The Study Of Automatic Spectral Imaging Protocol Selection In Optimizing Abdominal CT Scan And Diagnosis

Recently, with the rapid development of CT technology and the increase of clinical demands, dual energy CT has become the focus of radiology again. Under this development background, based on the accordant taking of dual-energy data,spectral CT can generate the conjunction of temporal and spatial data through the rapid alternation between two peak voltage settings(140 k Vp and 80 k Vp, i.e.“fast switching”), implementing the spectral resolution in the data space. Spectral CT can actrulize the energetic resolution and the physicochemical properties of resolution as well as the high spatial resolution and temporal resolution in conventional CT.Spectral CT can push the conventional diagnostic model based on the CT value toward the new of multi-parameter imaging diagnostic mode that is a five dimensional spatial model(x, y, z, time and energy). Spectral CT can acquire the qualitative images like conventional CT and the multi-parameter images generated from spectral imaging viewer such as: monochromatic image, material decomposition image, monochromatic spectral HU curve and effective atomic number image, which can give multi-dimensional evaluation about the nature and function of the organization. This technology has displayed huge application value in the scientific research and clinical work. The advantage of high contrast in low energy level will benefit the reduction of intake for contrast media.However, the image noise in low-energy image always high and will affect the diagnosis. Moreover, the radiation dose in spectral CT is always being studied and discussed. Application of adaptive statistical iterative reconstruction into monochromatic images in spectral CT will help reduce the image noise.Automatic spectral imaging protocol selection technique can automatically choose the optimal parameters for patients based on the patient’s body size and scanning parameters, according to the noise index of non-spectral imaging. It will optimize the radiation dose of patients in the spectral CT scanning. Hepatocelluar carcinoma is one of most maligment tumor in China, charatized by the high rate of death and rapid progress. Thus, early diagnosis and timely treatment evaluation is very importment. Spectral CT has revealed important clinical value in the detection of small hepatocelluar carcinoma and differential diagnosis of hepatocelluar carcinoma.However, the issue of radiation dose has limited spectral CT to be an imaging screening method. Therefore,the objective of the study is to evaluate the radiation dose and image quality of automatic spectral imaging protocol selection technique,as well as the value of maintain and improve the diagnostic efficacy in the hepatocellular carcinoma.Part 1 A comparison of automatic spectral imaging protocol selection scan and conventional CT scan in the image quality for a given radiation dose: phantom studyObjective:To compare image quality obtained in phantoms with automatic spectral imaging protocol selection(ASIS) scan with that obtained with conventional 80-k Vp,100-k Vp and 120-k Vp computed tomography(CT) scan for a given radiation dose.Materials and Methods:Eight test tubes were filled with a diluted contrast medium(each test tube contained a contrast medium with a different iodine concentration [0,0.5,1,2.5,5,10,20 or 50 mg of iodine per milliliter]), and a ninth syringe located in the center of the phantom was filled with water. The phantom was examined with conventional 80 k Vp mode(protocol A), 100 k Vp mode(protocol B), 120 k Vp mode(protocol C) and the use of the fast kilovoltage switching(80 and 140 k Vp)(protocol D). The ke V of monochromatic image in protocol D with equivalent CT value were calculated according to the conventional protocol(A, B or C).Images of all protocols were reconstructed with adaptive statistical iterative reconstruction( ASIR) with the percentage of 30%,50% and 70%. The contrast to noise ratio(CNR) of each tube relative to the center tube was calculated. Independent two sample t test was employed to compare the difference of image noise and CNR between protocol D and protocol A(B or C).Results:1. The ke V range of monochromatic image in protocol D with equivalent CT value were 40~55ke V according to protocol A, 43~62ke V according to protocol B and 48~68ke V according to protocol B, with the average energy level at 49 ke V, 55 ke V and 60 ke V, respectively.2. The image noise of 30%ASIR in protocol D [(12.68±2.32)HU] was higher than that of 30%ASIR、 50%ASIR and 70%ASIR in protocol A[(8.12±1.530)HU、(7.00±1.52)HU and(6.34±1.98)HU,P=0.001,<0.001 and<0.001 respectively],increased by 56%,81% and 100% respectively. The image noise of 50%ASIR in protocol D [(9.73±1.49)HU] was higher than that of 50%ASIR and 70%ASIR in protocol B[ P=0.005 and 0.004 respectively], increased by 39% and 