Ex-Vivo Measurements Of Tissue Electrical Properties And Preliminarily Theoretical Studies On MR EPT Technique

Electrical properties(EPs)of biological tissues,including conductivity(σ)and relative permittivity(εr),depend on the frequency of the externally applied electromagnetic field.Previous studies have shown that malignant and normal tissues existed large difference in EPs.Therefore,this EPs information could be used in tumor diagnosis,and may help to detect tumor in an early stage.The EPs of biological tissues could be measured using open-ended coaxial probe method ex vivo,or imaged using magnetic resonance electrical property tomography(MR EPT).This work measured the EPs of normal and malignant colorectum tissues using open-ended coaxial probe method ex-vivo.In addition,preliminarily theoretical studies on MR EPT technique were conducted.Firstly,the reconstruction errors of the currently popular algorithm of MR EPT were quantitatively investigated.Secondly,the intrinsic contrast capability of MR EPT was theoretically analyzed.In the study of ex-vivo measurements of the EPs of normal and malignant colorectum tissues,the EPs of colorectal tissues excised from 85 patients with colorectum tumor was measured using the open-ended coaxial probe method.The obtained EPs were fitted to the Cole-Cole model.The EPs of normal and malignant tissues were compared.Results showed that normal and malignant colorectal tissues existed significant difference in EPs.At 128MHz,the εr and σ of malignant tissue were 14.6%and 17%higher than those of the normal tissue,respectively.In the study of the reconstruction errors for the currently popular algorithm of MR EPT,at first,the reconstruction errors introduced at the interfaces of adjacent tissues were quantitatively analyzed,and then the reconstruction errors occurred in an inhomogeneous phantom at 64,128 and 298 MHz were compared.Results shown that various reconstruction errors existed at different mimicked tissue interfaces.The mean relative reconstruction errors at the interfaces were higher than 0.3986 for σand 0.2218 for εr.The reconstruction errors were decreased with the frequency.At 64MHz,the mean reconstruction error was 28.71%for εr and 9.11%for σ.In the theoretical analysis of the intrinsic contrast capability of MR EPT,a series of electromagnetic model with a region of interest(ROI)in the center were built and assigned with different EP contrasts.The B+1 of the model was simulated.The EPs maps were reconstructed using the currently popular algorithm of MR EPT.The intrinsic contrast capability of MR EPT were defined and estimated.Some factors that may influence the intrinsic contrast capability of MR EPT were discussed.Results shown that the intrinsic contrast capability of MR EPT was increased with ROI size.The highest intrinsic contrast capability was 1/1.02 for both εr and a.In this paper,the EPs of normal and malignant colorectum tissues were measured ex-vivo,and preliminarily theoretical studies on MR EPT technique were conducted.The results of ex-vivo measurement shown that the malignant and normal tissues of human colorectum existed large difference in EPs.The measured data could be used as base data for the future investigations.The preliminarily theoretical studies on MR EPT technique were meaningful for degradation of the reconstruction errors of the currently popular algorithm of MR EPT,and were helpful for the application of the technology of MR EPT in early detection of tumor.