Step-wedge sensitometry

An aluminum step-wedge filter placed far from the film cassette provides the constant variation of subject contrast required for quantitative sensitometry while virtually eliminating scatter radiations. Attenuation curves made with this configuration are almost exponentially linear.     

通过2°星卡测试研究论微焦点高仟伏摄影的优越性

作者用２°星模测试卡，在不同负载条件下，对微焦点和小焦点的“等效焦点”尺寸、焦点极限分辨率分别进行了测试对比。结果提示微焦点高仟伏摄影的成像质量显著优于常规摄影。其等效焦点受负载条件变化的影响很小，焦点极限分辨率高，成像质量稳定。微焦点高仟伏集两种摄影优势于一体，更加优化了焦点的成像质量，使Ｘ线影像质量得以稳步提高。     

双源CT低管电压冠状动脉成像技术的初步研究

目的 探讨双源CT(dual-source CT,DSCT)低管电压冠状动脉成像在正常体重指数患者的可行性.资料与方法 选择正常体重指数且临床拟诊冠状动脉疾病者60例进行DSCT冠状动脉成像,将60例分为两组:常规管电压扫描组(A组)和低管电压扫描组(B组),每组30例.A组采用常规120 kV管电压扫描,B组采用100 kV管电压扫描,然后对两组图像质量、对比噪声比(CNR)、容积CT剂量指数(CTDIvol)和有效剂量(ED)进行评估.结果 A组右冠状动脉(RCA)、左冠状动脉前降支(LAD)、回旋支(CX)的图像质量评分分别为(3.77±0.50)分、(3.80±0.48)分和(3.73±0.52)分,B组RCA、LAD、CX图像质量评分分别为(3.50±0.63)分、(3.53±0.60)分和(3.50±0.57)分,P值均＞0.05.两组图像CNR分别为(20.33±5.14)和(21.56±5.61),两组间差异无统计学意义(t=-0.88,P＞0.05).A组和B组的CTDIvol分别为(62.24±10.12)mCy、(36.50±8.45)mGy(t=10.7,P＜0.05),ED分别为(17.63±3.75)mSv、(10.03±2.23)mSv(t=9.55,P＜0.05).结论 DSCT低管电压冠状动脉成像技术可明显降低正常体重指数受检者所受辐射量,能满足临床诊断需求.     

千伏效应成像技术与成人胸片高千伏影像学分析

目的：评价不同屏胶组合,在不同电压下的成像技术,照片质量,影像特征性表现,肺野内细微结构显示率,并进行千伏效应分析,方法：３种屏胶组合３种电压进行成人胸部Ｘ线摄影,运用诊断学及技术学评审观点,经双盲法评审,通过统计学处理。结果：５００例胸片肺野内细微结构显示率中,钙屏蓝片１００例普通电压为１５％,１００例准高电压为８０％,１００例高电压为９８％,１００例快速屏蓝片准高电压为９５％,１００例绿屏绿片     

Early Clinical Experience With Kilovoltage Image-Guided Radiation Therapy for Interfraction Motion Management

Interest in image-guided radiation therapy (IGRT) reflects the desire to minimize interfraction positioning variability. Using a kilovoltage (kV) imaging unit mounted to a traditional LINAC allows daily matching of kV images to planning digitally reconstructed radiographs (DRRs). We quantify and evaluate the significance of calculated deviation from the intended isocenter. Since September 2004, 117 patients with various malignancies were treated using the On-Board Imaging (OBI) system, with 2088 treatment sessions. Patients were positioned by the treating therapist; orthogonal images were then obtained with the OBI unit. Couch shifts were made, aligning bony anatomy to the initial simulation image. Routine port films were performed weekly (after that day's OBI session). Ninety percent of all lateral, longitudinal, and vertical shifts were less than 0.8 cm, 0.6 cm, and 0.7 cm, respectively. The median vector shift for each anatomic site was: 0.42 cm for head and neck, 0.40 cm for CNS, 0.59 cm for GU/prostate, and 0.73 cm for breast; shift magnitude did not change with successive OBI sessions. The use of OBI effectively corrects setup variability. These shifts are typically small and random. The use of OBI likely can replace weekly port films for isocenter verification; however, OBI does not provide field shape verification.     

职业病(尘肺)体检胸部低千伏摄影要点及注意事项(附1840例分析)

以往职业病(尘肺)常采用胸部高千伏摄影来达到诊断要求.近年来,我院采用胸部低千伏、低毫安秒摄影,同样达到国家尘肺(矽肺)诊断要求.现报告如下.     

Assessing DTI data quality using bootstrap analysis.

Diffusion tensor imaging (DTI) is an established method for characterizing and quantifying ultrastructural brain tissue properties. However, DTI-derived variables are affected by various sources of signal uncertainty. The goal of this study was to establish an objective quality measure for DTI based on the nonparametric bootstrap methodology. The confidence intervals (CIs) of white matter (WM) fractional anisotropy (FA) and Clinear were determined by bootstrap analysis and submitted to histogram analysis. The effects of artificial noising and edge-preserving smoothing, as well as enhanced and reduced motion were studied in healthy volunteers. Gender and age effects on data quality as potential confounds in group comparison studies were analyzed. Additional noising showed a detrimental effect on the mean, peak position, and height of the respective CIs at 10% of the original background noise. Inverse changes reflected data improvement induced by edge-preserving smoothing. Motion-dependent impairment was also well depicted by bootstrap-derived parameters. Moreover, there was a significant gender effect, with females displaying less dispersion (attributable to elevated SNR). In conclusion, the bootstrap procedure is a useful tool for assessing DTI data quality. It is sensitive to both noise and motion effects, and may help to exclude confounding effects in group comparisons.     

