hivesetr.blogg.se - Mr contrast agent

Thermally driven motion of the strongly paramagnetic metal ions in the contrast agent generate the oscillating magnetic fields that provide the relaxation mechanisms that enhance the rate of decay of the induced polarization. Most clinically used MRI contrast agents work by shortening the T1 relaxation time of protons inside tissues via interactions with the nearby contrast agent. 1.5 Oral administration of contrast agents.1.1.3 Safety of gadolinium contrast agents.1.1.2 Gadolinium-containing contrast agents approved for human use.

1.1.1 Types of gadolinium contrast agents.

A contrast agent usually shortens, but in some instances increases, the value of T1 of nearby water protons thereby altering the contrast in the image. Water protons in different tissues have different T1 values, which is one of the main sources of contrast in MR images. The magnitude of the spin polarization detected by the receiver is used to form the MR image but decays with a characteristic time constant known as the T1 relaxation time. Random molecular rotational oscillations matching the resonance frequency of the nuclear spins provide the "relaxation" mechanisms that bring the net magnetization back to its equilibrium position in alignment with the applied magnetic field. An intense radiofrequency pulse is applied that tips the magnetization generated by the hydrogen nuclei in the direction of the receiver coil where the spin polarization can be detected. In MRI scanners, sections of the body are exposed to a very strong magnetic field causing primarily the hydrogen nuclei ("spins") of water in tissues to be polarized in the direction of the magnetic field. Such MRI contrast agents shorten the relaxation times of atoms within body tissues following oral or intravenous administration.

The most commonly used compounds for contrast enhancement are gadolinium-based. MRI contrast agents are a group of contrast media used to improve the visibility of internal body structures in magnetic resonance imaging (MRI).