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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 feasibility of the application of low tube potential scanning in dacryocystography CT.Methods:The mixture of iohexol and saline with the ration of 1∶3 as the dacryocyst was set on the nose wing of the head-neck phantom. The phantom was scanned at 80, 100, 120, 140 kV with appropriate mAs to set the volume CT dose index(CTDI vol)at 10, 15, 20, 25, 30, 35 or 40 mGy. All the images were objectively evaluated to find out the optimal scanning parameters of 80 kV/240 mAs with the same contrast-to-noise ratio(CNR)of conventional scanning condition of 120 kV/180 mAs. A total of 62 patients who conducted dacryocystography CT in Beijing Tongren Hospital from November 2019 to July 2020 were prospectively selected. They were randomly divided equally into conventional scanning group with 120 kV/180 mAs and low tube potential group with 80 kV/240 mAs. The CT number, noise (SD) and contrast-to-noise ratio (CNR) of the two groups were measured as the objective evaluation indicators of image quality. The subjective evaluation was performed by two senior radiologists using a double-blind method and a 5-scale system evaluation. Results:For the phantom study, the CNR was positively correlated with CTDI vol under the same tube potential ( r=0.985, 0.965, 0.971, 0.972, P < 0.05). With the same CNR, the radiation dose decreased with lower tube potential. Under the conventional scanning parameters of 120 kV/180 mAs, the CNR was 27.8. At the same CNR, the optimal scanning parameters were 80 kV/240 mAs. For the clinical study, the CTDI vol of conventional scanning group and low tube potential group were 31.2 and 12.8 mGy respectively, 59% decreased in low tube potential group. There were statistically significant differences in CT number of dacryocyst area, CT number of orbital fat area and noise between the two groups ( t=-3.476, 2.601, -5.704, P < 0.05). There was no statistically significante difference in CNR between 2 groups( P>0.05). Two observers had a good consistency ( Kappa >0.75). There was no statistically significante difference in subjective rating between 2 groups( P>0.05). Conclusions:Low tube potential scanning could obtain satisfactory image quality in dacryocystography CT at much lower radiation dose.
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Objective:To investigate the CT features and surgical treatment of mixed epithelial and stromal tumor of the kidney (MESTK).Methods:From April 2015 to August 2018, 13 patients with MESTK confirmed by pathology at the First Affiliated Hospital, College of Medicine, Zhejiang University, were enrolled in this study and their clinical data were analyzed retrospectively. These patients included 3 males and 10 females, with age ranging from 22 to 80 years old and the median age of 37 years old. Two patients complained of lumbar discomfort with urinary urgency and another 2 patients presented with hematuria. Nine patients were asymptomatic and their renal lesions were detected by abdominal ultrasonography for physical examination or other reasons. There were 2 cases had a history of polycystic kidney disease, 1 patient took contraceptive for 2 years, and 3 cases took antihypertensive agents for 5-10 years. The other patients denied any administration of hormone or other medicine for long time. The urine routine test was normal for these patients except for 2 patients did not take this test before operation. The creatinine value ranged from 45 to 486 μmol/L, with the median value of 67 μmol/L. The scope of glomerular filtration rate (GFR) was 6.98 to 132.28 ml/min, with the median value of 109.28 ml/min. The preoperative computer tomography (CT) showed single neoplasm in 11 patients and no obvious neoplasm was found in 2 patients who had polycystic kidney disease. Moreover, these lesions presented cystic neoplasm for 8 cases, cystic-solid neoplasm for 2 cases and solid neoplasm for 3 cases. Long diameter was measured about 2.5 to 7.5 cm, with the median of 5 cm, and calcification was found in 4 cases. These tumors manifested mild to moderate enhancement and delayed-enhancement for tumor parenchyma and intracapsular septum. The CT attenuation value was from 20 to 55 Hounsfield unit (HU). Base on the R. E.N.A.L. score system, these renal lesions got 4 to 10 points, with the median value of 7 points. Before operation, just 1 case was diagnosed as angiomyolipoma and 2 cases were diagnosed as polycystic kidney disease. No definitive diagnosis was made for the other 10 cases by CT imaging. In addition, the tumor staging based on preoperative imaging was made at T1a for 8 cases and T1b for 3 cases. Among these cases, 2 patients with polycystic kidney disease underwent open radical nephrectomy due to recurrent hematuria and uremia. One patient underwent laparoscopic radical nephrectomy due to perirenal fat adhesion. Partial nephrectomy was performed in remaining 10 patients by open surgery for 6 patients, robotic surgery for 3 patients and laparoscopic surgery for 1 patient. These renal tumors and 0.5-1.0 cm surrounding normal renal parenchyma were removed during operation.Results:In this study, 8 patients had blood loss of 30 to 100 ml during open operation, and 5 patients had blood loss of 20 to 100 ml during laparoscopic or robotic surgery. The warm ischemic time during partial nephrectomy was around 17 to 40 min, with the median value of 20 min. All of 13 cases were diagnosed as MESTK by postoperative pathology and the surgical margin was negative. There were no serious complications or special treatment after operation. The follow-up time ranged from 12 to 41 months, with the median time of 21 months. Obvious signs of tumor recurrence or metastasis were not detected in 13 cases during follow-up.Conclusions:CT images of MESTK mostly presented cystic or cystic-solid lesions, and solid lesions were relatively rare. This disease always showed mild to moderate enhancement and delayed enhancement of septal or tumor parenchyma. If there is coarse calcification in the lesions, it is more likely to be diagnosed as MESTK. Partial nephrectomy is preferred and radical nephrectomy should be considered when perirenal fat adhesion is suggested by the preoperative CT images.