Kilovoltage cone-beam CT imaging dose during breast radiotherapy: A dose comparison between a left and right breast setup

The purpose of this study was to investigate the delivered dose from a kilovoltage cone-beam computed tomography (kV-CBCT) acquired in breast treatment position for a left and right breast setup. The dose was measured with thermoluminescent dosimeters positioned within a female anthropomorphic phantom at organ locations. Imaging was performed on an Elekta Synergy XVI system with the phantom setup on a breast board. The image protocol involved 120 kVp, 140 mAs, and a 270° arc rotation clockwise 0° to 270° for the left breast setup and 270° to 180° for the right breast setup (maximum arc rotations possible). The dose delivered to the left breast, right breast, and heart was 5.1 mGy, 3.9 mGy, and 4.0 mGy for the left breast setup kV-CBCT, and 6.4 mGy, 6.0 mGy, and 4.8 mGy for the right breast setup kV-CBCT, respectively. The rotation arc of the kV-CBCT influenced the dose delivered, with the right breast setup kV-CBCT found to deliver a dose of up to 4 mGy or 105% higher to the treated breast′s surface in comparison with the left breast setup. This is attributed to the kV-CBCT source being more proximal to the anterior of the phantom for a right breast setup, whereas the source is more proximal to the posterior of the patient for a left-side scan.     

In vivo precision of bootstrap algorithms applied to diffusion tensor imaging data

Purpose:

To determine the precision for in vivo applications of model and non–model‐based bootstrap algorithms for estimating the measurement uncertainty of diffusion parameters derived from diffusion tensor imaging data.

Materials and Methods:

Four different bootstrap methods were applied to diffusion datasets acquired during 10 repeated imaging sessions. Measurement uncertainty was derived in eight manually selected regions of interest and in the entire brain white matter and gray matter. The precision of the bootstrap methods was analyzed using coefficients of variation and intra‐class correlation coefficients. Comprehensive simulations were performed to validate the results.

Results:

All bootstrap algorithms showed similar precision which slightly varied in dependence of the selected region of interest. The averaged coefficient of variation in the selected regions of interest was 13.81%, 12.35%, and 17.93% with respect to the apparent diffusion coefficient, the fractional anisotropy value, and the cone of uncertainty, respectively. The repeated measurements showed a very high similarity with intraclass‐correlation coefficients larger than 0.96. The simulations confirmed most of the in vivo findings.

Conclusion:

All investigated bootstrap methods perform with a similar, high precision in deriving the measurement uncertainty of diffusion parameters. Thus, the time‐efficient model‐based bootstrap approaches should be the method of choice in clinical practice. J. Magn. Reson. Imaging 2012;36:979–986. © 2012 Wiley Periodicals, Inc.     

Attenuation-Based Automatic Kilovoltage Selection and Sinogram-Affirmed Iterative Reconstruction: Effects on Radiation Exposure and Image Quality of Portal-Phase Liver CT

ObjectiveTo compare the radiation dose and image quality between standard-dose CT and a low-dose CT obtained with the combined use of an attenuation-based automatic kilovoltage (kV) selection tool (CARE kV) and sinogram-affirmed iterative reconstruction (SAFIRE) for contrast-enhanced CT examination of the liver.ResultsQualitative and quantitative analysis of protocol B demonstrated that SAFIRE level 2 (S2) was most appropriate in our study. Qualitative and quantitative analysis comparing S2 images from protocol B with images from protocol A, showed overall good diagnostic confidence of S2 images despite a significant radiation dose reduction (47% dose reduction, p < 0.001).ConclusionCombined use of CARE kV and SAFIRE allowed significant reduction in radiation exposure while maintaining image quality in contrast-enhanced liver CT.     

Quality assessment of high angular resolution diffusion imaging data using bootstrap on Q-ball reconstruction

Purpose:

To develop a bootstrap method to assess the quality of High Angular Resolution Diffusion Imaging (HARDI) data using Q‐Ball imaging (QBI) reconstruction.

Materials and Methods:

HARDI data were re‐shuffled using regular bootstrap with jackknife sampling. For each bootstrap dataset, the diffusion orientation distribution function (ODF) was estimated voxel‐wise using QBI reconstruction based on spherical harmonics functions. The reproducibility of the ODF was assessed using the Jensen‐Shannon divergence (JSD) and the angular confidence interval was derived for the first and the second ODF maxima. The sensitivity of the bootstrap method was evaluated on a human subject by adding synthetic noise to the data, by acquiring a map of image signal‐to‐noise ratio (SNR) and by varying the echo time and the b‐value.

Results:

The JSD was directly linked to the image SNR. The impact of echo times and b‐values was reflected by both the JSD and the angular confidence interval, proving the usefulness of the bootstrap method to evaluate specific features of HARDI data.

Conclusion:

The bootstrap method can effectively assess the quality of HARDI data and can be used to evaluate new hardware and pulse sequences, perform multifiber probabilistic tractography, and provide reliability metrics to support clinical studies. J. Magn. Reson. Imaging 2011;33:1194–1208. © 2011 Wiley‐Liss, Inc.