Objective To design a system of conductivity tomography using focused magnetic fields for data acquisition. Method A frequency modulation detection circuit with array of sources was employed to implement multi-frequency measurement. In the circuit, a specially designed coil with good focusing property was used to improve spatial resolution of the image. Acquired data of frequency changes from the detector was stored in the memory operated by a ping-pang pattern, then the data was transmitted into computer by serial communication interface whose transmitting rate reached 115. 2 KHz. Result Frequency stability of the signal source in the system reached 0. 2%; the total harmonic distortion of the signal was less than -43 dB; the signal noise ratio of the source was from 58 dB to 62 dB. The storage capacity of memory was 131 072-word by 16- bit. The system has good frequency resolution, and is easy to be analyzed and processed by the software after data acquisition. The conductivity of the computed results agreed with that in the given model. Conclusion The system is effective to detect and reconstruct the conductivity of stratified biological tissue for its high sensitivity.

Objective To study the application of the linear sampling method(LSM) in 2D electromagnetic inverse scattering imaging and to mainly discuss the imaging quality of LSM with partial-view data.Methods Get the norm of solution vector to the equivalent integral equation using numerical calculation in every sampling point at imaging region,and represent the norm with gray to reconstruct the scattering shape.Results Under all incident angles [0,360?] and all observation angles [0,360?],the imaging quality of the far-field pattern of scattering wave was obtained very well.But when reducing the range of the incident angles and observation angles,the imaging quality declined.Particularly,the imaging quality in the case of both incident angles and observation angles being at the same side of the observed object,were much better than both in opposite sides.Furthermore,the profile of the object was imaged more clearly as its position corresponding to the orientation of the incident/observation angle.Conclusion Although the imaging quality will decline with partial-view data in electromagnetic inverse scattering,the effectiveness of imaging with LSM still deserves attention.

It is the intent of this study to estimate the progression or regression of edema at the bedside continuously. Based on the theoretic model, the Adaptive Genetic Algorithm (AGA) has been applied in the calculation of conductivity reconstruction. Dynamic crossover and mutation operators which are based on Haiming Distance are brought forward in this paper to maintain generation's diversity. Then, both AGA and Standard GA (SGA) have been applied in the conductivity reconstruction of edema in human brain. It is shown that AGA not only has attained a higher degree of efficiency but also has enhanced the capability to converge to the best answer.
Algorithms ; Brain Injuries ; complications ; pathology ; Computer Simulation ; Edema ; pathology ; Electric Impedance ; Humans ; Models, Biological

Microwave imaging for dielectric objects was considered in this paper. Applying Bayesian approach to represent prior information about permittivity distribution of observed object by prior probability density and combine measurements information of scattering field, we obtained posterior probability density that included synthetic information about the observed object. And then, Gibbs sampler, one of Markov Chain Monte Carlo method, was used to sample the posterior probability density. The sample mean was regarded as an evaluation of the permittivity distribution. The results of simulation imaging with "blocky" objects showed that this set of methods made good use of information and had the advantages of feasibility and very strong anti-noise ability. In addition,it is capable of describing (definite or indefinite) prior information in a convenient and controllable way, as well as capable of giving the "complete" solution, i.e., the occurrence probability of every permittivity distribution.
Bayes Theorem ; Computer Simulation ; Image Processing, Computer-Assisted ; methods ; Markov Chains ; Microwaves ; Models, Theoretical ; Monte Carlo Method ; Neoplasms ; diagnosis

It is the intent of this paper to locate the activation point in Transcranial Magnetic Stimulation (TMS) efficiently. The schemes of coil array in torus shape is presented to get the electromagnetic field distribution with ideal focusing capability. Then an improved adaptive genetic algorithm (AGA) is applied to the optimization of both value and phase of the current infused in each coil. Based on the calculated results of the optimized current configurations, ideal focusing capability is drawn as contour lines and 3-D mesh charts of magnitude of both magnetic and electric field within the calculation area. It is shown that the coil array has good capability to establish focused shape of electromagnetic distribution. In addition, it is also demonstrated that the coil array has the capability to focus on two or more targets simultaneously.
Algorithms ; Brain ; physiology ; Electric Stimulation ; instrumentation ; Electromagnetic Fields ; Equipment Design ; Evoked Potentials, Motor ; physiology ; Humans ; Neurons ; physiology ; Transcranial Magnetic Stimulation

A wide-band patch probe excited by coaxial line, which is useful for noninvasive measurement of superficial tissues at high frequencies, is presented in this paper. Optimization of the probe is performed by genetic algorithm (GA) combined with Finite Difference Time Domain (FDTD). Then the optimized round patch probe is used to measure reflection coefficient for 1-7 GHz. The measured results show some interesting phenomena, which are very useful for reconstruction of electric properties of superficial tissues.
Algorithms ; Electric Conductivity ; Electromagnetic Phenomena ; Electrophysiology ; instrumentation ; Equipment Design ; Humans ; Muscle, Skeletal ; physiology ; Skin Physiological Phenomena