高场和超高场MR下人体内B<sub>1</sub>场均匀性及SAR随场强变化规律的研究

doi:10.3969/j.issn.0258-8021.2013.01.004

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Abstract High and ultrahigh field MRI are receiving more concerns in current clinical applications due to substantial enhancement of the signaltonoise ratio and spatial resolution. The uniformity of B₁field directly affects the quality of the image and the RF energy absorbed inside the tissues relates to the safety directly. Therefore, there is a great significance to study on the relationship between magnetic field strength and the B₁ field uniformity, specific energy absorption rate (SAR) at high and ultrahigh field MR. The finite difference time domain (FDTD) was utilized to accurately analyze the performance and safety of high and ultrahigh field MR system loaded with the real female pelvis electromagnetic model using the TEM body coil. The B₁ field and the SAR inside the pelvic region were calculated and analyzed at 1.5T, 3T and 7T magnetic flux densities respectively. The results indicated that the uniformity of B₁ field was reduced by 11.54% and 49.97%, the average SAR of various pelvic tissues was maximally increased by 4.7 times and 24.14 times, local maximum SAR were maximally increased by 5.5 times and 22 times and RF energy trended to focus on internal tissues, with the increase of the magnetic flux density from 1.5T to 3T and 7T. The SAR of skin, muscle and body fluid at 7T exceeds the safety threshold. Therefore, it is necessary to correspondingly optimize the TEM coil to improve the B₁field homogeneity and ensure the qualified SAR at high and ultrahigh field MR, according to the different main magnetic field strength.

Key words： uniformity of B1field SAR FDTD electromagnetic model

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	HUANG Qi Hua¹ GAO Yong^2XIN Xue Gang^1*

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HUANG Qi Hua¹ GAO Yong^2XIN Xue Gang^1*. Study on the Law of B₁ Field Homogeneity and SAR inside Human Body Varying with Field Strength at High and UltraHigh Field MR[J]. journal1, 2013, 32(1): 21-27.

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http://cjbme.csbme.org/EN/10.3969/j.issn.0258-8021.2013.01.004 OR http://cjbme.csbme.org/EN/Y2013/V32/I1/21

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