Study On Temperature Measurement And Spatial Distribution Imaging Of Magnetic Nanoparticle

In biomedical field,the in vivo temperature affects gene expression,enzyme activity,cell life cycle etc.,making noninvasive visualization temperature measurement attract great attention in recent years.Noninvasive visualization temperature measurement in living body not only needs precision detection of temperature,but also accurate localization of temperature probe.Using magnetic nanoparticle(MNP)as temperature probe and imaging tracer is a feasible way to solve the problem of noninvasive visualization temperature measurement in vivo.To provide a feasible solution for real-time and noninvasive temperature monitoring and magnetic probe localization in magnetic hyperthermia and magnetic drug targeting and temperature-controlled release,the temperature measurement using MNP and its spatial distribution imaging therefore have been studied in this dissertation.Considering the drawbacks of the existing temperature measurement model,this dissertation has made a theoretical study on the influence of particle size distribution on the ac magnetization of MNPs.The modified ac temperature measurement model that takes in account the particle size distribution proposed herein is only dependent of the six-order moment and/or twelve-order moment of particle size distribution whereas it is independent of the particle size distribution itself.The correctness and feasibility of the modified ac temperature measurement model is then verified by the experiments.In order to improve the temperature measurement accuracy,the ac temperature measurement model has been extended to the ac and dc excitation magnetic fields condition,and the corresponding ac and dc temperature measurement model is proposed.The influence of the magnetic properties of MNPs and the strength of excitation magnetic fields on temperature measurement accuracy has been studied by developing the mathematical models of the effective SNR and the temperature-sensitivity.It is found that the effective SNR can be improved to at least 1.65 times using the ac and dc temperature measurement model.Besides,the simulation and experimental results show that with the increase of saturation magnetic moment of MNPs,the temperature measurement accuracy monotonously increases while with the increase of dc excitation magnetic field strength,the temperature measurement accuracy first increases to the best and then decreases.To achieve real-time visualization of magnetic nano-probe in vivo,the magnetic particle imaging(MPI)has been studied.Due to the presence of residual oscillation of iterative image reconstruction algorithm used in harmonic-space MPI,the conjugate gradient squared algorithm with minimal residual smoothing technique is used for harmonic-space MPI reconstruction.In order to solve the problem of x-space MPI image degeneration,the Lucy-Richardson deconvolution algorithm is used to deblur the images.The performance indicators of MPI are studied,and an optimization model for MPI signal-to-noise ratio(SNR)estimatioin is established.It is found that with the increase of magnetic field gradient,the SNR increases first and then tends to be stable,while with the increase of scanning speed,the SNR increases first and then decreases.To reduce the effects of magnetic relaxations on image quality and to provide a more accurate map of heating efficiency for local magnetic hyperthermia,the magnetic particle susceptibility imaging(MPSI)method and the corresponding ac susceptibility estimation algorithm are further proposed based on the present MPI theory.The mathematical models of spatial resolution,signal bandwidth,and SNR of MPSI are then developed.It is found that:(1)the influence of magnetic relaxations can be suppressed and the image spatial resolution can be improved using imaginary part of ac susceptibility for image reconstruction;(2)the signal bandwidth of MPSI is much narrower than the signal bandwidth of MPI.In addition,a 2-D MPSI system is designed and built to verify the correctness of MPSI method.In order to improve the measurement sensitivity and spatial resolution of MPSI system,the resonance measurement circuit is adopted,besides the differential pick-up coil and background cancellation method are used to suppress the direct feedthrough interference.The influences of the bandwidth and the phase shift of resonance circuit on the spatial resolution of MPSI are quantitatively studied by modeling the frequency response function of the resonance circuit.Finally,experimental results show that the spatial resolution of MPSI system is better than 2.5 mm,the measurement sensitivity can reach 2 mmol-Fe/L,and the imaging speed is 1 fps.