When is a computed tomography (CT) head perfusion scan indicated versus a computed tomography (CT) angiography (Angio)?

From the Guidelines

CT head perfusion scans are primarily ordered in acute stroke settings to identify salvageable brain tissue, while CT angiography is ordered to visualize the vascular anatomy of the brain and neck. When deciding between a CT head perfusion scan and a CT angiography (CTA), it is essential to consider the specific clinical scenario.

• In acute stroke settings, CT perfusion is used to identify salvageable brain tissue (penumbra) by measuring cerebral blood flow, volume, and transit time, as seen in studies such as 1.
• CT angiography, on the other hand, is used to visualize the vascular anatomy of the brain and neck, making it useful for detecting aneurysms, arteriovenous malformations, vessel stenosis, occlusions, or dissections, as discussed in 1 and 1.
• CTA provides detailed images of vessel lumens and walls but doesn't assess tissue perfusion.
• In acute stroke, these studies are often complementary - CTA identifies the location of vessel occlusion while perfusion imaging determines the extent of compromised tissue.
• For subarachnoid hemorrhage, CTA is preferred to identify aneurysms, as stated in 1, while for trauma patients with suspected vascular injury, CTA better evaluates vessel integrity. The choice between these imaging modalities depends on the specific clinical question, with perfusion focusing on tissue viability and CTA on vascular anatomy, as highlighted in 1 and 1.
• CT perfusion has been studied in various clinical scenarios, including early prediction of delayed cerebral ischemia, late detection of vasospasm, and late detection of ischemic injury, as seen in 1.
• The use of CT head perfusion to guide treatment decisions in the setting of neurologic symptoms of delayed cerebral ischemia did not improve outcomes when compared with treating all patients without imaging guidance, as discussed in 1.
• However, CT perfusion can be useful in determining eligibility for endovascular therapy (EVT) for anterior circulation strokes due to large-vessel occlusion (LVO) confirmed on CTA presenting in the extended window of 6 to 24 hours, as stated in 1.
• The rapidity of diagnosis afforded by CT perfusion is a strongly relevant clinical consideration in this situation, as highlighted in 1.
• Ultimately, the decision to order a CT head perfusion scan or a CT angiography depends on the specific clinical scenario and the information needed to guide treatment decisions, with the goal of improving patient outcomes in terms of morbidity, mortality, and quality of life.

From the Research

CT Head Perfusion Scan vs CT Angio

• The decision to order a CT head perfusion scan versus a CT angio depends on the clinical context and the specific goals of imaging in acute ischemic stroke [(2,3,4)].
• CT perfusion is used to determine the ischemic core and the tissue at risk, aiding in therapeutic decision-making [(2,3)].
• CT angio is used to assess the intracranial and cervical vasculature, which is essential for identifying large artery occlusion and guiding mechanical thrombectomy [(3,4)].
• In patients with unknown symptom onset or known symptom onset up to 24 hours, advanced imaging with MRI or CT perfusion can guide effective acute reperfusion treatment with mechanical thrombectomy and intravenous alteplase 3.
• CT perfusion ASPECTS can detect reversible ischemia and is correlated with clinical outcome, making it a valuable tool in the evaluation of acute ischemic stroke 5.
• The choice of imaging modality should be guided by the patient's clinical presentation, time of symptom onset, and the availability of imaging technologies [(4,6)].