The Optimal Dose Reduction Level In Liver CT Using Iterative Reconstruction In Image Space Algorithm

Part 1 The optimal dose reduction level in liver CT using Iterative Reconstruction in Image Space Algorithmphantom studyObjective: To determine the feasibility and the optimal dose reduction of Iterative Reconstruction in Image Space Algorithm(IRIS) on abdominal CT which can provide image quality(IQ)comparable to filtered back projection(FBP).Methods: A Catphan phantom was scanned by a 16-slice CT(simens emotion 16 CT) with 130 KV and varied m As from 30 to 250, the axial images were reconstructed by FBP and IRIS. Image quality was assessed with following aspect: low contrast resolution,high contrast resolution,CT value accuracy and consistency. Meanwhile the volume CT dose index CTDIvol were recorded for dose evaluation.Result: The image noise can be reduced in different degree with IRIS. When m As reduced to 52%(130 m As), image noise of IRIS image is not significant difference regarding to the image noise compared to 250 m As FBP image,under the conditions of 60% initial m As(150 m As), low density resolution is not significant difference regarding to 250 m As FBP image.The high contrast resolution of variety of m As reconstructed image is the same,which is 7lp/cm, but the image noise of IRIS(150m As) is lower than FBP(250m As). The uniformity and accuracy of CT number with CTP486 module and CTP404 module meets the CT quality assurance testing standards with national standards.Conclution: IRIS technique can decrease the radiation dose by 40% without affecting the image quality. The uniformity and accuracy of CT number meet the national specification.Part 2 The optimal dose reduction level in liver CT using Iterative Reconstruction in Image Space Algorithmcadaver studyObjective:To evaluate image quality and radiation dose to liver CT with Iterative reconstruction in image space(IRIS) compared to Filtered back projection(FBP).Methods: A cadaver was scanned by a 16-slice CT(simens emotion 16 CT) with 130 KV and varied m As from 20 to 250, the axial images were reconstructed by FBP and IRIS. Subject image quality was graded using 4-point scale in a blinded manner, and analysised it using t-test.Result: The subjective image quality of image declins and image noise increases as the m As declining with 130 KV, there is no difference in subjective image quality of IRIS(from 230 m As to 150 m As) compared to FBP(with 250 m As),the subjective image quality of IRIS(from 130 m As to 30 m As) is lower than FBP(with 250 m As), but the image noise of the IRIS(150m As) is lower than FBP(with 250 m As).The image quality of IRIS is better than FBP under the same scan condition.Conclution: IRIS technique can decrease the radiation dose by 40% without influenced the image quality.Part 3 The optimal dose reduction level in liver CT using Iterative Reconstruction in Image Space Algorithmclinical studyObjective: To determine the feasibility and the optimal dose reduction of Iterative Reconstruction in Image Space Algorithm(IRIS) combined with CARE dose 4D on abdominal CT which can provide image quality(IQ) comparable to filtered back projection(FBP).Methods: 200 patients are divided into three groups at radom, who will be carried on liver CT: group A(100 patients, 130 KV, CARE dose 4D and reference m As of 250,images were reconstructed with FBP)and group B(100 patients, 130 KV, CARE dose 4D and reference m As of 150,images were reconstructed with IRIS),group C(100 patients, 130 KV, CARE dose 4D and reference m As of 130,images were reconstructed with IRIS),which was scaned two images in hilar of group B. CT dose index volumes(CTDIvol),dose length product(DLP)were reconded and effective dose(ED) were calculated. CT number was measured,the image quality was evaluated blindly with objective methods(noise measurement and CNR/SNR calculating etc)and subjective methods. Two radiologists graded subject image quality using 5-point scale in a blinded manner.Analysis of paired t test were used for comparisons of height, weight, BMI, and radiation dose(CTDIvol, DLP, ED).Analysis of variance(ANOVA)and LSD test were used for comparisons of CT number,objective image quality(SD,SNR,CNR) and sbjective image quality.Results: CTDIVOL,DLP and ED were 17.38 ± 4.84 m Gy, 344.07 ± 100.02 m Gycm and 5.16 ± 1.5msv in group A,while 10.36 ± 2.86 m Gy, 202.74 ± 64.27 m Gycm and 3.04 ± 0.96 msv in group B,which decreased by 40.39%,41.08% and 41.08% respectively(P<0.05). CT number was55± 4.5HU in group A, while 54 ±5.5HU in group B and 55 ±5.5HU in group C(P >0.05). SD, SNR and CNR were 7.31 ± 1.01, 8.29 ± 2.16 and 1.21 ± 1.98 in group A, 6.57 ± 1.21, 9.66 ± 3.18 and 1.56 ± 2.44 in group B, while 7.30 ± 1.21, 8.25 ± 3.1 and 1.22 ± 1.87 in group C.Objective image quality of group B is better than group A and group C(P <0.05), objective image quality of group C was no significant difference compared to group A(P > 0.05). The subjective score was 4.29 ± 0.32 in group A,while 4.29 ± 0.23 in group B and 3.51 ± 0.15 in group C, the subjective score of group B and group A was no significant difference(P > 0.05), the subjective score of group C is lower than group A and group B(P <0.05).Conclusion : Equivalent quality image can be acquired by both reference of 250 m As and reference of 150 m As with CARE Dose 4D,while the radiation dose reduced by 40.39%.IRIS combined CARE dose 4D can reduce the radiation dose of liver CT by 59.5% under the condition of guaranteeing the quality of the image.