Study Of Adult Chest Ct Examination Using Low Dose Discovery CT750HD Technique

X-ray bring enormous benefits to mankind, but it also has some harm andimpact on the health of the subjects. Although the advent of spiral CT is amilestone in the history of CT development, subjects received increasingradiation doses more than ever. At present, CT scan has become the mainsource of iatrogenic X-ray radiation. Low dose CT scanning was used for thecensus of chest diseases in foreign countries in recent years. In china,respiratory disease is serious, especially the incidence of lung cancer andchronic bronchitis increased year by year. Because of chest CT examinationis a reliable means of screening for lung disease, it is used increasingly year byyear in the clinical, but the larger X ray radiation are some hazards to the healthof the subjects. The manufacturers try to reduce the X-ray radiation dose bydifferent methods. Most of them are directly change the scanning conditions toreduce the dose of X-ray radiation, but this will increase the ratio of imagenoise, resulting in a declining quality of the image. Modern CT scanningtechnology is too complex, up to a dozen or even dozens of types of scanningconditions available for selecting, how to develop a simple scanning way hasbecome a competing research topic to the various manufacturers. In thisstudy,72patients were randomly selected for chest scanning by usingDiscovery CT750HD produced by American GE company. With its uniqueASIR technology, X-ray radiation dose was greatly reduced and clear imagecould also be achieved.Objective：To observe the effect of different noise index and ASIR valueto X ray radiation dose and image quality by setting different noise index andapplying its ASIR low-dose scanning technology during chest scanning by useof GE Discovery CT750HD. Methods：72respiratory outpatients randomly selected were divided intosix groups, which each group has12patients. All subjects were scanned withnoise index setting to13、15、17、19、21and23.Each noise index was matchedwith three ASIR values which are30%、50%and70%. CTDIvol and DLPwere recorded and ED was calculated that0.014times of DLP. The quality ofimage was evaluated by5-point score system which above3is the standard ofdiagnostic requirements. Finally, we statistical analysis the difference of indexsbetween each group.Results：SD value reduced by increasing ASIR value with the same noiseindex. When noise index was21and23,the noise of image was too loud toobserve the image which the score was less than3points. The image of theother four groups with three ASIR values can meet the requirements. Withincreasing noise index, SD value increased, but ED value reduced and thequality of image declined. Although ED value had no significant differencewhen NI value was17.0and19.0, the score of image was higher with17.0NIvalue. So the best parameters for chest scanning is that NI value is17.0andASIR value is50%.Conclusion：X-ray radiation dose was greatly reduced and clear image canalso be achieved by using ASIR technique of Discovery CT750HD. radiationdose was reduced and SD value increased by increasing noise index with thesame ASIR value, but the quality of image declined. When noise index was21and23,the quality of image was too poor to observe. The best parameters forchest scanning is that noise index and ASIR%value are set to17.0and50%respectively, while the quality of image is the best and radiation dose is low.