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Objective@#To investigate the relationship between current-exposure time products (mAs) and image quality in digital mammography.@*Methods@#The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes using Mo-Rh anode-filer combinations. The exposure parameters were set as follows: (2 cm, 27 kVp, 10 to 90 mAs); (3 cm, 29 kVp, 20 to 120 mAs); (4 cm, 29 kVp, 20 to 200 mAs); (5 cm, 30 kVp, 40 to 220 mAs); (6 cm, 31 kVp, 40 to 260 mAs); (7 cm, 32 kVp, 80 to 280 mAs). The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness was found from the calculated FOMs. The optimum mAs for each breast thickness were found from the calculated FOMs and IQFs. And the Pearson correlation analysis was used to analyze the correlations among AGD, CNR and IQF.@*Results@#With the increase of mAs, the average glandular dose were linearly increased, and the FOM first increased and then decreased or changed slowly. The AGD, CNR and IQF were significantly correlated when the compression thickness was less than 7 cm (r all>0.87, P<0.05). The optimized exposure parameters were list as follows (2 cm,27 kVp,20 to 30 mAs);(3 cm,29 kVp,30 to 50 mAs); (4 cm,29 kVp,80 to 100 mAs); (5 cm, 30 kVp, 80 to 120 mAs); (6 cm, 31 kVp, 100 to 140 mAs); (7 cm, 32 kVp, 80 to 120 mAs).@*Conclusion@#The optimum range of mAs can be confirmed with different breast compression thickness and the setting of automatic exposure parameters should be chosen in clinical practice.
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Objective:To investigate the relationship between current-exposure time products (mAs) and image quality in digital mammography.Methods:The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes using Mo-Rh anode-filer combinations. The exposure parameters were set as follows: (2 cm, 27 kVp, 10 to 90 mAs); (3 cm, 29 kVp, 20 to 120 mAs); (4 cm, 29 kVp, 20 to 200 mAs); (5 cm, 30 kVp, 40 to 220 mAs); (6 cm, 31 kVp, 40 to 260 mAs); (7 cm, 32 kVp, 80 to 280 mAs). The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness was found from the calculated FOMs. The optimum mAs for each breast thickness were found from the calculated FOMs and IQFs. And the Pearson correlation analysis was used to analyze the correlations among AGD, CNR and IQF.Results:With the increase of mAs, the average glandular dose were linearly increased, and the FOM first increased and then decreased or changed slowly. The AGD, CNR and IQF were significantly correlated when the compression thickness was less than 7 cm ( r all>0.87, P<0.05). The optimized exposure parameters were list as follows (2 cm,27 kVp,20 to 30 mAs);(3 cm,29 kVp,30 to 50 mAs); (4 cm,29 kVp,80 to 100 mAs); (5 cm, 30 kVp, 80 to 120 mAs); (6 cm, 31 kVp, 100 to 140 mAs); (7 cm, 32 kVp, 80 to 120 mAs). Conclusion:The optimum range of mAs can be confirmed with different breast compression thickness and the setting of automatic exposure parameters should be chosen in clinical practice.
