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Application Study of Automatic Tube Current Modulation (ATCM) for Abdominal Computed Tomography (CT)

Author: WangZuo
Tutor: ZhaoXinMing
School: Beijing Union Medical College
Course: Medical Imaging and Nuclear Medicine
Keywords: Pubmed CNKI Web of Science Low-dose CT TDAtomography、X-ray computed abdomen individualized image quality objective evaluationtomography、X-ray computed radiation dose phantom
CLC: R816.5
Type: Master's thesis
Year: 2013
Downloads: 15
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Abstract


Purpose:The purpose of this study was to evaluate the character and rule of the development in low-dose CT examination and supply some useful references for in-depth study in future.Materials and Methods:The journal articles on Pubmed included by Medline, Web of Science by SCI and CNKI by CAJD from2002to2011were processed by Thomson Data Analyzer (TDA) and analyzed from seven aspects:author collaboration, institution collaboration, countries, journals, highly cited literature, subjects and keywords, five aspects:time, authors, funds for scientific research, areal distribution, institutions journals, countries and keywords, and programmed by SAS8.2for cluster analysis.Results:The journal articles in low-dose CT examination add up to6433on Medline,3148on CNKI,6027on Web of Science. The famous authors were those doing more than4articles. There were9core journals in this research.Of those, the literature amount of Medical Physics, European Journal of Radiology and the American Journal of Roentgenology has been dramatically increased. The average author number of single papers is5.93,the cooperation rate was89.4%;The average institution number of single papers is2.63,the cooperation rate was77.3%.Divided by countries, U.S was3165,in49.2%,it has been a core zone in this research.However,174papers from our country were retrieved by SCI. Authors came from471institutions and8systems in China, who have distributed in33main areas. The top two were Beijing and Shanghai, in45.9%.There were10core journals in this research, of those, CHINESE JOURNAL OF MEDICAL IMAGING TECHNOLOGY and Chinese Journal of Radiology became most typical jouanals. The articles added up to868, in27.57%,from research projects funded by certain grants published in this field increased almost every year, which reflected timely and objectively a growing tendency in low-dose CT research In the last decade,the numbers and qualities of the journal articles in low-dose CT have been advanced. The hotspots of low-dose CT research involves screening for lung cancer, coronary angiography, pulmonary embolism examination, colonic CT virtual endoscopy technology, CT radiation dose.Conclusion:The attentions to the low-dose CT field have been more and more, and the researchers have been come in a team. The research in low-dose CT is a interdiscipline about medicine, medical physics, mathematics. The low-dose CT research domesticly was in the lower stage than the international level, and the research powers were not evenly distributed. Though the research has involved multi-institute, mulit-system, multi-subject, the quantities and qualities of papers were up to improvement. Strengthening the basic research and perfecting the lack of medical Ethics and clinical research method in low-dose CT field, which could develop more research in-depth study. Purpose:To investigate the relationship between the individualized factor in adult patients and objective image quality in abdominal CT, and determine the optimal region to measure and evaluate image quality in adult abdominal CT objectively.Materials and Methods:From March2012to October2012, one hundred and forty-four patients,who underwent clinical diagnosis or demand for treatment, were enrolled in this study and underwent non-contrast-enhanced abdominal CT scans in the constant tube current tube mode. All the individual variants, including height, weight, transverse diameter at the lever of LI pedicle and the first hepatic portal in positioning imaging, were measured and recorded. At the same time, percentage of fat content intra-abdominal and subcutaneous fat thickness data were also measured by X SECTION functions in3D reformat software to explore the relationship between these individualized factors and objective image quality in abdominal CT. The image noise was measured respectively at ten regions in the abdomen conventional CT images:the abdominal aortic of four levels (the liver top, the first hepatic portal, the renal hilum and the kidney pole),and six areas in the first hepatic portal level (the aorta the portal vein, the peripheral and the central hepatic portions, the spleen, the erector spinae, the anterior abdominal wall subcutaneous fat). The correlative coefficients between the noise value and the image quality of the measured region were compared at the base level of individualized factors of higher relationships, which ultimately determined the optimal area of the objective evaluation of the adult abdominal CT images.Results:The correlative coefficients between height,weight,weight-statue-ratio,BMI, weight,transverse diameter at the lever of LI pedicle,the maximum transverse diameter.the maximum anteroposterior diameter, the average