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Objective:To investigate the effect of different scanning modes, detector width and location in detector on high and low contrast resolution of wide-detector CT image.Methods:The Catphan600 phantom with high and low contrast resolution modules was scanned with GE Revolution CT at the same CTDI vol. The scans were performed with the detector widths of 40, 80 and 160 mm for sequential scanning mode and with the detector width/pitch combinations of 40 mm/0.516, 40 mm/0.984, 80 mm/0.508 and 80 mm/0.992 for spiral scanning mode. The resolution modules were placed at the adjacent region between two sequential scans, central and foot side edge in the longitudinal scanning range seperately. The subjective evaluation of the high and low contrast resolution was performed by two radiologists. Results:The high contrast resolution was 8 LP/cm at adjacent region between two sequential scans with the detector width of 80 mm or 160 mm in sequential scanning mode, and at the pitch of 0.5 in spiral scanning mode, while it was 7 LP/cm for the rest of detector combinations. The distinguishable diameter was 3 mm at 1% low contrast resolution at foot side edge with the detector widths of 80 mm or 160 mm in the sequential scanning mode, and it was 2 mm for all the other conditions. The distinguishable diameter was 2 mm at 1% low contrast resolution with the detector width of 40 mm and pitch 0.516 in the spiral scanning mode and it was worse with the wider detector and larger pitch.Conclusions:For the wide-detector CT, scanning mode, detector width, location in detector and pitches will affect the high and low contrast resolution to some degree. Appropriate selection should be done according to actual needs in clinical practice.
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Objective:To explore the application value of wide detector multi-slice spiral CT target scanning technique in the preoperative evaluation of pancreatic cancer.Methods:The clinical data of 22 patients with pancreatic cancer who underwent pancreatic arterial contrast enhanced CT scanning and were diagnosed by pathology in the First Affiliated Hospital of Naval Medical University from September 2019 to October 2019 were analyzed retrospectively. The CT phantom experiment was carried out on the international standard phantom CATPHON500. By changing the scanning radiation dose, scanning mode and scanning field of view, the spatial resolution and density resolution of the image were compared and analyzed. The target scan technical parameters obtained from the experiment were applied to the late arterial phase of MDCT enhanced scan in 22 patients with pancreatic cancer. Executive current, volume scanning mode and small scanning field were used for scanning. The attenuation value (CT value) and noise value (SD value) of pancreatic cancer tissue and normal pancreatic tissue were measured at different phases, the attenuation difference and contrast signal-to-noise ratio (CNR) of the two tissues were calculated, the contrast difference between the two tissues was evaluated, and the CT values of celiac trunk, renal artery and vein, superior mesenteric artery and vein, splenic vein and portal vein were measured, and the display of tumor tissue and peripancreatic important vessels was evaluated.Results:In the phantom experiment, under the condition of the same radiation dose, the image quality of the volume scan mode was better than that of the spiral scan mode (1%@4 mm versus 1%@9 mm at 5 mGy and 1%@2 mm versus 1%@6 mm at 25 mGy). In comparison between pancreatic tumor and pancreatic tissue, the enhancement process of pancreatic tumor tissue was increased at first and then decreased, while that of pancreatic tumor tissue was slightly enhanced. The attenuation difference between pancreatic tissue and tumor tissue and CNR also increased at first and then decreased, reaching the maximum at the late arterial stage [(91.96±29.29)HU, 8.60±5.71]. The differences between each phase were statistically significant ( F values were 47.20 and 19.80 respectively, all P values <0.05). The evaluation of vascular variation and invasion showed that a better arterial phase image could be obtained on the late arterial target scan images, while taking into account the display of splenic vein, mesenteric vein and portal vein. Conclusions:The wide detector MDCT target scanning technique can improve the spatial resolution and density resolution of the image, greatly improve the contrast between tumor tissue and peripancreatic tissue and blood vessels, and provide more accurate tumor staging and resectability evaluation information for preoperative evaluation of pancreatic cancer.
