婴幼儿胸部数字化X射线摄影曝光参数的优化

目的 通过优化婴幼儿胸部数字化X射线摄影（DR）曝光参数,在保证图像质量的前提下,降低辐射剂量。方法 选取100例进行胸部X射线检查的婴幼儿为对照组,测量胸部厚度,通过测量铝梯与不同胸厚婴幼儿拍片的灰度值,确定婴幼儿胸厚对应的铝当量。再以铝梯为体模进行曝光,采用自动曝光控制（AEC）,测量不同管电压（kV）曝光所显示的铝梯灰阶数及相应的辐射剂量,确定最佳曝光参数。以优化的曝光参数再进行100例拍摄为试验组,比较两组图像质量及辐射剂量。结果 对照组最大胸厚13.5 cm、最小胸厚8.0 cm和平均胸厚（10.6±1.3） cm对应铝当量分别为2.3、1.4和2.0 cm。试验组平均胸厚为（10.1±2.2） cm。在管电压55~65 kV时,设备显示入射体表剂量为0.068~0.056 mGy,曝光指数（EI）为0.60~0.74,在正常范围内,目测铝梯灰阶数8~11级,辐射剂量降至较低水平时,仍能获得满意的图像质量。总结优化婴幼儿胸部DR曝光参数的计算方案,即X射线管焦点到探测器距离（SID）为100 cm时,不使用滤线栅,以胸部厚度（cm）×2+38（常数）设定管电压（kV）,毫安秒（mAs）选择0.8至1.0。两组图像质量评分结果差异无统计学意义（P>0.05）。优化后设备显示体表入射剂量平均值为（0.048±0.007） mGy,低于AEC组的（0.066±0.008） mGy,差异有统计学意义（t=16.781,P<0.001）。结论 本研究公式：管电压（kV）=胸部厚度（cm）×2+38（常数）,优化了婴幼儿胸部DR曝光参数,图像质量满足临床诊断要求,患儿受到的辐射剂量降低。     

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。     

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。     

数字X射线摄影中入射表面剂量显示值与测量值相对偏差及影响因素的实验研究

目的 比较DR设备在不同管电压、源像距和模体厚度条件下入射表面剂量（entrance surface dose,ESD）显示值与测量值之间的相对偏差,为利用ESD显示值实时评估患者受辐射剂量大小和曝光参数适宜性提供依据。方法 在2种管电压、2种源像距条件下,用3个厚度分别为5、10和20 cm的聚乙烯模体（表面积30 cm×30 cm）进行曝光实验。每次曝光后记录DR设备上的ESD显示值以及辐射剂量检测仪测量值,采用Wilcoxon秩和检验对二者差异进行比较,并用公式计算ESD显示值相对偏差。结果 在相同管电压和源像距曝光条件下,ESD显示值不受模体厚度影响,但测量值随模体厚度变化;模体厚度10和20 cm时,ESD显示值均小于测量值,差异有统计学意义（Z=-2.201、-2.203,P<0.05）。模体厚度越厚,显示值与测量值的相对偏差越大,但只有模体厚度20 cm、源像距100 cm时的相对偏差>±20%。结论 DR设备中ESD显示值可以用于评估受检者皮肤入射剂量,但要考虑受检者的体厚影响。     

