Laird Harrison

May 08, 2014

When assessing bone healing, tomosynthesis is better than conventional x-ray, according to the results of a new study.

Although the tomosynthesis images, which are generated with standard digital radiography equipment, fell short of CT images, tomosynthesis is safer and more economical, said lead researcher Alice Ha, MD, assistant professor of radiology at the University of Washington in Seattle.

"We think this is an underused old tool that is low-radiation, low-cost," she told Medscape Medical News.

In tomosynthesis, digital x-ray machines rotate about 40 degrees around the subject, producing image slices. "You can look at it as the poor man's CT," said Dr. Ha.

She presented the study results at the American Roentgen Ray Society 2014 Annual Meeting in San Diego.

An Old Technology

Tomosynthesis was developed decades ago, but was not used much in the digital era because of the intensive computation required. But faster computers have now made it more feasible, and it has become popular in mammography, Dr. Ha said.

She explained that she became interested in the technique for other types of imaging after she discovered that the software was already loaded on the General Electric scanner in her department. "It was just sitting there and nobody was using it," she said.

The slices it produces reveal a single spot in a plane with high clarity, but leave everything else out of focus.

"It's really good for mammography because you're just looking for that 1 dot and nothing else around it. It's becoming popular in chest imaging because it's really good at looking at small nodules and foreign bodies in bronchial airways. I thought it would be good for bony details like the trabecular details of the bone," she reported.

The Bony Details

Dr. Ha and her colleagues decided to try tomosynthesis for postoperative imaging after hardware fixation of fractures, arthrodesis, and osteotomies because overlapping bone fragments and metal often limit the effectiveness of radiography.

For their study, 49 adults who had received wrist hardware placement in the previous year underwent radiography, tomosynthesis, and unenhanced CT on the same day.

Three readers evaluated radiographic and tomosynthesis images, in random order, for fracture healing and hardware complications. They looked at medial, lateral, anterior, and posterior cortices.

In the cohort, 43% had fractured distal radii, 18% had fractured scaphoids, and 18% had fractured metacarpals; the rest had a variety of other diagnoses.

Hardware obscured the cortex in 2% of the CT images, 8% of the tomosynthesis images, and 15% of the radiography images. The difference was statistically significant (< .01).

This is an underused old tool that is low-radiation, low-cost.

However, the readers found that they could detect cortical fractures much better with tomosynthesis than with radiography (area under the curve, 0.84 vs 0.76; = .01).

The readers varied only moderately from each other. There was no significant correlation between fracture scores and scores on the Disabilities of the Arm, Shoulder, and Hand questionnaire.

Tomosynthesis fracture scores were significantly correlated to reported pain levels (R, 0.28; = .03), as were CT fracture scores (R, 0.29; = .04).

Encouraged by these findings, the researchers plan to use a specially devised scanner to assess tomosynthesis images of ankles under weight-bearing conditions.

This study supports the wider use of tomosynthesis, said Michael Tuite, MD, assistant section editor for musculoskeletal imaging at the American Journal of Roentgenology.

"The technique could be particularly useful in clinics that don't have their own CT scanner, he told Medscape Medical News.

"I think the data are promising and kind of consistent with what we all suspected, which is that it's not as good as CT, but it's going to be a lot cheaper."

This study was funded by General Electric. Dr. Ha and Dr. Tuite have disclosed no relevant financial relationships.

American Roentgen Ray Society (ARRS) 2014 Annual Meeting: Abstract 165 Presented May 8, 2014.


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