What it means
On many MRI images, blood moving quickly through an artery or large vein gives no signal, so the inside of the vessel looks black. The blood has already left the thin slice being imaged before the scanner can read it. This black dot or line is called a flow void. It is a normal effect, not a hole or a gap, and it shows blood is moving.
When it matters
Normal flow voids are a reassuring routine line. When an expected flow void is missing, the vessel may have slow flow, a narrowing or a blockage. Doctors usually check this with a scan of the vessels, such as an MR or CT angiogram. Sometimes a missing flow void is only an effect of how the image was taken. Unusual clusters of flow voids can point to abnormal vessels and are checked the same way.
Questions to ask your doctor
- Were all the expected flow voids normal on my scan?
- Do I need a vessel scan, such as an MR angiogram, to check this?
- Could this be from how the images were taken rather than a real problem?
