数字X线成像系统图像质量影响因素的实验研究

目的 比较非晶体硒平板探测器DR系统和CR系统的图像噪声、空间分辨率和入射体表剂量（ESD），研究数字X线图像质量影响因素的相关性。方法 采用相同管电压（125kVp）和不同mAs对仿真胸部体模用分辨率测试卡进行DR和CR曝光成像，测量ESD、空间分辨率，计算均方根（RMS）值，分析mA8、ESD、RMS及空间分辨率之间的变化关系。结果 两种系统的RMS随mAs的增加而降低，ESD随mAs的增加而增加。两种系统成像相同ESD时，DR的RMS略高于CR。ESD增加至一定量时，空间分辨率达到极限值（CR为3．1lp／mm，DR为3．4lp／mm）。结论 数字系统放射线剂量的改变会导致噪声、分辨率变化。适度的噪声水平对空间分辨率影响不明显。     

CR与DR系统胸部摄影参数对比的实验研究

目的：比较CR、DR在胸部摄影中的最优化摄影参数。方法：CR、DR系统分别对胸部等效衰减模体行不同参数曝光成像,记录每次曝光的模体表面剂量,并计算模体影像图像质量因子反数值IQFinv。应用统计学软件分析获取CR组、DR组最佳图像的IQFinv值,并换算成摄影参数。结果：CR组、DR组摄影剂量和图像质量IQFinv值之间的线性回归方程为DR：IQFinv=0.005D＋3.359,CR：IQFinv=0.005D＋1.651,D为辐射剂量。ROC曲线分析（曲线下面积AUC=0.893,P〈0.001）,最佳IQFinv值为3.55,获得DR、CR最佳图像摄影参数分别为125 kV、1.6 mAs,125 kV、16 mAs。结论：要得到满足诊断要求且一致的图像质量,CR的摄影剂量大致是DR的4倍。     

数字X线摄影系统中低剂量应用的探讨

目的 通过数字X线摄影系统（DR）在胸部摄影检查中的应用评价DR的低剂量的优越性。方法 利用CDRAD 2.0低对比细节体模评价计算机X线摄影（CR）和DR的影像质量和表面空气吸收剂量（ESD）关系,分别利用两个系统（DR使用ESD约为CR的1/3）得到成人胸部30幅影像。由6位影像科医生来评价以上两者的影像系统对于肩胛骨内侧边缘等胸部结构的清晰程度。结果 CR影像和减少ESD的DR影像在影像诊断质量上差异没有统计学意义（P＞0.05）。结论 DR的较好的分辨率和低噪声特性,以及高DQE有助于减少患者接受的辐射剂量,而不影响诊断质量。     

X射线胸部摄影曝光剂量与图像质量相关性研究

目的 研究数字化X射线胸部高千伏摄影曝光剂量与图像质量的关系,确定数字化X射线摄影最佳曝光剂量。方法 选择胸部高千伏摄影管电压120 kV,摄影mAs从1 mAs逐档增加至25 mAs,对模拟人体胸部厚度摄影体模与CDRAD 2.0对比度细节体模进行摄影,测量体模表面X射线入射剂量,由5位观察者独立阅读体模影像,比较任意两曝光条件组之间的图像质量因子（IQF）,确定高千伏胸部摄影最佳条件。比较4和10 mAs条件下正常人体胸部摄影图像质量评分。结果 胸部高千伏摄影体模曝光条件从1 mAs增加到25 mAs,体模表面X射线入射剂量从0.067 mGy增加至1.468 mGy。随着X射线入射剂量的增加,影像质量影响因子IQF值不断减小,观察者阅读体模信号的IQF差异有统计学意义（F=31.00,P<0.05）,曝光剂量条件选择在1~4 mAs时所对应的IQF均值差异有统计学意义（F=15.3,P<0.05）,4~10 mAs时所对应的IQF差异无统计学意义,10~25 mAs时所对应的IQF均值差异有统计学意义（F=9.74,P<0.05）。曝光剂量条件选择4和10 mAs所对应的体模表面入射剂量为0.250和0.606 mGy,两种条件下胸部图像质量的综合评分分别为（24.8±1.64）、（25.8±2.05）分,差异无统计学意义。结论 随着数字化X射线摄影剂量的增加所获得图像信息量增加。满足临床诊断的标准人体胸部高千伏数字化X摄影最佳剂量为0.250 mGy左右。     

Radiation exposure and image quality in chest CT examinations.

