Use of contrast media in neuroimaging.

Since their introduction, gadolinium-based contrast media are routinely used in most CNS MR imaging indications. Due to their paramagnetic effect, they significantly shorten the T1 relaxation times of the tissue and are therefore applied to improve the sensitivity and specificity of CNS diseases and to allow a better treatment decision, planning, and follow-up. More recently, contrast media have also been used to allow the measurement of tissue perfusion and to follow the time course of enhancement in dynamic contrast-enhanced imaging studies or dynamic MRA studies. With the presence of the BBB, contrast media does not leak into the tissue. Only vascular structures and areas of the brain that have no BBB(choroid plexus, pineal and anterior lobe of pituitary gland) physiologically enhance after contrast injection. The mechanisms of tissue enhancement in the brain are related to a higher vascularity of the pathology or a disruption of the BBB.Tissue enhancement is, besides the degree of BBB disruption, further dependent on the applied magnetic field strength, with higher field providing a better enhancement and the applied dose of contrast media.