| Purpose:1.The repetitive scanning of the water modes with different concentrations of contrast agents is performed through different scan conditions with the tube voltages(KV)and tube currents(mAs),to investigate the relationship between tube voltage,tube current and contrast agent concentration,And which tube voltage and tube current scanning conditions can get better image quality,providing a certain basis for clinical experimental research.2.Limit scan condition of tube voltage and tube current range for three groups patients,compare effective radiation dose,subjective image score,objectively evaluated signal-to-noise ratio,contrast to noise ratio,image noise in upper abdominal enhanced scan patients,and exploring the feasibility of low dose abdominal CT scan and more suitable for tube voltage and tube currents of low-dose scans.3.Through subjective and objective evaluation of the upper abdomen adaptive iterative reconstruction-V images with different reconstruction grades,Exploring which ASIR-V reconstruction grades is best in reducing image noise,optimize the image reconstruction quality.Methods:1.The iodine and physiological saline is mixed in a proportion and made into Experimental water mold.All of the molds were fixed on the quality confirmation mold and placed In the center of the scanning bed.Select and fix the normal scanning condition of human abdomen scan(thickness,pitch,FOV,etc.),only change the mAs and the tube voltage.Scan the Seven test tubes with different iodine concentrations,measure the CT values of certain ROI in the CT images,The SNRs were calculated.Compare the CT values,SNR,image noise value with normal scanning condition and those with different tube,mAs,observing the effects of CT value,image noise value and SNR with different tube voltage,mAs.2.We collected 66 patients from May 2017 to December 2017 due to clinical suspicion of upper abdominal lesions,need the upper abdomen spiral CT enhancement scan,those patients body mass index have no statistical difference,and cardiopulmonary function is normal.those patients were randomly divided into three groups.The scan conditions are in turn 1group A: tube voltage120 KV,tube current range 100~250mA,NI select 10,tube current control adopts smart mA mode,2groupB : tube voltage 100 KV,tube current range100~250mA,NI selects 10,tube The current control adopts smart mA mode;3groupC : tube voltage 100 KV,tube current range 100~250mA,NI selects 12,tube current control adopts smart mode;other scan conditions such as fixed layer thickness,pitch,FOV are unchanged,and the resulting image is reconstructed with ASIR-V40 reconstruction algorithm.The scan ranged from the dome to the liver lower edge.The contrast-enhancing contrast agent1.3~1.5ml/kg was injected through the cubital vein and the injection rate was3ml/s.Measuring the CT values and its standard deviation of normal hepaticparenchyma,abdominal aorta,spleen,pancreas,right psoas muscle,and anterior abdominal wall in each phase of the three groups images.Quantitative calculation of signal-to-noise ratio,contrast-to-noise ratio,image noise for different groups;according to the image noise,contrast resolution and the lesions display,anatomy,The overall quality of each image is scoredby 1-5points(1 point indicates the worst,5 points Express the best);and record a DLP(Dose Length Product)of the upper abdomen to calculate the effective radiation dose to complete a multi-phase scan.3.Twenty-one patients with clinical suspicion abdomen lesions were selected.The upper abdomen was scanned with multi-phase scanning,the tube voltage was 100 KV,the tube current range was 100-250 mA,the noise index was 10.The CT values and standard deviation of normal liver parenchyma,abdominal aorta,spleen,pancreas,right psoas muscle and air in the anterior abdominal wall were measured in ASIR-V0%,10%,20%...90%,100%,quantitatively calculates the different groups image noise,SNR,CNR;The overall quality of each group images is scored on a scale of 1-5(1 for the worst,5 for the best);Record patients abdomen DLP of completing a multi-phase scan,calculate the effective radiation dose.Counting data were analyzed using randomized block analysis of variance,SNK test for multiple comparisons,and rank data using complete random design of multiple sample comparison rank sum test.Result:1.In the case that Tube voltage is 120 KV,the tube current down to 60 mAs,the image quality decreased significantly,the Tube voltage is 100 KV,the tube current down to 120 mAs,the image quality decreased significantly,the Tube voltage is 80 KV,tube current is 200 mAs or lower than 200 mAs,the Tube voltage is 70 KV,tube current is 200 mAs or lower than 200 mAs,the imagequality fail to meet the clinical diagnostic criteria.CT and SNR value both increase with the increase of the contrast agent iodine concentration.The CT value increase with the decrease of the tube voltage.When the Tube voltage is100 kv,the SNR value is the largest.2.The difference in body mass index among the three groups was statistically insignificant.The difference in effective dose was statistically significant.The effective dose of group A was the highest,about 10.01 mSv.The average scan dose was approximately 2.50 mSv.The effective doses of the group B and group C were 7.95 mSv and 5.94 mSv,respectively.The average scan dose was 1.99 mSv and 1.49 mSv.There was no significant difference in liver CNR and SNR among groups A,B and C.The CNR values of pancreatic arterial and portal phase,the spleen plain scan and arterial phase,the abdominal aorta plain scan and arterial phase in the groups A,B or C were statistically insignificant,but the pancreatic plain scan and balance period were statistically significant.The SNR values of spleen plain scan,arterial,portal and balance phase,pancreas and abdominal aorta portal,balance phase were statistically insignificant in groups A,B or C;but spleen plain scan,portal and balance phase,abdominal aortic portal and balance phase were statistically significant.The subjective scores of the three groups of different scanning conditions were statistically insignificant.3.In the arterial phase,except the normal hepatic parenchyma,there was significant difference in CNR among different levels of abdominal aorta,spleen and pancreas.Normal hepatic parenchyma,abdominal aorta,spleen and pancreas of the rest groups,the CNR value,SNR value and background noise of different iterative levels all have statistical significance.Subjective evaluation:ASIR-V90%,100% reconstruction of the upper abdomen image is poorer than the FBP image quality,the score was less than 3;ASIR-V10%,20%,80% ofreconstructed images and FBP images have no significant difference,The remaining reconstructed levels image quality better than FBP images,and the ASIR-V50% score is highest.The 21 patients mean DLP of upper abdomen scan was 525.96 ± 104.00 / mGy · cm,and the effective radiation dose was 7.89± 1.56 mSv.Conclusions:1.As for low-dose abdominal scan,the recommended scanning conditions is100 KV,150mAs,which can reduce the radiation dose and get the image with quality close to that with the condition of tube voltage 120 KV,tube current200 mAs at the same time.2.Lowering the tube voltage and tube current with iterative restriction can reduce the dose of radiation received by the patient without affecting the image quality.It is recommended that the scan conditions include a tube voltage of 100 kV,a tube current of 100 to 250 mA,and an NI selection of 10.3.With the increase of iterative grade,the SNR value and CNR value is gradually increased,and the background noise is gradually decreased.2 except ASIR-V90%,100%,other reconstructed levels optimize low dose upper abdominal images are feasible,ASIR-V40%,50%,60% can significantly improve the low-dose abdominal image quality compared with conventional FBP images,of which ASIR-V50% is the best. |
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