OBJECTIVE: The purpose of this study was to determine how changes in radiographic tube current affect patient dose and image quality in unenhanced chest CT examinations. SUBJECTS AND METHODS: Ten sets of CT images were obtained from patients undergoing CT-guided chest biopsies. For each patient, six images of the same region were obtained at settings between 40 and 280 mAs. CT data were used to reconstruct tomographic sections with a field of view limited to the normal contralateral lung. Images were printed using lung and mediastinal image display settings. Image quality was determined by asking radiologists to assess the perceived level of mottle in CT images. Five chest radiologists ranked the relative image quality of six images. Patient effective doses were computed for chest CT examinations performed at each milliampere-second setting. Radiologists indicated whether any perceived improvement of image quality at the higher radiation exposures was worth the additional radiation dose. RESULTS: The differences in quality of chest CT images generated at greater than or equal to 160 mAs were negligible. Reducing the radiographic technique factor below 160 mAs resulted in a perceptible reduction in image quality. Differences in CT image quality for radiographic techniques between 120 and 280 mAs were deemed to be insufficient to justify any additional patient exposure. However, the use of 40 mAs results in an inferior image quality that would justify increased patient exposure. CONCLUSION: Radiographic techniques for unenhanced chest CT examinations can be reduced from 280 to 120 mAs without compromising image quality.     

两种数字化X射线摄影技术影像质量与成像剂量的比较

目的对比研究非晶硒平板探测器直接数字化X射线摄影(DR)及计算机x射线摄影(CR)两种数字化X射线摄影技术影像质量与吸收剂量的关系。方法应用DR和CR系统分别对对比度．细节体模(CDRAD2．0)进行不同吸收剂量的曝光成像。记录每次曝光的体模表面吸收剂量，并将所获取的影像在图像诊断工作站显示器上由4位观片者进行观察，计算影像质量表征因子(IQF)。应用ANOVA检验法统计、比较两种数字化摄影技术的图像质量与吸收剂量的差别。结果与CR相比，DR具有更低的IQF值，对人体组织对比度和结构细节有更好的信息检出特性。两种成像技术产生相同IQF值时，DR系统在体模表面产生的表面剂量比CR系统降低了77％。结论DR技术对于低对比度组织细节的检测好于CR技术。在获得相同影像信息的前提下，与CR相比应用DR大大降低了被检者吸收剂量。     

膝关节置换术后X射线摄影中不同曝光模式对影像质量和辐射剂量的影响

目的 探讨膝关节置换术（TKA）术后最佳摄影条件及临床应用的可行性。方法 根据不同的曝光方式,分为自动曝光模式组（AEC）、手动曝光模式组（FIXED）,以固定kV、依次改变相应mAs的方式,对模体进行曝光,记录各曝光条件下入射剂量（ESD）、剂量曝光指数（DEI）、主观图像质量评价,经统计学分析后得出最优化试验组参数与回顾组进行辐射剂量及主观评价比较。结果 AEC组ESD与kV呈负相关（r=-0.973,P < 0.05）,在相同mA条件下,DEI随kV增加呈先减后增的弧线型变化,主观图像质量评价均值为（1.96±0.56）,DEI与主观图像评分呈负相关（r=-0.840,P < 0.05）。FIXED组ESD随mAs的增加而成线性增加,呈正相关（r=0.845,P < 0.05）,DEI与kV、mAs成正相关（r=0.628、0.674,P < 0.05）。主观图像质量评价均值为（4.33±0.79）,与DEI无相关性。选择最优化实验组与回顾组相比,主观图像质量评价分值增加,辐射剂量降低明显。结论 对于膝关节置换假体植入受检患者,采用手动曝光模式,80 kV/1.25~1 mAs、75 kV/2~1 mAs、70 kV/2.5~1.25 mAs、65 kV/3.2~1.6 mAs和60 kV/3.2~2 mAs为最优化区间。     