磁导航指导下心房颤动导管消融与手动消融辐射剂量的对比研究

目的 比较磁导航指导下心房颤动导管消融与手动消融时辐射剂量的差异.方法 连续收住入院的94例行房颤(AF)导管消融术患者,前60例为手动消融组(CON组),后34例为磁导航(MNS)指导下导管消融组(MNS组).对比两组患者的皮肤表面累积入射剂量(CD)、剂量面积乘积(DAP)、透视时间,以及医护人员的辐射剂量和透视时间.结果 MNS组和CON组两组患者的CD值分别为 (0.54±0.45)和(1.61±0.89)Gy (t=2.44,P<0.05),DAP值为(46.86±27.09)和(139.71±76.69)Gy·cm²(t=3.89,P<0.05),透视时间为(15.60±7.52)和(39.50±8.82) min (t=1.96,P<0.05).两组手术医师辐射剂量分别为(22.68±6.87)和(62.74±20.92)μSv(t=2.02,P<0.05),透视时间为(11.48±7.59)和(30.50±14.82)min(t=2.75,P<0.05),助手辐射剂量为(19.38±5.64)和(49.42±10.67)μSv(t=3.58,P<0.05)、透视时间为(8.96±5.88)和(24.49±9.09)min(t=4.20,P<0.05),护士辐射剂量为(18.98±4.99)和(47.77±13.65)μSv(t=3.17,P<0.05)、透视时间为(8.33±6.35)和(22.99±13.36)min(t=2.76,P<0.05).结论 与手动消融相比,磁导航指导下心房颤动导管消融具有明显减少医患辐射剂量的优点.     

基于两种靶-滤过的数字乳腺机对致密型厚乳腺摄影结果的对比研究

目的 探讨对模拟致密型厚乳腺（压迫厚度>65 mm）的模体行全景数字乳腺X射线摄影（FFDM）检查,钼-铑（Mo-Rh）和钨-铑（W-Rh）两种靶-滤过组合对其辐射剂量及图像质量的影响。方法 用聚甲基丙烯酸甲酯有机玻璃（PMMA）模拟标准乳腺,再将铝片置于PMMA板中模拟致密型乳腺,对两组不同致密型（分别放置0.1和0.2 mm铝片）厚度为68 mm的模体进行自动、半自动曝光以及手动曝光,记录靶-滤过（T-F）组合方式、管电压、管电流、平均腺体剂量（AGD）、表面入射剂量（ESE）和图像质量因子反数值（IQFInv）。采用Pearson相关及回归分析评价AGD对IQFInv的影响,两组模体的靶-滤过组合对IQFInv和AGD的差异采用配对样本t检验。结果 AGD和IQFInv具有正相关（r=0.806~0.953,P<0.05）。对于0.1 mm铝片的模体,固定100 mAs或固定28 kVp,两组靶-滤过组合的AGD差异和IQFInv差异均具有统计学意义（t=3.162~8.028,P<0.05）。对于0.2 mm铝片的模体,固定100 mAs时,AGD差异和IQFInv差异均具有统计学意义（t=8.028、4.768,P<0.05）;固定28 kVp时,AGD差异具有统计学意义（t=7.730,P<0.05）,IQFInv差异没有统计学意义（P>0.05）。此外,固定100 mAs时,采用W-Rh,两组模体的IQFInv差异具有统计学意义（t=2.345,P<0.05）。结论 对致密型厚乳腺模体采用W-Rh组合较Mo-Rh组合能在保证影像质量的前提下降低辐射剂量。相同管电流时,W-Rh组合在高管电压下对致密程度较高的乳腺模体的影像显示更佳。     

CR与非晶体硅DR胸部摄影曝光剂量优化的探讨

目的 比较CR与非晶体硅DR在胸部摄影中入射剂量的差异,探讨两者最优化曝光剂量。方法 应用CR、DR分别对胸部模体行不同入射剂量曝光成像,记录模体表面入射剂量,用CDRAD2.0评估软件计算模体影像图像质量因子反数值IQFinv。CR组、DR组图像IQFinv差异用两独立样本t 检验;CR组、DR组各自图像IQFinv与入射剂量的关系应用pearson相关;应用ROC曲线分析获取两组最佳图像IQFinv值,并换算曝光剂量。结果 CR和DR组入射剂量和图像质量IQFinv值之间呈明显的正相关(r =0.893、0.848, P<0.01),并存在线性回归。CR和DR组IQFinv值差异有统计学意义(t =5.455, P<0.05)。ROC曲线分析(曲线下面积AUC＝0.893, P<0.001),最佳IQFinv值为3.55。结论 CR、DR系统对于低对比度细节的检测能力均随着入射剂量的增加而增加。入射剂量相同时,DR系统对于低对比度细节的检测能力优于CR;在获得相同的图像质量时,与CR相比应用DR可大大降低被检者辐射剂量。     

