基于改进目标场法梯度线圈的感应式磁声磁粒子浓度成像研究OA北大核心CSTPCD

The magneto acoustic concentration tomography of magnetic nanoparticles(MNPs)with magnetic induction(MACT-MI)represents a novel approach to MNP concentration tomography.However,prior research revealed a limitation:the current MACT-MI yields a weak magneto acoustic signal due to the small magnetic force on MNPs,hindering experimental progress.Our study focuses on gradient magnetic field uniformity to enhance signal-to-noise ratio and imaging quality by designing a high-quality gradient magnetic field coil to amplify the magnetic force of MNPs. An improved gradient coil for MACT-MI is proposed.An intelligent optimization algorithm is incorporated to rectify the correlation error from representing continuous current density through the contour lines of the discrete flow function during the conventional target field method(TFM)coil design.This algorithm defines the fitness function for minimizing relative magnetic field error by optimizing current density coefficients.A gradient coil is produced for various coil spacing requirements in imaging.The proposed TFM coil shows a larger uniform space within the imaging area than the traditional gradient coil.Compared with the matrix coil,the TFM coil reduces the coil count by approximately 30%under equivalent conditions,decreases coil turns by about 65%,minimizes coil size by 84%,and lowers the maximum current by approximately 22%. Additionally,to investigate the influence of gradient magnetic field spatial distribution on MACT-MI,diverse distribution models for magnetic nano particles(MNPs)are constructed.With the multi physics simulation software COMSOL,the physical processes of MACT-MI are numerically solved.Variations in magnetic force and sound pressure acting on MNPs can be analyzed in both uniform and non-uniform magnetic fields.The magnetic force on MNPs exhibits enhanced smoothness and stability in a uniform magnetic field.Conversely,in a non-uniform field,as the gradient magnetic field's uniform space diminishes,the stability range of the magnetic force contracts significantly.Similarly,the sound pressure waveform is broad in a uniform field,accompanied by a wide effective range of sound pressure fluctuations.In contrast,sound pressure curve peaks gradually attenuate as the distance from the center increases in a non-uniform field. The results indicate a proportional relationship between the effective fluctuation range of magnetic force,sound pressure,and the uniform spatial extent of the gradient magnetic field.Moreover,as the uniform space decreases,the peak values of both magnetic force and sound pressure diminish.This phenomenon attests to the impact of the gradient magnetic field's spatial distribution characteristics on the magnitude of magnetic force and sound pressure amplitudes,which also contributes to the relatively weak magnetic-acoustic signals in MACT-MI.Enhancing the uniformity of the magnetic field emerges as apractical approach to bolstering the signal-to-noise ratio of the magnetic-acoustic signals.