Bedside chest radiography and optimization of radiographic conditions in the NICU with the Fuji Computed Radiography System

We devised an application that uses the "Maximum value reading method (AutoIV)" for bedside chest radiography in a neonatal intensive care unit (NICU) that used the Fuji Computed Radiography (FCR) System. The application, named AutoIV-N, uses the relationship for density correction between radiographic conditions (mAs) and the Display Parameter (GS). GS=f (mAs) can be considered the relationship that connects FCR and the X-ray generator. When AutoIV-N is used, radiographic image contrast does not change. Further, radiographic image density fluctuation can be eliminated by random elements such as X-ray output fluctuation of the X-ray generator and the decline of photo-stimulated luminescence caused by fading of the imaging plate. Accordingly, image recording that is suitable for follow-up chest radiography is made possible. We choose nine patients and performed a comparison of radiographic density fluctuation in AutoIV-N and Fix. AutoIV-N was found to be more stable than Fix. It is possible to use the radiographic imaging condition that is optimized for all patients in the NICU by AutoIV-N. This facilitates radiation exposure optimization in medicine. (Article in Japanese).     

Local diagnostic reference levels for typical radiographic procedures

Purpose

To establish local diagnostic reference levels (DRL) for typical radiographic examinations in a fully digital imaging institution.

Methods

The initial survey included 6 standard radiographic projections performed in 19 computed radiography (CR) and digital radiography (DR) rooms. Because of the expected difference in the performance, the local reference levels were analysed separately for those 2 modalities. Data of 226 average size adult patients were included in the analysis. Entrance surface dose (ESD) was calculated from the recorded radiographic techniques and tube radiation output measurements. After observing wide variations in the results of the patient survey, the examinations were repeated by using anthropomorphic phantoms. Initial efforts to understand the reasons for dose variations were focused on CR chest, abdomen, pelvis, and lumbar spine examinations.

Results

The average size patient doses for similar examinations were lower in the DR rooms than in the CR rooms by factors that ranged from 1.2 to 3, with the exception of the chest examination. Standardization of the CR exposure index value allowed us to decrease ESD by 21%-30%. Detector sensitivity had an insignificant effect (2%) on ESD; proper collimation lowered the dose by 17%. However, the major effect, up to 46% difference, was found because of antiscatter grids cutoff.

Conclusion

Modality specific local diagnostic reference levels for standard examinations have been established in a large digital imaging department with hybrid modalities. Typically the local reference values were lower than those recommended in Safety Code 35, except for CR chests. Factors that affect the dose variations have been investigated and determined.     

婴幼儿胸部DR摄影距离对体表入射剂量与图像质量的影响

目的 探讨胸部数字化X线摄影源像距(SID)对婴幼儿体表入射剂量(ESD)与图像质量的影响.方法 先进行仿真胸部体模实验性曝光,采用同一管电压(60 kVp)和不同SID(150 ～80 cm,10 cm为一组,共8组)进行曝光组合,记录每次曝光的毫安秒、ESD.选取试验中ESD相对剂量适中和较低的两组(110和90 ...     

Flat panel digital radiography compared with storage phosphor computed radiography: assessment of dose versus image quality in phantom studies

RATIONALE AND OBJECTIVE: To assess and quantify the dose reduction by use of a CsI-flat panel digital radiography (DR)-system compared with digital computed radiography (CR). MATERIALS AND METHODS: A TCDD-test using the CDRAD-phantom was performed at mAs-values of 5, 4, 2.5, 2, 1, and 0.5 mAs for both digital systems. Entrance surface doses were recorded for all images. Images were presented to four independent observers. For quantitative comparison the image quality figure (IQF) was calculated. Statistical analysis was performed using the Pearson correlation and the Wilcoxon test. A ROC analysis was performed using the TRG-phantom. Settings of 4, 2.5, 2 mAs for both systems were used. In addition, 1 and 0.5 mAs were used for the DR system only. Statistical significance was evaluated using Student test. RESULTS: The DR system provided equivalent results compared with CR with respect to high frequency information and superior results with respect to low contrast details. Compared with computed radiography, the flat panel detector demonstrated significantly lower IQFs, ensuring a better image quality with respect to contrast and detail detectability. IQFs for DR and CR were equal at a surface dose reduction of 87% for DR. ROC analysis revealed significantly higher values under the curve for DR up to a surface dose reduction of 70%. CONCLUSIONS: Image quality of DR proved to be far superior to CR in particular for low contrast details. The image quality of CR is similar to that of DR only at high dose levels.     

