Research On Intelligent Test Of Magnetic Resonance Imaging Spectrometer

The spectrometer is one of the most important components in the magnetic resonance imaging(MRI)system,which has a crucial influence on imaging function and quality.Due to the complexity of spectrometers,they are prone to fault phenomenon in the development of it.In the development of a MRI spectrometer,the equipment fault detection methods are mainly reliant on visual inspection of reconstructed images or k-space data,combined with observation of the output waveforms via an oscilloscope.However,it is difficult to detect these problems when the spectrometer or sequence has a slight design defect that leads to artifacts or other problems.In order to solve these problems,this paper studies and proposes a fault detection method based on the acquisition and analysis of its output waveform.The gradient waveform is a key element of imaging.This paper uses the high performance data acquisition card based on Lab VIEW software and design to implement multi-channel data acquisition system.The three ways gradient output and one-way digital gate signal are collected with 500 KSPS sampling rate.Waveform data are preprocessed to extract feature points.At the same time,a set of pre-predefined feature points are constructed based on sequence model.The extracted feature points are compared with the pre-defined points to find out the problem in the waveform.The method of feature-points extraction is studied,which includes two kinds of histogram statistical analysis and distance clustering analysis.The result of experiments show two kinds of methods can well extract the feature points of waveform.For the sake of improving processing speed,the graphics processing unit(GPU)is used to calculate and reduce the processing time apparently.In addition,this paper also study the acquisition and analysis of output radio frequency pulse combining with high resolution digitizer with 40 MSPS sampling rate for trigger acquisition and quadrature demodulation.The demodulated amplitude waveforms are fitted with the theoretical soft pulse modulation waveform to determine the accuracy of pulse generation.Experiments are conducted to judge and solve two kinds of artifacts of spectrometer and to prove the validity of this method,which is an auxiliary test method for the development of spectrometer and pulse sequence.