计算机X线摄影适宜照射线量的探讨

目的以噪声的频率特性评价计算机X线摄影系统(computed radiography, CR)的适宜曝光量.方法在相同摄影条件下获得中速 CaWO4屏-Fuji片组合照片和CR照片,以此为基础,改变mAs,获得不同照射剂量下的CR影像,经相同的后处理条件输出它们的CR照片.用显微密度计依次对这些照片进行扫描,每张获得10万个密度值,作为离散随机信号来处理,用快速傅立叶变换计算威纳频谱(Wiener spectrum, WS),测试CR照片噪声的WS与中速CaWO4屏-Fuji片组合的照片噪声WS值相等的曝光量值.结果 (1)在照射剂量均为5.61μGy、照片密度均为1.0的情况下,在空间频率(ω)=0.1 LP/mm处,CR系统的WS值为 23.1×10 -6 mm2,屏-片系统的为20.1×10 -6 mm2;在ω=0.5 LP/mm处,CR系统的WS值为 9.73×10 -6 mm2,屏-片系统的为8.41×10 -6 mm2 .(2)当ω=0.1 LP/mm时,照射剂量为5.61μGy的CR照片的WS值分别是照射剂量为1.40、2.80、8.76、13.67、21.11μGy CR片的0.53、0.75、1.14、1.44、1.80倍;当空间频率为0.5 LP/mm时,照射剂量为5.61μGy的CR片的WS值分别是照射剂量为1.40、2.80、8.76、13.67、21.11μGy CR片的0.40、0.58、1.26、1.47、2.16倍.(3)在ω=0.5 LP/mm时,与照射剂量为5.61μGy的屏-片组合有相当的噪声水平的CR照片照射剂量大致为7.70 μGy左右.结论相同摄影条件下CR照片的噪声要比中速 CaWO4屏-Fuji片组合的大;随着照射量的增加CR系统总WS将减小,噪声下降;如想获得和屏-片相同噪声的影像,应适当增大CR系统的照射量.     

优化组合CR系统自动曝光控制成像参数

目的:优化组合CR系统自动曝光控制成像参数.材料和方法:采用两种规格的成像(IP)板,用不同组合的成像参数对胸部拟人水模摄影,检测电离室密度补偿与曝光参数的变化.以所得成像数据和两种规格的IP板,对A、B、C三组患者(每组各180例),不同部位摄影,检测不同曝光剂量组合摄影的影像质量和影像的密度值.结果:A组以两种规格的IP板、125kV摄胸部,图像对比度差;病灶细微结构显示不清.以73～85kV摄胸部,其图像明显好于125kV;B组与C组的小规格IP板(20.5cm×25.6cm)优于大规格IP板的(35cm×35cm)图像质量;影像密度值均在0.8～1.30范围内.结论:CR系统不宜采用高kV摄影;应使用合适规格的成像板.     

CR系统在乳腺摄影中的应用分析

目的:评价CR系统在乳腺摄影中的应用价值。方法:抽取我院CR乳腺照片和传统钼靶X线照片各800张进行分析,统计出甲、乙、丙级片及废片率;统计CR片及传统屏-片乳腺癌的诊断正确率。结果:①照片影像质量:CR照片甲级片率67%,乙级片率26%,丙级片率7%,废片率0.25%。传统屏-片甲级片率36%,乙级片率50%,丙级片率11%,废片率2.5%。②照片诊断正确率:CR照片90%,传统屏-片73%。③摄影条件:CR系统比屏-片系统摄影管电压低4 kV,曝光量低4 mAs。结论:CR摄影影像质量好于传统屏-片摄影,可为临床提供可靠的诊断依据,且减少了病人的X线接受剂量。     

CR摄影与传统屏-片摄影的综合评价

屏-片系统摄影，被照体经X线照射后，将影像信息记录在胶片上，经过显、定影处理将潜影转化为可见影像显示在胶片上。计算机X线摄影（computed radiography，简称CR），投照后是将影像信息记录在影像板（image plate，简称IP板）经扫描仪读取后，再经模／数转换器转换成数字信号，于荧光屏上显示出灰阶图像，根据需要打出不同层次的优质照片。[第一段]     

高能射线下计算机摄影和屏-片系统的射野验证片图像质量探讨

目的 评价计算机摄影（CR）系统和普通屏-片系统两种方法拍摄直线加速器验证片的图像质量。方法 自制透过率为6．45％的铅模体，用影像板（IP）和X线胶片分别拍摄放射治疗验证图片。利用刃边法绘制各自的调制传递函数（MTT）曲线。分别用IP和屏-片系统拍摄40例鼻咽癌患者的验证片，由2名相同年资的医师来判断每幅验证片岩骨破坏的程度，根据结果分别绘制2名医师关于CR照片和普通照片的受试者操作特性曲线（ROC）。结果CR系统和屏-片系统的鉴别频率分别为1．159和0．806Lp／mm。医师1CR照片和普通照片ROC曲线下的面积（Az）值为0．802和0．742，医师2CR照片和普通照片ROC的舡值为0．751和0．600。CR的MTF曲线和ROC曲线均高于屏-片系统。结论 利用CR技术拍摄直线加速器射野验证片的图像质量优于屏-片系统，在临床上具有很大推广价值。     

乳腺计算机X射线摄影自动曝光模式的校正

目的 通过参照乳腺屏一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町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.     

