增感屏-胶片组合的噪声等价量子数和量子检出效率的测试

目的　测试增感屏 胶片组合的噪声等价量子数 (noiseequivalentquanta ,NEQ)和量子检出效率 (detectivequantumefficiency,DQE)。方法　用距离法测试T颗粒技术 (Green 40 0增感屏 /Kodakmgx 1胶片组合 )和MSCaWO4 增感屏 /FujiSuperRX胶片的特性曲线 ;矩形波法测试增感屏 胶片体系的调制传递函数 (modulationtransferfunction ,MTF) ;对 2种增感屏 胶片体系均匀曝光 ,用显微密度计扫描 ,通过快速傅立叶分析计算威纳频谱 (Wienerspectrum ,WS) ;由特性曲线的γ值、MTF、WS的测量计算NEQ ,并用入射量子数求DQE。结果　 (1)在空间频率为 0 6cycles/mm时 ,Green 40 0增感屏 /KodakMGX 1胶片组合的NEQ值为 1 148× 10 6 mm-2 ,是MSCaWO4 增感屏 /FujiSuperRX胶片组合的 0 65倍 ;在空间频率为 4 0cycles/mm时 ,Green 40 0增感屏 /KodakMGX 1胶片组合NEQ值为 0 3 2 9× 10 4mm-2 ,是MSCaWO4 增感屏 /FujiSuperRX胶片组合的 1 5 5倍。 (2 )在空间频率为 0 6cycles/mm时 ,Green 40 0增感屏 /KodakMGX 1胶片组合的DQE值为 0 2 2 4,是MSCaWO4 增感屏 /FujiSuperRX胶片组合的 1 6倍 ;在空间频率为 4 0cycles/mm时 ,Green 40 0增感屏 /KodakMGX 1胶片组合的DQE值为0 0 5 2 ,是MSCaWO4 增感屏 /FujiSuperRX胶     

高速增感屏在床边摄影中的应用

床边摄影是放射科工作的一个重要组成部分，床边片的好坏直接影响医生的诊断及治疗。病人，工作人员及所使用的机器设备等因素，都能影响床边片的质量。近年来，我们用高速增感屏进行床边摄影，取得了良好效果。下面着重谈谈增感屏对摄影质量的影响。     

X线胶片：增感屏组合的敏感度和剂量要求

X线防护法规§16不仅对使用者、放射科医师,也对生产厂家提出了一系列确保质量的要求,对投入市场的产品提供洋尽的说明也是生产厂家的责任,这在X线防护法规§16的准则中部有具体规定。例如屏胶组合(增感屏—X线胶片组合)的生产厂家应说明以下特性数据:①屏胶组合的敏感度(按照德国工业标准6867第1部分);②屏胶组合的临界分辨力;③X线胶片的明暗层次(按     

新型宽域X线增感屏的研制

目的　常规胸片上 ,在不改变投照条件下 ,使脊柱、纵隔、心后肺内占位病灶和两侧肺野内细小病变 ,均能清晰地显示在同一张照片上。方法　通过对现有增感屏的增感物质在布局上加以改变和技术处理 ,即中央部分涂成高速增感物质 ,两侧涂成中速增感物质。结果　用新屏对 7例患者进行投照 ,其结果是脊柱、纵隔、心后肺内占位病灶均较清晰地显示在同一张照片上 ,基本达到预期目的。结论　在常规胸片上 ,新型宽域X线增感屏能给X线诊断提供更多、更清晰、层次更加丰富的影像信息     

使用高速增感屏投照胸椎腰椎曝光条件的改进

作者为了提高胸、腰椎X线照片的影像质量，利用“一成法则”的逆法则，将中速屏的曝光条件递增、递减后而得到的一组，千伏值、毫安秒的换算方法。从而提高照片质量。     

增感屏-胶片组合体系的威纳频谱测试探讨

目的　通过实验测试增感屏-胶片组合体系的威纳频谱(Wienerspectrum,WS),评价X线照片的粒状性。方法　制作CaWO4屏-Kodak片、BaFClEu屏-Kodak片、T颗粒技术3种增感屏-胶片组合体系的10cm×10cm粒状性抽样照片,用显微密度计扫描,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（fastFouriertransform,FFT）计算WS。结果　（1）BaFClEu屏-Kodak片的WS值当空间频率为0.1LP/mm时,WS值为8.26×10     

