Yoshitake Yamada, Presenter: Nothing to Disclose

Masahiro Jinzaki MD, Abstract Co-Author: Nothing to Disclose

Yutaka Tanami MD, Abstract Co-Author: Nothing to Disclose

Kazuhiro Matsumoto MD, Abstract Co-Author: Nothing to Disclose

Kiyotaka Nakajima, Abstract Co-Author: Nothing to Disclose

Akihisa Yamazaki RT, Abstract Co-Author: Nothing to Disclose

Koichi Sugisawa, Abstract Co-Author: Nothing to Disclose

Yasuhiro Imai MS, Abstract Co-Author: Employee, General Electric Company

Kosuke Sasaki MS, Abstract Co-Author: Employee, General Electric Company

Sachio Kuribayashi MD, Abstract Co-Author: Research grant, General Electric Company

The purpose of this study was to assess the relationship between CT value (HU) in true non-contrast CT image (TNC) and water-equivalent density value (mg/cc) in virtual non-contrast CT image (VNC) derived from spectral imaging with fast kVp switching.

Twelve patients with liver metastases underwent both non-contrast scan at 120kVp and enhanced scan at spectral imaging with fast kVp switching (80kVp and 140kVp) on Discovery CT750 HD (GE Healthcare, WI). We used same helical pitch, detector collimation and CTDIvol for both scans (1.375, 0.625mm, 12.7mGy). VNC was reconstructed from enhanced spectral imaging (water-equivalent density image by cancelling iodine content with material decomposition method). CT value in TNC and water density value in VNC were measured by placing region of interest (ROI) on air, liver, spleen, pancreas, gallbladder, and metastatic lesion of liver. CT value in TNC and water density value were compared using R-square of linear regression. The difference between CT value in TNC and converted CT value in VNC were evaluated with the Student’s t-test.

The R-square of linear regression was excellent (1.000+/-0.01) between the measured value of VNC and TNC excluding the value of fat. The conversion equation of density value to CT value which obtained from linear regression was “converted CT value=1.02 x density value – 995.6”. There was no significant difference between CT value of TNC and converted CT value of VNC in air, liver, spleen, pancreas, gallbladder and metastatic lesion of liver (-993.6 +/-2.9 and -993.5+/-3.9 in air, 65.3+/-5.3 and 63.2+/-6.7 in liver, 51.4+/-6.8 and 51.6+/-5.9 in spleen, 43.7+/-8.9 and 41.9+/-10.9 in pancreas, 17.2+/-9.1 and 22.9+/-23.0 in gallbladder, 35.7+/-7.6 and 40.3+/-9.2 in metastatic lesion of liver, respectively).

Virtual non-contrast images derived from enhanced spectral imaging with fast kVp switching are equivalent to true non-contrast images. Virtual non-contrast images could be used for the detection of liver metastases as well as true non-contrast CT.

Virtual non-contrast image derived from spectral imaging with fast kVp switching has a potential to eliminate true non-contrast image acquisition, thus reducing radiation dose.

Yamada, Y, Jinzaki, M, Tanami, Y, Matsumoto, K, Nakajima, K, Yamazaki, A, Sugisawa, K, Imai, Y, Sasaki, K, Kuribayashi, S, Assessment of Density Value in Virtual Non-contrast CT Using Spectral Imaging with Fast kVp Switching in Patients with Liver Metastases.  Radiological Society of North America 2010 Scientific Assembly and Annual Meeting, November 28 - December 3, 2010 ,Chicago IL. http://archive.rsna.org/2010/9013788.html