The effects of stereo shift angle, geometric magnification and display zoom on depth measurements in digital stereomammography

Stereoscopic digital mammogram: Usefulness in daily practice

OBJECTIVES

To assess the benefit of stereoscopic digital mammography in daily practice.

METHODS

Stereoscopic digital (SD) mammography allows a fused 3D view of mammogram. A 4-degree cranio-caudal (CC) angle view matched with a regular CC view allows generating a stereoscopic view. Three breast radiologists reviewed retrospectively 1110 stereoscopic digital mammograms (1075 women) performed between November 2011 and February 2013 with the following sequence: each evaluated firstly conventional mammogram alone, and then integrated SD mammograms. The benefit was quoted in 3-grade scale: 0 for no benefit, 1 moderate and 2 excellent. The concordance between radiologists was evaluated by the W Randall coefficient. Subgroup analysis according to the BI-RADS classification, breast density and type of abnormalities were performed by calculating odds-ratio.

RESULTS

The readers had the same opinion regarding the value of stereoscopic digital mammograms in 87% of cases (962/1110). Benefit was null, moderate and excellent in 8, 52 and 26% respectively. The concordance of radiologists was excellent with a W coefficient above 0.89.

CONCLUSIONS

SD mammogram improved interpretation of abnormal mammograms. This potentially interesting and promising complementary tool might be beneficial in daily breast imaging practice.

Stereoscopic digital mammography: improved specificity and reduced rate of recall in a prospective clinical trial

PURPOSE

To compare stereoscopic digital mammography (DM) with standard DM for the rate of patient recall and the detection of cancer in a screening population at elevated risk for breast cancer.

MATERIALS AND METHODS

Starting in September 2004 and ending in December 2007, this prospective HIPAA-compliant, institutional review board-approved screening trial, with written informed consent, recruited female patients at elevated risk for breast cancer (eg, personal history of breast cancer or breast cancer in a close relative). A total of 1298 examinations from 779 patients (mean age, 58.6 years; range, 32-91 years) comprised the analyzable data set. A paired study design was used, with each enrolled patient serving as her own control. Patients underwent both DM and stereoscopic DM examinations in a single visit, findings of which were interpreted independently by two experienced radiologists, each using a Breast Imaging Reporting and Data System (BI-RADS) assessment (BI-RADS category 0, 1, or 2). All patients determined to have one or more findings with either or both modalities were recalled for standard diagnostic evaluation. The results of 1-year follow-up or biopsy were used to determine case truth.

RESULTS

Compared with DM, stereoscopic DM showed significantly higher specificity (91.2% [1167 of 1279] vs 87.8% [1123 of 1279]; P = .0024) and accuracy (90.9% [1180 of 1298] vs 87.4% [1135 of 1298]; P = .0023) for detection of cancer. Sensitivity for detection of cancer was not significantly different for stereoscopic DM (68.4% [13 of 19]) compared with DM (63.2% [12 of 19], P .99). The recall rate for stereoscopic DM was 9.6% (125 of 1298) and that for DM was 12.9% (168 of 1298) (P = .0018).

CONCLUSION

Compared with DM, stereoscopic DM significantly improved specificity for detection of cancer, while maintaining comparable sensitivity. The recall rate was significantly reduced with stereoscopic DM compared with DM.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120382/-/DC1.

