| Part I Effect of CT Tube Voltage and Tube Current on Image Quality and Radiation DoseObjective:this study intends to scan the body model and the iodine-solutions with different concentration by multi-parameter CT scanning protocal with different tube voltages and different tube currents,and quantitatively measured the changing tendency of CT values the materials with the different scanning conditions,to evaluate the influence of body image quality and radiation with different tube voltage and tube current.Methods: the experiment will be divided into two steps.NO.1.A total of 12 groups of different scan parameters groups(Ⅰ-Ⅱ): 50 m As + 90 KV,90 KV + 100 m As,90 KV+ 150 m As,90 KV + 200 m As,120 KV + 50 m As,120 KV + 100 m As,100 KV + 150 m As,120 KV,200 m As,140 KV + 50 m As,140 KV + 100 m As,140 KV,150 m As,140 KV + 200 m As to continuous scan of the body model by liver and spleen area.The routine scan parameters were used for the sequence: the FOV is 350.0 mm,rotating time of 0.75 s,3.00 mm of the thickness,with a thick layer of reconstruction interval is 3.00 mm,standard reconstruction algorithm,pitch of 0.94,and the window width and window level were to 350 HU and 50 HU.The image was transmitted to the PACS workstation for image observation and measurement after the scanning.Three consecutive layers of portal vein bifurcation were measured on the right posterior segment of the liver,the posterior portion of the spleen,and the paravertebral soft tissue region.The CT values of the fixed regions of interest(ROI=401 mm2)was measured,and the specific position of Z axis on the examination bed were recorded.The method of copying and pasting the ROI is used to ensure that the position of the ROI in the measured plane and layer is fixed.Measure and record the CT values of the liver and spleen in the region of interest as CTliver and CTpleen.Measure the noise of paravertebral soft tissue as background noise,as SD.According to SNR=CT liver/SD,contrast noise ratio CNR=(CT liver-CT spleen)/SD,SNR and CNR were calculated as objective evaluation criteria for evaluating image quality.Two doctors with rich experience in medical imaging diagnosis using the 5-point method to blindly evaluate the image as subjective evaluation criteria of the image.SPSS19.0 was used for statistical analysis of the data.The difference was considered statistically significant With P<0.05,.2.Mixed the original iodine solution and physiological saline with the ratio of 1:1,1:2,1:3 to 1:15,and were respectively packed in EP tube with a volume of 2 ml.To scan the prepared high-low density iodine-containing solution(No.1-15),the same tube current and different tube voltage parameters were scanned.The specific scanning parameters were as follows: 90KV+50m As,120KV+50m As,and 140KV+50m As.The images were transmitted to the PACS workstation for image post-processing and measurement.Measure the CT value of the continuous three-layer non-gas layer solution,take the average of the three as the final CT value of the solution,and perform statistical analysis and parallel regression analysis to find out the trend of the quantified solution CT value with the tube voltages.Results:1.With the same tube voltage,there was no significant difference in CT value of the liver with the increase of tube current,but under the same tube current conditions,the CT value of liver gradually decreased with the increase of tube voltage.2.Under the same tube voltage condition,as the tube current increases,the liver image noise gradually decreases.3.Under the same tube voltage condition,the image signal-to-noise ratio gradually increases with the increase of tube current.Under the same tube current condition,the signal-to-noise ratio of the image increases as the tube voltage increases as well.4.Under the same tube voltage condition,as the tube current keeps increasing,the image contrast noise ratio gradually increases.When the tube current is constant,the contrast-to-noise ratio of the image increases as the tube voltage increases gradually;at the tube current of 150 m As,the CNR is highest at 120 KV,and the difference is statistically significant under different tube voltage conditions(P<0.05).When the tube current was 200 m As,the CNR was the highest under 120 KV condition,and there was no significant difference between different tube voltage conditions(P>0.05).5.As the voltage increases,the slope of the image decreases and the contrast of the subject decreases.The smaller the voltage,the greater the slope of the image and the higher the density contrast between the subjects.Conclusions: 1.CT tube voltage can affect the CT value of the subject,the CT values of the subject were decreased with the tube voltage increasing,and the tube current has no obvious effect on the CT value of the subject.2.The increase of the tube current or tube voltage can reduce the image noise.3.Increase tube current and tube voltage may increase SNRs of the images.4.The increase of tube voltage and tube current can improve the contrast noise ratios of CT images.5.As the tube voltages increases,the slopes of the CT-density curve decreasing,the subject’s density contrast decreases.Otherwise the density contrast between the subjects might increase with the tube voltages decreasing.PartⅡ The value of the MSCT angiography for atypical hemorrhagic cerebrovascular diseasesObjective: To evaluate diagnostic value of multi-slice spiral CT(MSCT)angiography(Dynamic image post-processing? Again image post-processing?)in the diagnosis of atypical cerebrovascular hemorrhagic diseases.Methods:56 cases diagnosed with intracranial hemorrhage that recieved CT cerebral angiography(CTA)and diagnosed with no obvious vascular diseases by the general images post-processing were collected from January 2008 to march 2016.The images were post-processed again via changing threshold and angles of the VR、MIP to explore the potential causes of intracranial hemorrhage.The aquired data were compared to the Digital Subtraction Angiography(DSA)results and surgical exploration.Chi-square test was used for statistical analyses.A value of p<0.05 was considered to be statistically significant.Results:The further images post-processing discovered vascular hemorrhagic diseases in 51 cases,including 20 cases of intracerebral aneurysm,25 cases of arteriovenous malformation,4 cases of venous malformation and 2 cases of arteriovenous malformation with aneurysm.DSA and surgical exploration,by contrast,diagnosed vascular hemorrhagic diseases in 48 cases,including 19 cases of intracerebral aneurysm,24 cases of arteriovenous malformation,3 cases of venous malformation,1 cases of arteriovenous malformation with aneurysm,and 1 case of venous fistula.The diagnosis differences on cerebral vascular hemorrhagic diseases between CTA images post-processing again and DSA results or surgical exploration had no statistical significance(χ2=0.82,p>0.05).Conclusions:Dynamic image post-processing can significantly improve the relevance ratio of atypical cerebral vascular hemorrhagic diseases,reduce misdiagnosis and avoid repeating examinations.It’s of great value to be used in clinical practice for timely and efficient treatment,as well as reducing the economic burden for patients. |
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