The Chest Conventional Multi-slice Spiral CT Examination: Study Of The Optimal Parameter

The image quality of source image by multi-slice spiral CT (MSCT)was closely related with scanning parameters choosing and matching.According to literature reportes and practices, the optimal scanningparameters with 2.0-3.0mm collimation have been down in chest axialimage and research of postprocessing image. Image quality for 16 ormore-slice spiral CT scanning with 2.0 mm or less slice thickness has beenobviously improved because of increasing the number of Z row and channelof space sizes. At present, 64 slices CT scanner is the most advanted becauseits smallest slice thickness was 0.5mmth and conventional scanning couldget effect of isotopinsm scanning. So it can gather the most perfect sourceimage and postprocessing image. But such scanning parameters didn't applyin chest conventional 4-slice spiral CT scanner because of the restriction ofits frame of detector and scanning speed, and to consider of patient exposuredosage, examination cost, X-ray tube life and efficiency of work, etc. Theoptimizing patameter usually act as lamellar complementary scan afterconventional scan. In chest conventional scanning with 4-slicespiral CT, the parameters usually were 5.0-10.0 mmth, a pitch of 3.5. Although there were lots of choice and match of the parameters in chestconventional scanning, there were not the optimal parameters reported atpresent. In this study, every patient has got twice examination withfollowing two parameters: Group A: 8.0mmth, a pitch of 3.5, 8.0 mmreconstruction slice thickness; Group B: 5.0mmth, a pitch of 6.0, 8.0mmreconstruction slice thickness. We compared the axial images andpostprocessing images between two groups so as to explore the optimalparameter in chest conventional scanning.The results of the present study showed that:1. Axial image quality: lung and mediastinum image quality was better inGroup B than in Group A; blood vessels of hilum of lung image qualitywere better in Group A than in Group B. It was similar between Group Aand Group B on soft tissues and bones of thoracic wall image quality.2. Source image noise contrasting: the noise of Group B was bigger thanGroup A.3. Group B was significantly better than Group A on MPR, SVRthree-dimensional image and virtual bronchoscopy postprocessing image.The results indicate that:1. To compare two chest conventional scaning techniques using thefollowing parameters: 1) scan 1 was performed at 8mmth, a pitch of 3.5, 8mm reconstruction slice thickness, 2) scan 2 was performed at 5mmth,a pitch of 6.0, 8mm reconstruction slice thickness, The scan 2 hadsignificantly advantage than scan 1 on getting high quality image of lungmarkings and mediastinum, degrading motion artifact, increasing timeresolution, and outweighed on reducing exposure dosage and prolongingX-ray tube life. So it had higher value of clinical application in the chestconventional multi-slice spiral CT examination.2. Small slice thickness matching with large pitch were significantlysuperior to large slice thickness matching with small pitch onpostprocessing image quality.3. The postprocessing image quality was slice thickness dependent. Pitchproduced a little effect on image quality to some extend.