Reducing artifacts in computed tomography images

Approximately 20% of the 80 million CT scans performed annually in the US contain metal implants (hip replacements, dental fillings, surgical clips, and pacemaker wires). The metal creates streaks that degrade the image quality, and make the scan difficult to interpret. Several metal artifact reduction techniques have been developed, but none of them are in widespread clinical use, because they are too slow and can introduce new artifacts.

We have developed a new method for metal artifact reduction, called the Metal Deletion Technique (MDT). Our initial experience at Stanford Hospital shows that this technique results in:

Here is an example of streak artifacts from the metal in bilateral hip replacements (left). When the metal artifacts are reduced using MDT (right), enlarged lymph nodes around the rectum are seen much more clearly.

bilateral hip replacement metal artifact (FBP)bilateral hip replacement metal artifact reduction (MDT)

Metal streak artifacts are caused by the fact that filtered backprojection (FBP) assumes that each detector measurement is equally accurate. In reality, X-ray beams that pass through or near metal implants are highly attenuated and have a much larger error. MDT discards the inaccurate metal data, and only uses high quality data to reconstruct the non-metal portions of the image. The metal data are iteratively replaced with forward projected values. In the diagram below, metal pixels and projection data are shown in red. The original projection data are plotted with a thick line, and revised projection data are plotted with a thin line.

Metal Deletion Technique

MDT is available now, and it works with DICOM files from any CT scanner. Simply upload DICOM files, and the metal artifacts are automatically reduced.

Try it out now »




Talks and abstracts

Patent applications

Related links:
High dynamic range CT scans
Virtual angiography (aka "Google Maps" for IR)

Ed Boas' home page | Stanford radiology | CT metal artifact reduction