Scientists at the National Institute of Standards and Technology (NIST) have developed a new standard reference material (SRM), the first such measurement tool to enable hospitals to link important tissue density measurements made by CAT scans to international standards.

Computed tomography (CT or CAT) uses computer processing to combine multiple X-ray images into three-dimensional scans that resemble slices of the body. These cross-sections are useful for spotting changes that are difficult to discern from ordinary two-dimensional X-ray images alone, such as the changes in lung tissue that indicate cancer or emphysema. Millions of CAT scans take place every year in the United States alone, but over time, the devices’ outputs have a tendency to “drift,” according to NIST physicist Zachary Levine.

“Scanners are calibrated daily, but over periods of months you still see variations,” says Levine. “Some of these come from the physical degradation of the machine, or even from changes made by software upgrades. Doctors “get to know” their own machine’s idiosyncrasies and make good diagnoses, but they’d still like to be more certain about what they’re seeing, especially when it comes to lung tissue.”

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