实验猪胸部正位CR合理曝光条件研究

目的探讨计算机X线摄影(computed radiography,CR)的合理曝光条件。材料与方法以10mAs、20mAs、40mAs档,分别从50～150kV、步长为2kV对实验猪胸部进行系列曝光,用剂量计记录每次曝光的入射点的入射X线剂量、肺野和纵隔处的透射X线剂量,得到三个序列的X线剂量与kV的关系数据,绘制入射剂量、透射剂量与kV的关系图,然后用相同的步骤进行系列胸部正位CR摄影,以噪声不影响观察为前提,找出曝光量最低的CR图像及其对应的合理曝光剂量,分析合理曝光剂量与曝光条件的关系。结果(1)合理曝光条件对透射剂量有很强的依从关系,不管如何改变kV和mAs的组合,合理透射剂量均是一个相对的恒定值,三个序列间合理剂量差异性比较均无统计学意义(P>0.05);(2)合理曝光剂量相对应的入射剂量,低mAs高kV组合要比高mAs低kV组合的入射剂量低,三个序列间差异比较具有统计学意义(P<0.01);(3)入射点剂量与mAs呈正相关。结论(1)对于CR来说,透射剂量是合理曝光条件唯一考量的参数;(2)提高kV对降低患者辐射剂量有意义。     

Investigating the use of an antiscatter grid in chest radiography for average adults with a computed radiography imaging system

Objective:

The aim of this study was to investigate via simulation a proposed change to clinical practice for chest radiography. The validity of using a scatter rejection grid across the diagnostic energy range (60–125 kVp), in conjunction with appropriate tube current–time product (mAs) for imaging with a computed radiography (CR) system was investigated.

Methods:

A digitally reconstructed radiograph algorithm was used, which was capable of simulating CR chest radiographs with various tube voltages, receptor doses and scatter rejection methods. Four experienced image evaluators graded images with a grid (n = 80) at tube voltages across the diagnostic energy range and varying detector air kermas. These were scored against corresponding images reconstructed without a grid, as per current clinical protocol.

Results:

For all patients, diagnostic image quality improved with the use of a grid, without the need to increase tube mAs (and therefore patient dose), irrespective of the tube voltage used. Increasing tube mAs by an amount determined by the Bucky factor made little difference to image quality.

Conclusion:

A virtual clinical trial has been performed with simulated chest CR images. Results indicate that the use of a grid improves diagnostic image quality for average adults, without the need to increase tube mAs, even at low tube voltages.

Advances in knowledge:

