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Objective:To investigate the feasibility of simultaneous arteriovenous enhancement of neck CT with two-stage injection of contrast agent and its effect on image quality and radiation dose.Methods:A total of 30 patients undergoing neck CT enhancement scan due to space-occupying lesions in Beijing Tongren Hospital, Capital Medical University from February to April 2022 were prospectively included as the experimental group. The neck CT enhancement scan was performed with two-stage injection of contrast agent and arteriovenous simultaneous enhancement. The dosage of contrast agent was calculated according to the patient′s body weight, and the method of two-stage injection was adopted. The dosage of contrast agent in the first stage was 0.7 ml/kg, with normal saline in the middle stage, and the second stage (began at 35 s) was 0.3 ml/kg. A total of 30 patients with gender and age matching with the experimental group from December 2021 to January 2022 were retrospectively collected as the control group. The control group was treated with the traditional arterial phase and venous phase scanning method with the dosage of 1.0 ml/kg contrast agent. The arterial phase was scanned at the 30 s and the venous phase was scanned at the 60 s. The CT values of bilateral carotid arteries and jugular veins in the experimental group were measured, the CT values of bilateral carotid arteries in the arterial phase were measured in the control group, and the CT values of bilateral carotid arteries and jugular veins in the venous phase were measured. Carotid artery enhancement score was performed for images of experimental group and control group in arterial and venous phase, and jugular vein and lesion enhancement score was performed for images of experimental group and control group in venous phase. The effective dose was calculated for both groups. The difference of carotid artery CT values between images was compared by one-way analysis of variance, and LSD method was used for pairwise comparison. The CT values of jugular vein were compared using independent sample t test. Kruskal-Wallis test was used to compare carotid artery enhancement scores, and Nemenyi method was used for pairwise comparison. Jugular vein and lesion enhancement scores and effective dose were compared by Mann-Whitney U test. Results:The CT value of carotid artery of experimental group [left (276±24) HU, right (273±25) HU] was lower than that of control group in arterial phase [left (329±33) HU, right (327±32) HU], and higher than that in the venous phase [left (147±15) HU, right (148±16) HU]. All the differences were statistically significant ( P<0.001). The CT value of jugular vein of experimental group [left (206±18) HU, right (203±19)] was higher than that of control group in the venous phase [left (154±15) HU, right (151±15)], the difference was statistically significant ( t=11.88, 11.76, both P<0.001). There was no significant difference in carotid artery enhancement score between experimental group and control group in arterial phase ( P=0.624), but the carotid artery enhancement score of the experimental group was higher than that of the control group in the venous phase, and the difference was statistically significant ( P<0.001). The scores of jugular vein and lesion enhancement in experimental group were higher than those of control group in venous phase, and the difference was statistically significant ( Z=5.01, P<0.001). The effective dose of the experimental group [2.41(2.04, 2.72) mSv] was decreased by 52.2% compared with the control group [5.04(4.18, 5.44) mSv], and the difference was statistically significant ( Z=-6.24, P<0.001). Conclusions:The neck CT enhanced scan with two-stage injection of contrast agent and arteriovenous simultaneous enhancement method can obtain comprehensive images of arterial and venous phases, and realize simultaneous enhancement of carotid artery, jugular vein and lesions, and reduce radiation dose.
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Objective:To evaluate the influence of different detector widths and signal acquisition positions of wide-detector CT in different scanning modes on CT number and noise, and to provide a basis for reasonable selection of scanning modes and related parameters in clinical practice.Methods:The body dose phantom was scanned by GE Revolution CT. The scan was performed with detector widths of 40, 80 and 160 mm in sequential scanning mode and with detector width/pitch combinations of 40 mm/0.516, 40 mm/0.984, 80 mm/0.508 and 80 mm/0.992 in spiral scanning mode. The phantom was placed at the central and peripheral of the selected detector widths, and the adjacent positions between two axial scans. The images of the phantom were evaluated subjectively and the CT numbers and SDs were measured. The differences between the measured values at different imaging parameters were compared. The multi-group Friedman test was used to compare CT numbers and SD under different scanning parameters in sequential scanning mode, and the Wilcoxon test was used to compare CT numbers and SD in spiral scanning mode.Results:There was no statistically significant difference in the geometric shapes of the phantom images obtained at any combination of parameters. In sequential scanning mode, the differences at different detector widths were statistically significant (χ 2=14.00, P=0.001) with CT numbers at 40 mm and 160 mm greater than CT numbers at 80 mm ( P<0.05). The differences at different signal acquisition positions were statistically significant (χ 2=12.04, P=0.002) with CT numbers at peripheral and adjacent greater than CT numbers at central ( P<0.05). In spiral scanning mode CT numbers at detector width at 80 mm were greater than CT numbers at 40 mm ( Z=-2.10, P=0.036). For SD, the differences at different detector widths were statistically significant in sequential scanning modes (χ 2=8.17, P=0.017) with SD at 160 mm greater than SD at 80 mm ( P<0.05). The differences at different signal acquisition positions were statistically significant (χ 2=13.50, P=0.001) with SD at peripheral greater than SD at central ( P<0.05). In spiral scanning mode SDs at pitches 0.984 and 0.992 were greater than SDs at 0.516 and 0.508 ( Z=-2.66, P=0.008). There were no significant differences among other groups. Conclusion:The selection of scanning mode, detector width and signal acquisition position of wide-detector CT will affect the image CT numbers and SDs.
