General CNS imaging

In order to differentiate between tumours and other focal abnormalities, i.v. contrast media are used in CT. Iodinated contrast media normally remain in the blood stream because the so-called blood-brain barrier (BBB) is intact and does not allow large molecules to leak through the walls of the capillaries. If, on the other hand, the barrier is damaged because of a pathological process like tumour, infarction or infection, leakage of contrast media through the BBB will occur and so the structure will be readily seen on the CT image.

CT is a sensitive method to detect focal abnormalities in central nervous system (CNS), and is used world-wide. Because of the absence of bone artefacts as seen on CT, MRI is preferable in the posterior fossa of the skull; i.e. the cerebellum, brain stem and basal parts of the cerebrum.

In coming years, MRI will open up a new fascinating perspective, namely functional imaging, reflecting subtle changes in cerebral function due to biochemical/physiological and not necessarily structural changes.