Tony Svahn

Breast tomosynthesis and digital mammography: a comparison of breast cancer visibility and BIRADS classification in a population of cancers with subtle mammographic findings

The main purpose was to compare breast cancer visibility in one-view breast tomosynthesis (BT) to cancer visibility in one- or two-view digital mammography (DM). Thirty-six patients were selected on the basis of subtle signs of breast cancer on DM. One-view BT was performed with the same compression angle as the DM image in which the finding was least/not visible. On BT, 25 projections images were acquired over an angular range of 50 degrees, with double the dose of one-view DM. Two expert breast imagers classified one- and two-view DM, and BT findings for cancer visibility and BIRADS cancer probability in a non-blinded consensus study. Forty breast cancers were found in 37 breasts. The cancers were rated more visible on BT compared to one-view and two-view DM in 22 and 11 cases, respectively, (p < 0.01 for both comparisons). Comparing one-view DM to one-view BT, 21 patients were upgraded on BIRADS classification (p < 0.01). Comparing two-view DM to one-view BT, 12 patients were upgraded on BIRADS classification (p < 0.01). The results indicate that the cancer visibility on BT is superior to DM, which suggests that BT may have a higher sensitivity for breast cancer detection.

Breast tomosynthesis and digital mammography: a comparison of diagnostic accuracy

OBJECTIVE Our aim was to compare the ability of radiologists to detect breast cancers using one-view breast tomosynthesis (BT) and two-view digital mammography (DM) in an enriched population of diseased patients and benign and/or healthy patients. METHODS All participants gave informed consent. The BT and DM examinations were performed with about the same average glandular dose to the breast. The study population comprised patients with subtle signs of malignancy seen on DM and/or ultrasonography. Ground truth was established by pathology, needle biopsy and/or by 1-year follow-up by mammography, which retrospectively resulted in 89 diseased breasts (1 breast per patient) with 95 malignant lesions and 96 healthy or benign breasts. Two experienced radiologists, who were not participants in the study, determined the locations of the malignant lesions. Five radiologists, experienced in mammography, interpreted the cases independently in a free-response study. The data were analysed by the receiver operating characteristic (ROC) and jackknife alternative free-response ROC (JAFROC) methods, regarding both readers and cases as random effects. RESULTS The diagnostic accuracy of BT was significantly better than that of DM (JAFROC: p=0.0031, ROC: p=0.0415). The average sensitivity of BT was higher than that of DM (∼90% vs ∼79%; 95% confidence interval of difference: 0.036, 0.108) while the average false-positive fraction was not significantly different (95% confidence interval of difference: -0.117, 0.010). CONCLUSION The diagnostic accuracy of BT was superior to DM in an enriched population.

Breast tomosynthesis: Accuracy of tumor measurement compared with digital mammography and ultrasonography.

Background: Mammographic tumor size measurement can be difficult because breast structures are superimposed onto a two-dimensional (2D) plane, potentially obscuring the tumor outline. Breast tomosynthesis (BT) is a 3D X-ray imaging technique in which low-dose images are acquired over a limited angular range at a total dose comparable to digital mammography (DM). These low-dose images are used to mathematically reconstruct a 3D image volume of the breast, thus reducing the problem of superimposed tissue. Purpose: To investigate whether breast cancer size can be more accurately assessed with breast tomosynthesis than with digital mammography and ultrasonography (US), by reducing the disturbance effect of the projected anatomy. Material and Methods: A prototype BT system was used. The main inclusion criterion for BT examination was subtle but suspicious findings of breast cancer on 2D mammography. Sixty-two women with 73 breast cancers were included. BT, DM, and US sizes were measured independently by experienced radiologists without knowledge of the pathology results, which were used as reference. Results: The tumor outline could be determined in significantly more cases with BT (63) and US (60) than DM (49). BT and US size correlated well with pathology (R=0.86 and R=0.85, respectively), and significantly better than DM size (R=0.71). Accordingly, staging was significantly more accurate with BT than with DM. Conclusion: The study indicates that BT is superior to DM in the assessment of breast tumor size and stage.

