Artifacts in Digital Breast Tomosynthesis.

OBJECTIVE: Artifacts in digital breast tomosynthesis and synthesized 2D imaging reduce image quality. This article describes the appearance of these unique artifacts, reviews their causes, and discusses methods to ameliorate these artifacts. CONCLUSION: Artifacts in digital breast tomosynthesis and synthesized 2D imaging can obscure important findings on mammograms. The radiologist, mammography technologist, and medical physicist must be able to recognize these artifacts and use the vendor's new processing algorithms to mitigate the effects of such artifacts.

Effect of Mammography on Marker Clip Migration After Stereotactic-Guided Core Needle Breast Biopsy.

OBJECTIVE: To determine whether the type of projection used-same as or orthogonal to the projection used during a stereotactic-guided core needle biopsy procedure-to obtain the first view on a 2-view postbiopsy mammogram affects biopsy marker clip migration. PATIENTS AND METHODS: We prospectively recruited women scheduled to undergo stereotactic-guided core needle breast biopsy with marker clip deployment and categorized the women randomly into one of the following 2 groups: first view on the postbiopsy mammogram obtained in the same projection as that used during the biopsy procedure (group 1), or first view on the postbiopsy mammogram obtained orthogonally to the projection used during the biopsy procedure (group 2). Masks of the prebiopsy and postbiopsy mammograms were used to determine whether and how far the biopsy marker clip moved from the biopsy cavity. RESULTS: Sixty-two biopsies were performed in 60 patients (mean age = 56 years; range: 30-78 years); 30 women (32 lesions) were randomized to group 1 and 30 women (30 lesions) were randomized to group 2. Marker clip migration occurred in 10 cases in group 1 (20%, <1cm; 30%, 1-3cm; and 60%, >3cm) and 8 cases in group 2 (0%, <1cm; 75%, 1-3cm; and 25%, >3cm). The mean displacement distance was 0.84cm in group 1 and 0.67cm in group 2 (P = 0.83). The mean displacement distance difference was -0.17cm with a 95% bootstrap confidence interval from -0.87 to 0.57cm. CONCLUSION: The type of projection used to obtain the first view on the postbiopsy mammogram, relative to that used during the stereotactic biopsy procedure, did not affect biopsy marker clip migration.

Radiologist experience effects on contrast detection.

Current literature shows that radiologist experience does not affect detection tasks when the object does not require medical training to detect. However, the research was never sufficiently detailed to examine if the contrast detection threshold is also the same for radiologists versus nonradiologists. Previously, contrast threshold research was performed predominantly on nonradiologists. Therefore, any differences could lead to over- or under-estimation of the performance capabilities of radiologists. Fourteen readers, evenly divided between radiologists and nonradiologists, read a set of 150 mammogram-like images. The study was performed with the location of the objects known and unknown, requiring two separate readings. No difference in the contrast detection threshold between reader groups for either the location-unknown (4.9 just noticeable differences) or location-known (3.3 just noticeable differences) images was seen. The standard deviation for the location-unknown condition had no difference (p 0.91). But for the location-known condition, a significant difference (p 0.0009) was seen between radiologists and nonradiologists. No difference in contrast detection based on reader experience was observed, but decreased variance was seen with radiologists in the location-known condition.

Stereoscopic interpretation of low-dose breast tomosynthesis projection images.

The purpose of this study was to evaluate stereoscopic perception of low-dose breast tomosynthesis projection images. In this Institutional Review Board exempt study, craniocaudal breast tomosynthesis cases (N = 47), consisting of 23 biopsy-proven malignant mass cases and 24 normal cases, were retrospectively reviewed. A stereoscopic pair comprised of two projection images that were ±4° apart from the zero angle projection was displayed on a Planar PL2010M stereoscopic display (Planar Systems, Inc., Beaverton, OR, USA). An experienced breast imager verified the truth for each case stereoscopically. A two-phase blinded observer study was conducted. In the first phase, two experienced breast imagers rated their ability to perceive 3D information using a scale of 1-3 and described the most suspicious lesion using the BI-RADS® descriptors. In the second phase, four experienced breast imagers were asked to make a binary decision on whether they saw a mass for which they would initiate a diagnostic workup or not and also report the location of the mass and provide a confidence score in the range of 0-100. The sensitivity and the specificity of the lesion detection task were evaluated. The results from our study suggest that radiologists who can perceive stereo can reliably interpret breast tomosynthesis projection images using stereoscopic viewing.

How to establish a cost-effective mobile mammography program.

OBJECTIVE: The purpose of this article is to describe how to establish a cost-effective mobile mammography program on the basis of examples from a 20-year experience with film-screen and digital mammography units. CONCLUSION: Mobile mammography programs can reduce many barriers to breast cancer screening faced by medically underserved women. Finding and maintaining resources, having appropriate equipment and infrastructure, and having a dedicated team with an efficient workflow are the key elements of establishing a cost-effective mobile mammography program.