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Objective:To explore the image quality and its evaluation method using virtual grid under different tube voltages in the clinical chest X-ray exam.Methods:According to the conditions of chest X-ray photography commonly used in clinical practice, the corresponding thickness of plexiglass (20 cm, including CDRAD phantom) was determined as the experimental object. With a fixed tube loading of 4 mAs and the tube voltage from 60 to 125 kV, the experimental object was imaged in three ways: physical grid, none grid and virtual grid. The common physical parameters (CNR, σ, C, SNR), texture analysis (Angular second moment, texture Contrast, Correlation, Inverse difference moment, Entropy) and CDRAD phantom score (IQF inv) were evaluated. Two-way ANOVA test was used for each group of common physical parameters, and further pairwise comparisons were made. At the same time, applying virtual grids on the obtained images with chest anthropomorphic model and texture indexing the images with and without virtual grids, then rank sum test of paired sample can be conducted. Results:There were differences in image quality among the three groups of grid mode( P<0.05), and the physical grid delivered the best image quality. The tube voltage had an impact on all image quality evaluation indexes ( P<0.05). The tube voltage was positively correlated with CNR, SNR, angular second moment, inverse difference moment and IQF inv ( P<0.05), and negatively correlated with σ, C, texture contrast and entropy ( P<0.05). There was no significant correlation between the tube voltage and Correlation ( P>0.05). The chest anthropomorphic model images were used to evaluate the virtual grids, and the texture indexes (Angle second moment, Contrast, Correlation, Inverse difference moment, Entropy) were statistically significant (P<0.05). Conclusions:The virtual grid can improve the image quality of chest X-ray photography, and the image texture analysis method can be a useful supplement to the image quality evaluation parameters.
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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 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.
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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.
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Objective To investigate the effects of different tube voltages on the dose of superficial radiation-sensitive organs and image quality when using organ dose modulation( ODM) in chest CT. Methods Based on clinical chest CT protocol with the sameother parameters, chest phantom was scanned using 140, 120, 100, and 80 kv ( 100 kV was the recommended by the CT system) without ODM ( ODM off ) or with ODM from the starting layer to the breast area ( ODM part ) . A long rod ionization chamber was placed iat a fixed position in front of the right breast area. The scans were repeated for 7 times with each group of scanning parameters and dose values were measured for each scanning, the CTDIvol and breast skin dose measurements( D) were recorded. Coronal images of 5 mm thickness for the lung and soft tissue algorithms were reformatted. The images were divided into 8 parts along the z axis direction, the contrast noise ratios( CNR) for every region were measured. For CTDIvol , D, CNR for different ODM and tube voltage scanning modes, two factor non-repeat test ANOVA was performed. LSD method was used for comparison among groups. Results The CTDIvol was lowest at 80 kV, and the breast skin dose measurement was lowest at 100 kV, CTDIvol decreased in turn from140 to 80 kV ( F=105. 5795, P<0. 05) . The breast skin dose measurement decreased in turn from140 to 100 kV, but increased instead at 80 kV. The difference was statistically significant(F=27. 736, P<0. 05). Compared with ODM off , the CTDIvol and D for ODM part both declined and the differences were statistically significant ( F=39. 732, 81. 961, P<0. 05). The CNRs of the lung and soft tissue images decreased at every tube voltage(F=12. 809, 11. 261, P<0. 05 ) . The CNRs decreased from140 to 100 kV, but there was no statistical difference( P>0. 05) , and the difference was significant at 80 kV( P<0. 05) . Compared with ODM off, the CNRs of lung and soft tissue algorithm images with ODM part decreased, withnot statistically significant differences ( P>0. 05 ) . Conclusions In clinical practice, with the tube voltage not less than the recommended(100 kV), the optimal reduction of breast radiation dose can be achieved by reducing kV and using ODM on the premise of resonable image quality.
