Low-dose Radiation:the Study Of Interaction Effect Of The CT Values And The Image Quality Of CT Angiography

Objective:1. To explore the influence of the surrounding structures to the CT values measurement at different tube voltage.2. To evaluate the feasibility of lower extremity arterial CTA using lower tube voltage and tube current and its influence on image quality and radiation dose. Find out the reasonable tube voltage and tube current combination to the maximum reduction of radiation dose while not affect the diagnosis.Subjects and Methods:1.Setting the tube voltage as120,100,80kV, while other parameters were kept unchanged, scan14mgI/ml contrast media, medical silica gel, latex, biological glue and the arteriosclerosis vascular model made by these materials respectively. Measure the CT value of each structure at different condition, evaluate the influence of the surrounding structures to the CT values measurement at different tube voltage.2. Thirty patients underwent lower extremity arterial CTA examination using multi-spiral CT were randomly divided into three groups. In group Ⅰ100kV and260mA was adopted,100kV and210mA in group Ⅱ,80kV and260mA in group Ⅲ. Measure the CT value of arteries, surrounding soft tissues and background noise. The SNR, CNR, and FOM were calculated. Image quality was assessed by two independent readers.Results:1.At120kV, the CT values of14mgI/ml contrast media, medic al silica gel, latex, biological glue and these material in the arteriosclerosis vas cular were (380.63±8.49)HU and(377.03±3.83)HU(P=0.02),(293.94±17.83)HU an d(334.07±5.95)HU(P=0.00),(-154.64±12.56)HU and(-95.09±26.22)HU(P=0.00),(-54.66±2.09)HU and(-40.79±6.85)HU(P=0.00);at100kV, they were(442.97±6.48)H U and (439.77±4.95)HU(P=0.02),(332.79±6.78)HU and(383.90±6.14)HU(P=0.00),(-166.32±12.61)HU and(-122.43±27.71)HU(P=0.00),(-74.28±4.41)HU and(-64.74±10.65)HU (P=0.00);at80kV, they were(557.74±5.61)HU and(556.80±9.70)H U(P=0.62),(426.71±8.70)HU and(489.90±12.31)HU(P=0.00),(-202.30±27.10)H U and(-139.57±26.77)HU(P=0.00),(-87.64±4.77)HU and(-79.81±14.64)HU(P=0.00). When tube voltage decreased, the CT value of high density material incre ased; the CT value of low density material decreased. Surrounding structures also had influences on CT value, the more obvious density difference it was, more obvious the affection was.2. The CT value of arteries in groupⅢ were higher than group Ⅰ and group Ⅱ, and the difference was statiscally significant (P<0.05). But there was no statistics significance in group Ⅰ and group Ⅱ (P>0.05). At thicker area, the CT value of surrounding soft tissues in groupⅢ were1ower than group Ⅰ and group Ⅱ, and the difference was statiscally significant (P<0.05). But there was no statistics significance in group Ⅰ and group Ⅱ (P>0.05). At thinner area, the CT value of surrounding soft tissues in the three group s was no statistics significance. There were statistical differences at background noise in the three groups (P<0.05).There were no statistical differences in SNR, CNR, and image quality scores between the three groups. The CTDIvol, DLP, ED were5.41,635.00±11.25,12.07±0.24;4.02,488.89±25.94,9.29±0.55;2.63,304.56±9.50,5.79±0.20, and the difference was statiscally significant (P <0.05). The FOM had significance in statistics in the three groups(P<0.05), the biggest one was groupⅢ.Conclusion:1. As tube voltage changed, the CT value change. And the surrounding structures is also affect the CT value, but it is not obvious to contrast media.2. On CT quantitative study should pay attention to the influence of the CT value caused by the change of the tube voltage and surrounding structure.3. Lower tube voltage can obviously reduce the radiation dose.4. Lower radiation dose has no effect on blood vessels SNR, but affect the SNR of abdominal and pelvic soft tissue.5. Recommend80kV and260mA as a regular scans condition of the lower extremity arterial CTA examination.