[en] Objective: To evaluate the effect of spectral CT monochromatic imaging on the detection of hepatic tumors. Methods: Forty-two patients with hepatic tumors (14 patients with hepatocellular carcinoma, 12 patients with metastatic tumor, 16 patients with hemangioma) underwent CT spectral imaging. During arterial phase, portal phase and venous phase, 140 kVp polychromatic images and 70 keV monochromatic images were obtained. Paired-sample t tests were used to compare the image quality score, liver noise and tumor-to-liver contrast-to-noise ratio (CNR) between the two image data sets. The detection rates of various tumors during each phase were compared. Results: The image quality scores of various tumors during three phases were (4.30±0.25) and (3.63±0.22) averagely for the 70 keV and 140 kVp images. The liver noises were (8.82±0.82) and (10.66±1.10), and the CNRs were 5.39 and 3.89, respectively. The image quality score, the liver noise and the CNR of 70 keV images were significantly greater than those of 140 kVp images (P<0.05). The detection rates of various tumors during each phase were higher with 70 keV images (78%-100%) than with 140 kVp images (65%-96%), except the hepatic metastatic tumors and the hepatic hemangiomas during the arterial phase. The detection rate was more increased for the small lesions less than 1 cm (57%-100% vs. 14%-91%). Conclusion: By substantially improving the image quality and increasing the tumor-of-liver conspicuity, the 70 keV monochromatic imaging of spectral CT improves the detection of hepatic tumors and is more sensitive for the detection of small lesions. (authors)

[en] Objective: To compare radiation dose and image quality between prospective electrocardiograph (ECG)-triggered axial scan and retrospective ECG-gated helical scan in coronary 64-slice CT angiography (CTA). Methods: Seventy-seven consecutive patients [group A. Average body mass index (BMI): 24.6, heart rate < 70 bpm] underwent 64-slice CTA using prospective ECG-triggered axial scan protocol (120 kV, mA tailored to BMI). For each patient, the simulated radiation dose using retrospective ECG-gated scan protocol without ECG-driven X-ray current modulation technology was calculated and recorded at same kV and mA. Retrospective ECG-gated scan protocol was performed on 30 consecutive patients in another group (group B. Average BMI: 23.9, heart rate < 70 bpm). The image quality was blindly evaluated between group A and B (paired t-test was used and P<0.05 as a significant difference). Results: There was a significant difference (t=18.50, P<0.01) between radiation dose of group A (3.37 mSv) and that of group B (18.13 mSv), decreased by 81.4%. The image quality of group A could fulfill clinical diagnostic needs. The average radiation dose of using simulated helical scan without optimization was 17.29 mSv, which was similar to that of group B (18.13 mSv) (t=0. 87, P>0.05). Conclusion: Prospective ECG-triggered axial scan in 64-slice coronary CTA can significantly reduce radiation exposure and the image quality can fulfill clinical diagnostic needs. (authors)

[en] Objective: To evaluate radiation dose and image quality of prospective electrocardiograph (ECG)-triggered coronary 64-slice CT angiography (CTA) with different kV, and the feasibility of coronary scan with < 1 mSv radiation dose. Methods: Ninety consecutive patients [heart rate: (54±6) bpm, BMI < 21.5 kg/m²] underwent 64-slice CTA using prospective ECG-triggered axial scan protocol. They were divided into two groups: 45 were in group A(100 kV), 45 were in group B(120 kV), and their electric currents were tailored to patient's BMI. The radiation dose was recorded and the image quality (5 for excellent, 1 for bad) was blindly evaluated. Statistical t-test was performed between two groups on dose and image quality. Results: The radiation dose of group A, B was (0.88±0.32), (1.47± 0.41) mSv respectively. There was no significant difference between image quality of group A with 100 kV (4.32±0.28) and that of group B with 120 kV (4.52±0.34) ( t=0.771,P>0.05). And radiation dose of the patient using axial scan protocol at 100 kV was decreased by 40% compared with that of group B at 120 kV (t=12.125, P<0.01). Conclusion: Prospective ECG-triggered axial scan in 64-slice coronary CTA can significantly reduce radiation exposure. For low-BMI (< 21.5 kg/m²) patients, super low dose scan (< 1 mSv) at 100 kV using prospective ECG-triggered axial scan could be selected. And the image quality can meet clinical diagnostic needs. (authors)