乳腺计算机X射线摄影自动曝光模式的校正

目的 通过参照乳腺屏一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町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.     

影响CR系统影像质量的因素及其优缺点分析

CR系统是使用可记录并由激光读出X线影像信息的成像板（IP）作为载体，经X线曝光及信息读出处理，形成数字式屏一片影像、目前CR已在国内外临床上广泛应用。在CR系统成像的过程中，对影像质量影响的因素有很多，它们主要存在于信息的采集、信息的读出和信息的处理与记录三个环节中，尤以IP的特征和阅读器的性能更为重要。本文对影响CR系统影像质量的因素及其优缺点进行分析，旨在为提高CR系统影像质量寻找有效的措施和方法。     

乳腺计算机X射线摄影曝光条件的研究

目的通过比较乳腺摄影屏-片系统与计算机X射线摄影(CR)系统的曝光条件,以及不同曝光量对乳腺CR影像的影响,探讨乳腺CR摄影条件的优化原则。方法应用屏-片组合和CR,分别采用26、28、30 kV对fluke NA 18-220 乳腺模体采用自动曝光控制(AEC)模式进行摄影,并记录曝光量数值(mAs),对CR影像进行处理。同时CR采用上述相同kV、照射野,以及不同的曝光量对模体进行摄影,并对CR影像进行不同的处理。所获图像由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。结果采用自动曝光模式,乳腺CR摄影的曝光量明显高于传统屏-片组合的曝光量;乳腺CR摄影的曝光量降低到标准自动曝光模式的1/2~1/3时仍能满足诊断要求,此时的曝光量较屏-片组合采用自动曝光模式的曝光量低。结论乳腺CR摄影采用不经重新校正的自动曝光模式时,曝光量明显增加;符合诊断要求的乳腺CR摄影所需曝光量可低于屏-片组合,合理使用CR是降低乳腺CR摄影剂量的关键。     

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。     

旋转DSA技术在肺栓塞诊疗中应用的研究

目的研究旋转DSA技术在肺栓塞(pulmonary embolism，PE)诊疗中的应用。方法建立小型猪肺栓塞模型13头，进行常规肺动脉造影并应用旋转DSA技术，对造影结果进行分析、评价和研究。结果将每头猪的肺分为相应的15条血管，共有195条血管。以病理阳性结果为标准，评价肺动脉造影及旋转。DSA技术诊断PE的价值。肺动脉造影及旋转。DSA共有47个血管阳性(24．1％)，敏感性为98％，特异性为99％，诊断准确性98％；有2个血管数字减影肺动脉造影阳性，病理阴性，假阳性率为1％；有1个血管数字减影肺动脉造影阴性，病理阳性，假阴性率为2％。结论旋转DSA技术有助于肺栓塞诊断，尤其对疑似病变有一定临床意义。     

数字乳腺X线摄影中管电流量与影像质量的关系

目的探讨数字乳腺X线摄影中不同乳腺压迫厚度时管电流量与影像质量的关系。方法全数字乳腺摄影机中采用钼-铑靶滤过组合,对2~7 cm厚度的CDMAM模体选择适宜的管电压,不同管电流量下,进行手动曝光,参数(压迫厚度、管电压、管电流量)设定分别为2 cm、27 kVp、10~90 mAs,3 cm、29 kVp、20~120 mAs,4 cm、29 kVp、20~200 mAs,5 cm、30 kVp、40~220 mAs,6 cm、31 kVp、40~260 mAs和7 cm、32 kVp、80~280 mAs,计算图像影像质量因子(IQF)、对比噪声比(CNR),记录平均腺体剂量(AGD)。通过计算品质因子(FOM),找出各种厚度下最优管电流量及对应的AGD。根据2~7 cm压迫厚度下优化参数表和机器在各种厚度下自动曝光特性,列出2~7 cm厚度下自动曝光参数调整表。同时对不同厚度下IQF、CNR和AGD进行Pearson相关分析,对CNR和管电流量进行曲线拟合。结果在钼-铑靶滤过组合下,不同压迫厚度时,随着管电流量增加,AGD线性增加,FOM先增加后下降或平缓变化。AGD和CNR在2~7 cm厚度下均呈高度正相关,r值均>0.97,P均<0.01。AGD和IQF在2~6 cm时呈高度正相关,r值均>0.87,P均<0.01。参考IQF和FOM因子,不同压迫厚度下,管电压和管电流量适宜匹配参数分别为2 cm、27 kVp、20~30 mAs,3 cm、29 kVp、30~50 mAs,4 cm、29 kVp、80~100 mAs,5 cm、30 kVp、80~120 mAs,6 cm、31 kVp、100~140 mAs,7 cm、32 kVp、80~120 mAs。压迫厚度-自动曝光档的设置对应关系为2 cm-1档、3 cm-2档、4 cm-3档、5 cm-2档、6 cm-0档、7 cm--1档。结论不同乳腺压迫厚度下,具有适宜的管电流量范围,临床实践中应选择相应的自动曝光条件。     