Dose dependence of mass and microcalcification detection in digital mammography: free response human observer studies.

The purpose of this study was to evaluate the effect of dose reduction in digital mammography on the detection of two lesion types-malignant masses and clusters of microcalcifications. Two free-response observer studies were performed-one for each lesion type. Ninety screening images were retrospectively selected; each image was originally acquired under automatic exposure conditions, corresponding to an average glandular dose of 1.3 mGy for a standard breast (50 mm compressed breast thickness with 50% glandularity). For each study, one to three simulated lesions were added to each of 40 images (abnormals) while 50 were kept without lesions (normals). Two levels of simulated system noise were added to the images yielding two new image sets, corresponding to simulated dose levels of 50% and 30% of the original images (100%). The manufacturers standard display processing was subsequently applied to all images. Four radiologists experienced in mammography evaluated the images by searching for lesions and marking and assigning confidence levels to suspicious regions. The search data were analyzed using jackknife free-response (JA-FROC) methodology. For the detection of masses, the mean figure-of-merit (FOM) averaged over all readers was 0.74, 0.71, and 0.68 corresponding to dose levels of 100%, 50%, and 30%, respectively. These values were not statistically different from each other (F= 1.67, p=0.19) but showed a decreasing trend. In contrast, in the microcalcification study the mean FOM was 0.93, 0.67, and 0.38 for the same dose levels and these values were all significantly different from each other (F = 109.84, p < 0.0001). The results indicate that lowering the present dose level by a factor of two compromised the detection of microcalcifications but had a weaker effect on mass detection.

THE DIAGNOSTIC ACCURACY OF DUAL-VIEW DIGITAL MAMMOGRAPHY, SINGLE-VIEW BREAST TOMOSYNTHESIS AND A DUAL-VIEW COMBINATION OF BREAST TOMOSYNTHESIS AND DIGITAL MAMMOGRAPHY IN A FREE-RESPONSE OBSERVER PERFORMANCE STUDY

The purpose of the present study was to compare the diagnostic accuracy of dual-view digital mammography (DM), single-view breast tomosynthesis (BT) and BT combined with the opposite DM view. Patients with subtle lesions were selected to undergo BT examinations. Two radiologists who are non-participants in the study and have experience in using DM and BT determined the locations and extents of lesions in the images. Five expert mammographers interpreted the cases using the free-response paradigm. The task was to mark and rate clinically reportable findings suspicious for malignancy and clinically relevant benign findings. The marks were scored with reference to the outlined regions into lesion localization or non-lesion localization, and analysed by the jackknife alternative free-response receiver operating characteristic method. The analysis yielded statistically significant differences between the combined modality and dual-view DM (p < 0.05). No differences were found between single-view BT and dual-view DM or between single-view BT and the combined modality.

THE EFFECT OF REDUCED BREAST COMPRESSION IN BREAST TOMOSYNTHESIS: HUMAN OBSERVER STUDY USING CLINICAL CASES

The aim of this study was to investigate whether the compression force used with conventional mammography can be reduced with breast tomosynthesis (BT), without adversely affecting the visualisation of normal and pathological structures. Forty-five women were examined with BT using full (same as for 2D mammography) and half compression force. Both examinations were performed with the same acquisition parameters. A total of 103 paired structure images were evaluated according to specified image quality criteria. Three experienced radiologists participated in the study. They had to make a forced choice, i.e. choose the image they felt best fulfilled the image quality criteria. The results showed no evident difference in the image quality, indicating that BT may be performed with substantially less compression force compared with 2D mammography. A majority of the examined women felt that half compression was more comfortable than full compression.

Breast Cancer Screening With Tomosynthesis-Initial Experiences

Experiences gained so far using tomosynthesis for breast cancer screening will be reported. A short summary of results from preparatory studies will also be presented. The sensitivity and specificity of breast tomosynthesis (BT) will be compared with conventional two-dimensional digital mammography (DM) for breast cancer screening in a population-based study. Over 2000 women have been examined so far with BT and DM. The BT reading is significantly more time-consuming than the DM reading. Preparatory studies have shown that BT has a higher diagnostic precision and higher accuracy of size measurements and stage determination than DM. There is potential to use lower compression force with BT compared with DM, without decreasing the diagnostic accuracy. BT might play an important role in clinical as well as screening mammography. A large-scale population-based study to investigate BT as a screening modality is underway.

