T1 and T2. Intrinsic tissue relaxation occurs by two major pathways called longitudinal or T1 and transverse or T2 decay. These refer to CT angiography and MR angiography. CTA requires the intravenous injection of an iodinated contrast material with rapid scanning through the region of interest while MRA typically does not require injection of a contrast agent. Both of these techniques are in widespread use although they have not replaced the gold standard catheter cerebral arteriogram completely.
Stroke is a lay term for heterogenous group of cerebrovascular disorders.
The cardinal feature of stroke is sudden onset. This constitutes a group of often vague neurologic symptoms that are associated with occlusion of a dural sinus, cortical vein, or the deep venous system within the brain. This can be caused by a wide variety of underlying conditions such as dehydration, sepsis, hypercoagulable disorders and birth control pills, among others. This refers to hemorrhage located within the subarachnoid space. The most common cause is trauma.