非晶硒平板探测器DR与CR模拟病变描述和剂量降低的对比研究

目的 比较非晶硒平板探测器DR与CR对模拟肺部病变的描述,并对剂量降低情况进行评价。方法 模拟线状、网状和结节病变结构置入仿真胸部体模内,应用DR和CR分别对不同mAs设置的体模曝光,记录体模的入射体表剂量。收集不同剂量的硬拷贝照片,由4位放射医师随机地实施模拟肺部病变显示度评价。采用秩和(Wilcoxon)检验进行统计学分析。结果 用2.0、3.2 mAs曝光时,DR与CR对模拟线状、网状病变的显示度差异有统计学意义(模拟线状病变:Z=-2.032,P=0.042;Z=-2.375, P=0.018。模拟网状病变: Z=-2.680, P=0.007;Z=-2.670, P=0.008)。用5.0、6.3 mAs曝光时,两者对模拟线状、网状病变的显示度差异无统计学意义(P＞0.05)。2.0、3.2、5.0、6.3 mAs曝光档,对于小结节(直径小于10 mm)的检测DR均优于CR(Z=-2.237, P=0.018; Z=-2.384, P=0.017; Z=-2.388, P=0.017; Z=-2.366, P=0.018)。当3种模拟肺部病变都显示清楚时,用非晶硒DR系统的入射体表剂量降低约65%。结论 对微小低对比病变的描述,非晶硒平板探测器DR优于CR且明显地降低曝光剂量。     

乳腺计算机X射线摄影自动曝光模式的校正

目的 通过参照乳腺屏-片系统摄影自动曝光控制模式,对乳腺CR摄影自动曝光进行校正,从而实现影像质量与辐射剂量的最优化。方法 应用屏-片组合,28 kV条件下,对40 mm厚的有机玻璃进行自动曝光,以此所得曝光量(mAs)为基准,分10档分别采用±10 mAs的曝光量用CR进行曝光,选取LgM=2.0的曝光量作为基准,对CR的自动曝光模式进行校正。采用经校正后的CR自动曝光模式,分别采用26、28和30 kV对Fluke NA 18-220 乳腺模体进行摄影,模体采用自动曝光控制(AEC)模式进行摄影,记录曝光量数值(mAs),对CR影像进行处理。同时CR采用相同的kV和照射野及不同的曝光量对模体进行摄影,CR影像经后处理后请4位放射医师进行双盲阅片,按照美国放射学会(ACR)的评分标准评价打分。结果 采用稍高于传统屏-片组合的曝光量作为CR自动曝光校正基准值,可实现乳腺CR摄影自动曝光模式的校正,经校正后模体测试影像的评分均高于ACR的评分标准。结论 乳腺CR摄影自动曝光模式可根据CR特点进行校正,经校正后的乳腺CR摄影的自动曝光控制模式应用于临床既可明显降低病人辐射剂量,又可得到满足临床诊断需求的优质乳腺影像。     

