| [ Summary ] |
Computed tomography (CT) and magnetic resonance imaging (MRI) have become invaluable means of making clinical decisions regarding cerebrovascular diseases (CVD). However, controversy persists as to whether MRI offers advantages over CT scanning for detecting lesions in patients with acute CVD. MRI may not be able to replace CT, however, because of the difference in fundamental imaging principles between these two methods. At present, the imaging procedure of first choice for making a differential diagnosis in the acute period of CVD is CT scanning, and MRI should be done when the CT is negative for findings of intracerebral bleeding or subarachnoid hemorrhage. Recently, it has become more important to make a precise diagnosis of cerebral infarction in the ultra-acute period of the disease (i.e. within 3 hours after the onset of stroke), because therapeutic intervention is advancing. The infarcted area appears as a hypodense lesion, generally 24 to 48 hours after the onset. Thus, attention must be paid to findings other than the attenuation change. It is easy to diagnose cerebral bleeding by CT scanning, and it has become possible to diagnose subarachnoid hemorrhage by high resolution CT, which was developed recently, in more than 90% of patients with acute SAH, if the CT is performed within 4 to 5 days after the onset. However, lumbar puncture may be essential to confirm the diagnosis of SAH, in cases in whom the amount of bleeding is small or those who bled 1 week or more prior to the scanning. On the other hand, the development of high speed imaging, with MRI, makes it possible to document brain function(activation), cerebral circulation and even the diffusion of water molecules. We hope that experience will permit the judicious use of these morphological and physiological data for the prevention and the treatment of CVD. |