Evaluation of an optical electric field sensor for measurement of specific absorption rate (SAR) during magnetic resonance imaging

Abstract

This paper examines the measurement of the specific absorption rate (SAR) of radio frequency energy during magnetic resonance imaging using an optical electric field sensor (OEFS). The sensor was used to measure SAR in a simple phantom during a 3-Tesla MRI scan and the results compared to computer simulations and also those obtained through temperature measurements. Good agreement is demonstrated. The optical electric field sensor has much higher sensitivity for SAR measurement than thermometers and the measurements are much quicker. The application of this technology allows the spatial distributions of SAR within phantoms during MRI to be measured.

Estimation of Radiofrequency Power Leakage from Microwave Ovens for Dosimetric Assessment at Nonionizing Radiation Exposure Levels

“…The SAR value is obtained using the following expression: where conductivity ( σ ), tissue density ( ρ ), and electric field are considered. This SAR calculation method has been extracted from [ 66 ] and is implemented in some papers [ 67 , 68 ]. The human body model parameters used in this study, as the age (35–39 years old), the height (1.80 m), and the fat percentage (26.9%), have been chosen taking into account previously published works, as well as conductivity of the skin (10.18 S/m) [ 69 ] and the human body density (1043 Kg/m 3 ) [ 70 ].…”

Electro‐optic probe for real‐time assessments of RF electric field produced in an MRI scanner: Feasibility tests at 3 and 4.7 T

“…However, the direct measurement of SAR using the E‐field presents the advantage of providing a fast response with great sensitivity; thus, it could be considered as complementary to heating measurements. The detection and measurement of the RF E‐field has been investigated previously based on several different methods . Taylor et al designed dipole‐based probes to measure the transverse E‐field inside a biological phantom near a rectangular RF coil.…”

“…In this study, the quantitative value of the detected E‐field was not provided and the response of the dipole probe was not linear with the E‐field. Recently, optical measurement methods have also been proposed to limit distortions as a result of electrical connections . The optical method proposed by Reiss et al is based on the electro‐optic (EO) conversion of the detected electrical signal using specific anisotropic crystals.…”

“…The detection and measurement of the RF E-field has been investigated previously based on several different methods. [13][14][15][16][17][18] Taylor et al 13 designed dipole-based probes to measure the transverse E-field inside a biological phantom near a rectangular RF coil. The E-field value was determined using a self-made calibration system.…”

“…Recently, optical measurement methods have also been proposed to limit distortions as a result of electrical connections. [16][17][18] The optical method proposed by Reiss et al 18 is based on the electro-optic (EO) conversion of the detected electrical signal using specific anisotropic crystals. The EO probe has the advantage of being dielectric and thus non-perturbative with regard to the EM field.…”