The Feasibility And Clinical Application Of Low-dose CBCT

Background:In recent years,with the rapid development of dental imaging technology,the cone beam computed tomography(CBCT)has been widely used in clinical practice.It provides real and objective imaging evidence for clinical diagnosis and treatment options,and is of great significance for the timely and accurate diagnosis of patients' diseases.However,in the process of CBCT examination,patients receive X-ray,and inevitably are threatened by radiation.Although scholars at home and abroad have done a lot of research on how to reduce the radiation damage of patients in the process of CBCT,and have taken many useful measures,but the effect is still not very good.Therefore,it is of great significance and application prospect to explore effective methods and means to reduce the radiation dose received by patients in the process of CBCT.CBCT has been widely used in dental implant planning,orthodontic treatment,dental pulp disease,periodontal disease,children's oral disease and oral and maxillofacial surgery evaluation and many other fields of dentistry.The radiation dose of CBCT is lower than that of Computed Tomography(CT),but significantly higher than that of conventional X-ray examinations such as intraoral X-ray and curved body X-ray.With the wide application of CBCT,the radiation dose received by patients has attracted attention.The harmful health effects of CBCT belong to random effects,and the incidence of random effects is positively correlated with radiation dose.It has been reported that low dose diagnostic X-ray is directly related to the occurrence of salivary gland tumors.The risk of cancer will increase by 4.1% for every 1 Sv of radiation dose.Although the dose of X-ray produced by CBCT is not large,a person usually has 20 deciduous teeth and 28-32 permanent teeth,and the disease of each tooth may be subject to more than one radiation examination,so CBCT may cause damage to the body.Although in clinical work,we use physical protective equipment such as lead cap,lead collar and lead clothing to give certain radiation protection to other parts of the subject,but we can not fundamentally reduce the radiation dose of the subject.Therefore,to reduce the radiation dose of CBCT to the examinees,we can only adjust the parameters of CBCT itself.The radiation dose of CBCT is closely related to the scanning parameters such as tube voltage,tube current,scanning time,scanning field of view and scanning mode.The two most commonly used scanning modes in daily work are standard mode(Std)for adults and high speed mode(Hi-Speed)for children.Moreover,different scanning modes determine different scanning time,and the scanning field of vision is determined by the size of the area of interest that clinicians need to know.Therefore,in practical work,CBCT operators can freely adjust the two parameters of tube voltage and tube current.At present,there is no relevant literature about how to reduce the radiation dose as much as possible by adjusting the parameters of CBCT scan under the premise of ensuring the image quality.Based on the above basis and actual situation,this subject focuses on the feasibility and clinical application prospect of CBCT low-dose scanning,and provides a new strategy and method for effectively reducing the radiation dose received by patients in radiation diagnosis.Contents:Part one: Experimental study on the correlation between radiation dose and image quality of CBCT1?The influence of different radiation dose scan of CBCT on image quality: The pig head was selected as the research object,and the combination scanning of different tube voltage and tube current parameters was used to explore the relationship between tube voltage and tube current and image quality and radiation dose,and to find out the key parameter settings that affect image quality and radiation dose.2?The effect of low dose CBCT on the accuracy of tooth length measurement in vitro:According to the above experimental results,adjust the key parameter settings,and compare the length of teeth measured by low-dose CBCT image with the gold standard.Part two: A preliminary study on the clinical application of CBCT low-dose scanning1?CBCT low-dose scanning to evaluate the relationship between IMTM and MC in the population with normal body mass index: Taking the patients with IMTM as the research object,to compare the image quality evaluation results of CBCT low-dose group and conventional-dose group.2?The feasibility of CBCT low-dose scanning in the evaluation of dens invaginatus(DI):Taking the patients with DI as the research object,to compare the image quality evaluation results of CBCT low-dose group and conventional-dose group.3?The feasibility of CBCT low-dose scanning in the assessment of supernumerary teeth in children's maxillary anterior teeth: Taking the children with supernumerary teeth as the research object,to compare the image quality evaluation results of CBCT low-dose group and conventional-dose group.Method:1?In Std mode,the molar area was used as the scanning center.The volume computed tomographic dose index(CTDIvol)was recorded and the image quality was scored by blind method.2?In Hi-Speed mode,the incisor area was used as the scanning center.The volume computed tomographic dose index(CTDIvol)was recorded and the image quality was scored by blind method.3?In Std mode,the teeth in vitro were scanned with different key parameter settings,and the CTDIvol value was recorded.The length of the teeth was measured with digital vernier caliper and CBCT equipment software.4?Taking IMTM cases as the research object,CBCT scan was carried out with different key parameter settings,CTDIvol value was recorded and image quality was evaluated.5?Taking DI cases as the research object,CBCT scan was carried out with different key parameter