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Objective To explore the effects of detector width and pitch on radiation dose and image quality when using organ dose modulation (ODM) technology in a wide?area detector CT scanning. Methods Based on the clinical chest scan protocol,3 sets of scans of the chest phantom were performed using any combination of two detector width (40 mm and 80 mm) and pitch (0.500,1.000 and 1.375) with the same parameters:1 Do not use ODM technology (ODM off),2 open ODM (ODM part) 240 mm from scan start layer to breast area,3 open ODM (ODM all) in full 320 mm scan range. A long rod ionization chamber was placed in the fixed position in front of the right breast area. The scanning parameters of each group were measured 7 times, and the volume computed tomography dose index (CTDIvol) and breast skin dose measurement values D were recorded and the mean was calculated and recorded as Dav. The coronal 5 mm thick images of lung and soft tissue algorithms were reformed. It was divided into three parts in the Z?axis direction, and the contrast?to?noise ratio (CNR) and figure of merit (FOM) were measured separately. Independent sample t test was used for CTDI and breast skin doses D and CNR at both detector widths. ANOVA was used for dose and CNR of three sets of pitch (0.500, 1.000, and 1.375) and the three ODM techniques. Result The FOM factor was the largest when using an 80 mm detector with a pitch of 0.992 and partially turning on the ODM. The radiation dose of the three ODM groups decreased in turn, and the effect of ODM on CTDIvol (P=0.019) and breast skin dose (P=0.002) was statistically significant. The width of the detector increased and the dose was increased. The width of the detector was statistically significant for CTDIvol (t=-2.723, P=0.015). There was no statistically significant effect on the breast skin dose (t=-0.908, P=0.377). The effects of the pitch were not statistically significant for CTDIvol (P=0.254) and breast dose (P=0.146). The CNR of the three ODM groups decreased in turn, and the effect of ODM on the soft tissue image CNR was not statistically significant (P=0.146). The CNR of lung algorithm image (P=0.030) had significant effects. The multiple comparisons:only ODM all was significantly different from ODM off (P=0.009). With the increase of detector width,the values of CNR increased,the values of CNR (t=-4.128,P=0.001) of lung images were significantly affected. The effects on the soft tissue images were not statistically significant (P=0.187). There was no statistically significant difference in the effect of pitch on the CNR (P=0.660) of the lung images. The effects of the pitch on the values of CNR of soft tissue images (F=11.756,P=0.001) were statistically significant. By multiple comparisons, the difference of CNR between 0.500 (P=0.000) and 1.375 (P=0.013) was statistically significant compared with that when the pitch was 1.000. There was no significant difference among the three ODM modes (P>0.05) on the values of CNR of upper and middle parts of lung and soft tissue arithmetic images. The differences of CNR between ODM all and the other two groups were statistically significant (P<0.05) on the bottom part of images. Conclusion The changes of detector width and pitch will affect the organs dose modulation technique, and then affect the radiation dose and image quality. When using 80 mm detector with the pitch of 0.992 and partially turning on ODM in chest CT scan,achieving the optimized benefits of quality and dose.
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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 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.
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Objective To explore the effects on image quality and dose reduction to the lens when using bismuth shielding in head and neck MSCT.Methods The standard phantom and the cadaveric head with none,1,2 and 3 layers of bismuth shielding were scanned with protocols of brain,temporal bone and paranasal sinuses using a 16-MDCT scanner.The organ dose to the lens in each scanning was measured with thermoluminescence dosimeters(TLD).The above scanning with sinus protocol was repeated with a sponge with thickness of 5,10,15 and 20 mm placed between the shielding and phantom/head.The CT attenuation of phantom with the distance of 2,4,6 and 8 cm to shielding were measured.The image quality was subjectively evaluated by 2 physicians.Results The organ doses of the lens with protocols of brain,temporal bone and sinuses were 24.31,27.60 and 20.01 mGy,respectively.The doses were decreased significantly when using bismuth shielding.With the increase of the shield gap,the degree of dose reduction was reduced,but the increasing degree of CT attenuation significantly reduced.Using 2-layer and 3-layer bismuth shield in brain and temporal bone CT scan,the radiation doses were reduced by 47.1％ and 59.1％,respectively while maintaining the diagnostic image quality.Using 1-layer shield without gap and 2-layer shield with 1.5 cm gap in sinus CT,the radiation doses were reduced by 31.5％ and 34.5％,respectively.Conclusions Reasonable usage of bismuth shielding can effectively reduce the radiation dose to the lens of eye in head and neck MSCT.
