Optimization And Clinical Application Of 64-Slice Helical CT Scanning Parameters In The Lumbar Spine

ObjectiveTo evaluate the effect of different scanning conditions on image quality of 64-slice helical computed tomography(CT) in the lumbar spine examinations, to explore the possibility of optimal 64-slice helical CT scanning scheme in the lumbar spine and choose the suitable CT scanning parameters. We have also testified this optimal CT scanning scheme by clinical cases.MethodsTo evaluate image quality by adw 4.3 workstations, we have scanned the Catphan 500 phantom by adjusting the 64-slice helical CT(GE Light Speed VCT) scanning parameters. The CT dose phantom has been scanned by the same parameters, and we have measured the entrance dose of phantom by solidose metre and long pole ionization chamber. A scanning parameters optimization project by analyzing the results of the investigation has been proposed. Finally, we testified this optimal CT scanning scheme by clinical cases.ResultsUnder the same mAs, different conditions of scanning had little effect on image quality(P>0.05, large body SFOV and the changing in the focus of X-ray tube were excepted). But the radiation dose was different. Among three kinds of scan field of view, small body, medium body and large body, the radiation dose of small body was minimum.Under the condition of the 0.625mm thickness of layer of scanning, the effective dose at detector 20mm width with axial scan was the lowest. The scan time had little influence on the radiation dose. There were significant differences on image quality among the four reconstruction algorithm:STND, BONE, BONE PLUS and EDGE (P<0.001). The spatial resolution of BONE, BONE PLUS and EDGE algorithm was high, and the noise of BONE algorithm was lower than the last two algorithms. The density resolution of STND algorithm was the highest and the noise of which was the lowerest among them. When tube current was beening reduced, the density resolution declined, the noise increased(P<0.001), the spatial resolution also subsequently declined slightly (but not obviously), and the radiation dose reduced. All of the aspects scored more than 3 points at 80mAs, which could be seen from the doctors' evaluation of clinical testification. All of the cases scored more than 3 points at 40mAs for the bone structure. To compare with the effective dose at 240mAs, the effective dose at 80mAs could be reduced to 33.12% and the effective dose at 40mAs could be reduced to only 16.56%.ConclusionOptimal 64-slice helical CT scanning scheme in the lumbar spine is feasible. The suitable CT scanning parameters are:120kV tube voltage, small body SFOV, axial scanning,20mm detector width, BONE and STND reconstruction algorithm,0.625mm thickness of layer,15cm DFOV. The scanning at 80mAs can meet requirements of the imaging diagnose. To observe bone structure only, the scanning at 40mAs can meet requirements of the imaging diagnose. The radiation dose accepted by the patients reduces obviously.