Imaging Technology
Application of automatic tube current modulation on image quality and radiation dose at abdominal CT
WANG Qian, ZHAO Xin-ming, SONG Jun-feng, GUO Ning, ZHU Ying, LIU Jian-xin, QI Wei-wei, WU Jing, LIANG Yuan, FENG Shi-chao, HU Man-cang, ZHOU Chun-wu, WANG Xiaoying, HONG Nan
Published 2013-07-10
Cite as Chin J Radiol, 2013,47(07): 648-654. DOI: 10.3760/cma.j.issn.1005-1201.2013.07.015
Abstract
ObjectiveTo investigate the effect of automatic tube current modulation (ATCM) on image quality and radiation dose for abdominal CT.
MethodsAn abdomen-equivalent tissue model in the present study was developed,by referring to the CTP515 auxiliary performance testing model made by the internationally recognized Phantom Laboratory,in conjunction with the real data from 68 Chinese male subjects with BMI between 18 to 24 kg/cm2 (subjects with fatty liver,cirrhosis,intraperitoneal huge tumor,ascites or pleural effusion or who were under 18 years old were excluded).Catphan600 performance served as observation object,and simulating adult abdominal CT low and high contrast characteristics to research.Control groups were scanned with CT protocol at fixed 120 k V,450 m A and experimental group were scanned with the same tube voltage and variable current range from 10 to 450 m A (NI value:4 to 20),respectively.CT value was measured by homogeneous area in the center of Catphan600 to verify the phantom for X-ray attenuation of equivalence.CT dose index (CTDIvol),size-specific dose estimates (SSDE),dose length product (DLP),image noise (SD) and contrast to noise ratio (CNR) were recorded and measured.Fifteen mm diameter low-contrast detectability in CTP515 and high-contrast detectability in CTP528 at Catphan600 were evaluated independently by 3 doctors working in abdominal diagnosis for more than five years from three hospitals in a five-point scale.The correlation between NI value and objective,subjective evaluating indicator of image quality and radiation dose were analyzed,and SD,CNR and LCD,HCD scores in different NI group and those in control group were compared with parameter and non-parametric rank sum test.The differences of SD,CNR and CTDIvol scores between NI group and control group were compared with t test.Kruskal-Wallis test was used for intra-group comparison of LCD and HCD scores,Mann-Whiteney U Test for inter-group and Kappa analysis for consistency check of the subjective evaluation result of the 3 radiologists.
ResultsNo significant difference was found between the CT value of ROIin catphan 600 central area[ (50.8±1.0) HU] scanned under various NI and that of the normal liver tissue[ (52.8±9.1) HU]obtained from 68 Chinese male subjects (t=0.31,P>0.05),with a deviation degree of 4.9%.This phantom was equivalent to adult abdomen for X-ray attenuation.One unit increase in NI was associated with 1.23 mGy,2.03 mGy,13.20 mGy·cm,0.20 mSv decrease in CTDlvol,SSDE,DLP and ED respectively.NI and objective,subjective evaluating indicator of image quality and radiation dose was highly linear correlated (r=0.871 to 0.982,P<0.05).There were no significant differences in SD,CNR between NI group 4 to 7 and the control group (t=-1.63 to-0.17,0.03 to 1.12,P>0.05).No significant differences were found in LCD scores between NI group 4 to 10 and the control group (Z=-1.637 to 0.000,P>0.05).And the HCD scores between NI group 4 to 13 and the control group (Z=-1.423 to 0.000,P>0.05) were not significantly different either.The consistency check result ofKappaanalysis of the 3 doctors' LCD,HCD evaluation was 0.743 and 0.795.
ConclusionApplication of the ATCM technique in abdomen CT can reduce the radiation dose while ensuring the image quality.
Key words:
Tomography,X-ray computed; Radiation dosage; Abdomen; Phantom
Contributor Information
WANG Qian
Department of Diagnostic Imaging,Peking Union Medical College& Cancer Institute& Hospital,Chinese Academy of Medical Sciences,Beijing 100021,China
ZHAO Xin-ming
SONG Jun-feng
GUO Ning
ZHU Ying
LIU Jian-xin
QI Wei-wei
WU Jing
LIANG Yuan
FENG Shi-chao
HU Man-cang
ZHOU Chun-wu
WANG Xiaoying
HONG Nan