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Objective To study the effect of iterative algorithm (iDose algorithm) on image quality and radiation dose in paranasal sinus MSCT.Methods A proper cadaveric head based on the average CNR (contrast noise ratio) of paranasal sinus images in 53 patients was applied.The cadaveric head was scanned with different parameters of kV and effective mAs.The images were reconstructed with filtered back projection and iterative algorithm (iDose 1-7) respectively.The subjective and objective evaluations were performed for all the images and the optimal parameter combination was found out.Results The CNR of coronal images was slightly higher than that of axial images (t =-6.86,P ＜0.05).The image CNR of protocol (120 kV,100 mAs/slice and iDose5) was close to that of conventional protocol.The protocol of 100 kV,60 mAs/slice and iDose4 offered the images adaptable for diagnosis of inflammation.The protocol of 100 kV,80 mAs/slice and iDose4 offered the images adaptable for diagnosis of inflammation and fracture,and the radiation dose were reduced by 82％ and 75％,respectively.Conclusions Using the iDose algorithm could help to offer diagnostic images for inflammation and fracture and reduce the radiation dose in the paranasal sinus MSCT.
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Objective To explore the influence on image quality and the reduction of radiation dose to eye lens when using bismuth shielding in sinus MDCT.Methods The standard water phantom was scanned using clinical scanning protocols of sinus in 16-MDCT,and the images were acquired with none,1 layer,2 layers and 3 layers of bismuth shielding severally.Using the above protocol,the cadaveric head was scanned with no shield,1,2 and 3 layers of bismuth shielding material covered on both eyes,and the organ dose to eye lens in each scanning was measured with thermoluminescence dosimeter (TLD).The sponge with the thick of 0.5,1.0,1.5,2.0 cm was placed between the shielding material and the surface of subjects separately and the radiation doses to eye lens was measured with sinus scanning conditions in the same way.The CT values of phantom with the distances of 2.0,4.0,6.0 and 8.0 cm to shield material were measured.The influence of bismuth artifacts on anatomic structures was evaluated as well.Results The organ doses to the eye lens in the sinus clinical CT were 20.0 mGy.Doses decreased significantly to 13.7,10.9 and 9.4 mGy separately when using 3 types of bismuth shielding thickness.With different thicknesses of shielding material,the greater the shield gap,the smaller the degree of reduction of organ dose,but the increasment of CT value was significantly reduced.Using 1-layer shield no gap and 2-layer shield with 1.5 cm gap in sinus MDCT,the radiation doses were reduced to 13.7 and 13.1 mGy with the reduction rates of 31.5％ and 34.5％ respectively.Conclusion The reasonable bismuth shielding can effectively reduce the radiation dose to eye lens in sinus CT on the premise of ensuring image-diagnostic quality.
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Objective The objective of this article was to compare patients' dose with electrocardiographic gated mA modulation (ECG) and ECG＆CAREDose 4D mode during coronary MSCT angiography.Methods The research was based on phantom experiment and computer simulation to get the mean value of peak skin dose data and effective dose data respectively and to analyze deterministic and stochastic radiation risk.Results The peak skin dose using ECG mode alone and using ECG＆CAREDose 4D mode with the same image noise level was (87.4±0.9) and (45.9 ± 1.2) mGy respectively.Effective dose was 17 and 10 mSy for ECG mode and ECG＆CAREDose 4D mode respectively.Comparing with ECG mode alone, ECG＆CAREDose 4D mode reduced organ dose of gonad, red marrow, lung, stomach, breast and thyroid by 40.0%, 36.7%, 39.3%, 37.7%, 38.8% and 38.9%, respectively. Conclusion Results showed that ECG ＆ CAREDose 4D mode can reduce radiation dose effectively comparing using ECG mode alone, and that ECG ＆ CAREDose 4D mode should be widely applied ehnically with appropriate initial settings.