数字乳腺三维断层摄影技术平均腺体剂量与图像质量的关系

【摘要】目的:探究并分析数字乳腺三维断层摄影技术平均腺体剂量（AGD）与图像质量之间的关系。方法:收集在福建医科大学附属第二医院采用乳腺三维断层摄影技术进行检查的236例患者的临床资料,根据患者乳腺厚度的不同,分为4组,每组各59人。采用非参数统计以及相关性分析的方法,对不同厚度乳腺的曝光条件（mAs）和AGD的相关性进行分析。对同一厚度,不同AGD条件下成像的乳腺图片,分析其图像信噪比与AGD之间的关系。结果:当乳腺厚度增加时,曝光条件（mAs）与AGD均随之增加,具有明显的相关性（r=0.977, P<0.05）。对于相同厚度的乳腺图片,AGD越高,图像信噪比越高,具有明显的相关性（厚度≤29 mm:r=0.977, P=0.023;厚度30~45 mm:r=0.994, P=0.006;厚度46~59 mm:r=0.998, P=0.002;厚度≥60mm:r=0.980, P=0.020）。结论:乳腺的厚度越厚,其曝光条件（mAs）与AGD就越大;对同一厚度的乳腺,AGD越高,成像的图像信噪比越高,图像质量越好。     

Scatter radiation in digital tomosynthesis of the breast

Digital tomosynthesis of the breast is being investigated as one possible solution to the problem of tissue superposition present in planar mammography. This imaging technique presents various advantages that would make it a feasible replacement for planar mammography, among them similar, if not lower, radiation glandular dose to the breast; implementation on conventional digital mammography technology via relatively simple modifications; and fast acquisition time. One significant problem that tomosynthesis of the breast must overcome, however, is the reduction of x-ray scatter inclusion in the projection images. In tomosynthesis, due to the projection geometry and radiation dose considerations, the use of an antiscatter grid presents several challenges. Therefore, the use of postacquisition software-based scatter reduction algorithms seems well justified, requiring a comprehensive evaluation of x-ray scatter content in the tomosynthesis projections. This study aims to gain insight into the behavior of x-ray scatter in tomosynthesis by characterizing the scatter point spread functions (PSFs) and the scatter to primary ratio (SPR) maps found in tomosynthesis of the breast. This characterization was performed using Monte Carlo simulations, based on the Geant4 toolkit, that simulate the conditions present in a digital tomosynthesis system, including the simulation of the compressed breast in both the cranio-caudal (CC) and the medio-lateral oblique (MLO) views. The variation of the scatter PSF with varying tomosynthesis projection angle, as well as the effects of varying breast glandular fraction and x-ray spectrum, was analyzed. The behavior of the SPR for different projection angle, breast size, thickness, glandular fraction, and x-ray spectrum was also analyzed, and computer fit equations for the magnitude of the SPR at the center of mass for both the CC and the MLO views were found. Within mammographic energies, the x-ray spectrum was found to have no appreciable effect on the scatter PSF and on the SPR. Glandular fraction and compressed breast size were found to have a small effect, while compressed breast thickness and projection angle, as expected, introduced large variations in both the scatter PSF and SPR. The presence of the breast support plate and the detector cover plate in the simulations introduced important effects on the SPR, which are also relevant to the scatter content in planar mammography.     

Estimation of mean glandular dose for breast tomosynthesis: factors for use with the UK, European and IAEA breast dosimetry protocols

A formalism is proposed for the estimation of mean glandular dose for breast tomosynthesis, which is a simple extension of the UK, European and IAEA protocols for dosimetry in conventional projection mammography. The formalism introduces t-factors for the calculation of breast dose from a single projection and T-factors for a complete exposure series. Monte Carlo calculations of t-factors have been made for an imaging geometry with full-field irradiation of the breast for a wide range of x-ray spectra, breast sizes and glandularities. The t-factors show little dependence on breast glandularity and tables are provided as a function of projection angle and breast thickness, which may be used for all x-ray spectra simulated. The T-factors for this geometry depend upon the choice of projection angles and weights per projection, but various example calculations gave values in the range 0.93-1.00. T-factors are also provided for the Sectra tomosynthesis system, which employs a scanned narrow-beam imaging geometry. In this quite different configuration, the factor (denoted T(S)) shows an important dependence on breast thickness, varying between 0.98 and 0.76 for 20 and 110 mm thick breasts, respectively. Additional data are given to extend the current tabulations of g-, c- and s-factors used for dosimetry of conventional 2D mammography.     

