Paramagnetic contrast agents on the other hand may be either positive or negative MRI contrast agents. The majority of materials now being proposed as MRI contrast media achieve a contrast effect because they contain paramagnetic, superparamagnetic or ferromagnetic species.įor ferromagnetic and superparamagnetic contrast agents, which are negative MRI contrast agents, the enhanced image contrast derives primarily from the reduction in the spin reequilibration parameter known as arising from the effect on the imaging nuclei of the fields generated by the ferromagnetic or superparamagnetic particles. The enhanced contrast obtained with the use of contrast agents enables particular organs or tissues to be visualised more clearly by increasing or by decreasing the signal level of the particular organ or tissue relative to that of its surroundings, Contrast agents raising the signal level of the target site relative to that of its surroundings are termed "positive" contrast agents whilst those lowering the signal level relative to surroundings are termed "negative" contrast agents. The ability of the technique to generate high quality images and to differentiate between soft tissues without requiring the patient to be exposed to ionizing radiation has contributed to this success.Īlthough MRI can be performed without using added contrast media, it has been found that substances which affect the nuclear spin reequilibration of the nuclei (hereinafter the "imaging nuclei"-generally water protons in body fluids and tissues) responsible for the magnetic resonance (MR) signals from which the images are generated may be used to enhance image contrast and, accordingly, in recent years, many such materials have been suggested as MRI contrast agents. MRI is now well established as a medical diagnostic tool. The MRI contrast media may also be used for imaging the pancreas and the heart. The present invention relates to improvements on and relating to magnetic resonance imaging (MRI) and in particular to compositions for use as or in the preparation of MRI contrast media for imaging of the stomach, liver, bile duct and gall bladder.
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