64层螺旋CT噪声测试及其影响因素分析

目的测试和评价64层螺旋CT图像噪声及其影响因素。方法对SOMATOM Sensation 64层螺旋CT，使用临床常用的腹部扫描模式，采用不同直径的模体，不同层厚、毫安秒（mAs）、管电压（kV）、重建算法、视野和螺距等扫描参数，分别进行螺旋扫描和断面扫描，测量其图像中心感兴趣区内的标准差并进行分析。结果160mAs时，标称层厚10、7、5、3、1和0.6mm的噪声分别是8.4、9.3、10.7、13.0、21.8、28.3；120kV时，重建算法为B30 smooth、B40 smooth、B60 sharp、B70 sharp时的噪声分别是8.4、9.5、41.4、44.5；对于标称层厚5mm时，螺距为0.5、0.75、1、1.25、1.5时噪声为10．6、11、10．7、10．5、10．9；随着模体直径的增加，螺旋扫描和断面扫描时的噪声均增大；视野为200mm×200mm、150mm×150mm、100mm×100mm时的图像噪声是7．83、8．10、10．47。结论64层螺旋CT图像噪声随mAs、层厚、kV、视野的增大而减少，随模体直径的增加和高分辨率算法而增大，但不随螺距和扫描方式的改变而改变。     

Clinical evaluation of digital radiography based on a large-area cesium iodide-amorphous silicon flat-panel detector compared with screen-film radiography for skeletal system and abdomen

The aim of this clinical study was to compare the image quality of digital radiography using the new digital Bucky system based on a flat-panel detector with that of a conventional screen-film system for the skeletal structure and the abdomen. Fifty patients were examined using digital radiography with a flat-panel detector and screen-film systems, 25 for the skeletal structures and 25 for the abdomen. Six radiologists judged each paired image acquired under the same exposure parameters concerning three observation items for the bone and six items for the abdomen. Digital radiographic images for the bone were evaluated to be similar to screen-film images at the mean of 42.2%, to be superior at 50.2%, and to be inferior at 7.6%. Digital radiographic images for the abdomen were judged to be similar to screen-film images at the mean of 43.4%, superior at 52.4%, and inferior at 4.2%; thus, digital radiographic images were estimated to be either similar as or superior to screen-film images at over 92% for the bone and abdomen. On the statistical analysis, digital radiographic images were also judged to be preferred significantly in the most items for the bone and abdomen. In conclusion, the image quality of digital radiography with a flat-panel detector was superior to that of a screen-film system under the same exposure parameters, suggesting that dose reduction is possible with digital radiography.     

数字乳腺X线摄影中采用影像噪声特征评价图像质量的研究

目的 通过对数字乳腺X线摄影系统噪声特征的分析,评价影像噪声特性的适宜表达方式.方法 采用固定管电流量90 mAs,在钼(Mo)和铑(Rh)滤过下,在23 ～ 35 kVp范围内共13个不同的管电压对对比度细节模体CDMAM曝光;采用固定管电压29 kVp,Mo和Rh滤过下,在20～200 mAs范围内10个不同的管电流量对CDMAM模体曝光.对所得CDMAM模体影像分别测量和计算信号区和信号区旁背景区域的标准差、联合标准差、相减标准差和相对标准差,并用软件计算CDMAM模体的影像质量评分.采用秩和检验比较上述不同条件下计算的背景标准差、联合标准差、相减标准差值的差异,对不同曝光模式下的Mo、Rh滤过2组图像的CDMAM影像质量评分比较采用t检验.结果 在使用Mo靶、90 mAs时,分别采用Mo和Rh滤过,随管电压增加,标准差逐渐增大,相对标准差逐渐减小;采用Mo滤过,背景标准差、联合标准差和相减标准差的中位数分别为10.91、10.34和9.87,采用Rh滤过,上述标准差分别为11.24、10.57和9.96,差异有统计学意义(x2=26.0,P＜0.01).在使用Mo靶、29 kVp时,分别选择Mo和Rh滤过,随管电流增加,标准差逐渐增大,相对标准差逐渐减小;采用Mo滤过,背景标准差、联合标准差和相减标准差的中位数分别为12.30、11.61和11.05,采用Rh滤过,上述标准差分别为12.29、11.58和10.87,差异有统计学意义(x2=20.0,P＜0.01).管电流均采用90 mAs,采用不同管电压,Mo滤过条件下,影像评分为(149.14±23.87)分,Rh滤过条件下影像评分为( 139.16±23.14)分,差异有统计学意义(t=9.129,P＜0.01).管电压均采用29 kVp,采用不同管电流,Mo滤过条件下,影像评分为(149.75±34.85)分,Rh滤过条件下影像评分为(145.2±34.64)分,差异无统计学意义(t=1.304,P＞0.05).相对标准差的数值随着管电压或管电流量的增大而减小,同时影像质量上升.结论 相对标准差适于数字乳腺摄影影像噪声水平的表达,也可用于影像质量的评价.     

