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An Initial Simulation Study of Breast Implants for Clinical Breast MRI1Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States, 2Canon Medical Research USA, Mayfield Village, OH, United States, 3School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, United States, 4Purdue University Center for Cancer Research, Purdue University, West Lafayette, IN, United States
Synopsis
Breast augmentation continues to be the #1 cosmetic surgery for women, with approximately 4% of the US female adult population receiving an implant. Additionally, implants are commonly employed for breast reconstruction following mastectomy. Estimating from MR procedure statistics, the breast may be in the imaging volume for up to 10% of all US MRI procedures. This abstract investigates the implications of breast implants (silicone or saline composition with a wide range of conductive properties) on patient safety and suggests there are minimal effects on local (10-g average) SAR and B1 fields.
Introduction:
Breast implantation is a common procedure, typically using silicone and occasionally saline (0.9% NaCl) 1 filled shells. Since breast implants are relatively common, and the breast could be in the imaging volume for a multitude of procedures, investigating the implications of B1 field redistribution for patient SAR safety purposes is important. Silicone implants are the most common form and have gone through several generational designs since first introduced in 1962. 2 Silicone itself can be formulated to be either electrically conductive or as an insulator, and the electrical attributes of the various implant suppliers and formulations are unknown. This abstract assumes zero conductivity for the silicone implants and high conductivity for the saline implants where the salt content is nearly 7x the ASTM F2182 phantom, which targets average body conductivity levels. Thus, these two conductive extremes bracket the likely range of outcomes. The purpose of this abstract is the investigation of 10-g SAR and B1 changes relative to no-implants, of saline and silicone filled breast implants to understand the safety consequences of this common cosmetic or reconstructive procedure.Methods:
Finite-difference time-domain (FDTD) simulations are conducted for a generic 3T whole-body Tx coil (16-rung high-pass birdcage, diameter 750mm, length 650mm, RF shield diameter 790mm, length 850mm) 3,4 using a full-wave electromagnetics solver software package (Sim4Life v4.2, ZMT, Zurich, Switzerland). The coil was tuned to 128MHz and driven with quadrature voltage sources located on one end ring. In a realistic clinical breast imaging setup, Ella (version 3.1, 26 yr old, 1.63m, 57.3kg) 5 is placed in prone and feet-first orientation in the Tx coil; and due to the extension of breast Rx coil (which is not modeled here), the breasts are presented at isocenter of the Tx coil as shown in Figure 1. Bilateral breast models representing the BI-RADS category of mostly fatty breasts are morphed on the Ella model as previously reported. 6 The breast implants are modeled based on a 150 cc CPGTM Gel Breast Implants, Cohesive IIITM CONTOUR with density 1.06 g/ml. 7,8 Breast implants are filled with saline (0.9% NaCl) or silicone. At 128MHz and near body temperature, saline has conductivity 1.8125 S/m and relative permittivity 72.67; 9 and silicone gel has conductivity 0 S/m and relative permittivity 2. 10,11,12 Bilateral breast implants are inserted under the breast tissue and attached onto the chest muscle. One model with saline implants, one with silicone implants and a normal model without implants are simulated. B1 and SAR results are presented at normalized power 1 W at each voltage source.Results:
The B1 and 10-g SAR (W/kg) maps across the breast implants are shown in Figure 2. Similar levels of B1 are shown everywhere for all cases. Higher 10-g SAR level is shown within saline breast implants, and silicone implants have nearly zero 10-g SAR. The maximum 10-g SAR values, both in breast tissue and throughout the body, are listed in Table 1. In all cases, similar level of body peak 10-g SAR appears at the SAT (subcutaneous adipose tissue), skin, vein, muscle and artery of left wrist. Additionally, saline implants simulation has the highest peak 10-g SAR in breast tissue (breast fat) and breast implants compared to normal model and silicone implants simulations. The local SAR maxima within breast tissue was slightly elevated relative to the normal model, but well below the SAR reported in the wrist. Note that in both implant models, local SAR in the chest wall was slightly reduced.Discussion and Conclusion:
Simulations suggest that breast implantation has minimal impact on B1 fields, minor impact on local SAR within the breast and minimal impact on local SAR elsewhere in the body for the single model configuration investigated. Therefore, these results imply no SAR related safety concerns for patients with breast implants.Acknowledgements
No acknowledgement found.References
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