Validated with images containing realistic anatomical noise, it is possible to improve image quality by utilizing grids for chest radiography with CR systems without increasing patient exposure. Increasing tube mAs by an amount determined by the Bucky factor is not justified.Radiography of the chest is one of the most frequently performed diagnostic radiographic examinations in the UK. In 2010, the Health Protection Agency (now Public Health England) reported¹ that chest radiographs represented 19.6% of all radiographic examinations in 2008 (although the contribution to collective dose was small at about 0.5%), so optimization of radiation dose (i.e. ensuring dose is as low as reasonably practicable) and image quality (i.e. ensuring all required clinical structures are visible to the reporting healthcare professional so that an acceptable diagnosis is possible) in chest radiography is an important research area, especially since digital imaging has all but replaced its film-screen counterpart. It is also a legal requirement in the UK under the Ionising Radiation (Medical Exposure) Regulations 2000² to optimize all medical exposures, consistent with the intended purpose.One such technique to optimize image quality in chest radiography is to use a scatter rejection grid. They work by preferentially removing radiation scattered by the body prior to reaching the detector, and their improvement of image quality in film-screen imaging has been recognized for decades.^3–6 This improvement was described by the contrast improvement factor⁷ but came with a cost. Film requires a given level of incident exposure to ensure adequate optical density (OD), and because a grid attenuates most of the scattered radiation (as well as some primary radiation), this necessitates an increase in tube current–time product (mAs). The Bucky factor describes the necessary multiplication by which exposure parameters must be increased, and for film-screen can be anything between 2–6 times the “non-gridded” exposure.^8,9 Regardless of this, there are clear guidelines recommending the use of scatter rejection grids with film-screen systems for adult chest radiography,¹⁰ but none for digital imaging modalities, although Fritz and Jones¹¹ have recently published guidelines for scatter rejection techniques in paediatric digital radiology.Digital image detectors, such as computed radiography (CR) photostimulable powder phosphors, have a larger dynamic range than does film,¹² and grey levels in the resulting image are usually adjusted, irrespective of incident detector dose, to match the output of the display monitor. Therefore, unlike film, digital imaging is not contrast (OD) limited. At doses used clinically (e.g. air kerma of approximately 2–15 µGy at the receptor), digital images are dominated by quantum noise (i.e. other noise sources such as electronic and structural are typically ≤2% of the total noise as consistently demonstrated through in-house routine quality assurance testing of this CR system), which depends on the level of air kerma incident on the detector (signal) and the detector''s detective quantum efficiency. Therefore, when a scatter rejection grid is used, appropriate exposure factors (tube''s peak kilo-voltage and/or mAs) are required to maintain a level of image signal-to-noise ratio (SNR)^13,14 acceptable to the image evaluator, although there is no agreement as to what these appropriate exposure factors should be. A common school of thought, described in a considerable resource by Carlton and Adler,¹⁵ suggests that the lower limit on the increase in mAs should be the reciprocal of the primary transmission (T_p) of the grid and the upper limit, the Bucky factor. The reciprocal of T_p for modern grids is typically 1.2–1.4, which suggests that an increase in mAs of at least 20% is required. However, Tanaka et al¹⁶ have recently demonstrated that the use of grids (grid ratios 5 : 1 to 14 : 1) without increasing exposure factors (compared with “non-gridded” exposures), actually improved the effective noise equivalent quanta (eNEQ) when acquiring images of 20 cm of polymethylmethacrylate (PMMA). They concluded that the improvement to image quality owing to removal of scatter outweighs the increase in quantum noise when a grid is used, although they acknowledged that their work did not use any images with anatomical structure. Similarly, Fetterly and Schueler¹⁷ studied numerous grids with different thicknesses of uniform solid water and suggested that a scatter rejection grid can provide improvement in SNR without increasing exposure for large patients.Given the scarcity of evidence/guidelines in the literature, the aim of this study was two-fold: firstly, to investigate the validity of using a scatter rejection grid for chest radiography of average adults with an Agfa CR imaging system (Agfa, Peissenberg, Germany) across the diagnostic energy range (60–125 kVp); and secondly, to investigate appropriate tube mAs to identify what increase in patient dose (if any) there needs to be. Many recent studies have demonstrated that anatomical noise (the influence of projected anatomy on the image evaluator’s ability to detect potential abnormalities and provide an accurate diagnosis) is the limiting factor in chest radiography,^18–27 so it was felt that the inclusion of realistic anatomy in the images used in this study was of particular importance, rather than using uniform PMMA or solid water only. Therefore, computer-simulated chest radiographs (each containing realistic projected anatomical noise and lung abnormalities/nodules), reconstructed with a scatter rejection grid, were compared by expert image evaluators with images reconstructed without a grid (as per current clinical protocol in our radiology department).     

General equations for optimal selection of diagnostic image acquisition parameters in clinical X-ray imaging

The purpose of this work was to examine the effects of relationship functions between diagnostic image quality and radiation dose on the governing equations for image acquisition parameter variations in X-ray imaging. Various equations were derived for the optimal selection of peak kilovoltage (kVp) and exposure parameter (milliAmpere second, mAs) in computed tomography (CT), computed radiography (CR), and direct digital radiography. Logistic, logarithmic, and linear functions were employed to establish the relationship between radiation dose and diagnostic image quality. The radiation dose to the patient, as a function of image acquisition parameters (kVp, mAs) and patient size (d), was used in radiation dose and image quality optimization. Both logistic and logarithmic functions resulted in the same governing equation for optimal selection of image acquisition parameters using a dose efficiency index. For image quality as a linear function of radiation dose, the same governing equation was derived from the linear relationship. The general equations should be used in guiding clinical X-ray imaging through optimal selection of image acquisition parameters. The radiation dose to the patient could be reduced from current levels in medical X-ray imaging.     

