Imaging in stroke setting

CT without contrast- the large benefit of ordering this test is that it is very fast at determining if there was any intracranial hemorrhage which is important because the management of a stroke secondary to intracranial hemorrhage is very different than the management of an ischemic stroke. CT angiography and CT perfusion study has been added to the work up of stroke and has been shown to improve the detection of an acute infarction than using CT without contrast alone. In addition, the CTA and CTP may indicate the status of the vasculature and may show an occlusion in the vessel.

CT angiography — CT angiography (CTA) is performed by administering a bolus of standard intravenous CT contrast. The helical CT scan is timed to capture the arrival of dye into the brain. For the detection of intracranial large vessel stenosis and occlusion, CTA in various studies had sensitivities of 92 to 100 percent and specificities of 82 to 100 percent when compared with conventional angiography.

MRI - Has the advantage for further categorizing the stroke patients that may benefit from TPA and intravascular treatments. Studies that combines conventional MRI with diffusion-weighted imaging (DWI), perfusion-weighted imaging (PWI) can reliably diagnose both acute ischemic stroke and acute hemorrhagic stroke in emergency settings

Diffusion-weighted imaging (DWI)— DWI is based upon the capacity of fast MRI to detect a signal related to the movement of water molecules and  can detect abnormalities due to ischemia within 3 to 30 minutes of onset. In acute stroke, swelling of the ischemic brain parenchymal cells follows failure of the energy-dependent Na+/K + – ATPase pumps and is believed to increase the ratio of intracellular to extracellular volume fractions which will cause the DWI to detect abnomalities.

Perfusion Weighted Image - Diffusion-weighted imaging reveals evidence of ischemic injury, not ischemia itself which PWI will aid in. Perfusion-weighted imaging (PWI) uses fast MRI techniques to quantify the amount of MR contrast agent reaching the brain tissue after a fast intravenous bolus. Integration of the amount of gadolinium entering the brain on first pass allows construction of maps of cerebral blood volume as well as the transit time that it takes for the dye to reach and wash out of the tissue.

MR Angiogram - MR angiography (MRA) to detect vascular stenosis or occlusion is done at many centers as part of a fast MRI protocol for acute ischemic stroke. Results from a case series showed that the combined use of DWI with MRA within 24 hours of hospitalization substantially improved the early diagnostic accuracy of ischemic stroke subtypes. Most of my patients on the stroke service will get a MRA of the head and neck.