利用噪声等价图像和深度学习方法对低剂量CT降噪

目的:研究在常规剂量扫描情况下模拟低剂量CT图像的方法,以此生成训练数据集中与常规剂量CT具有对应关系的低剂量CT图像,并建立深度学习模型,用于低剂量CT图像的降噪。方法:使用Philip Brilliance CT Big Bore模拟定位机,其不同算法重建的CT图像具有不同的噪声水平,其中iDose4算法噪声较大,...     

冠状动脉CT成像钙化积分扫描噪声与增强扫描噪声的相关性分析

目的：分析冠状动脉CT血管成像（CCTA）中对比增强前后图像噪声值的关系,探讨一种预测CTCA图像噪声的方法,从而为实施个体化剂量管理提供依据。方法：回顾性分析固定各扫描序列曝光参数的82例64层螺旋CT回顾性门控冠状动脉CTA的图像资料,研究钙化积分扫描（CACS）图像噪声（SD1）与对比增强扫描图像噪声（SD2）之间的线性相关性,以及体重指数（BMI）与对比增强扫描图像噪声（SD2）之间的线性相关性,并拟合出直线方程。结果：SD1与SD2之间直线相关系数r=0.94（P〈0.0001）,线性方程为SD2=1.29624×SD1＋1.20457;BMI与SD2之间的直线相关系数r=0.80（P〈0.0001）,线性方程为SD2=1.56067×BMI-10.76970。结论：在CTA各序列的曝光参数不变的情况下,对比增强前后图像噪声值之间存在高度线性相关性。钙化积分扫描噪声比体重指数能更精确地预测增强扫描图像的噪声,从而使基于钙化积分扫描噪声的个体化剂量控制成为可能。     

Iterative reconstruction and automatic tube voltage selection reduce clinical CT radiation doses and image noise

IntroductionComputed Tomography (CT) use has increased in recent years with trends indicating increasing population doses as a result. Optimization of clinical radiation doses through technological developments has demonstrated potential to reduce patient dose from CT. This study aimed to quantify these dose reductions across a large clinical cohort.MethodsPatient cohort was divided into three groups, assigned by CT optimisation technique. Group one underwent scanning with automated tube current modulation only. Group two underwent scanning with automated tube current modulation and iterative reconstruction and group three underwent scanning with automated tube current modulation, iterative reconstruction and automatic tube voltage modulation. Patient dose length product doses were retrospectively collected for the three groups. Clinical radiation doses between the groups were compared for four common CT examinations (Brain, pulmonary angiography, abdomen and thorax abdomen pelvis scans).ResultsOf 4011 patients, group one comprised of 1643 patients (40.96%), group two 1077 patients (26.85%) and group three 1291 patients (32.19%). No differences were found when comparing AP diameter between groups (p ≥ 0.05). Statistically significant dose reductions of 16–31% were achieved using iterative reconstruction alone (p = 0.001) and 24–42% with both iterative reconstruction and automatic tube voltage selection (p = 0.001). Objective noise improved when iterative reconstruction was used (p < 0.05).ConclusionThe application of optimization software confers significant dose savings during routine clinical CT examinations. Figures are based on a large clinical cohort, with equipment, staff and procedural protocols remaining consistent throughout. Dose reductions are likely to reflect the clinical dose reducing potential of the optimization software investigated.     

Management of patient dose and image noise in routine pediatric CT abdominal examinations

The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDI_w) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32 cm in diameter at 80, 100, 120 and 140 kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5 mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDI_vol values of 6.7, 9.4, 15.9 and 24.5 mGy were proposed for the following weight classes: 2.5–5, 5–15, 15–30 and 30–50 kg with image noise levels in the range of 10–15 HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assessed.     