Compare display schemes for lung nodule CT screening

This study investigated the relative efficiencies of a stereographic display and two monoscopic display schemes for detecting lung nodules in chest computed tomography (CT). The ultimate goal was to determine whether stereoscopic display provides advantages for visualization and interpretation of three-dimensional (3D) medical image datasets. A retrospective study that compared lung nodule detection performances achieved using three different schemes for displaying 3D CT data was conducted. The display modes included slice-by-slice, orthogonal maximum intensity projection (MIP), and stereoscopic display. One hundred lung-cancer screening CT examinations containing 647 nodules were interpreted by eight radiologists, in each of the display modes. Reading times and displayed slab thickness versus time were recorded, as well as the probability, location, and size for each detected nodule. Nodule detection performance was analyzed using the receiver operating characteristic method. The stereo display mode provided higher detection performance with a shorter interpretation time, as compared to the other display modes tested in the study, although the difference was not statistically significant. The analysis also showed that there was no difference in the patterns of displayed slab thickness versus time between the stereo and MIP display modes. Most radiologists preferred reading the 3D data at a slab thickness that corresponded to five CT slices. Our results indicate that stereo display has the potential to improve radiologists' performance for detecting lung nodules in CT datasets. The experience gained in conducting the study also strongly suggests that further benefits can be achieved through providing readers with additional functionality.

Breast cancer imaging: a perspective for the next decade

Breast imaging is largely indicated for detection, diagnosis, and clinical management of breast cancer and for evaluation of the integrity of breast implants. In this work, a prospective view of techniques for breast cancer detection and diagnosis is provided based on an assessment of current trends. The potential role of emerging techniques that are under various stages of research and development is also addressed. It appears that the primary imaging tool for breast cancer screening in the next decade will be high-resolution, high-contrast, anatomical x-ray imaging with or without depth information. MRI and ultrasonography will have an increasingly important adjunctive role for imaging high-risk patients and women with dense breasts. Pilot studies with dedicated breast CT have demonstrated high-resolution three-dimensional imaging capabilities, but several technological barriers must be overcome before clinical adoption. Radionuclide based imaging techniques and x-ray imaging with intravenously injected contrast offer substantial potential as a diagnostic tools and for evaluation of suspicious lesions. Developing optical and electromagnetic imaging techniques hold significant potential for physiologic information and they are likely to be of most value when integrated with or adjunctively used with techniques that provide anatomic information. Experimental studies with breast specimens suggest that phase-sensitive x-ray imaging techniques can provide edge enhancement and contrast improvement but more research is needed to evaluate their potential role in clinical breast imaging. From the technological perspective, in addition to improvements within each modality, there is likely to be a trend towards multi-modality systems that combine anatomic with physiologic information. We are also likely to transition from a standardized screening, where all women undergo the same imaging exam (mammography), to selection of a screening modality or modalities based an individual-risk or other classification.

3D stereoscopic visualization of fenestrated stent grafts

The purpose of this study was to present a technique of stereoscopic visualization in the evaluation of patients with abdominal aortic aneurysm treated with fenestrated stent grafts compared with conventional 2D visualizations. Two patients with abdominal aortic aneurysm undergoing fenestrated stent grafting were selected for inclusion in the study. Conventional 2D views including axial, multiplanar reformation, maximum-intensity projection, and volume rendering and 3D stereoscopic visualizations were assessed by two experienced reviewers independently with regard to the treatment outcomes of fenestrated repair. Interobserver agreement was assessed with Kendall's W statistic. Multiplanar reformation and maximum-intensity projection visualizations were scored the highest in the evaluation of parameters related to the fenestrated stent grafting, while 3D stereoscopic visualization was scored as valuable in the evaluation of appearance (any distortions) of the fenestrated stent. Volume rendering was found to play a limited role in the follow-up of fenestrated stent grafting. 3D stereoscopic visualization adds additional information that assists endovascular specialists to identify any distortions of the fenestrated stents when compared with 2D visualizations.

Stereoscopic evaluation of fetal bony structures

OBJECTIVE

The purpose of this study was to assess the performance of stereoscopic compared with conventional viewing of 3-dimensional ultrasound (3DUS) data for evaluation of fetal bony structures.