Trend of contrast detection threshold with and without localization.

Published information on contrast detection threshold is based primarily on research using a location-known methodology. In previous work on testing the Digital Imaging and Communications in Medicine (DICOM) Grayscale Standard Display Function (GSDF) for perceptual linearity, this research group used a location-unknown methodology to more closely reflect clinical practice. A high false-positive rate resulted in a high variance leading to the conclusion that the impact on results of employing a location-known methodology needed to be explored. Fourteen readers reviewed two sets of simulated mammographic background images, one with the location-unknown and one with the location-known methodology. The results of the reader study were analyzed using Reader Operating Characteristic (ROC) methodology and a paired t test. Contrast detection threshold was analyzed using contingency tables. No statistically significant difference was found in GSDF testing, but a highly statistical significant difference (p value <0.0001) was seen in the ROC (AUC) curve between the location-unknown and the location-known methodologies. Location-known methodology not only improved the power of the GSDF test but also affected the contrast detection threshold which changed from +3 when the location was unknown to +2 gray levels for the location-known images. The selection of location known versus unknown in experimental design must be carefully considered to ensure that the conclusions of the experiment reflect the study's objectives.

Verification of DICOM GSDF in complex backgrounds.

While previous research has determined the contrast detection threshold in medical images, it has focused on uniform backgrounds, has not used calibrated monitors, or has involved a low number of readers. With complex clinical images, how the Grayscale Standard Display Function (GSDF) affects the detection threshold and whether the median background intensity shift has been minimized by GSDF remains unknown. We set out to determine if the median background affected the detection of a low-contrast object in a clustered lumpy background, which simulated a mammography image, and to define the contrast detection threshold for these complex images. Clustered lumpy background images were created of different median intensities and disks of varying contrasts were inserted. A reader study was performed with 17 readers of varying skill level who scored with a five-point confidence scale whether a disk was present. The results were analyzed using reader operating characteristic (ROC) methodology. Contingency tables were used to determine the contrast detection threshold. No statistically significant difference was seen in the area under the ROC curve across all of the backgrounds. Contrast detection fell below 50 % between +3 and +2 gray levels. Our work supports the conclusion that Digital Imaging and Communications in Medicine GSDF calibrated monitors do perceptually linearize detection performance across shifts in median background intensity. The contrast detection threshold was determined to be +3 gray levels above the background for an object of 1° visual angle.

Effects of exposure equalization on image signal-to-noise ratios in digital mammography: a simulation study with an anthropomorphic breast phantom.

PURPOSE: The scan equalization digital mammography (SEDM) technique combines slot scanning and exposure equalization to improve low-contrast performance of digital mammography in dense tissue areas. In this study, full-field digital mammography (FFDM) images of an anthropomorphic breast phantom acquired with an anti-scatter grid at various exposure levels were superimposed to simulate SEDM images and investigate the improvement of low-contrast performance as quantified by primary signal-to-noise ratios (PSNRs). METHODS: We imaged an anthropomorphic breast phantom (Gammex 169 "Rachel," Gammex RMI, Middleton, WI) at various exposure levels using a FFDM system (Senographe 2000D, GE Medical Systems, Milwaukee, WI). The exposure equalization factors were computed based on a standard FFDM image acquired in the automatic exposure control (AEC) mode. The equalized image was simulated and constructed by superimposing a selected set of FFDM images acquired at 2, 1, 1/2, 1/4, 1/8, 1/16, and 1/32 times of exposure levels to the standard AEC timed technique (125 mAs) using the equalization factors computed for each region. Finally, the equalized image was renormalized regionally with the exposure equalization factors to result in an appearance similar to that with standard digital mammography. Two sets of FFDM images were acquired to allow for two identically, but independently, formed equalized images to be subtracted from each other to estimate the noise levels. Similarly, two identically but independently acquired standard FFDM images were subtracted to estimate the noise levels. Corrections were applied to remove the excess system noise accumulated during image superimposition in forming the equalized image. PSNRs over the compressed area of breast phantom were computed and used to quantitatively study the effects of exposure equalization on low-contrast performance in digital mammography. RESULTS: We found that the highest achievable PSNR improvement factor was 1.89 for the anthropomorphic breast phantom used in this study. The overall PSNRs were measured to be 79.6 for the FFDM imaging and 107.6 for the simulated SEDM imaging on average in the compressed area of breast phantom, resulting in an average improvement of PSNR by ∼35% with exposure equalization. We also found that the PSNRs appeared to be largely uniform with exposure equalization, and the standard deviations of PSNRs were estimated to be 10.3 and 7.9 for the FFDM imaging and the simulated SEDM imaging, respectively. The average glandular dose for SEDM was estimated to be 212.5 mrad, ∼34% lower than that of standard AEC-timed FFDM (323.8 mrad) as a result of exposure equalization for the entire breast phantom. CONCLUSIONS: Exposure equalization was found to substantially improve image PSNRs in dense tissue regions and result in more uniform image PSNRs. This improvement may lead to better low-contrast performance in detecting and visualizing soft tissue masses and micro-calcifications in dense tissue areas for breast imaging tasks.

