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Objective:To investigate the effect of adjusting density exposure steps on image quality and radiation dose in digital mammography.Methods:Using the automatic exposure control (AEC) mode of the digital mammography machine, five different gland thicknesses of 4.3, 5.3, 6.3, 7.3, and 8.3 cm were simulated by attaching 0, 1, 2, 3, and 4 PMMA plexiglass plates under the RMI-156 modal body, and the density exposure steps were adjusted to -3, -2, -1, 0, 1, 2, 3, and 4 for each thickness. The target/filter combination, tube voltage, tube current, incident body surface dose (ESD), incident surface air kerma (ESAK), half-value layer (HVL) and the average glandular dose displayed by the device (displayed AGD) were recorded at each step and thickness, and the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), figure of merit (FOM) and the calculated average glandular dose (calculated AGD) were calculated. Then, the display effects of simulated fibers, simulated calcifications and simulated masses within the modal body were scored subjectively, and the changes in image quality and radiation dose at different steps were analyzed, and the relationships between ESD and ESAK, displayed AGD and calculated AGD, and displayed AGD/ESD and calculated AGD/ESAK were analyzed. A linear fit was used for the steps with SNR, CNR, and FOM, and an exponential function curve fit was used for the steps with mAs, ESAK, and calculated AGD. The differences between ESD and ESAK, displayed AGD and calculated AGD, and displayed AGD/ESD and calculated AGD/ESAK were analyzed by paired-samples t test. Results:The CNR and SNR of mammographic images rose and fell by about 8% with each increase or decrease of one step. The scores of image simulated fibers, simulated calcifications, and simulated masses showed an overall upward trend with increasing steps, but there were still cases where the scores decreased with increasing grades. FOM varied from 97% to 104% at each grade with little variability. ESD, ESAK, displayed AGD, and calculated AGD, which could measure radiation dose, showed an exponential trend of increasing function with increasing steps, with a variation of about 63% to 165%. There were statistically significant differences ( t=-9.61, P=0.001) between ESD (15.14±10.08) and ESAK (16.66±11.07). However, there were no statistically significant differences ( t=1.20, P=0.240) between displayed AGD and calculated AGD, which were 3.66±2.18 and 3.61±1.99, respectively. Conclusions:The adjustment of density exposure steps can make the image quality change linearly and the radiation dose change exponentially with increasing speed, and the mode and magnitude of the adjustment are appropriately stable with high application value.
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Objective To compare two exposure modes on image quality and radiation dose when used for double lower extremities full-length photography so as to provide guidance for clinical application. Methods Totally 60 patients undergoing double lower extremities full-length photography were selected with sequential experiment and then divided into two groups randomly and equally,of whom,there were four ones with genu varum.In the two groups,one group applied the exposure mode of AEC,and the other involved in FIXED mode.Then the two groups were compared on image quality and radiation dose. Results The exposure radiation to the patient under FIXED mode was higher than that under AEC mode although the common patients had the image quality with no significant difference in the two groups, and FIXED mode resulted in higher image quality for the patients with genu varum than AEC mode.Conclusion Exposure modes have effects on image quality and exposure dose,and it's suggested that AEC mode be applied for common patients from the aspect of radiation protection while FIXED mode be used for the patients with genu varum. [Chinese Medical Equipment Journal, 2018,39(5):68-70,74]
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Objective To study the optimal radiographic conditions for patients with knee arthroplasty (TKA) and the feasibility of clinical application.Methods According to the different exposure modes,including automatic exposure control (AEC) or manual exposure mode (FIXED),the human body specimen was exposed at a certain kV and different mA or mAs.The entrance surface dose (ESD) and dose exposure index(DEI) were recorded,and the subjective image quality was assessed.The test group with optimum parameters obtained with statistical analysis were compared with control group in radiation dose and subjective evaluation.Results In AEC group,ESD and kV showed a negative correlation (r =-0.973,P ＜ 0.05).At the same mA,DEI was firstly decreased and then increased with kV increasing.The subjective image quality score was (1.96 ± 0.56).DEI and physician ratings showed negative correlation (r =-0.840,P ＜ 0.05).In FIXED group,ESD increased with the increasing mAs (r=0.845,P＜0.05).DEI and kV,mAs indicated a positive correlation(r=0.845,P＜0.05).The subjective image quality scores was(4.33 ±0.79) without correlation with DEI.Compared with the control group,the subjective image quality scores of test group increased,and the radiation dose decreased significantly.Conclusion It is optimal using manual exposure mode with 80 kV/l.25-1 mAs,75 kV/2-1 mAs,70 kV/2.5-1.25 mAs,65 kV/3.2-1.6 mAs and 60 kV/3.2-2 mAs for patients with TKA.
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Objective To study the difference of image quality and radiation dose between different exposure modes with full-field digital mammography (FFDM).Methods The Fluke18-220mammographic phantom was exposed by FFDM system with different exposure modes at automatic exposure control ( AEC ) ,including contrast mode,standard mode and dose mode,and the exposure factors and radiation dose were recorded.The images on monitor with the best window width and window level were read by four independent radiologists.The images of specks groups,nylon fibers and masses was assessed by the four experienced readers at the criterion of American College of Radiology.Results The detection of specks groups,nylon fibers and masses were statistically different at the contrast mode and standard mode (F =41.321,P ＜ 0.05),further at the contrast mode and dose mode.The detection of specks groups、nylon fibers and masses were not statistically different( P ＞ 0.05 ) at standard mode and dose mode,but the radiation doses were different.The ESD at standard mode and dose mode was 4.5 and 3.15 mGy,respectively.The AGD of standard mode and dose mode was 1.18 mGy and 0.78 mGy,respectively.Conclusions The standard mode and dose mode of FFDM might be fit for most patients,especially at the dose mode.Contrast mode of FFDM should be strictly controled in use.