Voting strategy for artifact reduction in digital breast tomosynthesis

Artifacts are observed in digital breast tomosynthesis (DBT) reconstructions due to the small number of projections and the narrow angular range that are typically employed in tomosynthesis imaging. In this work, we investigate the reconstruction artifacts that are caused by high-attenuation features in breast and develop several artifact reduction methods based on a "voting strategy." The voting strategy identifies the projection(s) that would introduce artifacts to a voxel and rejects the projection(s) when reconstructing the voxel. Four approaches to the voting strategy were compared, including projection segmentation, maximum contribution deduction, one-step classification, and iterative classification. The projection segmentation method, based on segmentation of high-attenuation features from the projections, effectively reduces artifacts caused by metal and large calcifications that can be reliably detected and segmented from projections. The other three methods are based on the observation that contributions from artifact-inducing projections have higher value than those from normal projections. These methods attempt to identify the projection(s) that would cause artifacts by comparing contributions from different projections. Among the three methods, the iterative classification method provides the best artifact reduction; however, it can generate many false positive classifications that degrade the image quality. The maximum contribution deduction method and one-step classification method both reduce artifacts well from small calcifications, although the performance of artifact reduction is slightly better with the one-step classification. The combination of one-step classification and projection segmentation removes artifacts from both large and small calcifications.     

Computerized mass detection for digital breast tomosynthesis directly from the projection images

Digital breast tomosynthesis (DBT) has recently emerged as a new and promising three-dimensional modality in breast imaging. In DBT, the breast volume is reconstructed from 11 projection images, taken at source angles equally spaced over an arc of 50 degrees. Reconstruction algorithms for this modality are not fully optimized yet. Because computerized lesion detection in the reconstructed breast volume will be affected by the reconstruction technique, we are developing a novel mass detection algorithm that operates instead on the set of raw projection images. Mass detection is done in three stages. First, lesion candidates are obtained for each projection image separately, using a mass detection algorithm that was initially developed for screen-film mammography. Second, the locations of a lesion candidate are backprojected into the breast volume. In this feature volume, voxel intensities are a combined measure of detection frequency (e.g., the number of projections in which a given lesion candidate was detected), and a measure of the angular range over which a given lesion was detected. Third, features are extracted after reprojecting the three-dimensional (3-D) locations of lesion candidates into projection images. Features are combined using linear discriminant analysis. The database used to test the algorithm consisted of 21 mass cases (13 malignant, 8 benign) and 15 cases without mass lesions. Based on this database, the algorithm yielded a sensitivity of 90% at 1.5 false positives per breast volume. Algorithm performance is positively biased because this dataset was used for development, training, and testing, and because the number of algorithm parameters was approximately the same as the number.of patient cases. Our results indicate that computerized mass detection in the sequence of projection images for DBT may be effective despite the higher noise level in those images.     

全数字化乳腺摄影与乳腺三维断层摄影对乳腺钙化的对比研究

目的:研究全数字化乳腺摄影（FFDM）及数字乳腺断层摄影（DBT）对于钙化征象及其在乳腺疾病诊断效能的对比。 方法:收集福建医科大学附属第二医院2013年6月~2017年4月期间就诊的97例经FFDM及DBT检查发现有钙化征象,并具有病理结果的患者,根据乳腺影像报告和数据系统进行阅片诊断,同时计算出在FFDM及COMBO（DBT结合FFDM）两种摄片模式下的钙化分数。 结果:通过秩和检验分析两种方法下钙化分数存在显著性差异（P<0.05）。通过ROC曲线分析两种方法在乳腺疾病诊断效能发现,两者曲线下面积均大于0.5,具有诊断价值,FFDM与COMBO敏感度（95.7%）一致;COMBO特异性（92%）较FFDM特异性（76%）高。 结论:COMBO相对于FFDM能更好地观察钙化征象,提高诊断效能。     

