| Magneto-acoustic tomography (MAT) is a new functional imaging methods, which converts the electromagnetic energy into sound energy. The electrical characteristics of biological tissue is employed to reflect the physiological status and pathological condition of the organizations. The MAT takes the advantages of non-invasive, high contrast and high spatial resolution for the potential applications in early detection of tumors. In research, there are several important issues for the final reconstruction of conductivity distribution, this involves the scanning mode of the transducer, the accuracy of scanning motion control, sample characteristics and signal detection.A scanning device was designed to control the motion of the transducer, which was applied in the experimental study of magneto-acoustic tomography. In the device, the precision motion control together with data acquisition was implemented by using National Instrument (NI) platform. Effectively, not only could the transducer move along X axis, Y axis, Z axis, but also rotate around the Z axis. Meanwhile, the experimental sample loading plate could rotate around the Z axis. By using LabVIEW software tool, program was edited to realize real-time data acquisition, display and storage. Accuracy of the transducer’s position was measured firstly. Comparison experiments were then carried out to verify the accuracy by analyzing a copper-ring sample’s acoustic signal, while the transducer’s motion was controlled by hands and the scanning device, respectively. The results show that the scanning device can meet the requirements of magneto-acoustic tomography experiment.Using the device, we designed Translational-Circular Scan (TC-Scan) mode to detect the sample’s acoustic signal. With bi-layer graphite sample, we simulated the imaging process with Comsol Multiphysics and Matlab, then carried out a TC-Scan experiment. Using the reconstruction algorithm for conductivity profile based on TC-Scan, the magneto-acoustic signals acquired by both simulation and experiment were used to reconstruct sample conductive distributions, respectively. Because of the different acoustic velocity in sample and coupling agent, the reconstructed image is distorted. And after the acoustic velocity is corrected, the reconstructed image has good agreement with the sample.We investigated magneto-acoustic signal frequency shift on copper wire, sheet, graphite, agar phantom, etc., with simulation and experiments. Time-frequency analysis on collected signals of the first boundary were conducted to discuss the frequency shifts pattern of different sizes of various materials. The results show that the distance between the acoustic transducer and the sample, the change of the acoustic characteristic of the sample have certain effect on the signal frequency.Gel phantom with different conductivities is necessary for magneto-acoustic experiment. In this study, we developed the preparation process, and measured the conductivities. Additional works were done to account for the conductivity change caused by ions diffusing into the water during the experimental process, the results showed that the loss of ions can be reduced to a certain extent.In conclusion, we designed five-dimension scanning device, carried out the TC-Scan experiment, took time-frequency analysis on collected signals, optimized the preparation process of gel phantom. All the work established experimental conditions for magneto-acoustic signal detection and imaging with different scanning mode, also for research of reveling the magneto-acoustic tomography mechanism. |
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