Lifeng Yu PhD, Presenter: Nothing to Disclose

Xin Liu PhD, Abstract Co-Author: Nothing to Disclose

Hua Li PhD, Abstract Co-Author: Nothing to Disclose

Christian Eusemann PhD, Abstract Co-Author: Employee, Siemens AG

Joel Garland Fletcher MD, Abstract Co-Author: Research grant, Siemens AG

Cynthia H. McCollough PhD, Abstract Co-Author: Research grant, Siemens AG

To evaluate the image quality of monochromatic images synthesized from dual-energy CT in comparison with conventional polychromatic single-energy CT for the same radiation dose.

In dual-energy CT, besides the material-specific information, one may also synthesize monochromatic images at different energies, which can be used for diagnosis similar to conventional polychromatic single-energy images. In this work, we assess whether monochromatic images can have an image quality similar to that of polychromatic single-energy images for the same radiation dose. First, we showed analytically that an optimal monochromatic energy exists for either the minimum noise level or the highest contrast to noise ratio (CNR) for a given patient size and dose division between the low- and high-energy scans. Second, we performed an experimental study on a dual-source CT scanner (Definition DS, Siemens) to evaluate the noise and iodine CNR in monochromatic images. A thoracic phantom with three sizes of attenuating ring was used to represent 4 adult sizes. For each phantom size, 3 dose divisions were used in the dual-energy scan. Monochromatic images at 8 energies (40 to 110 keV) were generated for each scan. The phantoms were also scanned at 80, 100, 120, and 140 kV with the same total radiation dose.

Optimal monochromatic energy depended on patient size, dose division, and the image quality metric to be optimized. For minimum noise, the optimal energies were 68, 71, 74, and 80 keV for small, medium, large and xlarge phantoms, respectively. For highest iodine CNR, the optimal energies were 65, 68, 70, 72 keV. With the optimal energy, the noise level was similar to and the CNR was better than that in a single-energy scan at 120 kV for the same radiation dose. Except for the extra-large phantom, the CNRs were significantly lower in monochromatic images relative to the 80 kV images.

Image quality of monochromatic images synthesized from a dual-energy CT scan was evaluated in comparison with single-energy scans for the same radiation dose. With the optimal monochromatic energy, the noise level was similar to and the CNR was better than that in 120 kV images for the same radiation dose.

With the optimal energy, image-based monochromatic imaging in dual-energy CT can provide image quality comparable to single-energy CT at 120 kV with no increase in patient dose.

Yu, L, Liu, X, Li, H, Eusemann, C, Fletcher, J, McCollough, C, Monochromatic Imaging in Dual Energy CT: Optimal Energy and Image Quality.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8009121.html