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Objective To investigate the image quality and average glandular dose from different breast compression thickness, and to provide recommendations for filtration material and tube voltage in digital mammography. Methods The CDMAM phantom of 2 to 7 cm thickness were exposed by manual exposure modes(proper mAs, 21 to 39 kVp range) using Mo/Mo and Mo/Rh anode/filer combinations at full-field digital mammography. The image quality figure (IQF), contrast to noise ratio (CNR), figure of merit (FOM) and the average glandular dose (AGD) were obtained from images. The optimum filtration and kVp for each breast thickness were found from the calculated FOMs. And the paired sample rank sum test was used to analyze the difference of AGD, CNR, IQF and FOM for Mo and Rh filters. Results For both Mo and Rh as used filter, under the compression of 2 to 7 cm thickness and the fixed mAs, with the increasing of tube voltage, AGD, CNR and IQF will gradually increase as following:AGD had the significant increasing while CNR and IQF gradually increasing to balance. Under different compression thickness, the AGD for Mo and Rh were statistically different (P<0.05). When the compression thickness were 2 and 3 cm, CNR for Mo was higher than Rh, with the statistically significant difference (P<0.05) while the IQF for Mo and Rh with no statistical significance (P>0.05). When the compression thickness was 4 cm, CNR for Mo and Rh were with no statistical significance (P<0.05) while IQF for Mo was higher than Rh, with statistically significant difference (P<0.05). When the compression thickness were 5 to 7 cm, CNR for Mo was lower than Rh, but only under the thickness of 6 cm with statistically significant difference (P<0.05), while there was no statistical significance (P>0.05) under the thickness of 5 cm and 7 cm; the IQF for Mo and Rh with no statistical significance (P>0.05). The FOM in each thickness for Mo and Rh filtration had statistical significance (P<0.05), and FOMRh>FOMMo. For different compression thickness, the suitable matching of tube voltage and filter material were Rh filtration, 2 cm and 27 kVp, 3 cm and 29 kVp, 4 cm and 29 kVp, 5 cm and 30 kVp, 6 cm and 31 kVp, 7 cm and 32 kVp. Conclusion Considering both image quality and radiation dose, Rh filtration is the optimum selection material and there is a corresponding optimal energy response in all kinds of thickness.
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Objective To investigate the influence of additional filter on image quality and radiation dose in chest digital radiography (DR). Methods The adult chest phantom was exposed under the different additional filter by 0, 1.0 mm Al,1.0 mm Al+0.1 mm Cu,1.0 mm Al+0.2 mm Cu while the kV was 110 kV and the AEC parameter selection were -4,-2, 0, 2, and 4 respectively. Image quality was evaluated by the relative noise and the contrast-to-noise ratio (CNR). The radiation dose was evaluated by the entrance skin dose (ESD) and the effective dose. Linear regression analysis was used to analyze the relationship between the ESD and the effective dose, and the correlation between the image quality and the effective dose was analyzed by Pearson correlation analysis. Results The ESD were (0.023 ± 0.004), (0.034 ± 0.007),(0.045 ± 0.009),(0.056 ± 0.010),(0.067 ± 0.012)mGy and the effective dose were(6.15 ± 0.09)×10-3,(9.02±0.15)×10-3,(11.94±0.16)×10-3,(14.89±0.09)×10-3,(17.80±0.12)×10-3 mSv when the AEC parameter selection were -4,-2, 0, 2, and 4 respectively. The effective dose was linearly positively correlated with the ESD and the regression coefficient were(r=1.000, P<0.01)under different additional filter. The ESD decreased with the additional filter increased under the same AEC, and the maximum could be reduced by 34%. The relative noise was decreased with the effective dose increased and there was a negative correlation between the two and the Pearson correlation coefficient were(r=-0.970,-0.966,-0.971,-0.971;P<0.01)under different additional filter. The CNR was increased with more effective dose and there was a positive correlation between the two and the Pearson correlation coefficient were (r=0.952, 0.947, 0.908, 0.944;P<0.05)under different additional filter. The relative noise decreased with the additional filter increased under the same AEC, and the maximum could be decreased by 13%. The CNR values increased with the additional filter under the same AEC, and the maximum could be increased by 4%. Conclusions The use of additional filter in chest digital radiography can reduce the ESD and improve the quality of the image to some extent, but the effective dose change is not significant.
