AAPM: CT reconstruction technique improves joint replacement images

A new CT method could produce significantly improved images of knee, spine and hip implants, and may lower radiation exposure, according to preliminary research presented Aug. 1 at the 54th annual meeting of the American Association of Physicists in Medicine (AAPM) in Charlotte, N.C.

Although patients with joint replacement require CT imaging to assess wear, loosening of the prosthesis, fractures or infection, device interference often taints the images with streaks or blurring, which makes diagnosis and assessment of the area around the implant difficult or impossible.

Researchers at Johns Hopkins University in Baltimore have developed a method called known component reconstruction (KCR) which incorporates a computerized model of the implant’s shape and material content into the 3D image reconstruction process to improve image quality. Researchers are studying the method in CT systems and assessing its potential for routine use in hospitals. 

“Every year more than 600,000 people get total knee replacements, which are among the most difficult implants to image around. We truly need a better way to image knee replacements and other implants, and this method is promising,” J. Webster Stayman, PhD, a faculty research associate in biomedical engineering at Johns Hopkins, said in a release. “This technique is particularly well-suited for implant assessment because surgeons typically know the specific model of the implant. Getting that information into the imaging system could allow them to clearly see tissues around the implant and measure its exact orientation.”

Stayman and colleagues tested the method in computer simulations and the laboratory using knee implants as well as surgical screws and rods used in spinal fixation. The results verified the method using real data and demonstrated that it potentially could be applied generally to CT systems.

The researchers found that the technique provides very good visualization of implants, even in images that may not have been diagnostically useful using filtered back projection, Stayman said in a press conference.

“The KCR technique is an exciting advance that combines iterative reconstruction for reduction in radiation dose with strong prior information about implants that are known to be in the image,” Wojtek Zbijewski, PhD, a senior research scientist at Johns Hopkins, said in the release. “We’re working on extending the technique to situations in which the implant changes shape and applying it for the first time to new CT systems for diagnostic radiology and surgery.”