The New Advances in the Clinical Applications of the MRI Cantrast Media
Magnetic resonance imaging is produced by the hydrogen proton(1H)which is excited by a spe- cific radiofrenquence pulse(RF)in a strong magnetic field.At the termination of the RF,the MR signals generated by the excited proton can be detected and the MR images came into being after the processing of the computer. As with the ongoing developments of magnetic resonance imaging(MRI),the application of MRI contrast media is also quickly developing. According to the mechanism,the MRI contrast media can be classified into two subclasses:paramagnetic, positive enhancers and susceptibility-effect,negative enhancers.Paramagnetic positive enhancers can pri- marily shorten the T_1 relaxation time of the proton.The signal intensity of the tissue with the agents can be increased on T_1 weighted images.The signal intensity of the tissues with the susceptibility-effect nega- tive enhancers can be decreased on T_2 weighted images by mainly shortening the T_2 relaxation time of the proton. In recent years,in addition to more intensive research for the first paramagnetic agent:Gd-DTPA,many new types of MRI contrast agents have emerged,such as super-paramagnetic iron oxide particles,hepato- cyte-directed,and some kinds of tissue-directed agents,etc.All these have shown bright prospects for the applications of MRI,which is one of the newest imaging modalities.This paper was designed to in- troduce the MRI contrast media mechanism and new advances in the clinical applications of the contrast media,used in the central nervous system,cardiovascular system,liver,gastrointestinal tract,muscu- loskeletal system,etc.The contrast media primarily shortens proton relaxation times(T_1 and T_2)in order to enhance the signal intensity contrast among the different types of tissue.In addition it distinguishes the lesions from the surrounding structures.By using MRI contrast media,the imaging quality and the detec- tion sensitivity of the lesions would be improved,and thus prove helpful to the diagnosic process.The contrast media should be applied properly and efficiently.Moreover,accelerating the domestic production process of these contrast agents is crucial for its extensive use in China.