METHODS

A series of 47 human fetuses were evaluated with conventional 3DUS scanning systems. Twenty-five volumes of the fetal head, thorax, and abdomen were acquired. Volume-rendered images of the fetal cranium and spine were displayed interactively on a real-time stereoscopic graphics workstation. Visualization parameters were interactively optimized. Both conventional and stereoscopic images were evaluated for the clarity of structure visualization (0, nonvisualized; 1, nondiagnostic; 2, adequate; and 3, excellent), the ability to identify key anatomic landmarks (eg, sutures, palate, vertebrae, and ribs), artifacts, and evaluation time.

RESULTS

Fetal bony structures, especially high-contrast structures, were readily identified with both conventional and stereoscopic. Overall, stereoscopic viewing provided a statistically significant improvement compared with conventional viewing (P < .01), improved conspicuity of complex bony structures, and added structural detail information that assisted in identification of complex anatomy in 14% of the fetal skull and 26% of the fetal spine cases. Overlapping structures were better identified on the volume-rendered stereoscopic display, with stereoscopic viewing improving differentiation of near and far structures. An interactive display and inclusion of a planar slice review further assisted in identification of structures. The evaluation times were comparable for the two methods.

CONCLUSIONS

The stereoscopic display of rendered 3DUS data adds valuable information that assists in identification of fetal bony structures, such as cranial sutures and spinal vertebrae, particularly in complex formations. The increasing availability of stereoscopic visualization workstations will offer an additional tool for fetal diagnosis and evaluation.

Computer-aided detection system for breast masses on digital tomosynthesis mammograms: preliminary experience

The purpose of the study was to design a computer-aided detection (CAD) system for breast mass detection on digital breast tomosynthesis (DBT) mammograms and to perform a preliminary evaluation of the performance of this system. Twenty-six patients were imaged with a prototype DBT system. Institutional review board approval and written informed patient consent were obtained. Use of the data set in this study was HIPAA compliant. The CAD system first screened the three-dimensional volume of the mass candidates by means of gradient-field analysis. Each mass candidate was segmented from the structured background, and its image features were extracted. A feature classifier was designed to differentiate true masses from normal tissues. The CAD system was trained and tested by using a leave-one-case-out method. The classifier calculated a mean area under the test receiver operating characteristic curve of 0.91 +/- 0.03 (standard error of mean). The CAD system achieved a sensitivity of 85%, with 2.2 false-positive objects per case. The results demonstrate the feasibility of the authors' approach to the development of a CAD system for DBT mammography.

ROC study of the effect of stereoscopic imaging on assessment of breast lesions

An observer performance study was conducted to evaluate the usefulness of assessing breast lesion characteristics with stereomammography. Stereoscopic image pairs of 158 breast biopsy tissue specimens were acquired with a GE Senographe 2000D full field digital mammography system using a 1.8x magnification geometry. A phantom-shift method equivalent to a stereo shift angle of +/- 3 degrees relative to a central axis perpendicular to the detector was used. For each specimen, two pairs of stereo images were taken at approximately orthogonal orientations. The specimens contained either a mass, microcalcifications, both, or normal tissue. Based on pathological analysis, 39.9% of the specimens were found to contain malignancy. The digital specimen radiographs were displayed on a high resolution MegaScan CRT monitor driven by a DOME stereo display board using in-house developed software. Five MQSA radiologists participated as observers. Each observer read the 316 specimen stereo image pairs in a randomized order. For each case, the observer first read the monoscopic image and entered his/her confidence ratings on the presence of microcalcifications and/or masses, margin status, BI-RADS assessment, and the likelihood of malignancy. The corresponding stereoscopic images were then displayed on the same monitor and were viewed through stereoscopic LCD glasses. The observer was free to change the ratings in every category after stereoscopic reading. The ratings of the observers were analyzed by ROC methodology. For the 5 MQSA radiologists, the average Az value for estimation of the likelihood of malignancy of the lesions improved from 0.70 for monoscopic reading to 0.72 (p=0.04) after stereoscopic reading, and the average Az value for the presence of microcalcifications improved from 0.95 to 0.96 (p=0.02). The Az value for the presence of masses improved from 0.80 to 0.82 after stereoscopic reading, but the difference fell short of statistical significance (p=0.08). The visual assessment of margin clearance was found to have very low correlation with microscopic analysis with or without stereoscopic reading. This study demonstrates the potential of using stereomammography to improve the detection and characterization of mammographic lesions.

