The Research Of Positioning Method Of Ultrasound Probe In Magnetic Resonance System

Therapeutic ultrasound is sound wave with low frequency and highenergy. As it goes through human body, it will affect the tissues, leading tosome changes physiologically. Ultrasound working with MRI has apromising future, MRI has a high definition and can be used inthermometry, too. That gives a Great prospects for coalesce MRI andultrasound. The key to guide ultrasound with MRI is positioning theultrasound system in MR system.This article present a method of positioning the ultrasound probe inMR system. The method is based on the HIFU system developed byBiomedical instrument research institute.In this article, the research on the coordinate system in ultrasoundsystem and MR system is proposed. The MR’s coordinate systemcorrespond DICOM3.0standard, that means the coordinates of a point onthe DICOM format MR image can be calculated based on DICOM3.0standard. The coordinate system of ultrasound is based on the ultrasoundprobe. These two coordinate systems fit affine transformation.Based on the theory described, a method by using the ultrasoundprobe as the key is presented. By taking images of the ultrasound probe inMR system, the position of ultrasound probe in MR system can becalculated. With this information, and the ultrasound’s coordinate system isrelated to it’s probe, the relationship between these two coordinate systemcan be found.According to the method, a probe with markers is designed, themarkers are tubes or slot beside the probe. Because the probe is immersedin water, although the probe can’t be seen in MR images, it’s outline can beseen in MR images, then it can be calculated. The markers’ number is morethan the least number that needed to calculate the transformation. Withthese redundant information, the error of each markers can be calculated,and the precision can be improved by taking advantage of the redundant information.Then, a program is developed to cooperate with the probe described.The program is written in C++, VTK(visualization toolkit) is used to readthe DICOM format images. As C++is not proper for numericalcomputation, the program uses DLL generated by MATLAB to do somecomputation. The program is part of the main operating system of HIFU, itaccepts DICOM-formated MR images, and returns a Four order phalanx asthe transformation of the two coordinate system.An experiment is carried out to check the method. The experimentuses a simulate probe made in organic glass, and the experiment is carriedout in a1.5T MR system. The result of the experiment confirms themethod.