乳腺三维断层摄影与乳腺彩超在乳腺疾病诊断中的效能对比

【摘 要】 目的:研究数字乳腺三维断层技术（DBT）和乳腺超声在诊断乳腺病变效能的不同以及联合应用对于乳腺诊断的价值。 方法:收集1 065例乳腺病变患者,其中333例有完整的病理检查资料。以乳腺影像报告和数据系统（BI-RADS）分类为标准,分析DBT、超声、DBT+超声在乳腺病变诊断中的分布差异。根据333例病理结果,比较3种诊断模式的诊断效能。 结果:DBT与超声的BI-RADS分布有显着性差异（P=0.001）,DBT与DBT+超声或超声与DBT+超声的BI-RADS分布无显著性差异（P=0.258, 0.394）。3种诊断模式均可明显区分恶性和良性乳腺病变（P<0.001）。多组独立样本Kruskal-Wallis秩和检验分析显示3种诊断模型存在差异（[χ2]=14.982, P=0.001）。DBT的特异性、误诊率、准确性和阳性预测值明显优于超声。超声显示囊性病变优于DBT,且超声对确定良性肿块的敏感性优于DBT。DBT+超声的特异性为99.5％,误诊率为0.5%,阳性预测值也达到99%。DBT+超声的检查模式优于单独使用DBT或超声。 结论:与单独的DBT或超声相比,DBT和超声的组合可以提高乳腺病变的诊断效能。     

Imaging performance of an amorphous selenium digital mammography detector in a breast tomosynthesis system

In breast tomosynthesis a rapid sequence of N images is acquired when the x-ray tube sweeps through different angular views with respect to the breast. Since the total dose to the breast is kept the same as that in regular mammography, the exposure used for each image of tomosynthesis is 1/N. The low dose and high frame rate pose a tremendous challenge to the imaging performance of digital mammography detectors. The purpose of the present work is to investigate the detector performance in different operational modes designed for tomosynthesis acquisition, e.g., binning or full resolution readout, the range of view angles, and the number of views N. A prototype breast tomosynthesis system with a nominal angular range of +/-25 degrees was used in our investigation. The system was equipped with an amorphous selenium (a-Se) full field digital mammography detector with pixel size of 85 microm. The detector can be read out in full resolution or 2 x 1 binning (binning in the tube travel direction). The focal spot blur due to continuous tube travel was measured for different acquisition geometries, and it was found that pixel binning, instead of focal spot blur, dominates the detector modulation transfer function (MTF). The noise power spectrum (NPS) and detective quantum efficiency (DQE) of the detector were measured with the exposure range of 0.4-6 mR, which is relevant to the low dose used in tomosynthesis. It was found that DQE at 0.4 mR is only 20% less than that at highest exposure for both detector readout modes. The detector temporal performance was categorized as lag and ghosting, both of which were measured as a function of x-ray exposure. The first frame lags were 8% and 4%, respectively, for binning and full resolution mode. Ghosting is negligible and independent of the frame rate. The results showed that the detector performance is x-ray quantum noise limited at the low exposures used in each view of tomosynthesis, and the temporal performance at high frame rate (up to 2 frames per second) is adequate for tomosynthesis.     

Characteristics of megavoltage cone-beam digital tomosynthesis

This article reports on the image characteristics of megavoltage cone-beam digital tomosynthesis (MVCB DT). MVCB DT is an in-room imaging technique, which enables the reconstruction of several two-dimensional slices from a set of projection images acquired over an arc of 20 degrees-40 degrees. The limited angular range reduces the acquisition time and the dose delivered to the patient, but affects the image quality of the reconstructed tomograms. Image characteristics (slice thickness, shape distortion, and contrast-to-noise ratio) are studied as a function of the angular range. Potential clinical applications include patient setup and the development of breath holding techniques for gated imaging.