53% respectively.There was no significant difference in image noise with 70%ASIR and in CNR with all ASIR percentage levels between protocol D and protocol A.3. The image noise of 30%ASIR in protocol D [(9.91±3.40)HU] was higher than that of 50%ASIR and 70%ASIR in protocol B[(6.38±1.80)HU and(5.93±2.22)HU,P=0.032 and0.023 respectively], increased by 55% and 67% respectively,and similar to 30%ASIR of protocol B. There was no significant difference in image noise of protocol D with 50%ASIR and 70%ASIR and in CNR with all ASIR percentage levels between protocol D and protocol A.4. The image noise of 30%ASIR in protocol D [(7.95±2.80)HU] was higher than that of 70%ASIR in protocol C [(5.15±1.67)HU,P=0.042], increased by 54%. The image noise of 50%ASIR in protocol D was similar to the image noise of protocol C.The image noise of 70%ASIR in protocol D [(4.94±1.18) HU] was lower than that of70%ASIR in protocol C(P=0.021), decreased by 23%. There was no significant difference in CNR with all ASIR percentage levels between protocol D and protocol A.Conclusion:Automatic spectral imaging protocol selection scan yielded similar image noise and CNR than did conventional CT scan for a given radiation dosePart 2 The application value of automatic spectral imaging protocol selection technique in abdominal CTObjective:To evaluate the image noise and radiation dose of automatic spectral imaging protocol selection technique(ASIS) technique in abdominal CT and identify the relation between the radiation dose and body mass index(BMI).Materials and methods:In this prospective study, 60 patients underwent whole abdominal dynamic enhanced CT scans were included with each patient’s BMI recorded. Plain CT scan was performed with the mode of 120 k Vp and automatic exposure control technique(protocol A) and two-phase contrast enhanced CT scan was performed with CT spectral imaging mode. According to the maximum m As of the plain scan,corresponding spectral imaging modes were manually selected for arterial phase(protocol B). With ASIS technique, spectral imaging modes were automatically selected for portal venous phase(protocol C). With the gemstone spectral imaging viewer, monochromatic enegy images at the level of 65 ke V were generated for analyses. Image noise of bladder and fat, volume CT dose index(CTDIvol) and dose length product(DLP) were recorded and compared between protocol A(or B) and C with paired t-test. The relationship between BMI and the CTDIvol of protocol C was assessed using Pearson test.Results:The CTDIvol and DLP in protocol C was(13.81±6.18) m Gy and(650.3±343.1)m Gycm respectively, similar to that in protocol A [CTDIvol and DLP:(13.98±5.38)m Gy and(654.5±297.7) m Gy?cm]and protocol B[(12.98±6.97) m Gy and(636.3±315.4) m Gy?cm](both P values >0.05).The image noises of protocol C in bladder and fat [(8.89±1.65)、(6.09±1.38)HU] were lower than those of protocol A[(11.5±1.88) 、(8.27±1.66)HU](all P values <0.001), and had no significant difference with protocol B [(8.95±1.35)、(6.38±1.22)HU](both P values >0.05).There was a positive correlation between the CTDIvol of protocol C and patients’ BMI(r=0.932, P<0.001)(all P values >0.05).Conclusion:The radiation dose of ASIS technique is equivanlent with manual spectral imaging protocol selection and conventional 120 k Vp scan and had positive correlation with BMI. The image noise of 65 ke V monochromatic images with ASIS technique is lower than conventional 120 k Vp but similar to manual spectral imaging protocol selection.Part 3 Effect of automatic spectral imaging mode selection and adaptive statistical iterative reconstruction at abdominal CT with low contrast agent doseObjective:To investigate the image quality and radiation dose of automatic spectral imaging mode selection and adaptive statistical iterative reconstruction(ASIR) at abdominal CT with low contrast agent dose.Materials and methods:One hundred patients underwent the arterial-phase(AP) and portal venous phase(PVP) contrast-enhanced abdominal CT scan were analyzed prospectively. Patients were randomly assigned to the study group and control group(n=50 each). In the study group, automatic spectral imaging mode selection and contrast agent dose of300 mg I/kg were used and spectral monochromatic images(40 ~ 60 ke V) were reconstructed using either filtered back-projection(FBP)(group A) or ASIR(group B). In the control group, the fixed tube potential of 120 k Vp and contrast agent dose of 450 mg I/kg were used with images reconstructed using FBP(group C).Quantitative parameters(image noise in HU and contrast-to-noise ratio of the liver,pancreas, aorta and portal vein) and qualitative visual parameters(overall image quality as graded on a 5-point scale) were compared among the groups by using One-way ANOVA or Kruskal-Wallis H test. Two sample t tests were used compare the radiation dose difference.Results:There had no significant difference in CTDIvol [both(12±5) m Gy] and DLP[(364±142) m Gy.cm versus(377±131) m Gy.cm] between the study group and control group(t=-0.408 and-0.428, All P values > 0.05). During the AP and PVP, at the energy level of 40 ke V, group B showed higher CNRs than group A and group C,lower image noise[(29±6)HU in AP,(24±6)HU in PVP] than group A[(43±11)HU,(44±10)HU] but higher image noise than group C[(18±4)HU,(18±4)HU], lower overall image quality scores [(3.0±0.2)point,(2.9±0.3) point] than group C [(3.6±0.4)point,(3.6±0.5) point] but similar scores to group A[(2.9±0.4) point、(2.8±0.4)point].At the energy level of 50 ke V, group B showed higher CNRs than group A but higher than or similar CNRs to group C, lower image noise[(20±5)HU,(20±4)HU] than group A[(31±8)HU,(31±7)HU] but similar image noise to group C, higher overall image quality scores [(3.6±0.4)point,(3.5±0.4) point]than group A[(3.3±0.3) point、(3.3±0.3) point] but simlar scores to group C. At the energy level of 60 ke V, group B showed lower image noise[(14±4)HU,(14±3)HU],higher CNRs and overall image quality scores[(3.9±0.4) point,(3.9±0.3) point] than group A [(19±5) and(20±5)HU in image noise,(3.7±0.4) and(3.7±0.3) point in overall image quality scores ]and group C. Except for monochromatic images at 40 ke V, the overall image quality scores in group B were all greater than 3 point and met the clinical diagnostic level.Conclusion:The radiation dose of CT spectral imaging and conventional 120 k Vp CT scan is equivalent with the use of automatic spectral imaging mode selection; combined use of ASIR technique, monochromatic images at 50 and 60 ke V can improve CNR and reduce contrast agent dose while maintain or improve overall image quality.Part 4 Comparison of low k Vp and automatic spectral imaging mode selection with adaptive statistical iterative reconstruction at abdominal CT with low contrast agent dose and in the detectability of hepatocellular carcinomaObjective:To investigate the image quality and radiation dose of low k Vp and automatic spectral imaging mode selection with adaptive statistical iterative reconstruction(ASIR) at abdominal CT with low contrast agent dose, and the ability in the detection of hepatocellular carcinoma.Materials and methods:Two hundred and forty patients underwent the arterial-phase(AP) and portal venous phase(PVP) contrast-enhanced abdominal CT scan were analyzed prospectively. Patients were randomly assigned to the study group and control group(n=120 each). The control group was assigned to subgroups as follows(n=60 each):group A: 80 k Vp,300 mg I/kg,BMI≤23.9 kg/m2; group C:100k Vp,450 mg I/kg,24 kg/m2≤BMI < 28.9 kg/m2.The study group, automatic spectral imaging mode selection was used and the other scanning parameters were matched group A or group C to generate group B or group D respectively(n=60 each). ASIR was used to reconstruct the images in the control group and spectral monochromatic images(40-60 ke V) in the study group.Quantitative parameters(image noise in HU and contrast-to-noise ratio of the liver, pancreas, aorta and portal vein) and qualitative visual parameters(overall image quality as graded on a 5-point scale) were compared.Leison to normal parenchyma ratio and lesion detectabilty were calculated.Independent two sample t tests were used compare the parameters and radiation dose difference.Results:The image noise in the control group was lower compared to the study group,except the image nosie at 60 ke V. At the energy level of 40 ke V and 50 ke V, the CNR in the study group was lower than or similar to the study group in AP while were higher than or similar to the study group in PP. There was no significant differences between the the study group and control group at the energy level of 60 ke V. Overall image quality scores in AP were similar between the study group and control group except the higher scores in group C compared to group D at 40 ke V, while the overall image quality scores in PP were higher at 50 ke V and 60 ke V in the study group than the control group but lower at 40 ke V.The lesion detectability in the the study group at 40 ke V and 50 ke V were higher than or similar to the control group, while lesion detectability in group B at 60 ke V was lower than group A but was similar beween group D at 60 ke V and group C. The CTDIvol and DLP in group A were lower than group B(P = 0.001 and 0.042 respectively),but were similar between group C and group D。Conclusion:Given the same BMI,contrast agent and scanning parameters, the radiation dose of automatic spectral imaging scann was higher than or similar to 80 k Vp scan while overall image quality and the lesion detectability at 50 ke V were higher than or similar to the 80 k Vp scan. The radiation dose of automatic spectral imaging scann was similar to 100 k Vp scan while overall image quality and the lesion detectability at50 ke V and 60 ke V were higher than or similar to the 100 k Vp scan.