| PrefaceSince Naidich first introduced low - dose CT technique in the early 1990s, it has been developed for past 10 years. Improvements in computed tomographic technology and thoracic imaging have paralleled advances in lung cancer biology. People have received low - dose spiral CT screening for high detection rate of lung cancer in its early stages. And the radiation dose ranged from 1/10 to 1/6 as compared with conventional CT. The present study investigated the low - dose technique focused on decreasing mAs, but for pitch and kilovolt had not received much attention in the recent literatures.Airway diseases in thorax were also suited for low - dose examination. By far there was no literature was seen about airway reconstruction with low - dose multi - slice spiral CT. The purpose of this study was to discuss the feasibility of low - dose MSCT tracheobronchography.ObjectiveFor the aim of lowering MSCT radiation dose, we investigate the influence on the image quality by adjusting scanning parameters. To determine whether low - dose CT can provide sufficient information compared with standard dose CT in tracheobronchography.Materials and MethodsTesting animalsEight healthy dogs offered from test animal center in China Medical University, which weight ranged from 11 to 13Kg. After being anaesthetized, every dog was fixed on a CT scanner protocol on supine position to be performed seven series of scanning. Immediately after scanning, dogs were euthanized, and the airways were harvested, counted, mounted, and photographed.Imaging ProtocolThe experiment was performed on Mx8000 spiral CT system ( Philips Co. ). According to the scanning parameters that can affect the CT dose, 8 dogs, each performed 7 series of scanning separately: mill ampere setting ( 150, 100, 50, 20 mAs ) , section thickness (6.5, 3.2 mm), kilovolt setting (90,120KVp) and pitch (1.25, 1.75 ). We defined the standard dose group as the following parameters: 3.2 mm section thickness, 150 mAs, 120KVp and pitch 1.25. Scanning extended from the lung apices to below the costophrenic angles. Images were reconstructed with a high - spatial - frequency algorithm. All CT scans were obtained with window settings appropriate for lung parenchyma ( window width 1,500 HU; level - 600 HU ) and mediastinum (window width 300 HU; level 10 HU). All images were transferred to sgiO2 workstation. The data was used to create multi -planar reconstruction ( MPR) , shadow surface display ( SSD) and voyager bronchoscope ( VB) images on workstation. Images were obtained at four sites for each serial. Each site was kept constant for the various imaging parameters.Image AnalysisTwo blinded, experienced chest radiologists who analyzed all of the images separately reviewed the CT images, and final decisions were determined by consensus, (a) Qualitative analysis - image quality evaluation: the quality of axial images and tracheobronchography images were evaluated by a five - point scoring system: 1 : very poor, 2: poor, 3: fair, 4; good, 5: excellent. The images were graded separately according to artifacts , sharpness of bronchi wall and the detail of the tracheal rings , which came from MPR , SSD and VB reconstruction image , as compared with those of standard dose group. (b) Count the numbers of 0-4 stage bronchi: which were compared with standard dose group, (c) Quantitative analysis -the bronchi inner diameters were measured at four sites (2cm above the carina, left main bronchi, left upper lobar bronchi and segmental bronchi) of all series of tracheobronchography images on the screen of the workstation , compared with the true diameters of bronchi of dogs measured with a vernier caliper.Statistical AnalysisScores were presented as means +SDs , comparison of standard dose group was performed using pair rank statistics. Measurements compared between low - dose groups and standard dose groups were assessed with a paired - sample Student t test. All statistical tests were two tailed, and a probability level of less than 0. 05 was...
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