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.

Objective:To investigate the uncertainty of the dose measurements of superficial organs and the image noise in CT scanning.Methods:GE Revolution CT was used to perform 20 repeated scans on the isolated skull specimen in sequential and helical mode. The chest phantom was scanned for 45 times with the pitch 1.0 and the collimation 80 mm for two scanners (GE Revolution CT, Philips Brilliance iCT) and 40 mm for the Siemens Somatom Definition Flash CT. The volume CT dose index (CTDI vol) was maintained during the above scannings. A dosimeter was used to measure the dose at the position of the right eye lens of the specimen and the center of right breast of the chest phantom. The position of dosimeter sensor remained unchanged. The standard deviation of CT values (image noise) in the air region of cross-sectional images at the center of the sensor reconstructed with lung/soft tissue algorithms were measured. The mean values ( Av), standard deviations ( SD), coefficients of variation ( CV) and relative ranges ( RR) of the dosimetric values and the standard deviations of CT values of 3, 5, 10, 20, 30 and 45 scans were calculated. Pearson and Spearman correlation analysis were used to evaluate the correlation between the dosimetric values and the standard deviations of CT values. Results:The measured dosimetric values of the skull specimen were almost unchanged in the sequential scannings. The relative range of dose in helical mode was 10.67%. The relative ranges of the measured values of the three CT scanners for 45 scans reached 43.83%, 25.31%, and 14.32%. The standard deviations of CT values of the lung/soft tissue images varied greatly and the differences were not completely related to the dosimetric values.Conclusions:The dosimetric values of superficial organs were stable in the sequential scanning mode. The dose measurements of superficial organs and the image noise changed greatly in helical scanning mode.

Objective:To investigate the effect of organ dose modulation (ODM) technique on reducing the breast radiation dose in chest CT scanning.Methods:In the phantom test, the PBU-2 adult chest module was used. The clinical chest scan protocol was used and three sets of scans performed on the chest module： (1) ODM off group, ODM was not used; (2) ODM part group, ODM was applied only in the breast region； (3) ODM all group, ODM was applied in the whole scan scope. Other scan parameters were same for the three groups, with smart mA applied. The volume CT dose index (CTDI vol) was recorded for all three groups. A long rod ionization chamber was placed in a fixed position in front of the right breast area to measure the breast skin dose (D). The contrast noise ratio (CNR) and the figure of merit (FOM) were measured respectively. In clinical research, 72 female patients who underwent chest CT scanning in Beijing Tongren Hospital Capital Medical University from August to November 2018 were retrospectively recruited. According to the application of ODM, the patients were divided into ODM off group (without ODM, 36 cases) and ODM part group (ODM applied in the breast region, 36 cases). The CTDI vol and the dose length product (DLP) were recorded. CNR, noise of images were measured and calculated, respectively. The image quality was evaluated by subjective evaluation scores. The one way ANOVA analysis was used in comparing the difference of CNR among the 3 groups in module test. As for clinical cases, the independent samples t test was used to compare the difference in CTDI vol, DLP, CNR and the noise between two groups; and the rank-sum test was used for comparison in image quality subjective evaluation. Results:In module test, the radiation dose was highest in ODM off group, and lowest in ODM all group. The CTDI vol were (6.90±0.02), (6.26±0.02) and (5.99±0.02) mGy, and the D values were (9.17±1.01), (8.01±0.92) and (7.58±0.87) mGy for ODM off group, ODM part group and ODM all group respectively. The CNR values of images with soft tissue algorithm reconstruction were highest in ODM off group and lowest in ODM all group, while no statistically significant difference was displayed ( P>0.05). The CNR values of the images with lung algorithm reconstruction showed the same trend, with statistically significant difference among the three groups ( F=154.732, P=0.006). The FOM of the lung and soft tissue algorithm images was maximized when the ODM was partially applied. As for clinical cases, compared with ODM off group, the dose of ODM part group showed significantly decreased, with CTDI vol decreased by 16.12% ( t=2.604, P=0.011), and the DLP decreased by 16.85% ( t=3.293, P=0.002). No significant difference was found in CNR, noise and subjective score by two doctors between two groups ( P>0.05). Conclusion:The application of ODM in chest CT imaging can reduce the radiation dose of breast with simultaneously maintaining the image quality.

Objective To study the impact on the radiation dose,organ doses of eye lens and thyroid and image quality with different scanning modes in head and neck CT scan.Methods The simulation phantom of head and neck was scanned by using fixed scanning condition (120 kV and 200 mAs),as well as the combinations of automatic tube current modulation (CARE Dose 4D),automatic tube voltage modulation technique (CARE kV) and partial angle scanning mode (X-CARE) respectively.Six kinds of scanning modes were adopted,including 120 kV +200 mAs,120 kV + 200 mAs + X-CARE,CARE Dose 4D + 120 kV,CARE Dose 4D + 120 kV + X-CARE,CARE Dose 4D + CARE kV,CARE Dose 4D + CARE kV + X-CARE.Two thermolumineseece dosimeters (TLDs) were exposed at the skin surface positions of eye lens and thyroid,and the values measured with two TLDs were averaged.The CT dose index volume (CTDIvol) and dose length product (DLP) for every scan were recorded,and the contrast to noise ratio (CNR) in eye lens section and thyroid section were measured.Results The crgan doses of lens and thyroid were 19.8 and 26 mGy at 120 kV and 200 mAs,as well as 13.3 and 22.2 mGv at X-CARE mode.Compared with the manual selection of 120 kV,the combination of CARE kV and CARE Dose 4D made the values of CTDIvol drop from 13.1 to 10.1 mGy,the doses of eye lens and thyroid from 16.6 and 20.8 mGy to 23.7 and 19.9 mGy respectively,while the image quality reducedsignificantly.Compared with CARE Dose 4D + 120 kV,the organ doses of eye lens and thyroid were reduced from 20.8 and 23.7 mGy to 9.6 and 15.1 mGy for with additional X-CARE,while CTDIvol dropped from 13.1 to 9.3 mGy.When the combination of CARE Dose 4D + CARE kV + X-CARE was used,CTDIvol and organ doses were reduced to a minimum,when the CNRs of head and neck were also minimized.Conclusions The scanning mode CARE Dose 4D + 120 kV + X-CARE for head and CARE Dose 4D + CARE kV for neck can effectively reduce the radiation dose while keeping good image quality.When requirements for image quality are not high,CARE Dose 4D + CARE kV + X-CARE mode can be selected to reduce the radiation dose significantly.

胸部的数字化X线摄影(DR)以优良的图像质量、优化的工作流程、较大的曝光动态范围~([1]),在临床上广为应用.然而,DR摄影也存在一定的辐射损害,特别是婴幼儿处于发育阶段,胸部摄影时婴幼儿腺体对X线尤为敏感~([2])。