[en] Objective: To assess the value of spectral CT in reducing artifacts caused by metallic implants. Methods: Porcine lumbar spines were chosen as anthropomorphic phantom. The model was examined before and after implanting the titanic nail into the second and fourth lumbar vertebral body using gemstone spectral CT protocol and standard 120 kVp spectra. Specific post-processing technique was applied to generate 11 kinds of images of monochromatic energy and Metal Artifacts Reducing system (MARs) with the interval of 10 keV ranging from 40-140 keV. The image quality was compared subjectively between 120 kVp group and GSI group after implantation. Three regions of interest based on distances along the most pronounced artifact were chosen and marked as ROI_near, ROI_mid, ROI_far successively. Artifacts parameters including CT value and SD value were measured. The CT value of different ROIs were compared with LSD and Bonferroni test. Contrast-to-noise ratio and artifacts index were calculated. An optimal range of keV was determined according to artifacts index. Results: Image quality of' Gemstone spectra images was rated superior to the standard images. An optimized spectrum of keV based on artifacts index was from 80 keV to 100 keV. For ROI_near, CT value was (80.25±16.00) HU and (30.10±10.45) HU respectively in group Mono before implantation and group Mono + MARs after implantation. The differences were significant (Z= 2.978, P<0.05 ). For ROI_mid and ROI_far, CT value was (63.21±6.61) HU and (54.84±10.60) HU, (76.54±9.07) HU and (73.20±5.39) HU respectively. There was no significant differences (t=0.530, P>0.05; t=0.822, P>0.05). Conclusion: Metal artifacts could be reduced effectively at the site 3 cm away from implants using gemstone spectral CT. An accurate CT value of surrounding tissue can be obtained. (authors)

[en] Objective: To assess the clinical value of volume helical shuttle (VHS) of high definition CT (HDCT) in the diagnosis of congenital heart disease (CHD). Methods: Forty-three patients suffering from CHD were examined with VHS of HDCT and echocardiography (ECHO). Twenty-four patients (21 children, 3 adults) received surgery. Based on surgical data,the diagnostic accuracy of CHD by VHS of HDCT was compared with that by ECHO with respect to the intra-cardiac lesion, extra-cardiac lesion and hemodynamics. The visibility of the origin and proximal course of coronary arteries was also evaluated on VHS. CT effective doses were calculated,using mSv =DLP × K. Results: Thirty-six intra-cardiac deformities were found by operation, and the diagnostic accuracy of both VSH and ECHO were 100.0% (36/36). VHS successfully detected 42 of 44 (95.4%) cardiac-vascular connection and large vascular deformities, whereas ECHO only detected 26 (59.1% ). The right-to-left shunt and left-to-right shunt of septal defects revealed by VHS were 5 and 6 patients respectively, which all coincided with the results of ECHO.Fourteen bi-directional shunt of septal defects were detected by ECHO, and 13 of them were diagnosed as right-to-left shunt by HDCT except an illegibility in 1 patient. The origin and proximal course of coronary arteries were all visible on VHS. Effective dose for children was (3.38 ± 1.86) mSv, and for adults was (10.27 ± 2.59) mSv. Conclusions: VHS of HDCT scan is advantageous in the diagnosis of CHD. It can depict the intra- and extra- cardiac structures as well as coronary arteries and provide hemodynamic information. (authors)

[en] Objective: To analyze the distribution of image noise in low-dose chest CT scan and optimize the relative scanning parameters. Methods: The CT images of the Chinese anthropomorphic chest phantom (CDP-1 C) were simulated into six groups of low-dose images with different noise indexes by using an image noise addition tool. The difference between the preset noise index and analog noise value was compared. The CT images of 20 volunteers were also simulated into nine groups of low dose scans with the tube currents of 10, 30, 50, 80, 100, 120, 150, 180 and 240 mA. The noise values of images were recorded and analyzed. Results: There was no statistical difference between the analog noise value and the noise index. The image noise of low-dose chest scan was increased with the decrease of tube current. The noise was increased quickly when the current was decreased from 50 to 30 mA (F=24.09 - 40.79, P<0.05), but the noise increased slowly when the current decreased from 240 to 80 mA. There was no statistical difference between the noise of 80 mA group and that of 120 mA (P>0.05). Conclusions: The noise addition tool can be used to evaluate the image noise of low-dose chest CT scan. Adoption of 80 mA in chest CT scan would result in low radiation dose without adding image noise. (authors)