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.     

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.     

A circuit modification that improves mammographic phototimer performance

The typical mammographic phototimer does not track with breast thickness. For four common, relatively new mammographic units, phototimed density decreases markedly as breast thickness increases. This trend is attributed to three factors: beam hardening, film reciprocity law failure (RFL), and photosensor dark or leakage current. The contributions of these three factors were experimentally quantitated for the phototimer of a Senographé 500T mammography unit. For a phototimed 28-kVp nongrid technique, the density varied from 2.0 for a 2.5-cm-thick phantom to 0.3 for one 7.6 cm thick. Of the 1.7 difference in film density, 1.1 was attributed to beam hardening, 0.2 to RFL, and 0.4 to photomultiplier tube dark current. A circuit modification was installed in the phototimer that offsets the photomultiplier dark current and has a nonlinear response to compensate for beam hardening and RFL effects. The modified phototimer tracked to within +/- 0.06 density for a 28-kVp grid technique as phantom thickness was varied from 2.0 to 6.0 cm. Similar results were obtained for nongrid techniques.     

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.     

Patient-circumference-adapted dose regulation in body computed tomography. A practical and flexible formula

PURPOSE: To illustrate that the attenuation formula based on monochromatic radiation in homogeneous objects may be used for dose regulation in body computed tomography (CT) based on patient circumference and using a simple cloth measuring tape. MATERIAL AND METHODS: Based on the attenuation formula for monochromatic radiation the following Microsoft Excel equation was derived: mAs(x) = mAs(n)*EXP((0.693/ HVT)*(O(x)-O(n))/PI()), where mAs(x) (milliampere second) in a patient with circumference O(x) is calculated based on the nominal mAs(n) set for a reference patient with the circumference O(n) with regard to indication, scan protocol, and available CT scanner. The HVT = half-value thickness (object thickness change in cm affecting mAs setting by a factor of 2) resulting in the least mAs difference compared with published studies investigating the mAs needed for constant image noise in abdominal CT phantoms at 80-140 kVp was evaluated. Clinically recommended HVT values were applied to 20 patients undergoing abdominal CT using 130 effective mAs and 94 cm circumference as nominal settings, and an HVT of 9 cm. RESULTS: The object-sized dependent mAs for constant image noise at 80-140 kVp in 10-47 cm diameter abdominal phantoms (31-148 cm in circumference) differed, with few exceptions, by no more than 10% from those obtained with our formula using an HVT of 3.2-3.8 cm. An HVT of 9 cm in the patient study resulted in the same image noise-patient circumference relation as a phantom study using a "clinically adapted mAs" resulting in an acceptable noise according to diagnostic requirements. Clinical experiences recommend an HVT of about 8 cm for abdominal CT and 12 cm in thoracic CT. Changing the kVp from 120 to 80, 100, or 140 requires a mAs change roughly by factors of 4, 2, and 0.6, respectively, for constant image noise. CONCLUSION: Until fully automatic automatic exposure control systems have been introduced, applying the formula in a computer program provides the radiologist with an easy, quick, flexible, and practical instrument for reasonably good patient-sized adjusted exposure levels in clinical practice.     