Increasing source to image distance for AP pelvis imaging – Impact on radiation dose and image quality

AimA quantative primary study to determine whether increasing source to image distance (SID), with and without the use of automatic exposure control (AEC) for antero-posterior (AP) pelvis imaging, reduces dose whilst still producing an image of diagnostic quality.MethodsUsing a computed radiography (CR) system, an anthropomorphic pelvic phantom was positioned for an AP examination using the table bucky. SID was initially set at 110 cm, with tube potential set at a constant 75 kVp, with two outer chambers selected and a fine focal spot of 0.6 mm. SID was then varied from 90 cm to 140 cm with two exposures made at each 5 cm interval, one using the AEC and another with a constant 16 mAs derived from the initial exposure. Effective dose (E) and entrance surface dose (ESD) were calculated for each acquisition. Seven experienced observers blindly graded image quality using a 5-point Likert scale and 2 Alternative Forced Choice software. Signal-to-Noise Ratio (SNR) was calculated for comparison. For each acquisition, femoral head diameter was also measured for magnification indication.ResultsResults demonstrated that when increasing SID from 110 cm to 140 cm, both E and ESD reduced by 3.7% and 17.3% respectively when using AEC and 50.13% and 41.79% respectively, when the constant mAs was used. No significant statistical (T-test) difference (p = 0.967) between image quality was detected when increasing SID, with an intra-observer correlation of 0.77 (95% confidence level). SNR reduced slightly for both AEC (38%) and no AEC (36%) with increasing SID.ConclusionFor CR, increasing SID significantly reduces both E and ESD for AP pelvis imaging without adversely affecting image quality.     

上气道DR管电压与辐射剂量和图像质量的关系

目的 探讨成人上气道DR管电压选择与辐射剂量和图像质量的关系.方法 用聚甲基丙烯酸甲酯( PM MA)模拟成人上气道厚度和对比度细节体模(CDRAD2.O)组合,以不同管电压自动曝光控制系统(AEC)摄影,记录入射体表剂量(ESD)、剂量面积乘积(DAP)和曝光量(mAs),计算体模图像质量因子(IQF值),选定适宜管电压.结果 ESD、DAP、mAs随着管电压升高而下降,IQF值却增大,其间差异有统计学意义(F =45.15、26.41、29.26、56.53,P＜0.05).75 kV以下ESD、DAP、mAs明显增大,75 kV以上逐渐降低,75～80 kV趋于平衡.50～75 kV之间IQF值差异无统计学意义,75～90 kV之间IQF值差异有统计学意义(F=11.35,P＜0.05).不同管电压的正常人体上气道的图像质量无明显差异.结论 成人上气道DR的适宜管电压范围为75～80 kV,用IQF值对照图像质量评分可为临床评价图像质量提供依据.     

Effect of high- and low-energy entrance surface dose allocation ratio for two-shot dual-energy subtraction imaging on low-contrast resolution

IntroductionDual-energy subtraction (DES) imaging can obtain chest radiographs with high contrast between nodules and healthy lung tissue, and evaluating of chest radiography and evaluating exposure conditions is crucial to obtain a high-quality diagnostic image. This study aimed to investigate the effect of the dose allocation ratio of entrance surface dose (ESD) between high- and low-energy projection in low-contrast resolution of soft-tissue images for two-shot DES imaging in digital radiography using a contrast-detail phantom (CD phantom).MethodsA custom-made phantom mimicking a human chest that combined a CD phantom, polymethylmethacrylate square plate, and an aluminum plate (1–3 mm) was used. The tube voltage was 120 kVp (high-energy) and 60 kVp (low-energy). The ESD was changed from 0.1 to 0.5 mGy in 0.1 mGy increments. Dose allocation ratio of ESD between 120 kVp and 60 kVp projection was set at 1:1, 1:2, 1:3, and 2:1. Inverse image quality figure (IQF_inv) was calculated from the custom-made phantom images.ResultsWhen the total ESD and aluminum thickness were constant, no significant difference in IQF_inv was observed under most conditions of varied dose allocation ratio. Similarly, when the total ESD and the dose allocation ratio were constant, there was no significant difference in IQF_inv based on the aluminum plate thickness.ConclusionUsing IQF_inv to evaluate the quality of the two-shot DES image suggested that dose allocation ratio did not have a significant effect on low-contrast resolution of soft-tissue images.Implications for practiceThe present results provide useful information for determining exposure conditions for two-shot DES imaging.     

