heart, pelvic) were compared for a high-pass birdcage and a transverse electromagnetic 3T body coil. Local SAR values were normalized to the IEC whole-body average SAR limit of 2.0 W/kg for normal scan mode.Results: Local SAR distributions were highly variable. Consistent with previous reports, the peak local SAR values generally occurred in the neck-shoulder area, near rungs, or between tissues of greatly differing electrical properties. The HBM type significantly influenced the peak local SAR, with stockier HBMs, extending extremities towards rungs, displaying the highest SAR. There was also a trend for higher peak SAR in the head-centric and heart-centric positions. The impact of the coil types studied was not statistically significant. Conclusion:The large variability in peak local SAR indicates the need to include more than one HBM or landmark position when evaluating safety of body coils. It is recommended that an HBM with arms near the rungs be included to create physically realizable high-SAR scenarios.

Tissue Electrical Property Mapping From Zero Echo-Time Magnetic Resonance Imaging

“…For example, specific absorption rate (SAR) modeling relies on the availability of spatially resolved maps of tissue electrical properties (EPs) as input [1]. Accurate classification of tumor tissue as benign or malignant can also benefit from the additional information provided by EP mapping; while some disagreement exists in literature [2], prompting for further, properly controlled experimental verification, it is generally agreed upon that cancers tend to exhibit higher conductivity and permittivity than normal tissues [3–5].…”

Local SAR management by RF Shimming: a simulation study with multiple human body models

“…For MR systems with a single transmit coil, significant variations of the SAR values have been reported when comparing different models [20][21][22][23] and different positioning within the MR scanner [24,25]. However, these aspects have so far rarely been discussed in the context of parallel transmission.…”

Specific absorption rate in a standard phantom containing a Deep Brain Stimulation lead at 3 Tesla MRI

“…Four traces are shown: the unloaded coil, the coil loaded with the ASTM phantom, and the ASTM phantom augmented with each of the two DBS leads configurations. The load sensitivity of the coil can be observed as [18], ** Lead dimensions [19].…”

“…The model, shown in Figure 1, included a typical clinical RF transmit coil [18] loaded with the ASTM phantom. 32 total driving ports with characteristic impedance of 50 Ω each were defined along the upper and lower rings where capacitors would be placed in the physical coil.…”

“…Solution convergence was determined by ensuring that the maximum change in the magnitude of any component of the S-Matrix between the two solutions was not greater than 0.5%. The S-parameters at frequencies above and below the Larmor frequency were generated using the inductive interpolation method described in [18]. Once the converged HFSS solution was obtained, a circuit model was created with the ANSYS Designer software.…”