Tomosynthesis Shows Promise in Knee Imaging

Tomosynthesis has been around for more than a decade, most recently being used in breast imaging, but new research indicates it could be useful in diagnosing osteoarthritis of the knee.

Investigators from Boston University School of Medicine (BUSOM) determined tomosynthesis is more proficient than radiography in identifying the hallmarks of knee osteoarthritis - bony spurs and fluid-filled cysts. As a modality, tomosynthesis is much like an X-ray/CT hybrid that can be conducted while the patient is standing. It’s technically an X-ray, but the method produces CT-like thin slices that can give you 360-degree views.

The flexibility of letting the patient stand makes tomosynthesis a good fit for knee imaging, said Daichi Hayashi, PhD, a BUSOM musculoskeletal radiology research fellow and lead author of the study published in April issue of Radiology.

“CT is a more sophisticated technology than tomosynthesis, but patients must be lying down in order for it to work. That prevents us from getting images of the knee being exposed to tension that usually arises from standing or walking under normal conditions,” Hayashi said. “Tomosynthesis lets us image the patient when the knee is exposed to gravity and weight.”

Hayashi’s team received a grant from GE to study whether tomosynthesis could provide acceptable images for osteoarthritis diagnoses. To date, it is the first study to examine the use of this modality in knees.

Overall, the team imaged 40 adults - 80 knees total - over age 40, irrespective of knee pain or pre-existing osteoarthritis. Using tomosynthesis, MRI, and radiography, they screened four locations in the knee for any bony spurs or cysts. Results showed tomosynthesis identified 178 bony spurs, and radiography pinpointed 150. Additionally, tomosynthesis caught more than double the number of cysts - 31 compared to 15.

Current research, published in the January 2011 Radiology, reported tomosynthesis is also superior to radiography in highlighting rheumatoid arthritis in the hands and wrists. In these cases, tomosynthesis identified about 20 percent more lesions.

Even though it offers greater specificity, the spurs tomosynthesis identifies might not be of significant importance, Hayashi said. It discovers smaller spurs that are less strongly associated with pain than the larger spurs found through radiography. This difference shows tomosynthesis isn’t wholly superior to X-ray technology and that more research is needed to determine the extent to which it can actually contribute to the clinical management of osteoarthritis, he said.

“Tomosynthesis doesn’t overcome the biggest limitation of X-ray: the need to see more bone and soft tissue changes,” Hayashi said. “But, in the healthcare system we have now, it could be an alternative option for visualizing some of the most prevalent features of knee osteoarthritis, providing a more complete image compared to normal X-ray.”

Despite its limitations, however, choosing tomosynthesis over other modalities for knee imaging does offer both clinical and financial benefits.

According to Hayashi, tomosynthesis exposes patients to more radiation than radiography due to the 360-degree imaging, but the level is still lower than CT scans. It’s also much faster at gathering images, collecting the studies you need in only a few seconds. MRI is still considered the best imaging option, he said, but it is difficult in the current healthcare environment to justify the expense and length of time associated with MRI imaging.

But, even with its benefits, it’s still too early to recommend using tomosynthesis as a standard practice.

“We can’t say on the basis of this paper that everyone should use tomosynthesis for daily clinical practice,” Hayashi said. “We can suggest, however, that there is, perhaps, a greater scope for using tomosynthesis that needs to be explored.”

(a) Radiograph shows no obvious osteophyte in the right lateral femur (arrow). (b) Tomosynthesis image shows an osteophyte in the same compartment (arrow) as in a. (c) Coronal proton density-weighted MR image (9000/10) confirms presence of osteophyte (arrow); a focal cartilage defect is also noted (arrowhead). Courtesy Radiological Society of North America