Study On The Optimized Scanning Conditions Of Cerebral CT Angiography Based On The Angiographic CT Head Phantom And The Assessment Of It's Diagnostic Value

Part One Study on the optimized scanning conditions of cerebral CT angiography based on the angiographic CT head phantomObjectiveTo study the impacts of different tube voltage and different noise index(NI)guiding automatic tube current modulation technique on the image quality and radiation dose in cerebrovascular imaging and determine the optimal scanning condition.MethodsPH3 angiographic CT head phantom was used for head CTA examination.Scanning protocols:All the scanning programs were divided into three groups according to the different tube voltages of 80,100 and 120 kV.Each group has 10 kinds of tube current parameters of fixed tube current(300 mA,400 mA)and NI of 3-10 guiding automatic tube current.There are 30 different parameter combinations of tube voltage and tube current.The radiation dose[(CT dose index volume(CTDIvol),dose length product(DLP)and effective dose(ED)],objective indicators of images(CT value of the transverse blood vessels and its noise,CT value of brain tissue and its noise,signal-to-noise ratio,contrast-to-noise ratio)and the subjective scores of the five cerebrovascular segments were recorded.Differences of CT value of the transverse blood vessels and its noise,CT value of brain tissue and its noise,signal-to-noise ratio and contrast-to-noise ratio between different tube voltages and tube currents were analyzed by One-Way ANOVA.ResultsWhen the tube voltage was kept constant,CTDIvol,DLP and ED were all dropped while NI was increased from 3 to 10.Compared with group(120 kV,300 mA),CTDIvol of group(100 kV,300 mA)reduced 35.32%,CTDIvol of group(100 kV,NI=6)reduced 46.72%.Compared with group(100 kV,300 mA),CTDIvol of group(100 kV,NI=6)reduced 17.61%.When the tube voltage was kept constant,CT values of blood vessel and brain tissue had no statistical difference(p>0.05),while blood vessel noise,noise of brain,SNR and CNR showed statistical difference(p<0.05)at different tube current parameters.When tube current and NI were not changed while tube voltage was varied,all objective indicators above exhibited statistical difference(p<0.05).Compared with group(120 kV,300 mA),SNR and CNR of group(100 kV,NI=6)were enhanced by 6.31%and 7.18%.Changes of tube voltage,NI and tube current had no effect on the subjective scores of first and second grade vessel but greater impact on the fourth and fifth grade vessel.ConclusionIn the head CTA examination,use of NI 6 guiding automatic tube current combined with low tube voltage(100 kV)dose not only can get better image quality but also radiation dose were significantly lower.Part Two Evaluation of diagnostic value of cerebral CTA scanning using noise index guiding automatic tube current modulation in combination with low tube voltageObjectiveTo evaluate the diagnostic value of cerebral CT angiography using the optimized scanning parameters which is NI 6 guiding automatic tube current combined with low tube voltage(100 kV).MethodsBetween April 2018 and July 2018,a total of 60 patients who were emergency visits and requiring cerebral CT angiography were enrolled in this study.All the patients were given cerebral CTA scanning by using NI 6 guiding automatic tube current combined with low tube voltage(100 kV).After scanning,the raw data were processed by MIP,MPR and VR.The CT dose index volume(CTDIvol),dose length product(DLP)and effective dose(ED)were recorded.Two doctors evaluated the subjective evaluation index of images by four points.Kappa test was used for the consistency check of the results.The diagnosis of CTA were compared with DSA or the surgical results.The diagnose accordance rate was analyzed and the diagnostic value was evaluated.ResultsThe radiation dose of CTA scanning is:CTDIvol:(12.57±2.56)mGy?DLP:(233.74±53.21)(mGy·cm)and ED:(0.49±0.11)mSv.The consistency of subjective evaluation between two doctors is better.The Kappa value was 0.77.The value of the detail display of arterioles was 2.9 while the other evaluating indicators were all above 3 points.The sensitivity,specificity and accuracy of CTA in diagnosis of aneurysms were 94.44%,95.23%and 95.00%,respectively.The sensitivity,specificity and accuracy of CTA in diagnosis of AVM were 100.00%,98.03%and 98.33%,respectively.ConclusionIn the head CTA examination,use of NI 6 guiding automatic tube current combined with low tube voltage(100 kV)dose not only can reduce radiation dose but also can get better image quality and provide reliable,comprehensive and beneficial information for clinician to choose treatment plan.