| Part Ⅰ:The study of Iterative model reconstruction technique combined with low tube-current:bone mineral density accuracy of lumbar vertebrae phantomObjective:To explore the affect of the bone mineral density accuracy of lumbar vertebral phantom among Iterative model reconstruction technique(level 1,2,3)、Filtered reflection projection、Iterative Reconstruction Algorithm(level 1,2,3,4,5,6)and low tube-current on.Materials and methods:European spine phantom(ESP),the number is 145,QCT calibration were selected for multi-slice spiral CT scans,tube voltage and tube currents were 120KV and 20、30、40、50、60 mAs,table height was 146mm,Scanning layer thickness and layer spacing are 5mm,pitch 0.976,tube speed 0.5s/r,DFOV 500mm,matrix 512x512,bed height 146mm.Reconstructed layer thickness 1mm,layer spacing lmm,combined with IMR(level 1,2,3)、FBP、iDose4(level 1,2,3,4,5,6)reconstructed,CTDIvol、DLP)were recorded,noise,SNR、CNR were measured and recorded The differences in bone mineral density(BMD)values of L1,L2,and L3 of ESP between ten reconstruction techniques and tube currents were compared.Results:1.When tube voltage 120KV is constant,mAs are correlated with CTDIvol and DLP,and they are positively correlated(r=1,p<0.05).As the mAs increase,the ESP phantom radiation dose increases.2.Under the same iterative algorithm,The BMD values of the ESP phantoms L1,L2,and L3 were not statistically significant at 20,30,40,50,and 60 mAs(all,p>0.05).At the same mAs,No statistically significant differences in BMD values were seen when IMR(level 1,2,3),FBP,and iDose 4(level 1,2,3,4,5,6)were reconstructed(all,p>0.05).3.The image noise of IMR(level 1,2,3)three groups was significantly lower than that of FBP group and iDose4 group.In addition,with the continuous increase of mAs,the image noise is getting lower and lower;The CNR of IMR(level 1,2,3)group was significantly higher than that of FBP group and iDose4 group.The noise of IMR(level 2)group decreased by 66.67%compared with FBP image group under 20mAs condition.CNR increased by 569%,and the difference was statistically significant(p<0.01).Conclusions:The iterative model reconstruction technique IMR(level 2)combined with low current(20 mAs)can reduce the radiation dose,improve the image quality,and at the same time satisfy the accuracy of bone mineral density measurements.Part Ⅱ:The study of Iterative model reconstruction techniquecombined with low tube-current:image quality of chest phantom CT Objective:To explore the affect of the image quality of chest phantom among Iterative model reconstruction technique(level 2)、Filtered reflection projection、Iterative Reconstruction Algorithm(level4)and low tube-current on.Materials and methods:Adult male chest phantom was selected for multi-slice spiral CT scans,tube voltage and tube currents were 120KV and 20、30、40、50、60 mAs,Scanning layer thickness and layer spacing are 5mm,pitch 0.976,tube speed 0.5s/r,DFOV 500mm,matrix 512x512,bed height 146mm.Reconstructed layer thickness 1mm,layer spacing 1mm,combined with IMR(level 2)、FBP、iDose4(level4)reconstructed,CTDIvol、DLP)were recorded,noise,SNR、CNR were measured and recorded The differences in CT、SD values of chest phantoms and image quality of nodules between reconstruction techniques and tube currents were compared.Results:1.When tube voltage 120KV is constant,mAs are correlated with CTDIvol and DLP,and they are positively correlated(r=1,p<0.05).As the mAs increase,the chest phantom radiation dose increases.2.Different tube currents and reconstruction techniques,chest phantom CT values did not have statistically significant differences(p all>0.05),There was a statistically significant difference in SD values(p<0.05).And when the mAs value is smaller,the SD value is larger.At the same mAs,the SD values were statistically significant under different reconstruction techniques(p<0.05).3.There was no significant difference in subjective scores of image quality between the 20 mAs of tube current,the IMR iterative algorithm and the current of 60 mAs,and the image quality of the mediastinal window and the lung window using the FBP iterative algorithm(P>0.05).And the consistency of the lung window and the longitudinal window was good between the two observers(Kappa values were 0867、0.823,respectively).Conclusions:The iterative model reconstruction technique IMR(level 2)combined with low current(20mAs)can reduce radiation dose,improve image quality,and at the same time meet the diagnosis of chest CT images.Part Ⅲ:Clinical Application of Iterative Model Reconstruction Technique in Low Dose Chest Combined with Lumbar QCTObjective:To explore the feasibility of iterative model reconstruction(IMR),filtered reflectance projection(FBP),and low-tube currents for chest CT images quality and the affect of the bone mineral density accuracy of lumbar vertebral.Materials and methods:A total of 399 Health checker were collected for chest CT scans and lumbar QCT bone density examinations in medical examinations,divided into two groups:Low-dose group 20mAs and conventional dose group 40mAs.Chest CT and lumbar QCT scan with 20mAs and 40mAs respectively,Scan range from the entrance to the thorax to the level of the lower third lumbar vertebral body,Two groups of iterative model reconstruction(IMR)(Level 2),filtered back projection algorithm(FBP)reconstruction,Record the CT dose volume index(CTDIvol)and dose length production(DLP)generated automatically after multi-slice spiral CT scan.Measure and record noise,SNR,CNR,BMD,Subjective ratings of image quality were made by two attending physicians.The differences in BMD of L1,L2,and L3and chest CT image quality were compared between the two groups.Results:1.When the tube voltage was constant,the CTDIvol in the low-dose group had a statistically significant difference from the conventional dose group(p=0.001).The low-dose group was at least 60%lower than the conventional dose group.2.After low-dose group and conventional-dose group were reconstructed with FBP and IMR(2)iterative techniques respectively,There was no significant difference in BMD values of L1-L3(p>0.05).3.The difference was statistically significant between the low-dose group(20mAs IMR(2))and the conventional dose group(p<0.05).the low-dose group(20mAs IMR(2))reduced image noise about by55%in compared to the conventional dose group(40mAs FBP)(p<0.05).The SNR and CNR in the low dose group were significantly higher than those in the conventional dose group,and the difference was statistically significant(p<0.05).Conclusion:Iterative model reconstruction IMR(level 2)combined with low current(20 mAs)can reduce radiation dose,improve image quality,and at the same time meet the accuracy of lumbar spine BMD. |
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