settings,CTDIvol value was recorded and image quality was evaluated.6?Taking supernumerary teeth cases as the research object,CBCT scan was carried out with different key parameter settings,CTDIvol value was recorded and image quality was evaluated.7?Statistical analysis: SPSS 25.0 software was used for correlation analysis,t-test,Fisher exact probability test.The statistical results showed that P<0.05 was the significant difference.Results:1?The tube voltage remains the same as the manufacturer's recommended setting(Std mode: 87 k V,Hi-Speed mode: 90 k V).With the decrease of the tube current,the image quality decreases gradually.In Std mode,the image quality of tube current 5.5m A and above can meet the clinical diagnosis and treatment needs.Hi-Speed mode,tube current 4.0m A and above scanning image quality can meet the clinical diagnosis and treatment needs.2?The current of the tube remains the same as that recommended by the manufacturer(Std mode: 5.5m A,Hi-Speed mode: 7.0m A).With the decrease of the tube voltage,the image quality gradually decreases.In Std mode,only the image quality of 90 k V and 87 k V tube voltage scanning can meet the clinical diagnosis and treatment needs.Hi-Speed mode,the scanning image quality of tube voltage 78 k V and above can meet the clinical diagnosis and treatment needs.3?In Std mode,the image quality decreases slowly when the tube current is reduced,while the image quality decreases sharply when the tube voltage is reduced.In Hi-Speed mode,the image quality decrease caused by reducing the tube current is relatively gentle,while the image quality decrease rapidly caused by reducing the tube voltage.4?Std and Hi-Speed mode:The tube voltage remains the same as recommended by the manufacturer.With the decrease of the tube current,the radiation dose decreases gradually.The radiation dose is linearly related to the tube current.The current of the tube remains the same as the recommended setting of the manufacturer.With the decrease of the tube voltage,the radiation dose also decreases gradually.The radiation dose has an exponential relationship with the tube voltage.5?An experiment on the accuracy of length measurement of teeth in vitro: There was no significant difference between the CBCT images of 4.0m A group and the length of teeth measured by digital vernier caliper(P>0.05).6?IMTM preoperative evaluation: The image quality scores of 4.0m A group and 2.5m A group were lower than those of the control group.In terms of result evaluation composition,all images of 4.0m A group were qualified.There was no statistically significant difference between the 2.5m A group and the control group(P>0.05).The CTDIvol of 4.0m A group was 72% of the control group.The CTDIvol of 2.5m A group was 47% of the control group.7?DI: The image quality score of the 4.0m A group was lower than that of the control group.In terms of result evaluation composition,there was no statistically significant difference between the 4.0m A group and the control group(P>0.05).The CTDIvol value of the 4.0m A group was equivalent to 72% of the control group.8?Supernumerary teeth in maxillary anterior area: The image quality scores of 5.0m A group,3.0m A group and 1.0m A group were lower than those of the control group.In terms of result evaluation composition,all images of 5.0m A group were qualified.There was no significant difference between the 3.0m A group and the control group(P>0.05).There was no significant difference between the 1.0m A group and the control group(P>0.05).The CTDIvol of 5.0m A group was 71% of the control group.The CTDIvol of 3.0m A group was 44% of the control group.The CTDIvol of 1.0m A group was 15% of the control group.Discussion:Radiation damage caused by CBCT belongs to random effect,and its incidence is positively correlated with radiation dose,which means that the larger the radiation dose received by patients,the greater the probability of random effect.Therefore,it is of great significance to reduce the radiation dose of each radiation examination and find the balance point between CBCT radiation dose and image quality.The radiation dose of CBCT is directly related to the setting of scanning parameters.The reduction of radiation dose can be achieved by using a lower exposure parameter setting.In practice,CBCT operators can freely adjust the two parameters of tube voltage and tube current.Using different tube voltage and tube current to scan the pig head,we found that reducing tube current or tube voltage can reduce the radiation dose of CBCT,and the image quality will also be reduced.The decrease of tube voltage leads to the decrease of image quality more serious than the decrease of tube current.The low-dose CBCT images achieved by reducing the tube current have no effect on the accuracy of tooth length measurement in vitro.The low-dose CBCT scan of IMTM in the normal population with body mass index was performed with tube current of 2.5m A.The image can accurately show the position relationship between IMTM root and MC.Low-dose CBCT scan was performed in patients with DI with 4.0m A tube current.The images can clearly show the invagination.The number,position,shape,growth direction of the supernumerary teeth and the relationship between them and the adjacent teeth can still be accurately displayed in the low-dose CBCT scan of the supernumerary teeth in the maxillary anterior area of children with a tube current of 1.0m A.Conclusion:Reducing the tube current is more suitable for CBCT low-dose scanning than reducing the tube voltage.The length of teeth in vitro can be accurately measured by the low-dose CBCT image obtained by reducing the tube current.It is feasible to use the method of reducing the tube current to evaluate IMTM,the diagnosis of DI and the preoperative evaluation of children's supernumerary teeth in the anterior maxillary region.