胸部DR摄影中管电压对影像质量和辐射剂量影响的模体研究

目的 研究胸部数字X射线摄影(DR)中,不同管电压对影像质量以及受检者辐射剂量的影响。方法 管电压在80~130 kV范围内间隔10 kV变化,每种管电压设置下自动曝光控制(AEC)范围在-4~4对成人胸部模体进行曝光。测量模体表面的皮肤入射剂量,计算相对噪声值和对比度噪声比(CNR),并估算每次曝光时受检者的有效剂量。结果 皮肤入射剂量为(0.062 9±0.027 4)mGy,有效剂量为(0.012 7±0.004 5)mSv,有效剂量随着皮肤入射剂量的增加而呈线性增加,两者呈正相关关系(r=0.912,P<0.01)。随着有效剂量的增加,相同管电压下,相对噪声与有效剂量呈负相关关系(r=-0.967、-0.969、-0.968、-0.969、-0.968、-0.970, P<0.01);CNR与有效剂量呈正相关关系(r=0.987、0.987、0.986、0.987、0.988、0.989,P<0.01)。AEC不变时,随着kV值增加,皮肤入射剂量和有效剂量均降低,最大可降低50%和20%;相对噪声值降低,最大可降低23%;CNR增加,最大可增加8%。结论 胸部DR摄影中,在满足影像质量要求的前提下,高kV值可有效降低受检者辐射剂量。     

Image quality and dose analysis for a PA chest X-ray: Comparison between AEC mode acquisition and manual mode using the 10 kVp ‘rule’

PurposeTo compare the image quality and effective dose applying the 10 kVp rule with manual mode acquisition and AEC mode in PA chest X-ray.Method68 images (with and without lesions) were acquired using an anthropomorphic chest phantom using a Wolverson Arcoma X-ray unit. These images were compared against a reference image using the 2 alternative forced choice (2AFC) method. The effective dose (E) was calculated using PCXMC software using the exposure parameters and the DAP. The exposure index (lgM provided by Agfa systems) was recorded.ResultsExposure time decreases more when applying the 10 kVp rule with manual mode (50%–28%) when compared with automatic mode (36%–23%). Statistical differences for E between several ionization chambers' combinations for AEC mode were found (p = 0.002). E is lower when using only the right AEC ionization chamber. Considering the image quality there are no statistical differences (p = 0.348) between the different ionization chambers' combinations for AEC mode for images with no lesions. Considering lgM values, it was demonstrated that they were higher when the AEC mode was used compared to the manual mode. It was also observed that lgM values obtained with AEC mode increased as kVp value went up. The image quality scores did not demonstrate statistical significant differences (p = 0.343) for the images with lesions comparing manual with AEC mode.ConclusionIn general the E is lower when manual mode is used. By using the right AEC ionising chamber under the lung the E will be the lowest in comparison to other ionising chambers. The use of the 10 kVp rule did not affect the visibility of the lesions or image quality.     

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.     

Gonad dose in AP pelvis radiography: Impact of anode heel orientation

PurposeFor antero posterior (AP) pelvis radiographic examination, determine the impact of anode heel orientation on female/male gonad dose.MethodsHigh sensitivity thermo-luminescent dosimeters (TLDs) were used with an ATOM dosimetry phantom; the phantom was positioned for AP pelvis. TLDs were placed into the testes and ovaries. Radiation dose received by these organs was measured with the feet toward anode and feet toward the cathode. kVp, mAs and SID were manipulated to generate a range of exposures. A dose profile was also generated using Unfors Mult-O-Meter 401 along the long axis of the phantom.ResultsA decrease in dose from the central ray toward the anode was noted, with a marked increase toward the cathode. A significant reduction in dose was received by the testes with feet towards the anode compared with feet towards cathode (P˂0.001). No difference was seen for ovarian dose (P˃0.05). kVp, mAs and SID all have an effect on male and female gonad dose.ConclusionFor male pelvis imaging, placing feet towards the anode can be used as a simple dose reduction method.     

