CT imaging provides profoundly valuable anatomic information to radiologists and physicians. It not only provides 3D information about the size and shape of lesions, but also a rough fourth dimension of information in the form of grayscale Hounsfield Units (HU).
Now, with the use of dual-energy CT (DECT), radiologists can mine even more information from this fourth dimension by simply obtaining data at both a high- and low-energy X-ray spectrum.
Discussing DECT during a Tuesday session, Benjamin Yeh, MD, a radiologist at the University of California San Francisco (UCSF) Medical Center, noted that every atom on the periodic table blocks X-rays at high and low energy slightly differently.
"With DECT, structures with different atomic make-up, such as iodine, calcium and dense blood or metal, are vividly differentiated," he said. "Even when they have identical HU on a regular CT, with DECT different materials appear like different colors."
Benefits of Everyday DECT
According to Dr. Yeh, this "color vision" positions DECT as a potentially transformative technology. "In our daily practice, we encounter ambiguous lesions at CT where we cannot tell whether a density is enhancing, calcified or hemorrhagic because each of those may have similar HU values," he said. "DECT allows for confident and definitive diagnoses by showing us what the underlying atoms are."
DECT also affects the way contrast material is used. For example, with simulated low-energy images derived from DECT, the HU values of contrast enhancement may be doubled or tripled so imagers can better see hypovascular or hypervascular lesions.
"Alternatively, we get diagnostic-quality images with lower contrast material doses, as is often needed in patients with renal insufficiency or poor IV access," Dr. Yeh added. "Conversely, DECT can simulate what the scan would look like if the IV contrast was not given at all."
Dr. Yeh also pointed out that DECT resolves many artifacts, including those from metal, motion and beam hardening. Furthermore, DECT can reveal "invisible" lesions like hard-to-see tumors, CT-isodense gallstones and bone contusions by revealing differences in atomic makeup between the lesion and similar-HU background tissue or fluid.
DECT Shows Promise for Providing More Data
As DECT becomes more widely available on premium and mid-level CT scanners, radiologists are learning to find intuitive ways to display and interpret the images.
"For many radiologists, handling the large number of possible DECT image reconstructions, which can be unwieldy and confusing, was a hurdle to increased usage," Dr. Yeh said. "Smarter systems now allow radiologists to rapidly switch between DECT reconstructions without having to sort through piles of image series."
Updates have also made DECT scanning easier to use, with some machines not even requiring the technologists to turn on DECT mode anymore.
More profoundly, experimental DECT machines promise to provide data on not just two, but multiple energy spectra, resulting in even better interrogation of atomic makeup.
"Perhaps most exciting are the new contrast agents with vivid 'colorsʼ that are already in clinical trials," Dr. Yeh said. "Preliminary results suggest that such multi-color contrast, multi-energy CT images allow novice readers to outperform experts using conventional CT in many diagnostic tasks – and may better enable artificial intelligence to interpret CT images."