Angiography is a medical imaging technique used to make blood vessels visible inside the body. It helps doctors find narrowed arteries, blockages, aneurysms, bleeding sites, and abnormal vessel growth. The method matters because many serious conditions, such as stroke and heart attack, involve changes in blood flow.
By mapping vessels clearly, angiography can guide diagnosis and treatment with high precision.
In many angiography procedures, a thin catheter is placed into a blood vessel and a contrast dye is injected. The dye absorbs or changes the imaging signal so vessels stand out from nearby tissue during X-ray, CT, or MRI imaging. Digital subtraction angiography improves vessel visibility by subtracting a before-contrast image from an after-contrast image.
The resulting image highlights the dye-filled vessels and reduces background anatomy.
Key Facts
- Angiography uses contrast dye to make blood vessels easier to see on medical images.
- In X-ray angiography, iodine contrast absorbs X-rays more strongly than soft tissue.
- Digital subtraction image = post-contrast image - pre-contrast image.
- Blood flow rate can be estimated with Q = V/t, where Q is flow rate, V is volume, and t is time.
- Catheters allow contrast dye to be delivered close to the vessel or organ being studied.
- CT angiography uses X-ray slices and computer reconstruction, while MR angiography uses magnetic fields and radio waves.
Vocabulary
- Angiography
- Angiography is an imaging method that shows the inside shape and path of blood vessels.
- Contrast dye
- Contrast dye is a substance injected into the body to make certain structures stand out in medical images.
- Catheter
- A catheter is a thin flexible tube used to deliver dye or instruments into a blood vessel.
- Digital subtraction angiography
- Digital subtraction angiography is a technique that removes background anatomy by subtracting a pre-contrast image from a post-contrast image.
- Stenosis
- Stenosis is an abnormal narrowing of a blood vessel that can reduce blood flow.
Common Mistakes to Avoid
- Thinking angiography is only one type of scan is wrong because angiography can be performed with X-ray, CT, or MRI depending on the clinical need.
- Forgetting the role of contrast dye is wrong because many vessels are difficult to separate from surrounding tissues without a signal difference.
- Assuming digital subtraction adds two images is wrong because it subtracts the background image to isolate the contrast-filled vessels.
- Ignoring timing after injection is wrong because images must be captured while contrast is in the target vessels for the clearest result.
Practice Questions
- 1 A contrast injector delivers 24 mL of dye in 6 s. What is the average injection flow rate in mL/s?
- 2 A vessel has an original diameter of 4.0 mm and is narrowed to 2.0 mm at a stenosis. By what percent has the diameter decreased?
- 3 Explain why taking a pre-contrast image before injecting dye helps digital subtraction angiography show blood vessels more clearly.