CT: How many slices are enough?

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"CT is about more than the number of detectors; it's about the ability to detect disease," said Elliot K. Fishman, MD, professor of radiology and oncology at Johns Hopkins Hospital and director of diagnostic imaging and body CT at The Johns Hopkins University School of Medicine. Fishman spoke at the opening session of the 91st Scientific Assembly and Annual Meeting of the Radiological Society of North America on Monday.

"We should worry less about scanner parameters and more about patient parameters," he said. The technology in and of itself is not enough. "It's only useful if it's used." Fishman said a lot of facilities that have installed a 64-slice CT scanner are still using protocols for 16-slice CT scanners. He said that only about 20 percent of the people who purchase the most advanced multidetector CT actually use the scanners to their capability. "Radiology has never been busier and there have never been more challenges. Everyone is spinning in place even as the ability for visualization has never been stronger."

That visualization allows physicians to define the presence as well as the extent of disease. "The goal is to limit what radiology does." So the ability to segment out nonessential information becomes more important. And, the more complications, the more important is the ability to use available information.

Soft plaque is rarely seen with 16 slice CT, but it's routine with 64 slices. Segmenting out vessels saves lots of time, Fishman said. That provides the ability to look at coronary stents and their patency, to look inside the heart chambers, and look at cardiac motion. "There's no other noninvasive way to look at these things. CT means we're not talking about static imaging anymore."

And that requires changing protocols. "The future of CT requires seamless integration of data with software," he said. Fishman encouraged the audience to embrace the necessary changes because "64 slice is nowhere near the end of the road."

"We need to step up to the plate in the radiology community and make optimal use of this technology. To do that we need, as radiologists and physicists, to change the way we've thought about CT," said John M. Boone, PhD, professor at the Departments of Radiology and Biomedical Engineering at the University of California, Davis. Boone is also the chairman of the Committee on Patient Dose and Image Quality in CT for the International Commission on Radiologicial Units and Measurement.

There are several ways we can address the capabilities of new CT scanners, Boone said. One problem with the new technology is that non-radiology physicians may look at the images and think they can read them. "It's a little about protecting our turf," he said. It's also about embracing the technology, minimizing CT risk, and monitoring CT utilization.

Radiation dose is one way to monitor CT use. Although geometric dose efficiency has improved, 60 million scans will be performed this year. We need to optimize radiation dose by adjusting to accommodate the dimensions of the patient, he said.

Boone also recommends that institutions have a "CT doctor"-someone who can champion the technology and serve as a good resource. Users should know the radiation risk and know the difference between risk and dose. Risk includes the absorbed dose, patient age and health status, and the part of the body scanned.

The technology is not excessive, Boone said, "but if you embrace and adapt it, we can all do better for patient care." Making optimal use of this technology includes considering and adapting infrastructure needs, such as bandwidth of PACS, storage requirements, and lead shielding in the walls. "All these things need to be addressed simultaneously or you're not going to be able to use this technology to its fullest capabilities."