| Objective:According to the waist circumference and the current of different tubes,the monte carlo analysis platform was used to collect and count the radiation dose,and the application value of tube current time product(m As)in the image quality of lumbar CT imaging and the radiation dose of sensitive organs was discussed.Materials and methods:A total of 80 patients were prospectively designed and consecutively collected from outpatient or inpatient visits between September 2017 and June 2018,who were considered to have lumbar spine diseases by clinical history and physical examination,orthopaedic or sports medicine doctors as requiring lumbar spine CT scans.The waist measurement method is to find two points at the bottom of ribs and the top of hip on both sides of the body.In this study,24 males and 56 females were aged 16-78 years with an average age of 48.5 years and a waist circumference of 66cm-116 cm.Eighty patients were grouped.First,10 patients were randomly selected as the conventional group without limiting waist size,and the waist size measured in the conventional group was 80cm-107 cm.The remaining 70 patients were classified into the low-dose group.The low-dose group was further divided into three subgroups according to different waist sizes.The waist size of group A ranged from 66 cm to 80 cm,A total of19 cases.The waist circumference of group B was 81cm-99 cm,a total of 30 cases.The waist circumference of group C ranged from 101 cm to 116 cm,with a total of 21 cases.All patients were performed on GE Hi Speed Nx/ I bilateral spiral CT.Beforethe experiment,three groups of volunteers with different waist circumference were firstly selected for lumbar spine pre-scanning,which was performed at 260 m As of normal adult exposure,and then10 m As was decreased for scanning each time,until the image quality fails to meet the diagnostic needs.Thus,it was determined that the tube current(m As)of the conventional group and the low-dose groups A,B and C were 260 m As,100 m As,180 m As and 220 m As,respectively.Other parameters were exactly the same: flat sweep parameters were tube voltage 120 k V,layer thickness3 mm,speed 1.0s/ turn.The patient was in supine position,and the scanning range was from the lower margin of the thoracic 12 vertebra to the upper margin of the sacral 1vertebra.All the 4 groups were reconstructed using iterative reconstruction algorithm.Monte carlo analysis platform(Radimetrics,Byer Healthcare,Germany)was used to record the specific radiation dose values of sensitive organs(adrenal,kidney,liver,pancreas and bone).The subjective image quality was evaluated.All statistical analyses were performed using SAS9.4/SPSS21.0 statistical software,and the difference was considered statistically significant if P ? 0.05.The mean and standard deviation were described by quantitative data.Comparison between groups was performed by anova or kruskal-wal lis test.LSD-t test or dwas-steel-critchlowfligner test(DSCF)was used for multiple comparisons between groups.Pearson correlation test was used for correlation of bivariate quantitative data.LSD-t test was used to check the consistency of the analysis results of the two radiologists,and P <0.05 was considered statistically significant.Results:The dose of adrenal radiation in the routine group and the low dose groups A,B and C were respectively27.15±8.48 m Sv,11.50±0.28 m Sv,22.80±6.12 m Sv,24.40±2.10 m Sv;The radiation dose of kidney was 34.62±10.92 m Sv,14.38±0.08 m Sv,27.77±5.81 m Sv,31.27±4.20 m Sv;The radiation dose to the liver was 30.12±9.34 m Sv,12.82±0.21 m Sv,25.04±5.89 m Sv,27.22±2.81 m Sv;The pancreatic radiation dose was25.87±8.12 m Sv,10.87±0.19 m Sv,21.43±5.33 m Sv,23.20±2.06 m Sv;Bone radiation dose was 12.14±3.75 m Sv,5.55±0.52 m Sv,10.82±2.56 m Sv,11.50±1.65 m Sv.The difference was statistically significant(P<0.001).In other words,the radiation doses of adrenal,kidney,liver,pancreas and bone in the low-dose group A,B and C were all lower than those in the conventional group,with statistical significance.The CT image quality scores of the two physicians in the conventional group and the low-dose group showed good consistency(P < 0.001),and the scores were both greater than or equal to 3 points,which could meet the needs of clinical diagnosis.The subjective image quality scores of the conventional group and the low-dose group A,B and C were 4.90 0.32,4.05 0.85,4.30 0.75 and 4.29 0.72,respectively.There were statistically significant differences in image quality scores between the conventional group and the low-dose groups A,B and C(P < 0.05).There was no significant difference in image quality score between low-dose group A and low-dose group B(pa-b =0.251).There was no significant difference in image quality score between low-dose group A and low-dose group C(pa-c =0.316).There was no significant difference in image quality score between low dose B group and low dose C group(pb-c =0.945).Conclusion:Adjusting tube current according to waist size can make the scanning scheme more personalized and precise,and reduce the radiation dose of sensitive organs on the premise of guaranteeing the image quality. |
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