Purpose Strict regulations are imposed on the amount of radiofrequency (RF)

Purpose Strict regulations are imposed on the amount of radiofrequency (RF) energy that devices can emit to prevent excessive deposition NU 6102 of RF energy into the body. house measurements were PIK3R2 used to reconstruct 10-g average SAR. Results The maximum temp change for any dipole antenna and the maximum 10-g normal SAR were 1.83° C and 12.4 W/kg respectively for simulations and 1.73° C and 11.9 W/kg respectively for experiments. The difference between MR and probe thermometry was <0.15° C. The maximum temp change and the maximum 10-g average SAR for any cell phone radiating at maximum output for 15 min was 1.7° C and 0.54 W/kg respectively. Summary Information acquired using MR temp mapping and thermal house measurements can assess RF/microwave security with high resolution and fidelity. is the warmth capacity (in Joules per kilogram per degree Celsius) is the thermal conductivity (in Watts per meter per degree Celsius) and is the Specific Absorption Rate (in Watts per kilogram). SAR the traveling force for temp rise as result of Joule/dielectric heating mechanisms is defined as: (in degrees Celsius) is the temp NU 6102 switch induced during time interval Δt (in mere seconds). NU 6102 However keeping the period NU 6102 of heating short requires adequate device output RF power NU 6102 in order to minimize the heat diffusion by taking the initial slope of the temp increase and using Equation 3. In practice the magnitude of the E field produced NU 6102 by an antenna is limited by the maximum power capabilities of the RF amplifiers conductivity of the phantom and additional factors. Because of these limiting factors longer RF heating durations are often needed to induce temp changes detectable using MRI. In such cases warmth diffusion needs to be taken into account to avoid introducing major errors on security assessment (20). Temp to SAR Inversion Using MR Thermometry Proton resonance rate of recurrence (PRF) temp switch reconstruction using MRI relies on phase subtractions between two phase images acquired before and after RF/microwave heating. A linear relationship between temp and phase change is demonstrated in the equation (21): is the gyromagnetic percentage of protons (~42.58 × 106 in Hertz per Tesla) TE is the echo time of the GRE sequence B0 is the main magnetic field strength (in Tesla) and a is the temperature dependency of the chemical shift (in parts per million per degrees Celsius). In order to guarantee RF security regulations using SAR (6) ΔT from MR thermometry measurements needs to be converted to spatial-average SAR. In temperature-based RF security assessment methods RF/microwave heating duration plays an important role in computing SAR as SAR is definitely no longer directly proportional to the temp change for longer heating periods. With this section the inversion of the heat equation is explained concisely [observe Alon et al. (22) for a more detailed description]. The inversion of the heat equation is used to overcome RF security assessment errors associated with the warmth diffusion. Using the finite difference approximation in space and time the heat equation (Eq. 1) can be written in the polynomial form are the initial and final temp of the sample respectively and Δis definitely the time interval. L is definitely a linear Laplace operator defined as and can become measured using a thermal probe and Δ= using MRI) the perfect solution is to this problem can be written inside a linear matrix notation. norm weighted least-squares minimization which has been shown to be robust with respect to noise for sparse representations (23): is the regularization parameter. The minimization function demonstrated in Equation 6 once solved facilitates the computation of SAR from MR thermometry measurements (22). METHODS Simulation Technique EM field simulations were performed within the dipole antenna – phantom setup demonstrated in Number 1B in order to obtain the SAR distribution induced from the dipole antenna inside the phantom. The commercial Microwave Studio software suite (CST Framingham Massachusetts USA) using the finite integration technique (Match) was utilized for simulations. The guidelines used in the Match calculations were as follows: 9.3 million mesh cells with edge lengths ranging from 0.4 to 11 mm feeding having a voltage resource operating at 1.96 GHz. Simulated EM fields were exported to 83 × 82 × 83.