Mammography shifts toward spectral imaging

X-ray imaging has provided important diagnostic information for clinical applications for almost a century. The sight of a medical doctor holding up a black and- white radiograph against the light is common in TV programs and films.

It is well known that variations in x-ray attenuation create different gray-scale levels that reveal detailed structural information with high spatial resolution. This remains true so long as long as the object's components have differing x-ray absorption properties.

X-rays have a spectrum of wavelengths that correspond to different energies and different colors, just as visible light does. Colors in visible light can help us to detect details in our environment. The same color information from x-rays might be able to help improve diagnostic imaging. The only problem is that detector technology has been unable to resolve the different colors of the x-ray spectrum.

The detection of color requires that each x-ray photon be counted and processed individually and its energy measured (Figure 1). High-speed x-ray counting is now possible, thanks to developments in CT detector technology. The first color CT images were displayed at the November 2008 meeting of the Radiological Society of North America (Figure 2).¹

The prospect of color imaging with x-rays has spurred substantial activity among the major medical imaging vendors.^2-4 Additional data provided by color for different elements in an object greatly increases the information content of images.⁵ This could be used to improve visual discrimination between bone and soft tissue and between atherosclerotic plaque and calcifications, or to reduce the required concentration of injected contrast media (Figure 3).^6-8