降低儿童16层螺旋CT检查辐射剂量的研究

目的论证CT扫描参数kVp和mAs与剂量和图像噪声的关系,在不影响临床诊断的基础上,修正并验证一种基于成人扫描参数的安全可行的儿童16层螺旋CT检查的扫描参数。方法利用16层螺旋CT,采用标准CT剂量指数(CTDI)测试仪、100mm笔型电离室,分别测量16cm和32cm直径模体在2mm×5mm准直宽度时不同kVp和mAs的CTDI;采用20cm标准水模,测量单一感兴趣区域(ROI)标准偏差值SD代表噪声水平。以成人扫描参数的不同百分比修正为不同年龄段儿童CT扫描的参数供临床验证。结果随着kVp和mAs的增加,CTDI随之增加,并与mAs呈线性关系;16cm直径模体的表面CTDI要高于32cm模体58%;实际的加权CTDIw值高于CT扫描仪显示的CTDIw;mAs相同时,kVp越高,图像噪声SD值越低,在kVp固定时,随着mAs的增加,图像噪声SD随之减少,当mAs增加到一定程度后,图像噪声趋向平稳。结论在不影响临床诊断的图像噪声水平下,根据年龄和体型特点,儿童16层CT检查mAs可以比成人降低10%～85%。     

Optimising image quality and radiation dose for neonatal incubator imaging

IntroductionNeonates often require imaging within incubators however limited evidence exists as to the optimal method and acquisition parameters to achieve these examinations. This study aims to standardise and optimise neonatal chest radiography within incubators.MethodsA neonatal anthropomorphic phantom was imaged on two different incubators under controlled conditions using a DR system. Exposure factors, SID and placement of image receptor (direct v tray) were explored whilst keeping all other parameters consistent. Image quality was evaluated using absolute visual grading analysis (VGA) with contrast-to-noise ratio (CNR) also calculated for comparison. Effective dose was established using Monte Carlo simulation using entrance surface dose within its calculations.ResultsVGA and CNR reduced significantly (p < 0.05) whilst effective dose increased significantly (p < 0.05) for images acquired using the incubator tray. The optimal combinations of parameters for incubator imaging were: image receptor directly behind neonate, 0.5 mAs, 60 kV at 100 cm SID, however, if tray needs to be used then these need to be adapted to: 1 mAs at maximum achievable SID. Effective dose was highest for images acquired using both incubator tray and 100 cm SID owing to a decrease in focus to skin distance. There is significant increase (p < 0.01) in VGA between using 0.5 mAs and 1 mAs but an apparent lack of increase between 1 and 1.5 mAs.ConclusionUsing the incubator tray has an adverse effect on both image quality and radiation dose for incubator imaging. Direct exposure is optimal for this type of examination but if tray needs to be used, both mAs and SID need to be increased slightly to compensate.Implications for practiceThis study can help inform practice in order to both standardise and optimise chest imaging for neonates in incubators.     

10 kVp rule – An anthropomorphic pelvis phantom imaging study using a CR system: Impact on image quality and effective dose using AEC and manual mode

PurposeThis study aims to investigate the influence of tube potential (kVp) variation in relation to perceptual image quality and effective dose (E) for pelvis using automatic exposure control (AEC) and non-AEC in a Computed Radiography (CR) system.Methods and materialsTo determine the effects of using AEC and non-AEC by applying the 10 kVp rule in two experiments using an anthropomorphic pelvis phantom. Images were acquired using 10 kVp increments (60–120 kVp) for both experiments. The first experiment, based on seven AEC combinations, produced 49 images. The mean mAs from each kVp increment were used as a baseline for the second experiment producing 35 images. A total of 84 images were produced and a panel of 5 experienced observers participated for the image scoring using the two alternative forced choice (2AFC) visual grading software. PCXMC software was used to estimate E.ResultsA decrease in perceptual image quality as the kVp increases was observed both in non-AEC and AEC experiments, however no significant statistical differences (p > 0.05) were found. Image quality scores from all observers at 10 kVp increments for all mAs values using non-AEC mode demonstrates a better score up to 90 kVp. E results show a statistically significant decrease (p = 0.000) on the 75th quartile from 0.37 mSv at 60 kVp to 0.13 mSv at 120 kVp when applying the 10 kVp rule in non-AEC mode.ConclusionUsing the 10 kVp rule, no significant reduction in perceptual image quality is observed when increasing kVp whilst a marked and significant E reduction is observed.     