Mammography equipment: principles, features, selection

1. Three-phase and constant potential generators may offer advantages over single-phase generators. These include shorter exposure times with less chance for motion unsharpenss, more adequate exposure and possible lower dose, and longer tube life. 2. Control of tube voltage in increments of 1 kVp are desirable for screen-film mammography and 2 kVp for xeromammography. 3. Tube loading limitations should be capable of allowing an adequate mA and mAs output. A mammography unit with a lower mA output may require longer exposure times with consequent motion unsharpness and/or higher dose. The maximum mA output is limited by the power rating of the tube and not by the power rating of the generator, which is usually much higher. Thus, tube rating charts rather than generator power rating should be used to compare the mA output of different mammography units. 4. Phototimer capability can reduce exam time, facilitate proper exposure, and reduce radiation dose. Units with a greater number of density steps and three or more photocell locations, one of which is near the edge of the film holder, provide better phototimer results. 5. A molybdenum target, beryllium window tube with 0.03 mm molybdenum added filtration is presently preferred for screen-film mammography. A tungsten target tube with 1 to 2 mm added aluminum filtration is advised for xeromammography. 6. Effective local spot size for contact mammography should be in the range of 0.2 to 0.5 mm. However, high resolution also requires sufficiently long source-to-image-receptor distances. Using measured focal spot size and source-to-image-receptor distance, it has been shown that some mammography units do not fully utilize the resolution capabilities of some available screen-film systems. On the other hand, a focal spot that is too small may limit the field size and lead to uneven energy distribution in the x-ray field. 7. In order to perform standard and supplementary mammographic projections, the C arm assembly must be capable of being located at multiple positions within a 180 degrees rotation. Greater degrees of rotation are not required. 8. The heat dissipation capability should be adequate to accommodate the anticipated work-load in terms of number of patients and patient scheduling. A mammographic unit with an anode heat capacity of 90,000 heat units or more should be adequate for most practices. A mammography unit with a heat capacity of 20,000 heat units or less may require waiting time between exposures or studies in a high-volume mammography practice. 9. The compression plate should be made of plastic, usually 1 to 4 mm thick.(ABSTRACT TRUNCATED AT 400 WORDS)     

Investigation of optimum X-ray beam tube voltage and filtration for chest radiography with a computed radiography system

The purpose of this study was to determine the optimum tube voltage and amount of added copper (Cu) filtration for processed chest radiographs obtained with an Agfa 75.0 Computed Radiography (CR) system. The contrast-to-noise ratio (CNR) was measured in the lung, heart/spine and diaphragm compartments of a validated chest phantom using various tube voltages and amounts of Cu filtration. The CNR was derived as a function of air kerma at the CR plate and with the effective dose. As rib contrast can interfere with detection of nodules in chest radiography, a tissue-to-rib ratio (TRR) was derived to investigate which tube voltages suppress the contrast of rib. Although processing algorithms affect the signal and noise in a way that is hard to predict, we found that, for a given set of processing parameters, the CNR was related to the plate air kerma and effective dose in a logarithmic manner (all R(2) >or=0.97). For imaging of the lung region, a low voltage (60 kVp) produced the highest CNR, whereas a high voltage (125 kVp) produced the highest TRR. In the heart/spine region, 80-125 kVp produced the highest CNR, while in the diaphragm region 60-90 kVp produced the highest CNR. For chest radiography with this CR system, the optimal tube voltage depends upon the region of interest. Of the filters tested, a 0.1 mm Cu thickness was found to provide a statistically significant increase in the CNR in the diaphragm region with tube potentials of 60 kVp and 80 kVp, without affecting the CNR in the other anatomical compartments.     

Dose reduction in full-field digital mammography: an anthropomorphic breast phantom study

The aim of this study was to evaluate the potential for radiation dose reduction by using other beam qualities in full-field digital mammography (FFDM) compared with screen-film mammography (SFM). FFDM was performed using an amorphous silicon detector with a caesium iodide scintillator layer (Senographe 2000D, GE, Milwaukee, USA). SFM was performed using a state-of-the-art conventional system (Senographe DMR, GE, Milwaukee, USA) with a dedicated screen-film combination. An anthropomorphic breast phantom with superimposed microcalcifications (50-200 microm) was used to evaluate the detectability of microcalcifications. Contact mammograms and magnification views (m=1.8) performed with both the digital and the screen-film system were compared. Images were exposed automatically. Molybdenum/Molybdenum (Mo/Mo) anode-filter combination, 28 kVp and 63 mAs were selected by the automatic optimization of parameters (AOP) of the conventional system. This exposure protocol (protocol A) was also used as baseline for the digital system. Dose reduction in digital mammography was achieved by using protocol B with Mo/Rh and 31 kVp and protocol C with Rh/Rh and 32 kVp. The detectability of microcalcifications was assessed by 3 experienced readers with a confidence level ranging from 1 to 5. A receiver operating characteristic (ROC) analysis was performed. In protocol A the area under the ROC-curve (A(z)) for contact views performed by the screen-film system was 0.64 and for those performed with the FFDM system 0.68. The A(z) values were 0.74 in protocol B and 0.65 in protocol C for the digital system. For the conventional and digital magnification views A(z) values were 0.71 and 0.79, respectively. For protocol B the A(z) value was 0.81 and for protocol C it was 0.76. There is no statistically significant difference in the A(z) values for the different protocols in digital mammography and no significant difference from the screen-film system. A potential for dose reduction by using other beam qualities seems to be possible with this digital system.