Discordant and false-negative interpretations at digital breast tomosynthesis in the prospective Oslo Tomosynthesis Screening Trial (OTST) using independent double reading.

OBJECTIVES: To analyze discordant and false-negatives of double reading digital breast tomosynthesis (DBT) versus digital mammography (DM) including reading times in the Oslo Tomosynthesis Screening Trial (OTST), and reclassify these in a retrospective reader study as missed, minimal sign, or true-negatives. METHODS: The prospective OTST comparing double reading DBT vs. DM had paired design with four parallel arms: DM, DM + computer aided detection, DBT + DM, and DBT + synthetic mammography. Eight radiologists interpreted images in batches using a 5-point scale. Reading time was automatically recorded. A retrospective reader study including four radiologists classified screen-detected cancers with at least one false-negative score and screening examinations of interval cancers as negative, non-specific minimal sign, significant minimal sign, and missed; the two latter groups are defined "actionable." Statistics included chi-square, Fisher's exact, McNemar's, and Mann-Whitney U tests. RESULTS: Discordant rate (cancer missed by one reader) for screen-detected cancers was overall comparable (DBT (31% [71/227]) and DM (30% [52/175]), p = .81), significantly lower at DBT for spiculated cancers (DBT, 19% [20/106] vs. DM, 36% [38/106], p = .003), but high (28/49 = 57%, p = 0.001) for DBT-only detected spiculated cancers. Reading time and sensitivity varied among readers. False-negative DBT-only detected spiculated cancers had shorter reading time than true-negatives in 46% (13/28). Retrospective evaluation classified the following DBT exams "actionable": three missed by both readers, 95% (39/41) of discordant cancers detected by both modes, all 30 discordant DBT-only cancers, 25% (13/51) of interval cancers. CONCLUSIONS: Discordant rate was overall comparable for DBT and DM, significantly lower at DBT for spiculated cancers, but high for DBT-only detected spiculated lesions. Most false-negative screen-detected DBT were classified as "actionable." CLINICAL RELEVANCE STATEMENT: Retrospective evaluation of false-negative interpretations from the Oslo Tomosynthesis Screening Trial shows that most discordant and several interval cancers could have been detected at screening. This underlines the potential for modern AI-based reading aids and triage, as high-volume screening is a demanding task. KEY POINTS: • Digital breast tomosynthesis (DBT) screening is more sensitive and has higher specificity compared to digital mammography screening, but high-volume DBT screening is a demanding task which can result in high discordance rate among readers. • Independent double reading DBT screening had overall comparable discordance rate as digital mammography, lower for spiculated masses seen on both modalities, and higher for small spiculated cancer seen only on DBT. • Almost all discordant digital breast tomosynthesis-detected cancers (72 of 74) and 25% (13 of 51) of the interval cancers in the Oslo Tomosynthesis Screening Trial were retrospectively classified as actionable and could have been detected by the readers.

Metal artifact reduction on musculoskeletal CT: a phantom and clinical study.

BACKGROUND: Artifacts caused by metal implants are challenging when undertaking computed tomography (CT). Dedicated algorithms have shown promising results although with limitations. Tin filtration (Sn) in combination with high tube voltage also shows promise but with limitations. There is a need to examine these limitations in more detail. The purpose of this study was to investigate the impact of different metal artefact reduction (MAR) algorithms, tin filtration, and ultra-high-resolution (UHR) scanning, alone or in different combinations in both phantom and clinical settings. METHODS: An ethically approved clinical and phantom study was conducted. A modified Catphan® phantom with titanium and stainless-steel inserts was scanned with six different MAR protocols with tube voltage ranging from 80 to 150 kVp. Other scan parameters were kept identical. The differences (∆) in mean HU and standard deviation (SD) in images, with and without metal, were measured and compared. In the clinical study, three independent readers performed visual image quality assessments on eight different protocols using retrospectively acquired images. RESULTS: Iterative MAR had the lowest ∆HU and ∆SD in the phantom study. For images of the forearm, the soft tissue noise for Sn-based 150-kVp UHR protocol with was significantly higher (p = 0.037) than for single-energy MAR protocols. All Sn-based 150-kVp protocols were rated significantly higher (p < 0.046 than the single-energy MAR protocols in the visual assessment. CONCLUSIONS: All Sn-based 150-kVp UHR protocols showed similar objective MAR in the phantom study, and higher objective MAR and significantly improved visual image quality than single-energy MAR. RELEVANCE STATEMENT: Images with less metal artifacts and higher visual image quality may be more clinically optimal in CT examination of musculoskeletal patients with metal implants. KEY POINTS: • Metal artifact reduction algorithms and Sn filter combined with high kVp reduce artifacts. • Metal artifact reduction algorithms introduce new artifacts in certain metals. • Sn-based protocols alone may be considered as low metal artifact protocols.

Digital Mammography versus Breast Tomosynthesis: Impact of Breast Density on Diagnostic Performance in Population-based Screening.

