Research Of Shimming And Homogeneity Test For Permanent-Magnet Of MR

BackgroundAs one of the most advanced and expensive diagnosis equipment in the area of medical imageology, the application extent of MRI goes to be extended constantly, and it turns to be more and more important recent years. Due to the especial imaging effect and mode, there are good marketing and prospect for MRI in the area of medical diagnosis. In fact, domestic medical surrounding can be improved by only using the high cost-performance ratio medical equipment in the opinion of popular using. For MRI which is indispensable for clinical diagnosis, it is sensible to make effort on developing permanent-magnet MRI that is middle-low field and low cost. Magnet sub-system is a key component in MRI system, and the most two important performance are homogeneity and stability of magnetic field, which are able to influence the imaging quality directly. So, the design of shimming is important direction about MRI theory, and also significant. Many research institutes overseas prefer the excellent superconducting magnet to permanent magnet, and they have fell behind some institutes domestic on the aspects of magnetic circuit and structure improvement. To improve the domestic development of MRI for better, the author has made a research on shimming and its test way by experiment in a famous MR center. With deserting traditional shimming mode which is depended on experience, this investigation contents include optimization and design for shimming, furthermore, a new design for homogeneity testing has been introduced here.Objective1. With deserting traditional shimming mode which is depended on experience, to establish a rational shimming process for boosting efficiency of shimming.2. To gather consecutive data about homogeneity from static magnetic field plane with deserting traditional discrete data.Methods1. Taking a 0.35T permanent magnet as the object, and using the programming shimming radius, gradually stacking shimming, and finally comparing before shimming data with after shimming data to display the shimming result based on math-model of matrix rectification generated by solo magnetic piece.2. Using mobile detector and comparing the traditional methods of gathering data based on finite measuring point via simulation modeResults1. The homogeneity had been improved from 2045ppm before shimming to 58ppm after shimming by pasting systematically.2. The result data generated by discrete data was not stable, and it changed as different distribution quantity and different distribution position. The more of the sample points gathered, the closer this result gets to the result of the new design. Conclusions1. The process of passive shimming can be programmed systematically by computation to boost efficiency of shimming.2. Homogeneity-detecting of static magnetic field should better gather data fromcontinual plane, especially in irregular heterogeneity.