Optimisation of the AP abdomen projection for larger patient body thicknesses

IntroductionThis study aims to identify optimal exposure parameters, delivering the lowest radiation dose while maintaining images of diagnostic quality for the antero-posterior (AP) abdomen x-ray projection in large patients with an AP abdominal diameter of >22.3 cm.MethodologyThe study was composed of two phases. In phase 1, an anthropomorphic phantom (20 cm AP abdominal diameter) was repetitively radiographed while adding 3 layers (5 cm thick each) of fat onto the phantom reaching a maximum AP abdominal diameter of 35 cm. For every 5 cm thickness, images were taken at 10 kVp (kilovoltage peak) intervals, starting from 80 kVp as the standard protocol currently in use at the local medical imaging department, to 120 kVp in combination with the use of automatic exposure control (AEC). The dose area product (DAP), milliampere-second (mAs) delivered by the AEC, and measurements to calculate the signal to noise ratio (SNR) and contrast to noise ratio (CNR) were recorded. Phase 2 included image quality evaluation of the resultant images by radiographers and radiologists through absolute visual grading analysis (VGA). The resultant VGA scores were analysed using visual grading characteristics (VGC) curves.ResultsThe optimal kVp setting for AP abdominal diameters at: 20 cm, 25 cm and 30 cm was found to be 110 kVp increased from 80 kVp as the standard protocol (with a 56.5% decrease in DAP and 76.2% in mAs, a 54.2% decrease in DAP and 76.2% decrease in mAs and a 29.2% decrease in DAP and 59.7% decrease in mAs, respectively). The optimal kVp setting for AP abdominal diameter at 35 cm was found to be 120 kVp increased from 80 kvp as the standard protocol (with a 50.7% decrease in DAP and 73.4% decrease in mAs). All this was achieved while maintaining images of diagnostic quality.ConclusionTailoring the exposure parameters for large patients in radiography of the abdomen results in a significant reductions in DAP which correlates to lower patient doses while still maintaining diagnostic image quality.Implications for clinical practiceThis research study and resultant parameters may help guide clinical departments to optimise AP abdomen radiographic exposures for large patients in the clinical setting.     

Dose Calculation on KV Cone Beam CT Images: An Investigation of the Hu-Density Conversion Stability and Dose Accuracy Using the Site-Specific Calibration

Precise calibration of Hounsfield units (HU) to electron density (HU-density) is essential to dose calculation. On-board kV cone beam computed tomography (CBCT) imaging is used predominantly for patients' positioning, but will potentially be used for dose calculation. The impacts of varying 3 imaging parameters (mAs, source-imager distance [SID], and cone angle) and phantom size on the HU number accuracy and HU-density calibrations for CBCT imaging were studied. We proposed a site-specific calibration method to achieve higher accuracy in CBCT image-based dose calculation. Three configurations of the Computerized Imaging Reference Systems (CIRS) water equivalent electron density phantom were used to simulate sites including head, lungs, and lower body (abdomen/pelvis). The planning computed tomography (CT) scan was used as the baseline for comparisons. CBCT scans of these phantom configurations were performed using Varian Trilogy? system in a precalibrated mode with fixed tube voltage (125 kVp), but varied mAs, SID, and cone angle. An HU-density curve was generated and evaluated for each set of scan parameters. Three HU-density tables generated using different phantom configurations with the same imaging parameter settings were selected for dose calculation on CBCT images for an accuracy comparison. Changing mAs or SID had small impact on HU numbers. For adipose tissue, the HU discrepancy from the baseline was 20 HU in a small phantom, but 5 times lager in a large phantom. Yet, reducing the cone angle significantly decreases the HU discrepancy. The HU-density table was also affected accordingly. By performing dose comparison between CT and CBCT image-based plans, results showed that using the site-specific HU-density tables to calibrate CBCT images of different sites improves the dose accuracy to ～2%. Our phantom study showed that CBCT imaging can be a feasible option for dose computation in adaptive radiotherapy approach if the site-specific calibration is applied.     

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.