maximum diameter of abdomen, visceral and subcutaneous fat measured values, and noise image quality were 0.267,0.702,0.7,0.661,0.744,0.739,0.712,0.765,0.613and0.431,respectively.Compared with transverse diameter at the lever of the first hepatic portal,transverse diameter at the lever of LI pedicle showed greater relationship(R=0.931). The correlative coefficients between the noise value and the image quality of the abdominal aortic regions of four levels was0.522-0.765at the base level of the average diameter of abdomen in the constant tube current tube mode, and the first hepatic portal level showed great est relationship. The correlative coefficients between the noise value and the image quality of the peripheral hepatic portions in the first hepatic portal level, the abdominal aortic, and the anterior abdominal wall subcutaneous fat were0.74-0.802,0.712-0.765, and0.412(P>0.05) at the base level of individualized factors of higher relationships, respectively.Conclusion:The correlative coefficients between all the individualized factors involved in our study and objective image quality was0.267-0.765. Of them, transverse diameter at the lever of L1pedicle showed greatest relationship. In short, it can be used as a parameter adjusting the scanning paramerers in abdominal CT of adults. The abdominal aortic region in the first hepatic portal level was the optimal region to measure and evaluate image quality in adult abdominal CT objectively,and its noise value can be a indicator of objective image quality in the abdominal routine CT scanning Purpose:To investigate the effect of ATCM on image quality and radiation dose at abdominal CT.Materials and Methods:(1) Phantom study:Catphan600performance for observation object, with adult abdominal body ring simulating adult abdominal CT low and high contrast characteristics, were scanned with CT protocol at fixed120kV,450mA and120kV, ATCM of tube current range from10to450mA (NI value:4-20),respectively. CT value was measured by homogeneous area in the center of Catphan600to 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.15mm diameter low-contrast detectability in CTP515and high-contrast detectability in CTP528at Catphan600were evaluated independently by three doctors experienced in abdominal diagnosis more than five years 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 one were compared with parameter and non-parametric rank sum test.(2) Clinical study:6groups of120patients who had examination of non-enhanced abdominal CT within one year were enrolled in the control and study groups, and they were blocked by the difference of transverse diameter(D/cm) at the lever of LI pedicle on the scout image in proportional allocation in stratified random sampling. The control group was scanned with a fixed120kv and450mA, and the study one with120kv and NIat10(10-450mA).The standard deviation(SD) at the abdominal aortic area was measured at anatomic levels (the liver top, the first hepatic portal and the lower pole kidney).CT images were graded in terms of the diagnosis acceptability at three major levels (the first hepatic portal,the renal hilum and pancreas),and the image subjective noises of six organs including abdominal aorta, portal vein, liver, spleen, pancreas, kidney were graded by using1five-point scale. The exposure dose values were recorded. The image quality was compared with non-parameter test, and SDs and exposure values in different block were compared with the AVONA. The pairing data was compared with t test.Results:(1)This phantom is equivalent to adult abdomen for X-ray attenuation. NI and objective, subjective evaluating indicator of image quality and radiation dose is highly linear correlation (r=0.758-0965, p<0.05). There were no significant differences in SD,CNR between NI4-7group and control one(t-0.17-1.63,0.03-1.12, P>0.05). There were no significant differences in LCD scores between NI4-10group and control one (Z-0.313-1.637, P>0.05). There were no significant differences in HCD scores between NI4-13group and control one (Z-0.147--1.423, P>0.05).2) There were no significant differences in image quality between the study and control one (Z=-1.831~-1.000, P>0.05). There were significant differences in exposure values in D≤33.4cm groups (t=-6.13--3.93, P<0.05).There were no significant differences at three anatomic levels in SDs in study group (F=0.46~1.37, P>0.05).There were significant differences in dose values in three blocks in study group (F=15.88~42.78, P<0.05)Conclusion:Radiation dose can be effectively reduced by using the ATCM technique in abdomen CT. Compared with fixed tube current mode, when NI value was8to10, radiation dose can guarantee that the low contrast objects are detected, which reduces by25.33%; radiation dose does by65.1%with high contrast objects detected when NI≥14. The application of ATCM(NI=10) at abdominal CT can guarantee the low contrast lesions are detected, meanwhile, the radiation dose can be reduces by11.2%to78.3%, compared with fixed tube current mode.

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CLC: > Medicine, health > Of Medical > Radiation Medicine > Each location and course of disease X - ray diagnosis and therapy > Stomach and digestive
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