A Research Of The Correction Of The Intensity Inhomogeneity Inmagnetic Resonance Imaging

The tissue of brain structure, including its morphology, volume, density, and so on, is the vector of the brain functional activity. So it is a hot and important research of the biomedical sciences all the time. The development of the modern medical imaging technology brings good ways to the research of the tissue of brain structure. Whereby, the magnetic resonance imaging(MRI) is widely used in the clinical diagnosis of brain disease and basic research, for it is noninvasive, zero radioactivity, high spatial resolution, good soft tissue contrast, and have received a large number of important research results.The image processing occupies an important position in the research of the medical image. The earliest way to analysis the images was qualitative analysis based on the conventional method, after years of research, there emerged quantitative analysis based on region of interest, recently, the widely used method is the voxel-based morphometry. In this way, the aim of the data analysis of the brain imaging is to extract the regions with intensity non-uniformity related to the lesions. Nevertheless, the intensity inhomogeneity(IIH) of the image is not only influenced by the lesions, but also by the noises, especially by the radiofrequency(RF) coils.The radiofrequency coils are the components of the signal emission and reception, and the surface coil is an important frequently-used RF coil for signal reception, for it will get high signal noise ratio and low warp artifact. However, the surface coil receive the signal in only one side of the subjects, so the regions nearer the surface coil, the higher the signal, that is, the surface coil will brings out heavy intensity non-uniformity in the images, especially in the high field intensity equipment for an animal experiment. The IIH by the surface coil mixed in the intensity non-uniformity by the lesions, in this way destroys the image intensity value, and brings heavy errors in the image analysis. Hence, the correction of the IIH by the surface coil is the precondition and assurance of a precise analysis of the brain images, and it’s also the key point and difficult point of this thesis.Currently, the research of the correction of the IIH in MRI is widely developed, such as the segment-based methods and the surface fitting methods, yet, the accuracy of these two methods relies on the prior knowledge, the leads a low objectivity; the filtering based methods improve the objectivity, but will easily overcorrect the images and destroy the signal of the images. So, set up an objective and effective correction method is a problem that needs to be addressed urgently.This thesis presents a method based on the water phantom MRI images to correct the rat brain structure images. Firstly, to get the water phantom MRI image, then use the surface fitting method to get the fitting equation of the IIH field, use the equation to rebuild the intensity non-uniformity field, model the correction of IIH. Lastly, use the correct model to do the correction of the rat brain MRI images, then evaluate the results by comparing the results with the images gained by body coil and the existing methods. It turned out that the method in this thesis can do an accurate correction of the image intensity non-uniformity.