BackgroundPrevious studies comparing digital breast tomosynthesis (DBT) to digital mammography (DM) have shown conflicting results regarding breast density and diagnostic performance.PurposeTo compare true-positive and false-positive interpretations in DM versus DBT according to volumetric density, age, and mammographic findings.Materials and MethodsFrom November 2010 to December 2012, 24 301 women aged 50-69 years (mean age, 59.1 years ± 5.7) were prospectively included in the Oslo Tomosynthesis Screening Trial. Participants received same-compression DM and DBT with independent double reading for both DM and DM plus DBT reading modes. Eight experienced radiologists rated the images by using a five-point scale for probability of malignancy. Participants were followed up for 2 years to assess for interval cancers. Breast density was assessed by using automatic volumetric software (scale, 1-4). Differences in true-positive rates, false-positive rates, and mammographic findings were assessed by using confidence intervals (Newcombe paired method) and P values (McNemar and χ2 tests).ResultsThe true-positive rate of DBT was higher than that of DM for density groups (range, 12%-24%; P < .001 for density scores of 2 and 3, and P > .05 for density scores of 1 and 4) and age groups (range, 15%-35%; P < .05 for all age groups), mainly due to the higher number of spiculated masses and architectural distortions found at DBT (P < .001 for density scores of 2 and 3; P < .05 for women aged 55-69 years). The false-positive rate was lower for DBT than for DM in all age groups (range, -0.6% to -1.2%; P < .01) and density groups (range, -0.7 to -1.0%; P < .005) owing to fewer asymmetric densities (P ≤ .001), except for extremely dense breasts (0.1%, P = .82).ConclusionDigital breast tomosynthesis enabled the detection of more cancers in all density and age groups compared with digital mammography, especially cancers classified as spiculated masses and architectural distortions. The improvement in cancer detection rate showed a positive correlation with age. With use of digital breast tomosynthesis, false-positive findings were lower due to fewer asymmetric densities, except in extremely dense breasts.© RSNA, 2019Online supplemental material is available for this article.See also the editorial by Fuchsjäger and Adelsmayr in this issue.

Performance of breast cancer screening using digital breast tomosynthesis: results from the prospective population-based Oslo Tomosynthesis Screening Trial.

PURPOSE: Digital breast tomosynthesis (DBT) has the potential to overcome limitations of conventional mammography. This study investigated the effects of addition of DBT on interval and detected cancers in population-based screening. METHODS: Oslo Tomosynthesis Screening Trial (OTST) was a prospective, independent double-reading trial inviting women 50-69 years biennially, comparing full-field digital mammography (FFDM) plus DBT with FFDM alone. Performance indicators and characteristics of screen-detected and interval cancers were compared with two previous FFDM rounds. RESULTS: 24,301 consenting women underwent FFDM + DBT screening over a 2-year period. Results were compared with 59,877 FFDM examinations during prior rounds. Addition of DBT resulted in a non-significant increase in sensitivity (76.2%, 378/496, vs. 80.8%, 227/281, p = 0.151) and a significant increase in specificity (96.4%, 57229/59381 vs. 97.5%, 23427/24020, p < .001). Number of recalls per screen-detected cancer decreased from 6.7 (2530/378) to 3.6 (820/227) with DBT (p < .001). Cancer detection per 1000 women screened increased (6.3, 378/59877, vs. 9.3, 227/24301, p < .001). Interval cancer rate per 1000 screens for FFDM + DBT remained similar to previous FFDM rounds (2.1, 51/24301 vs. 2.0, 118/59877, p = 0.734). Interval cancers post-DBT were comparable to prior rounds but significantly different in size, grade, and node status from cancers detected only using DBT. 39.6% (19/48) of interval cancers had positive nodes compared with only 3.9% (2/51) of additional DBT-only-detected cancers. CONCLUSIONS: DBT-supplemented screening resulted in significant increases in screen-detected cancers and specificity. However, no significant change was observed in the rate, size, node status, or grade of interval cancers. ClinicalTrials.gov: NCT01248546.

Average glandular dose in paired digital mammography and digital breast tomosynthesis acquisitions in a population based screening program: effects of measuring breast density, air kerma and beam quality.

