Jingmin Liao, Abstract Co-Author: Nothing to Disclose

Fajin Lv MD, Presenter: Nothing to Disclose

Ken Chen, Abstract Co-Author: Nothing to Disclose

Yun Shen PhD, Abstract Co-Author: Employee, General Electric Company

Axial subtraction CTA is a useful technique for displaying cerebral and carotid artery without bony structure, but the reformatted 3D image isn't good enough. Helical subtraction CTA could improve the 3D image quality but it depends on the match of two scans. The purpose of this study is to confirm the synchronous condition of helical subtraction CTA.

A skull phantom underwent 20 helical subtraction examinations with 64-row MDCT (GE LightSpeed VCT). The scan protocol was: rotation speed 0.4s, 120kV, 100mA, 64×0.625mm and pitch 0.531:1. Each examination included two scans at the same region, which represented non-enhanced and contrast-enhanced scan in actual CTA. All examinations were divided into 2 groups: synchronous group (exposure time of the 1st scan + delay time of the 2nd scan = integral times of rotation speed) and non-synchronous group (not accordance with above synchronous condition). For each group, the difference of tube start angle between two scans was recorded. The mean and standard deviation (SD) of subtraction image (the 2nd scan subtracts the 1st scan) were calculated and statistical test was performed to compare the subtraction image quality between two groups. Another 5 axial subtraction examinations were performed to compare with synchronous and non-synchronous helical subtraction.

For synchronous and non-synchronous group, the average difference of tube start angle were 4.41 and 180.77 degrees, the mean and SD of subtraction image were 0.08, 10.63 and 0.54, 17.74, respectively. All above differences were statistically significant (p<0.05). A significant positive correlation existed between mean, SD and the difference of tube start angle (rmean=0.935, rSD=0.841). The mean and SD of axial subtraction were 0.04 and 11.65, but no significant statistical difference with synchronous helical subtraction (p>0.05).

Match of tube start angle is an important synchronous condition because of the difference of helical data set. Optimizing scan delay time could meet this synchronous condition and improve the image quality of helical subtraction CTA.

Synchronous helical subtraction CTA has the potential in displaying cerebral and carotid artery.

Liao, J, Lv, F, Chen, K, Shen, Y, Synchronous Helical Subtraction 64-Row MDCT Angiography.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6006380.html