Experitment Of The Image Noise And Detection Of Lung Nodule With MSCT

Objective: To investigate the characteristic of image noise and imagequality in different tissues with different scanning parameters byanthropomorphic chest phantom. Methods: The anthropomorphicphantom equivalent to human tissue was scanned by16slices spiralscanner (GE BrightSpeed) with different voltage (80,100,120and140kV),tube current (80,100,120,180,240and300mA) and pitch (0.562,0.938,1.375and1.75). One of three scanning parameter was changed and otherscanning parameters were fixed. The CT value and image noise (SD,standard derivation) were recorded and analyzed. Results: There was nostatistical difference between noise of lung in groups of80kV,100kV,120kV,140kV(F=0.966,P＞0.05). There was statisticaldifference between group of80kV and120kV in noise of chest wall, softtissue of spine and aortic, P＜0.05. The noises of different tissues were statistical difference in groups of80mA,100mA,120mA,180mA,240mA,300mA, Lung F=3.28， P＜0.05; soft tissue of spineF=11.89， P＜0.05， aortic F=196.67， P＜0.05, there was statisticaldifference between group of80mA and group of300mA, P＜0.05. Thenoise of lung, soft tissues of chest wall and spine were no statisticaldifference in different groups of pitch (0.562,0.938,1.35and1.75),LungF=0.23,P＞0.05；chest wall F=1.53,P＞0.05；soft tissue of spine F=2.27,P＞0.05.There was statistical difference in the noise of aortic with differentgroups of pitch, F=9.68,P＜0.05. Conclusions: The noises of differenttissues were increasing with the decrease of tube voltage, tube current andincrease of pitch, but the increase of noise in lung is not obviously. The lowdose chest scan reduce radiation dose and keep the image quality withoutobviously increase of noise in lung. Objective: To analyze characteristic of image noise on low dose chestscan and to optimize the scanning parameters by adding noise on raw data to simulate low dose scan. Methods: The image noise of the Chineseanthropomorphic chest phantom（CDP-1C）which scanned with six groupsof noise index was calculated by the image noise addition tool. The data ofchest phantom images was compared the difference between the noiseand the noise index. The noise was artificially introduced to the images of20volunteers using an image space noise addition tool to simulated9groups of low dose scans with tube current of10,30,50,80,100,120,150,180and240mA. The noise of images was recordedand analyzed. Results:There was no statistical difference compared the estimated noise with thenoise index（P>0.05）. The image noise of low dose chest scan wasincreasing with the decrease of tube current. The noise increased significantin groups of10,30and50mA. The noise increased slowly in groups of80-240mA. There was no statistical difference compared the noise of80mA group with that of120mA（P>0.05）. Conclusions: The noise additiontool can be used to evaluate the image noise of low dose chest scan. Thetube current of MSCT may be used as low as80mA to120mA in low dosechest scan to reduce radiation dose and keep the image quality. Objective: To assess detection rate of pulmonary nodules and the theradiation dose of digital tomosynthesis (DTS) and multi-slice CT (MSCT)chest scanning by using the anthropomorphic chest phantom which layingthermoluminescent dosimeters(TLD) and simulated pulmonary nodules.Methods: The organic radiation dose of DTS and MSCT scanning wasmeasured by using the anthropomorphic chest phantom which laying TLDand simulated pulmonary nodules. The organic radiation dose wasconverted into effective dose(ED). Three radiologists of differentexperiences independently reviewed and recorded the density, diameter andposition of pulmonary nodules. The sensitivity of nodule detection by DTSand MSCT were compared by Fisher’s Exact Test and Chi-square test. Thepaired t-test was conducted to analyze the dose levels of DTS and MSCT.Results: The sensitivity of detection nodule of DTS and MSCT were66.7%and91.1%. Statistical significance between the two examinations wasexisted (X2=8.073，P<0.05). The sensitivity of detection-650HU groundglass opacity pulmonary nodule of DTS and MSCT were93.3%and73.3%.There were no significance different between DTS and MSCT (P>0.05).The sensitivity of detection-800HU ground glass opacity nodule and ground glass opacity nodule (d<8mm) of DTS were33.3%and16.7%,which were lower than that of CT(80%and66.7%). The organic radiationdoses of chest were lower than that of CT. Statistical significance betweenDTS and MSCT were existed (Lung t=19.69P＜0.05，Thoracic Vertebralt=30.01P＜0.05，Heart t=16.33P＜0.05，Liver t=5.06P＜0.05，Breastt=9.43P＜0.05，Thyroid gland t=8.05P＜0.05). The ED of the DTS andMSCT were0.65mSv and7.71mSv. The effect dose of DTS is less thanthat of MSCT scanning. Conclusions: There is no difference between theDTS and MSCT in the detection rate of-650HU ground glass opacitynodule. The ground glass opacity nodule（-800HU）and ground glassopacity nodule (d<8mm) detection rate of DTS is obviously lower thanthat of MSCT. The radiation dosage of DTS is8.41percent of the MSCTscanning.