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Objective To explore the distribution characteristics on z-axis of scattered radiation from a wide-detector CT with different scan modes and detector widths.Methods The CT standard-dose phantom was scanned using a 16 cm wide detector Revolution CT.Thermoluminescent dosimeters (TLDs)were placed on the central axis (z-axis) of the scan hole at given intervals.As scan modes,both axial scan mode (using detector with width in 4,8 or 16 cm) and the helical scan mode (using detector with width in 4 and 8 cm) are used.The scan parameters were as follows:tube voltage 120 kV;effective tube current 200 mAs;scan length 16 cm;pitch (for helical scan):0.984 ∶ 1 and 0.516 ∶ 1,and all scans were repeated for 4 times.All TLDs were measured,after exposure,and divided by four for further analysis.Results The scattered radiation on z-axis was higher at the direction of human head than at the direction of human foot (Z=-2.366,-2.197,-2.366,-2.371,-2.028,-2.236,-2.028,P＜0.05).Under the axial scan,the difference in distribution of scattered radiation with different detector widths was statistically significant.The maximum increase for detector width of 4 cm and 16 cm was 67.5 μ Gy(x2=28.000,P＜0.05).Under the helical scan,the difference in distribution of scattered radiation with different detector widths was statistically significant (Z =-3.233,-2.982,P＜0.05).The largest distribution of scattered radiation was found when the detector width was 8 cm and the smallest at the detector width is 4 cm.The maximum increase for detector width of 8 and 4 cm was 97.67 μGy at a pitch of 0.516 ∶ 1.Furthermore,when the detector width and effective mAs were the same,the scattered radiation at a pitch of 0.516∶1 was greater than that at a pitch of 0.984 ∶ 1,with the statistically significant difference(Z =-3.296,-3.296,P＜0.05).The maximum increase was 49.95 μGy when the detector width was 8 cm.Conclusions In a 16 cm wide-detector CT,the selection of different detector widths can significantly influence the distribution of radiation field and related radiation values.Suitable detector width and relevant parameters shall be chosen according to the specific clinical requirements so as to reduce the radiation doses to workers,patients and carers.
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Objective To investigate the value of wide-detector helical CT combined with adaptive statistical iterative reconstruction-V (ASIR-V) in the low radiation dose CT examination of upper abdomen in obese patients.Methods In the first phantom experiment part,the optimal percentage of pre-and post-ASIR-V of abdominal scanning (120 kVp,NI =10 HU) were explored.The second human experiment was performed based on the phantom study,and our institutional review board approved this prospective study,each participant provided written informed consent.87 obese patients (body mass index,BMI ≥30 kg/m2) underwent contrast-enhanced abdominal CT scan were randomly divided into two scan protocols [protocol A:n =43,120 kVp,detector coverage of 80 mm,40％ pre-ASIR-V (group A1)and combined with 60％ post-ASIR-V (group A2) respectively;protocol B,n =44,120 kVp,detector coverage of 40 mm,40％ ASIR (group B)].Quantitative parameters [image noise and contrast-to-noise ratio (CNR)] and qualitative visual parameters (overall image quality as graded on a 5-point scale) were compared.Weighted effective dose (E) were assessed.Results The optimal percentage of pre-and post-ASIR-V of abdominal scanning were 40％ and 60％,respectively.The effective radiation dose in protocol A [(4.55 ± 0.95) mSv] was decreased for 53％ as compared with protocol B [(9.58 ± 2.04) mSv](t =-14.773,P ＜ 0.001).During the arterial phase and portal venous phase,except for the CNRs of liver,Group A2 showed higher CNRs (q =2.160-3.209,P ＜ 0.05),lower image noise(q =-4.212--3.202,P＜0.05),and higher overall image quality scores(Z =-5.155--2.561,P ＜0.05) as compared with group A1 and group B.Group A1 showed similar CNRs,similar image noise(P ＞ 0.05),and lower overall image quality scores (Z =-3.298--3.030,P ＜ 0.05) than group B.The overall image quality scores in group A were all greater than 3 point and met the clinical diagnostic level.Conclusions Compared with stand-detector helical CT in obese patients,the wide-detector helical CT combined with 40％ pre-ASIR-V could reduce the radiation dose by 53％,and improve overall image quality by combining post-ASIR-V technique.