Challenges in mammography: part 1, artifacts in digital mammography.

OBJECTIVE: Early detection of breast cancer is directly related to the radiologist's ability to detect abnormalities visible only on mammograms. Artifacts on mammograms reduce image quality and may present clinical and technical difficulties for the radiologist, mammography technologist, medical physicist, and equipment service personnel. CONCLUSION: In this article, we will illustrate the appearance of artifacts in full field digital mammography, review the causes of these artifacts, and discuss methods to eliminate artifacts in digital mammography.

Interpretation time of computer-aided detection at screening mammography.

PURPOSE: To prospectively determine the interpretation time associated with computer-aided detection (CAD) and to analyze how CAD affected radiologists' decisions and their level of confidence in their interpretations of digital screening mammograms. MATERIALS AND METHODS: An Institutional Review Board exemption was obtained, and patient consent was waived in this HIPAA compliant study. The participating radiologists gave informed consent. Five radiologists were prospectively studied as they interpreted 267 clinical digital screening mammograms. Interpretation times, recall decisions, and confidence levels were recorded without CAD and then with CAD. Software was used for linear regression fitting of interpretation times. P values less than .05 were considered to indicate statistically significant differences. RESULTS: Mean interpretation time without CAD was 118 seconds ± 4.2 (standard error of the mean). Mean time for reviewing CAD images was 23 seconds ± 1.5. CAD identified additional findings in five cases, increased confidence in 38 cases, and decreased confidence in 21 cases. Interpretation time without CAD increased with the number of mammographic views (P < .0001). Mean times for interpretation without CAD and review of the CAD images both increased with the number of CAD marks (P < .0001). The interpreting radiologist was a significant variable for all interpretation times (P < .0001). Interpretation time with CAD increased by 3.2 seconds (95% confidence interval: 1.8, 4.6) for each calcification cluster marked and by 7.3 seconds (95% confidence interval: 4.7, 9.9) for each mass marked. CONCLUSION: The additional time required to review CAD images represented a 19% increase in the mean interpretation time without CAD. CAD requires a considerable time investment for digital screening mammography but may provide less measureable benefits in terms of confidence of the radiologists.

Measurement of focal spot size with slit camera using computed radiography and flat-panel based digital detectors.

The purpose of this study was to evaluate the use of digital x-ray imaging detectors for the measurement of diagnostic x-ray tube focal spot size using a slit camera. Slit camera images of two focal spots for a radiographic x-ray tube were acquired with direct-exposure film (DF) (as specified by the National Electrical Manufacturers Association [NEMA] Standards Publication No. XR 5, 1992), computed radiography (CR) imaging plates, and an a-Si:H/CsI:Tl-based flat-panel (FP) detector. Images obtained with the CR and the FP were acquired over a broad range of detector entrance exposure levels. The DF slit images were evaluated according to NEMA specifications (visually, using a 7x magnifying glass with reticule) by six medical physicists. Additionally, the DF images were digitized and the focal spot sizes obtained from the digital profiles of the slit. The CR and the FP images were analyzed in a manner similar to the digitized DF images. It took less than 20 minutes for a complete CR or FP measurement of focal spot size in two dimensions. In comparison, a typical DF measurement with visual evaluation takes at least 60 minutes, in our experience. In addition to a great reduction in measurement time achieved by using digital detectors, the tube loading requirements were reduced to approximately 20 mAs compared with approximately 1000 mAs when using the DF technique. The calculated focal spot sizes for CR and FP differed from those of digitized DF by -2.4% to +4.8% (sigma=2.5%), far less than the -16.6% to +9.3% (sigma=8.1%) variability introduced by the visual evaluation of the slit image. In addition, the calculated focal spot sizes for the CR and the FP images maintained a coefficient of variation <1.0% over the broad range of exposure levels. Based upon these results, we conclude that (1) FP and CR detectors yield consistent results in measurements of x-ray tube focal spot sizes, (2) compared to DF, CR and FP significantly reduce measurement time and tube loading requirements, (3) CR and FP readily permit digital profile analysis, thereby eliminating observer error, and (4) unlike DF, CR and FP are independent of exposure level.