An observer study comparing spot imaging regions selected by radiologists and a computer for an automated stereo spot mammography technique

We are developing an automated stereo spot mammography technique for improved imaging of suspicious dense regions within digital mammograms. The technique entails the acquisition of a full-field digital mammogram, automated detection of a suspicious dense region within that mammogram by a computer aided detection (CAD) program, and acquisition of a stereo pair of images with automated collimation to the suspicious region. The latter stereo spot image is obtained within seconds of the original full-field mammogram, without releasing the compression paddle. The spot image is viewed on a stereo video display. A critical element of this technique is the automated detection of suspicious regions for spot imaging. We performed an observer study to compare the suspicious regions selected by radiologists with those selected by a CAD program developed at the University of Michigan. True regions of interest (TROIs) were separately determined by one of the radiologists who reviewed the original mammograms, biopsy images, and histology results. We compared the radiologist and computer-selected regions of interest (ROIs) to the TROIs. Both the radiologists and the computer were allowed to select up to 3 regions in each of 200 images (mixture of 100 CC and 100 MLO views). We computed overlap indices (the overlap index is defined as the ratio of the area of intersection to the area of interest) to quantify the agreement between the selected regions in each image. The averages of the largest overlap indices per image for the 5 radiologist-to-computer comparisons were directly related to the average number of regions per image traced by the radiologists (about 50% for 1 region/image, 84% for 2 regions/image and 96% for 3 regions/image). The average of the overlap indices with all of the TROIs was 73% for CAD and 76.8% +/- 10.0% for the radiologists. This study indicates that the CAD determined ROIs could potentially be useful for a screening technique that includes stereo spot mammography imaging.

Effects of magnification and zooming on depth perception in digital stereomammography: an observer performance study

We are evaluating the application of stereoscopic imaging to digital mammography. In the current study, we investigated the effects of magnification and zooming on depth perception. A modular phantom was designed which contained six layers of 1-mm-thick Lexan plates, each spaced 1 mm apart. Eight to nine small, thin nylon fibrils were pasted on each plate in horizontal or vertical orientations such that they formed 25 crossing fibril pairs in a projected image. The depth separation between each fibril pair ranged from 2 to 10 mm. A change in the order of the Lexan plates changed the depth separation of the two fibrils in a pair. Stereoscopic image pairs of the phantom were acquired with a GE full-field digital mammography system. Three different phantom configurations were imaged. All images were obtained using a Rh target/Rh filter spectrum at 30 kVp tube potential and a +/- 3 stereo shift angle. Images were acquired in both contact and 1.8X magnification geometry and an exposure range of 4 to 63 mAs was employed. The images were displayed on a Barco monitor driven by a Metheus stereo graphics board and viewed with LCD stereo glasses. Five observers participated in the study. Each observer visually judged whether the vertical fibril was in front of or behind the horizontal fibril in each fibril pair. It was found that the accuracy of depth discrimination increased with increasing fibril depth separation and x-ray exposure. The accuracy was not improved by electronic display zooming of the contact stereo images by 2X. Under conditions of high noise (low mAs) and small depth separation between the fibrils, the observers' depth discrimination ability was significantly better in stereo images acquired with geometric magnification than in images acquired with a contact technique and displayed with or without zooming. Under our experimental conditions, a 2 mm depth discrimination was achieved with over 60% accuracy on contact images with and without zooming, and with over 90% accuracy on magnification images. This study indicates that stereoscopic imaging, especially with magnification, may be useful for visualizing the spatial distribution of microcalcifications in a cluster and for differentiating overlapping tissues from masses on mammograms.