Xiaochao Guo, Presenter: Nothing to Disclose

Yongwei Zhao, Abstract Co-Author: Nothing to Disclose

Jian-Xing Qiu MD, Abstract Co-Author: Nothing to Disclose

JIANXIN LIU, Abstract Co-Author: Nothing to Disclose

Xiaoying Wang MD, Abstract Co-Author: Nothing to Disclose

To study whether change of scan field of view (FOV) has effect on measurement of CT value and material decomposition when using gemstone spectral imaging (GSI).

Discovery CT750HD (GE Healthcare) was used in this study. A set of 17 test tubes containing water-iodine mixed solution with different known iodine concentrations were scanned with GSI mode. The iodine concentrations of these test tubes were 0 (water only), 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0 and 20.0 mgI/ml, respectively. The scans were performed two times for each test tube by using large and medium scan FOV, respectively (Group A: Large FOV; Group B: Medium FOV). Other scanning parameters were identical as follows: collimation thickness of 0.625 mm, detector width of 40 mm, rotation speed of 0.6 second, and helical pitch of 0.984. Aw4.5 workstation was used to measure CT value, water and iodine concentrations in each test tube. The CT value was measured on conventional polychromatic images obtained at 140 kVp. The water and iodine concentrations were measured by using a circular region of interest that covered 80% of the test tube cross section on the water- and iodine-based material decomposition images. Paired sample t-test was used to analysis the variance of CT value, water and iodine concentrations between two groups.  

The measured iodine concentration was highly consistent with actual concentration (rA = 0.9995, rB = 0.9996, P = 0.000). Mean measured CT value were 86.86 ± 131.78 HU for group A versus 106.89 ± 141.51 HU for group B, respectively. Mean measured water density were 977.14 ± 10.54 mg/ml for group A versus 994.39 ± 12.35 mg/ml for group B, respectively. The measured CT value and water density were statistically different between the two groups (P < 0.01). There was no statistical difference on measured iodine concentration between the two groups (3.91 ± 5.37 mg/ml for group A; 3.82 ± 5.59 mg/ml for group B, P = 0.19).

GSI-based material decomposition can reflect the content of iodine in different concentrations and can be used for quantitative analysis. Changing scan FOV will affect the measurement of CT value, but has no effect on quantification of iodine concentration.

GSI-based material decomposition is an important approach for tissue quantitative analysis. The quantification may be more reliable and stable than measurement of CT value on conventional CT scan.

Guo, X, Zhao, Y, Qiu, J, LIU, J, Wang, X, Effect of Scan Field of View on Measurement of CT Value and Material Decomposition When Using Fast kVp Switching Dual-Energy CT: A Phantom Study.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12043887.html