An innovative combination of existing technologies shows promise for noninvasive, high-resolution imaging of cartilage in research on the progression and treatment of the common degenerative disease osteoarthritis.

Microcomputed tomography (microCT) – which yields three-dimensional X-ray images with a resolution 100 times higher than clinical CT scans – is commonly used to image bone for osteoporosis research but has not been useful for imaging soft biological tissues such as cartilage. These tissues simply don’t interfere with the microCT’s X-rays as they pass through a sample, and therefore don’t show up on scans.

But by combining microCT with an X-ray-absorbing contrast agent that has a negative charge, researchers at the Georgia Institute of Technology were able to image the distribution of negatively charged molecules called proteoglycans (PGs). These molecules are critical to the proper functioning of cartilage.


“By detecting PG content and distribution, the technique reveals information about both the thickness and composition of the cartilage -- important factors for monitoring the progression and treatment of osteoarthritis,” said Associate Professor Marc Levenston in Georgia Tech’s George W. Woodruff School of Mechanical Engineering.

He and Associate Professor Robert Guldberg, also in the School of Mechanical Engineering, collaborated to establish and validate the principle of the technique, dubbed Equilibrium Partitioning of an Ionic Contrast agent-microCT, or EPIC-microCT. Then they applied the technique in vitro to monitor the degradation of bovine cartilage cores and to visualize the thin layer of cartilage in an intact rabbit knee.

“This technique will allow pharmaceutical researchers to obtain more detailed information about the effects of new drugs and other treatment strategies for treating osteoarthritis,” Levenston said.

A report on the research was published Dec. 19 in the journal Proceedings of the National Academy of Sciences. The National Science Foundation, National Institute of Arthritis and Musculoskeletal and Skin Disorders, and the Arthritis Foundation funded the work.

Experiments conducted by Ph.D. student Ashley Palmer established the principles and protocol of EPIC-microCT. Researchers first immersed cartilage samples in the contrast agent solution and waited for the agent to diffuse into the tissue. Tissue with fewer negatively charged PGs absorbed more of the negatively charged contrast agent, and tissue with a higher PG concentration repelled it.

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