Image quality and breast dose of 24 screen-film combinations for mammography

In this study the effect of different mammographic screen-film combinations on image quality and breast dose, and the correlation between the various image quality parameters, breast dose and the sensitometric parameters of a film were investigated. Three Agfa (MR5-II, HDR, HT), two Kodak (Min-R M, Min-R 2000), one Fuji (AD-M), one Konica (CM-H) and one Ferrania (HM plus) single emulsion mammographic films were combined with three intensifying screens (Agfa HDS, Kodak Min-R 2190 and Fuji AD-MA). The film characteristics were determined by sensitometry, while the image quality and the dose to the breast of the resulting 24 screen-film combinations were assessed using a mammography quality control phantom. For each combination, three images of the phantom were acquired with optical density within three different ranges. Two observers assessed the quality of the 72 phantom images obtained, while the breast dose was calculated from the exposure data required for each image. Large differences among screen-film combinations in terms of image quality and breast dose were identified however, that, could not be correlated with the film's sensitometric characteristics. All films presented the best resolution when combined with the HDS screen at the expense of speed, and the largest speed when combined with the AD-MA screen, without degradation of the overall image quality. However, an ideal screen-film combination presenting the best image quality with the least dose was not identified. It is also worth mentioning that the best performance for a film was not necessarily obtained when this was combined with the screen provided by the same manufacturer. The results of this study clearly demonstrate that comparison of films based on their sensitometric characteristics are of limited value for clinical practice, as their performance is strongly affected by the screens with which they are combined.     

胸部低剂量CT扫描管电流与噪声分布相关性研究

目的 分析胸部低剂量CT图像噪声分布特点,优化低剂量扫描参数.方法 利用图像空间添加噪声软件对中国人仿真胸部体模CT图像进行6种不同噪声指数的模拟,并分析预设噪声指数与模拟图像噪声值的差异.使用该软件对20例志愿者常规扫描图像进行噪声添加,模拟出10、30、50、80、100、120、150、180及240 mA 9组胸部低剂量图像,记录每幅图像模拟噪声值,并对不同剂量组模拟噪声值进行统计学分析.结果 图像噪声添加法计算的模拟噪声值与预设噪声指数差异不大.胸部低剂量扫描时,图像模拟噪声值随着管电流的降低而增加,当管电流在30～50 mA时,噪声降低显著(F=24.09 ～ 40.79,P＜0.05);80～240 mA时,噪声值降低幅度变缓;80mA组与120 mA组之间差异不大.结论 图像空间添加噪声软件可应用于胸部低剂量CT图像噪声的评价研究.胸部低剂量CT检查采用管电流80 mA,能够保证图像噪声较小,同时明显降低辐射剂量.     

Impact of image noise levels, scout scan dose and lens shield on image quality and radiation exposure in z-axis dose-modulated neck MSCT on 16- and 64-slice Toshiba Aquilion scanners

Objective

Assessing the impact of image noise (IN) levels, scout scan dose and lens shield use on image quality and radiation exposure in neck multislice CT (MSCT) when using z-axis dose modulation (DM).

Methods

Neck MSCT phantom studies with/without z-axis DM were performed by using different IN levels (S.D. 7.5-30 HU) and scout scan tube currents (7.5-50 mA) on Toshiba Aquilion scanners (16-/64-slice). Image quality indices were evaluated by two radiologists and radiation exposure parameters calculated. Cadaveric phantom measurements elucidated lens shield interactions with DM efficacy. The lowest dose scan protocol with diagnostic image quality was introduced into the clinical imaging routine and retrospectively evaluated in 20 age-matched patients undergoing neck MSCT with/without DM.

Results

The highest image noise level in DM neck studies with comparable image quality to standard neck CT amounted to 20 HU, resulting in a mean tube current of 50 mAs (CTDI_w 6.3 mGy). DM reduced effective dose by 35% and organ dose figures (lens, thyroid) by 33%. Scout scan dose lowering to 20 mA resulted in an effective dose (ED) decrease of 0.06 mSv (5%). Avoiding lens shield placement during scout scan effected an organ dose decrease of 20%. Overall contour sharpness and image contrast did not differ significantly (DM/without DM) whereas image noise was rated higher in DM neck CT studies (p < 0.05).

Conclusions

z-Axis dose modulation, as assessed on 16- and 64-slice Toshiba Aquilion scanners, is effective and mandatory in neck MSCT. DM efficacy can be enhanced by optimising scout scan doses and lens shield use.