A Study On Influence Factors On Radiation Dose And Image Quality In SPECT/CT Examinations

Research ObjectiveThe objective of this projectwillprovide a basis for reducing the radiation dose for some CT examinees during SPECT/CT examinations,without compromising the image quality,by making a statistical analysis of the radiation dose generated by and the quality of images captured by CT scanning during SPECT/CT examinations.Research MethodsUsing a Symibia T2 SPECT/CT manufactured by Siemens,Catphan600 and Catphan500 CT performance test phantoms were scanned,the volume CT dose index(CTDIvol)under 43 conditions,as well as the quality indexes of scanned images under different conditions,were measured.Existing studies have shown that an effective way to reduce CT radiation dose is to decrease tube voltage and tube current-time product(mAs)and increase pitch during CT scanning.For this reason,this paper mainly analyzes the influence of three factors,i.e.,tube voltage,mAs and pitch,on radiation dose and image quality.(1)SPECT/CT radiation dose indexes:the readings of volume CT dose index(CTDIvol)were analyzed using the Dose Profiler Analyzer software attached to the Black Piranha multifunctional X-ray meter.?The influence of tube voltage on radiation dose:three kinds of tube voltage conditions(80kV,110kV,and 130kV)were adjusted,under the pitch conditions of 0.6,1.2 and 2.0 and the mAs conditions of 100mAs,130mAs,160mAs,190mAs,and 230mAs.The resulting CTDIvoldata were statistically analyzed and the relationship between tube voltage and radiation dose was concluded.?The influence of mAs on radiation dose:five kinds of mAs conditions(100mAs,130mAs,160mAs,190mAs and 230mAs)were adjusted,under the pitch conditions of 0.6,1.2 and 2.0 and the tube voltage conditions of 80kV,110kV and 130kV.The resulting CTDIvoldata were statistically analyzed and the relationship between mAs and radiation dose was concluded.?The influence of pitch on radiation dose:three kinds of pitch conditions(0.6,1.2 and 2.0)were adjusted,under the mAs conditions of 100mAs,130mAs,160mAs,190mAs and 230mAs and the tube voltage conditions of 80kV,110V and 130kV.The resulting CTDIvoldata were statistically analyzed and the relationship between pitch and radiation dose was concluded.(2)SPECT/CT image quality indexes:the image quality of CT scanning during SPECT/CT was determined usingCT performance indexes.CT performance was evaluated by high contrast resolution,low contrast detectability,CT number,uniformity,noise and linearity of CT number.A data analysiswascarriedoutontheimages captured by scanning Catphan500 and Catphan600 phantoms under 43 conditions.The high contrast resolution,low contrast detectability,CT number,uniformity,noise and linearity of CT number of CT scanningunder 43 conditions were obtained.A statistical analysis was wascarried out on the results and the relationship between tube voltage,mAs,pitch and CT image quality was concluded.Results1.The relationship between tube voltage,mAs,pitch and adiation dose.When the pitch was 0.6,1.2 and 2.0,the influence of tube voltge and mAs on CTDIvolwas statistically significant,and CTDIvolincreased linearly with the increase of tube voltage and mAs.A pairwise comparison was made under different pitch conditions:the differences of radiation dosebetween 0.6 and 1.2 groups,0.6 and 2.0 groups,1.2 and 2.0 groups were statistically significant.That is,the greater pitch,the smaller radiation dose.2.The relationship between tube voltage,mAs,pitch and image quality?High contrast resolution43 high contrast resolution images were captured under different scanning conditions.All of the detection results were 7.0Lp/mm,indicating that tube voltage,mAs and pitch had no influence on the high contrast resolution of images.?Low contrast detectabilityUnder the pitch conditions of 0.6,1.2 and 2.0,different tube voltages had a statistical significance on low contrast detectability of images.That is,the greater tube voltage,the better low contrast detectability.When the tube voltage was fixed at 80kV,110kV and 130kV respectively,an ANOVA analysis showed that the influence of mAs and pitch on low contrast detectability was statistically significant.That is,when the tube voltage and pitch were fixed,the greater mAs,the better low contrast detectability.When the tube voltage and pitch were fixed,the smaller pitch,the better low contrast detectability.?CT numberWhen the pitch was fixed at 0.6,1.2 and 2.0 and mAs remained unchanged,the influence of three kinds of tube voltage conditions on CT number was statistically significant.With the increase of tube voltage,the CT number gradually increased,too.When the tube voltage was fixed,the influence of mAs on CT number was not statistically significant.That is,the CT number wouldn't change with mAs.Under the same tube voltage and mAs,the influence of pitch on CT number was not statistically significant.the CT number wouldn't increase with the increase of pitch.?UniformityWhen the pitch was fixed at 0.6,1.2 and 2.0 and mAs remained unchanged,the influence of tube voltage on uniformity was statistically significant.The greater tube voltage,the better uniformity the scanned image had.When the tube voltage was fixed,the influence of mAs on uniformity was statistically significant.The greater mAs,the better uniformity the image had.When the tube voltage was fixed at 80kV,110V and 130kV,the analysis results showed that when the pitch was fixed,the influence of mAs on uniformity was statistically significant.The greater mAs,the better uniformity the image had.When mAs was fixed,the influence of pitch on uniformity was not statistically significant.No matter how the pitch changed,the uniformity was basically the same.?NoiseWhen the pitch was fixed at 0.6,1.2 and 2.0 and mAs remained unchanged,the influence of tube voltage on noise was statistically significant.The greater tube voltage,the smaller noise and the better image quality.When the tube voltage was fixed,the influence of mAs on noise was statistically significant.The greater mAs,the smaller noise and the better image quality.When the tube voltage and mAs were fixed,the influence of pitch on noise was statistically significant.The smaller pitch,the smaller noise and the better image quality.?Linearity of CT numberWhen the pitch was fixed at 0.6,1.2 and 2.0,the influence of tube voltage and mAs on linearity under different scanning conditions was not statistically significant.That is,the linearity of images wouldn't change with tube voltage or mAs.When the tube voltage was fixed,the influence of mAs and pitch on linearity under different scanning conditions was not statistically significant.That is,the linearity of images wouldn't change with pitch or mAs.Conclusion1.It was found that the radiation dose of CT in SPECT/CT varied with the influencing factors:The radiation dose increases with the increase of tube voltage and mAs,but decreases with the increase of pitch.2.1t was found that the image quality of CT in SPECT/CT varied with the influencing factors:The tube voltage,mAs and pitch had no influence on the high contrast resolution and CT number of images.The greater tube voltage and mAs and pitch,the better uniformity and low contrast detectability the scanned image had.The greater tube voltage and mAs and pitch,the smaller noise and the better image quality.With the increase of tube voltage andthedecreaseofpitch,the CT number gradually increased.3.Determining the optimum conditions for SPECT/CT examination under the research condition of this subject.it can be seen that under the premise that the image quality meets the standard requirements,the radiation dose produced to the examinee is the lowest under the condition of 130 kV,100 mAs and 2.0 pitch.condition of 130 kV,100 mAs and 2.0 pitch.