In-plane artifacts in breast tomosynthesis quantified with a novel contrast-detail phantom

The purpose of this work was to develop a contrast-detail phantom that can be used to evaluate image quality in breast tomosynthesis (BT) and as a first step use it to evaluate in-plane artifacts with respect to object size and contrast. The phantom was constructed using a Polylite® resin as bulk material, as it has x-ray mass attenuation properties similar to polymethyl methacrylate (PMMA), a common phantom material in mammography. Six different materials - polyoxymethylene (POM), bakelite®, nylon, polycarbonate (PC), acrylonitrilebutadienestyrene (ABS) and polyethene (PE) - were selected to form the phantom details. For each of the six materials, five spherical objects were manufactured (diameters of 4, 8, 12, 16, and 20 mm) resulting in 30 objects that were embedded with their centres approximately aligned at the central plane of a 26 mm thick Polylite® block (210 mm x 300 mm). A 20 mm thick PMMA block was added to yield a phantom with attenuation properties similar to 45 mm PMMA that could simulate a so-called standard breast (50 mm thick, 50% glandular tissue). Images of the phantom were acquired using a BT prototype system that employs filtered backprojection for image reconstruction. The magnitude of the in-plane artifacts was evaluated and was found to increase linearly with increasing contrast (signal) level and size of the embedded objects. The contrast-detail phantom was found to be a useful tool for evaluating BT in-plane artifacts and might also be used to study out-of-plane artifacts and the effect of different acquisition and reconstruction parameters on image quality in BT.

BIRADS Classification in Breast Tomosynthesis Compared to Mammography and Ultrasonography

This paper presents the Malmo Breast Tomosynthesis project. The tomosynthesis equipment is described as well as the patient selection and image acquisition. Special focus is given to one of the studies of the project, which is a comparison of the diagnostic performance between breast tomosynthesis (BT), digital mammography (DM) and ultrasonography (US): Tumor classification according to the BIRADS system was performed on 40 cancers imaged with DM, US and BT. The patients were selected on the basis of subtle signs of breast cancer on DM or negative findings on DM but suspicious lesions on US. The BIRADS scores based on the BT images were significantly higher than 1-view DM and 2-view DM, and equal to 2-view plus US. The results suggest that BT may be a suitable technique for breast cancer screening.

Impact of dose on observer performance in breast tomosynthesis using breast specimens

The purpose of this study was to investigate the effect of dose on lesion detection and characterization in breast tomosynthesis (BT), using human breast specimens. Images of 27 lesions in breast specimens were acquired on a BT prototype based on a Mammomat Novation (Siemens) full-field digital mammography (FFDM) system. Two detector modes - binned (2×1 in the scan direction) and full resolution - and four BT exposure levels - approximately 2×, 1.5×, 1×, and 0.5× the total mAs at the same beam quality as used in a single FFDM view with a Mammomat Novation unit under automatic exposure control (AEC) conditions - were examined. The exposure for all BT scans was equally divided among 25 projections. An enhanced filtered back projection reconstruction method was applied with a constant filter setting. A human observer performance study was conducted in which the observers were forced to select the minimum (threshold) exposure level at which each lesion could be both detected and characterized for assessment of recall or not in a screening situation. The median threshold exposure level for all observers and all lesions corresponded to approximately 1×, which is half the exposure of what we currently use for BT. A substantial variation in exposure thresholds was noticed for different lesion types. For low contrast lesions with diffuse borders, an exposure threshold of approximately 2× was required, whereas for spiculated high contrast lesions and lesions with well defined borders, the exposure threshold was lower than 0.5×. The use of binned mode had no statistically significant impact on observer performance compared to full resolution mode. There was no substantial difference between the modes for the detection and characterization of the lesion types.