Influence Of CT Effective Dose On The Detection And Measurement Of Pulmonary Nodules:a Phantom Study

Part One Repeatability of small lung nodule volume measurement in low-dose CT: a phantom studyPurpose: The aim of this phantom study was to investigate whether images captured with low dose computed tomography(CT)in different tube voltages and tube currents can improve the repeatability of small nodule volume measurement.Method: An anthropomorphic chest phantom containing artificial solid and ground glass nodules(GGNs),3?5?8?10 mm,was examined with a multi-detector CT scanner with nine tube currents of 20?30?40?50?60?70?80?90?100mAs in combination with four tube voltages of 70,80,100 and120 kVp.The volume of all nodules were measured on a workstation.Statistical analysis was performed.Result: Compared to the standard CT(120kVp?100mAs),the volume of all solid nodules had no difference(P>0.05).: Compared to the standard CT(120kVp?100mAs),volume of GGNs(10mm)with more than 80 kVp?50mAs had no difference(F=48.555 ? P=0.000,P=0.109);volume of GGNs(8mm)with more than 80 kVp?70mAs had no difference(F=55.645?P=0.000,P=0.205);volume of GGNs(5mm)with more than 80 kVp?70mAs had no difference(F=30.539?P=0.000,P=0.138);volume of GGNs(3mm)with more than 80 kVp?80mAs had no difference(F=28.183?P=0.000,P=0.191).Conclusion: Our results suggest a CT protocol with more than 80 mAs and 80 kVp is optimal for volume measurement of small nodules.Part Two Comparison between Different CT Protocols(LowDose and Conventional CT)for Lung Nodules Detection in a PhantomPurpose: To compare the detection rate of simulated lung nodules in a chest phantom using different computed tomography low dose(LD)protocols,and conventional CT(CCT),and to quantify their respective amount of radiation.Methods: A chest phantom containing simulated lung nodules was scanned using five different protocols: LDCT(80kVp/80 mA ?100kVp / 40 mA ?100 kVp/80 mA?120 kVp/40 mA)and CCT(120 kVp/200 mA).Four chest radiologists analyzed a selected image from each protocol and registered in diagrams the nodules they detected.Kruskal–Wallis and McNemar's tests were performed to determine the difference in nodule detection.Equivalent doses were estimated.Results: There was no significant difference in lung nodules' detection when comparing different LD protocols(P =0.205 to 1.000),but there was a significant difference when comparing each one of those against CCT(P < 0.001).the detection rate of nodules with CT attenuation values-600 and-800 HU was different when comparing all protocols against CCT(P < 0.001 to P = 0.007).there was at least moderate agreement between observers in all protocols(?-value >0.41).Equivalent dose values ranged from 0.53 to 4.24 mSv.Conclusion: There is no significant difference in simulated lung nodules' detection when comparing different LD protocols(ED = 0.53-1.05 mSv),but differ from CCT,these differences should be taken into account when selecting a protocol for the implementation of lung cancer screening programs.Part Three Influence of CT effective dose on the Detection of Pulmonary Nodules Using Deep Learning and Iterative Reconstruction: a PhantomStudyPurpose: To investigate the effective dose(E)effects on the detection of pulmonary nodules using deep learning and iterative reconstruction.Methods: Simulated nodules of various sizes and densities in a lung phantom were scanned at different levels of E(3-5,1-3,0.5-1 mSv)and were reconstructed with deep learning image reconstruction(DL-L?DL-M?DL-H)and iterative reconstruction(ASIR-V40%).Mean attenuation ?noise and signal-to-noise ratio of the nodules were obtained.CT images were also obtained.The number of nodules and corresponding volumes in different images were detected by CAD software system.Sensitivity,false positives(FPs),false negatives(FNs),and relative volume error(RVE)were calculated and compared to the aspects of the E.Results: The mean noise and SNR in ASIR-V40% and DL-H groups were not significantly different(P>0.05),while higher than other two groups(SNR)and lower than other two groups(noise)(P<0.05).The median sensitivity of ASIR-V40% and DL-H groups was significantly higher than other two groups(P<0.0001).The median FPs ?FNs and RVE of ASIR-V40% and DL-H groups was significantly lower than other two groups(P<0.0001).The median sensitivity?FPs ?FNs of ASIR-V40% and DL-H groups was not significantly different(P>0.05).Conclusion: Compared with ASIR-V40%,DL-H has similar detection efficiency and stability of pulmonary nodules,and has good clinical application prospects.