Cerebral CT Angiography: Comparative Study Of The Difference Image Quality And Radiation Dose Using Various Tube Voltage

Objectives：1To explore the affect of tube voltage for image quality andradiation dose in cerebral CT angiography.2Comparative evaluation the feasibility of low tube voltage scan protocol incerebral CT angiography.Materials and Methods： Prospective method was used in this study. Allexaminations were performed with a128-section CT scanner. BetweenFebruary and May2013, One hundred and twenty consecutive patients (60female,60male; mean age44.1±2.8years; range40-50years) checked inSiChuan Province People Hospital radiology department. All patients weredivided into A,B,C,D four groups according to the check sequence. Eachgroup has30persons (15male,15female). The tube voltage of A,B,C,D wererespectively defined as80KV,100KV,120KV,140KV, others scanningparameters remained constant. Intravascular attenuation values, contrast-to-noise ratio(CNR) and signal-to-noise ratio(SNR), imaging noise, backgroundsignal and radiation dose measurements were performed at two sides. Twoblinded radiologist independently evaluated the subjective image quality on a 4-point scale using volume rendering (VR) and multi-planar reconstructed（MPR), maximum intensity projection(MIP).Results:1All the120patients accomplished the inspection successfully.There was no statistical significance in head circumference, age and scancoverage length among the4groups.2Image quality2.1Objective image quality2.1.1The intravascular attenuation intracranial artery and superior sagittalsinus among the4groups A,B,C,D are as the followings:393.2±48.5HU,286.1±32.3HU,239.1±29.1HU,204.2±27.5HU and228.2±47.8,165.0±52.7,149.6±51.9,125.1±23.3HU. The two index of group A rise about37.4%,64.4%,92.6%and38.5%,53.9%,82.4%than B,C,D. The comparison of thedifferences among each group have remarkable statistical significance. Therewas substantially significant negative correlation between the tube voltageand intravascular attenuation values （correlation coefficient： r=-0.896，P=0.000).2.1.2Imaging noise of the4groups are as then followings:13.0±2.1HU,10.0±1.4HU,8.0±0.7HU,6.4±0.6HU. Group A rise about30.0%,62.5%,100.3%than group B,C,D. The comparison of the differences between eachtwo groups have remarkable statistical significance.There was a apparently significant negative correlation between the tube voltage and image noise（correlation coefficient：r=-0.920，P=0.000).2.1.3The SNR and CNR of the4groups are as the followings:30.2±5.1,28.5±4.5,29.0±4.3,31.9±4.2and23.4±4.2,20.2±3.3,19.8±4.0,18.9±4.5.SNR did not differ obviously among4groups, the differences among groupshave no statistical significance. However, the four group of CNR increasedalong with the reducing of tube voltage, which showed significant differencestowards group B,C,D. There was no significant correlation between the tubevoltage and SNR（correlation coefficient：r=-0.143，P=0.259),but slightlynegative correlation with CNR(correlation coefficient：r=-0.369，P=0.000)2.2Subjective image qualityThe mean VR scoring of the4groups are as the followings:3.6±0.6,3.5±0.5,3.4±0.5,3.3±0.5and the rates image that quality achieve good are respectivelyabout96.7%,96.7%,96.7%,86.7%. The mean MIP/MPR scoring of the4groups are3.4±0.6,3.4±0.5,3.5±0.3,3.6±0.6， the rate that image qualityachieve good are about93.3%,100%,100%,100%. The differences amongthe4groups regarding to the VR and MIP/MPR scoring have no statisticalsignificance. Meanwhile, as the tube voltage decreasing the VR scoring hasslightly rise and the MIP/MPR scoring mild drop. There was no significantcorrelation among4groups with regard to the VR and MIP/MPR scoring （correlation coefficient：r=-0.196, P=0.325and r=0.175, P=0.698).3Radiation DoseThere is obvious decline of each index of radiation dose with thereduction of tube voltage.The differences of each two compared groupshave statistical significance. The CTDIvol and DLP,ED of the4groupsare as the followings:19.6±4.6mGy,28.4±4.5mGy,39.8±4.2mGy,50.0±5.9mGy and163.5±19.2mGy*cm,352.2±41.8mGy*cm,519.7±40.3mGy*cm,703.3±35.6mGy*cm and0.34±0.04mSv,0.68±0.09mSv,1.10±0.08mSv,1.50±0.10mSv. The three index of group A decrease about31.1%,50.8%,61.7%and53.5%,68.9%,76.8%and50%,69.1%,77.3%comparingwith group B,C,D. As the low tube voltage the radiation dose has signi-ficant drop. There was a substantially significant positive correlationbetween the tube voltage and radiation dose.（correlation coefficient：r=0.912，P=0.000; r=0.933，P=0.000；r=0.937，P=0.000）。Conclusion:Tube voltage changes will affect image quality of the various factors incerebral CT angiography. The Reduction of tube voltage results in higherintravascular attenuation values and imaging noise and CNR. However, theSNR, background signal and subjective image scoring have no obviouschanges among groups. Reducing tube voltage can reduce radiation dose obviously. So reasonably lower tube voltage can reduce radiation dose to themaximum level without obviously degrading image quality. Tube voltage of80kV can be used in cerebral CT angiography, as when Tube voltage is80KVbrain CTA image quality can meet the clinical requirements.