Lifeng Yu PhD, Presenter: Nothing to Disclose

Joshua Grimes PhD, Abstract Co-Author: Nothing to Disclose

Shuai Leng PhD, Abstract Co-Author: Nothing to Disclose

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

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

The purpose of this work was to determine the dose efficiency of virtual non-contrast (VNC) imaging from various kV combinations in dual-energy (DE) CT if the VNC were to replace the true non-contrast (TNC) scan, and to select the optimal kV combination for different patient attenuation levels.

VNC image quality is fundamentally limited by the noise magnification in the material decomposition, which is determined by both the spectrum separation and the noise in the original low- and high-kV images. For the commercially available 5 DE kV combinations: 70/150Sn (“Sn”: an added tin filter), 80/150Sn, 90/150Sn, 100/150Sn, and 80/140, we derived the lowest noise on the VNC image that is achievable when the optimal dose fractions at low- and high-kV scans were used, given a fixed total radiation output. The lowest VNC noise was compared with the noise in optimally mixed images to calculate the percent of dose reduction at each kV combination if VNC were to replace the TNC scan. The effect of patient attenuation was studied by scanning a series of semi-anthropomorphic phantoms with lateral width of 25, 30, 35, 40, 45, and 50 cm at each of the 5 kV combinations. To determine the optimal DE kV combination used for each phantom size, the noise power spectrum (NPS) at each lower kV was measured and compared with a reference single energy 120 kV, and the artifacts due to photon starvation, if any, were analyzed. Finally, the dose reduction by VNC at each kV combination for the applicable phantom sizes was determined.

The optimal DE kV combination was determined for each phantom size (25 cm: 70/Sn150, 30 cm: 80/Sn150, 35 cm: 80/Sn150, 40 cm: 90/Sn150, 45 cm: 100/Sn150, 50 cm: none). The dose reduction achievable by VNC increases with more separation of the spectra between low- and high-kV x-ray beams. For a 25 cm phantom that all kV are applicable, the dose reductions were 39%, 35%, 30%, 27%, and 10% for 70/150Sn, 80/150Sn, 90/150Sn, 100/150Sn, and 80/140, respectively.

With the optimal DE kV combination, radiation dose reduction achievable by using VNC to eliminate the true non-contrast scan increases from 10% to up to 39% for adult patients.

Optimal DE kV combination was determined for different patient attenuation levels. The amount of dose reduction achievable by VNC imaging increases from 10% to up to 39% for adult patients when using these optimal DE kV combinations.

Yu, L, Grimes, J, Leng, S, Fletcher, J, McCollough, C, Dose Efficiency of Virtual Non-contrast Imaging from Optimal kV Combination in Dual-energy CT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14013902.html