section_path: Diagnosis/Imaging
section_name: Imaging
paragraph_text: Imaging
  
  For diagnosing ischemic (blockage) stroke in the emergency setting:
  
  For diagnosing hemorrhagic stroke in the emergency setting:
  
  For detecting chronic hemorrhages, an MRI scan is more sensitive.
  
  For the assessment of stable stroke, nuclear medicine scans such as single-photon emission computed tomography (SPECT) and positron emission tomography–computed tomography (PET/CT) may be helpful. SPECT documents cerebral blood flow, whereas PET with an FDG isotope shows cerebral glucose metabolism.
  
  CT scans may not detect ischemic stroke, especially if it is small, of recent onset, or in the brainstem or cerebellum areas (posterior circulation infarct). MRI is better at detecting a posterior circulation infarct with diffusion-weighted imaging. A CT scan is used more to rule out certain stroke mimics and detect bleeding. The presence of leptomeningeal collateral circulation in the brain is associated with better clinical outcomes after recanalization treatment. Cerebrovascular reserve capacity is another factor that affects stroke outcome – it is the amount of increase in cerebral blood flow after a purposeful stimulation of blood flow by the physician, such as by giving inhaled carbon dioxide or intravenous acetazolamide. The increase in blood flow can be measured by PET scan or transcranial doppler sonography. However, in people with obstruction of the internal carotid artery of one side, the presence of leptomeningeal collateral circulation is associated with reduced cerebral reserve capacity.