A CT perfusion scan is an imaging technique that measures blood flow within tissues. It helps medical professionals understand how effectively blood reaches specific organs or areas, highlighting regions with reduced or absent supply.
The Science Behind CT Perfusion
The process involves injecting a contrast agent into a vein, typically in the arm. As the contrast travels through the bloodstream, rapid, repeated CT scans are performed. These scans capture the contrast’s passage through the targeted tissue.
A computer processes this data to generate “perfusion maps.” These color-coded images represent various blood flow parameters. Key measurements include cerebral blood flow (CBF), the volume of blood flowing through brain tissue per unit of time, and cerebral blood volume (CBV), the total blood present in a specific tissue volume.
Mean transit time (MTT) measures the average time blood takes to pass through a tissue region. These measurements offer insights into blood circulation, helping medical teams identify areas with compromised or altered blood supply.
Diagnosing with CT Perfusion
CT perfusion plays a role in evaluating acute ischemic stroke, a condition where a blood clot blocks brain blood flow. The scan distinguishes between the “ischemic core” (irreversibly damaged brain tissue) and the “penumbra” (tissue at risk but potentially salvageable if blood flow is restored). This distinction is important for guiding urgent treatment decisions, such as administering clot-busting medications or performing mechanical clot removal.
The perfusion maps help doctors identify the extent of damaged and salvageable brain tissue, guiding appropriate and timely intervention. The scan can also assess treatment effectiveness by showing changes in blood flow post-intervention.
Beyond stroke, CT perfusion evaluates certain brain tumors. It helps differentiate tumor types or distinguish tumors from other conditions like infections by analyzing their unique blood flow patterns. The scan also monitors tumor response to treatment, as changes in blood supply indicate therapy effectiveness.
What to Expect During the Procedure
Before the scan, an intravenous (IV) line will be placed in your arm to administer the contrast agent. You will then lie on a movable table that slides into the CT scanner. The technologist will provide instructions, such as holding your breath briefly during certain parts of the scan.
When the contrast material is injected, you might feel a warm sensation spreading through your body or experience a metallic taste in your mouth. These sensations are normal and typically subside quickly. The scanning process itself is relatively brief, often lasting only a few minutes.
While CT scans use X-rays, medical staff take precautions to minimize radiation exposure, using the lowest dose necessary to obtain clear images. The contrast agents used are generally safe, though potential risks like allergic reactions are discussed beforehand. After the scan, the IV line is removed, and you can typically resume your normal activities.