Generally, images produced by CT scanners are accurate representations of the scanned object. The technology is a mainstay in the imaging stables of most hospitals. In spite of this, CT is commonly susceptible to a number of image anomalies1, including streak artifacts.
What Is a Streak Artifact?
The name should suffice to tell you what a streak artifact looks like, but the causes bear some explanation. Most streak artifacts occur near materials such as metal or bone, primarily as a result of beam hardening and scatter. These phenomena produce dark streaks between metal, bone, iodinated contrast, barium, and other high-attenuation materials. Bright streaks are seen adjacent to the dark streaks2. See an example of an artifact caused by beam hardening below.3
Here's an analogy to help understand beam hardening: Pretend I’m swimming across a pool. I am an X-ray beam and the pool is the part of the body being scanned. As I swim, I lose energy as I cross the pool; I’m more tired the further I go. And if I’m swimming through water, I expend less energy than if I were swimming through, say, Jell-o. In the same way, X-rays lose their energy, or "harden", more quickly as they pass through metal or bone than as they pass through muscles or organs.
The other big issue that causes streak artifacts is something called Compton scatter. Basically, scatter causes X-ray photons to change direction and change energy. This means photons could end up in a different detector than they should be in. The biggest problem is when scattered photons end up in a detector that would usually have very few photons. For example, if a metal implant blocks all photons, then the corresponding detector element will only detect scattered photons2.
How to Correct Streak Artifacts
Streak artifacts can be reduced using newer reconstruction techniques or metal artifact reduction software. A radiologist can also try scanning at a higher kV in order to get a harder X-ray beam and thus, fewer beam hardening artifacts. However, there is a tradeoff in that the higher kV will reduce the tissue contrast of the scan2.
If your reconstruction techniques and reduction software are current and your radiologist is scanning with the highest kV they are comfortable with and streak artifacts are still appearing, it's probably time to call in a service engineer to diagnose underlying causes.
James Porchik is the Field Service Engineer Manager at Block Imaging. James enjoys the growth aspect that comes in the engineering field – growth in relationships, growth in knowledge, and growth in capacity. When he is not turning the wrench, James enjoys martial arts, hiking, and listening to podcasts.