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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 investigate the influence of tube voltage on image quality and radiation dosage to subjects in chest digital radiography (DR).Methods An adult chest phantom was exposed in the range of 80-130 kV with the interval of 10 kV and the automatic exposure control (AEC) setting was selected from-4 to 4.The entrance skin dose (ESD) of the phantom was measured,and the relative noise,contrast-to-noise ratio (CNR) and the effective dose of each exposure was calculated.Results The ESD was (0.062 9 ±0.027 4) mGy,and the effective dose was (0.012 7 ±0.004 5) mSv.The effective dose increased linearly with the ESD,and there was a positive correlation (r =0.912,P ＜ 0.01).When the tube voltage was held constant,the relative noise decreased as the effective dose increased (r =-0.967,-0.969,-0.968,-0.969,-0.968,-0.970,P ＜ 0.01).The CNR increased with the effective dose increasing under the same tube voltage(r =0.987,0.987,0.986,0.987,0.988,0.989,P ＜0.01).The ESD and effective dose decreased as the kV values increased under the same AEC,and the degree of decrease could be up to 50％ and 20％.The relative noise decreased as the kV values increased under the same AEC,and the degree of decrease could be up to 23％.The CNR values increased up to 8％.Conclusions The use of higher kVp in chest digital radiography can reduce the radiation dose to some extent
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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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ObjectiveTo find the proper way of assessing the image noise characteristic through the analysis of noise characteristic in the digital mammographic images.MethodsThe CDMAM phantom was firstly exposed with different filter materials and tube voltages in the range of 23 to 35 kVp at a fixed tube current 90 mAs,then exposed with different filter materials and tube current in the range of 20 to 200 mAs at a fixed tube voltage 29 kVp.The parameters such as background standard deviation,joint standard deviation,subtracted standard deviation and relative standard deviation were calculated and measured from both 60 pixels of signal disc and background beside of the disk for all the images.The IQFinvs were calculated for the achieved images.Non-parametric rank sum tests were used to compare the difference of the background standard deviation,joint standard deviation and subtracted standard deviation,t test was used to compare the IQFinvs between Mo and Rh filers in each group.ResultsWith the same exposure parameters in the test above,the maximum value was the background standard deviation,while the subtracted standard deviation was the minimum,and the value of joint standard deviation was in the middle. With other parameters unchanged,the values of three kind of standard deviation increased with the increasing of tube voltage or tube current,while the differences between them getting more significant.Under the condition of 90 mAs and Mo filter material,background standard deviation,joint standard deviation,subtracted standard deviation were 10.91,10.34 and 9.87,the results were 11.24,10.57 and 9.96 while Rh filter material was used,significant difference was found ( x2 =26.0,P ＜ 0.01 ). Under the condition of 29 kVp and Mo filter material,background standard deviation,joint standard deviation,subtracted standard deviation were 12.30,11.61 and 11.05,the results were 12.29,11.58 and 10.87 while Rh filter material was used,significant difference was found( x2 =20.0,P ＜ 0.01 ).The IQFinvs were 149.14 ± 23.87 and 139.16 ± 23.14 under the condition of 90 mAs and Mo filter material ( t =9.129,P ＜ 0.01 ).The IQFinvs were 149.75 ±34.85 and 145.2 ±34.64 while the parameters were 29 kVp and Rh filter material(t =1.304,P ＞0.05 ).The value of relative standard deviation decreased with the increasing of tube voltage or tube current,and the image quality got better with the decreasing of relative standard deviation.ConclusionRelative standard deviation is suitable not only for the expression of the digital mammographic images,but also for the evaluation of the image quality.
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Objective To investigate the radiation dose to the lens of patients in temporal bone CT scanning with different protocols. Methods With the same values of kV and effective mAs, the tranaxial and coronal scans of exsomatize cadaveric head was performed with conventional sequential scan mode,routine multi-slice helical scan and modified multi-slice helical scan, respectively. The values of CT volume dose index (CTDIvol) and dose length product (DLP) at various scanning mode were anylyzed, and effective doses of subject were calculated. Organ doses of the lens were measured with thermoluminescence dosimetry (TLD). Results When sequential scan mode was selected, gross effective dose was 1.21 mSv,while organ doses to lens were 50.96 and 1.73 mGy separately in axial and coronal slice scan,respectively. Effective dose was 0. 803mSv at helical scanning, while dose to lens was 40. 17 mGy. With modified helical scan mode, the effective dose was similar to routine helical scan, but dose to lens was 10.33 mGy which was significant lower than that of routine helical scan (40.17 mGy). Conclusions With the same values of kV and effective mAs, the effective doses and lens dose obtained in sequential axial and coronal scan were 1.51 times and 1.31 times higher than helical scan, respectively. With modified helical scan mode thinner slice images could be used to reformat axial, coronal and sagittal plane images, and lens dose was reduced by 74.3%. The modified helical CT scan mode of temporal bone could be selected in the clinical application.