A study of entrance surface dose with CR and film/screen systems, and analysis of the X-ray conditions for chest radiography

Several previous studies have indicated that the medical exposure dose(entrance surface dose) is lower with Computed Radiography(CR) than with the Film/Screen(F/S) system. We conducted a questionnaire survey of 1,297 hospitals regarding the radiation exposure conditions of X-ray examinations. From the survey results, we calculated the entrance surface dose(first quartile, median, third quartile, and mean) using the NDD calculation method. In the case of chest radiography(adult patients) by CR, the entrance surface dose was 150% of the median value for the overall examination and 160% of the median value for orthochromatic screen systems. The CR exposure set-up using a lower voltage and higher mAs than the F/S method was found to result in a high entrance surface dose. We also found a difference in patient dose among hospitals using CR. Mean surface dose in CR system was 0.12 mGy in a quartile, 0.19 mGy in the middle and 0.27 mGy in the third quartile. Among the hospitals which showed higher doses of third quatile them above mentioned, dose differences of a quartile were distributed 2 to 10 times higher them mean exposure doses.     

A pilot study investigating two dose reduction techniques for AP lumbar spine radiography using direct dosimetry and Projection VR

IntroductionThe purpose of this study was to compare radiation dose measurements generated using a virtual radiography simulation with experimental dosimeter measurements for two radiation dose reduction techniques in digital radiography.MethodsEntrance Surface Dose (ESD) measurements were generated for an antero-posterior lumbar spine radiograph experimentally using NanoDOT™, single point dosimeters, for two radiographic systems (systems 1 and 2) and using Projection VR™, a virtual radiography simulation (system 3). Two dose reduction methods were tested, application of the 15% kVp rule, or simplified 10 kVp rule, and the exposure maintenance formula. The 15% or 10 kVp rules use a specified increase in kVp and halving of the mAs to reduce patient ESD. The exposure maintenance formula uses the increase in source-to-object distance to reduce ESD.ResultsIncreasing kVp from 75 to 96 kVp, with the concomitant decrease in mAs, resulted in percent ESD reduction of 59.5% (4.02–1.63 mGy), 60.8% (3.55–1.39 mGy), and 60.3% (6.65–2.64 mGy), for experimental systems 1 and 2, and virtual simulation (system 3), respectively. Increasing the SID (with the appropriate increase in mAs) from 100 to 140 cm reduced ESD by 22.3% 18.8%, and 23.5%, for experimental systems 1 and 2, and virtual simulation (system 3), respectively.ConclusionPercent dose reduction measurements were similar between the experimental and virtual measurement systems investigated. For the dose reduction practices tested, Projection VR™ provides a realistic alternate of percent dose reduction to direct dosimetry.     

Radiation dose in pelvic imaging

OBJECTIVE: To compare the radiation dose during pelvic x-ray examinations using computed radiography (CR) and film-screen (FS) radiography at various x-ray tube voltages (kV) and tube-current time product (mAs) values. METHODS: A pelvic phantom was imaged using FS and CR systems. The entrance surface dose was measured using an ionization chamber, and the gonadal dose and effective dose were calculated using the XDOSE program. The diagnostic quality of the images was assessed using a 5-point subjective scoring system. RESULTS: At standard kV values, the image quality did not vary significantly between the CR and the FS system, but at higher kV values, the CR images werefound to be of better quality than FS images. In addition, the lower limit of entrance skin dose consistent with diagnostically acceptable CR images was 50% lower than that for FS images. CONCLUSION: The gonadal dose and effective dose for pelvic x-ray examinations can be reduced by 50% when CR systems are used and appropriate exposure factors are established.