The Array-Type Gauss Meter Decicated To MRI Magnetic Field Homogeneity Measurement

In order to solve the problem that the traditional MRI technology does not perform well in lung imaging,the development of low-field MRI device for lung which is based on hyperpolarized ~3He is launched.In the MRI equipment,homogeneity of main magnet is a key indicator which directly affects image’s quality.The homogeneity of main magnet is unable to meet imaging requirement without magnetic field homogeneity measurement and shimming.The traditional method of magnetic field homogeneity detection is relatively cumbersome,so this paper designs a set of array-type gauss meter dedicated to magnetic field homogeneity measurement for the purpose of improving efficiency.The main works of this paper as follows:First,the basic principles of low-field MRI for lung are introduced.The design of array-type gauss meter with magnetoresistive sensor array is established according to characteristics and needs of main magnet in the low-field MRI equipment for lung.Second,the hardware circuit design of array-type gauss meter is completed,which mainly includes sensors control circuit,signal conditioning circuit,AD conversion circuit,serial port communication circuit,button and display circuit,power supply circuit and temperature acquisition circuit.Thirdly,causes of the errors in array-type gauss meter are analyzed and corresponding error elimination schemes are proposed.The random noise is filtered by median average filtering.The 50Hz and its higher harmonic is filtered by a digital Sinc filter.Aiming at eliminating the measurement error caused by the performance difference of different sensors in the sensor array,a SA-BP neural network compensation model is established.Next,microcontroller program and host computer software of the array-type gauss meter are designed by Keil and Visual Studio.So that,the array-type gauss meter could be controlled through the host computer software interface and the measurement is stored and processed on the host computer.Finally,magnetic field homogeneity of the existing electromagnetic coil are measured with array-type gauss meter and traditional gauss meter.Analyze result shows that the array-type gauss meter can improve the efficiency of magnetic field homogeneity measurement.