The main purpose was to compare average glandular dose (AGD) for same-compression digital mammography (DM) and digital breast tomosynthesis (DBT) acquisitions in a population based screening program, with and without breast density stratification, as determined by automatically calculated breast density (Quantra™). Secondary, to compare AGD estimates based on measured breast density, air kerma and half value layer (HVL) to DICOM metadata based estimates. AGD was estimated for 3819 women participating in the screening trial. All received craniocaudal and mediolateral oblique views of each breasts with paired DM and DBT acquisitions. Exposure parameters were extracted from DICOM metadata. Air kerma and HVL were measured for all beam qualities used to acquire the mammograms. Volumetric breast density was estimated using Quantra™. AGD was estimated using the Dance model. AGD reported directly from the DICOM metadata was also assessed. Mean AGD was 1.74 and 2.10 mGy for DM and DBT, respectively. Mean DBT/DM AGD ratio was 1.24. For fatty breasts: mean AGD was 1.74 and 2.27 mGy for DM and DBT, respectively. For dense breasts: mean AGD was 1.73 and 1.79 mGy, for DM and DBT, respectively. For breasts of similar thickness, dense breasts had higher AGD for DM and similar AGD for DBT. The DBT/DM dose ratio was substantially lower for dense compared to fatty breasts (1.08 versus 1.33). The average c-factor was 1.16. Using previously published polynomials to estimate glandularity from thickness underestimated the c-factor by 5.9% on average. Mean AGD error between estimates based on measurements (air kerma and HVL) versus DICOM header data was 3.8%, but for one mammography unit as high as 7.9%. Mean error of using the AGD value reported in the DICOM header was 10.7 and 13.3%, respectively. Thus, measurement of breast density, radiation dose and beam quality can substantially affect AGD estimates.

Quantitative Measurements Versus Receiver Operating Characteristics and Visual Grading Regression in CT Images Reconstructed with Iterative Reconstruction: A Phantom Study.

RATIONALE AND OBJECTIVES: This study aimed to evaluate the correlation of quantitative measurements with visual grading regression (VGR) and receiver operating characteristics (ROC) analysis in computed tomography (CT) images reconstructed with iterative reconstruction. MATERIALS AND METHODS: CT scans on a liver phantom were performed on CT scanners from GE, Philips, and Toshiba at three dose levels. Images were reconstructed with filtered back projection (FBP) and hybrid iterative techniques (ASiR, iDose, and AIDR 3D of different strengths). Images were visually assessed by five readers using a four- and five-grade ordinal scale for liver low contrast lesions and for 10 image quality criteria. The results were analyzed with ROC and VGR. Standard deviation, signal-to-noise ratios, and contrast-to-noise ratios were measured in the images. RESULTS: All data were compared to FBP. The results of the quantitative measurements were improved for all algorithms. ROC analysis showed improved lesion detection with ASiR and AIDR and decreased lesion detection with iDose. VGR found improved noise properties for all algorithms, increased sharpness with iDose and AIDR, and decreased artifacts from the spine with AIDR, whereas iDose increased the artifacts from the spine. The contrast in the spine decreased with ASiR and iDose. CONCLUSIONS: Improved quantitative measurements in images reconstructed with iterative reconstruction compared to FBP are not equivalent to improved diagnostic image accuracy.

[Radiation-induced cataracts]. / Strålingsindusert katarakt.

The dose limit for the lens of the eye for occupationally exposed workers that is stipulated in the Norwegian Regulation on radiation protection is based on outdated threshold doses for radiation-induced cataracts. Recent studies have shown that injuries may occur at significantly lower radiation doses than previously assumed. The results from the new studies will impact upon future legislation and recommendations regarding radiation hygiene for personnel in x-ray laboratories and operating theatres who may be exposed to significant radiation doses in the course of their work.

Can use of adaptive statistical iterative reconstruction reduce radiation dose in unenhanced head CT? An analysis of qualitative and quantitative image quality.

BACKGROUND: Iterative reconstruction can reduce image noise and thereby facilitate dose reduction. PURPOSE: To evaluate qualitative and quantitative image quality for full dose and dose reduced head computed tomography (CT) protocols reconstructed using filtered back projection (FBP) and adaptive statistical iterative reconstruction (ASIR). MATERIAL AND METHODS: Fourteen patients undergoing follow-up head CT were included. All patients underwent full dose (FD) exam and subsequent 15% dose reduced (DR) exam, reconstructed using FBP and 30% ASIR. Qualitative image quality was assessed using visual grading characteristics. Quantitative image quality was assessed using ROI measurements in cerebrospinal fluid (CSF), white matter, peripheral and central gray matter. Additionally, quantitative image quality was measured in Catphan and vendor's water phantom. RESULTS: There was no significant difference in qualitative image quality between FD FBP and DR ASIR. Comparing same scan FBP versus ASIR, a noise reduction of 28.6% in CSF and between -3.7 and 3.5% in brain parenchyma was observed. Comparing FD FBP versus DR ASIR, a noise reduction of 25.7% in CSF, and -7.5 and 6.3% in brain parenchyma was observed. Image contrast increased in ASIR reconstructions. Contrast-to-noise ratio was improved in DR ASIR compared to FD FBP. In phantoms, noise reduction was in the range of 3 to 28% with image content. CONCLUSION: There was no significant difference in qualitative image quality between full dose FBP and dose reduced ASIR. CNR improved in DR ASIR compared to FD FBP mostly due to increased contrast, not reduced noise. Therefore, we recommend using caution if reducing dose and applying ASIR to maintain image quality.

BI-RADS Density Classification From Areometric and Volumetric Automatic Breast Density Measurements.

RATIONALE AND OBJECTIVES: The aim of our study was to classify breast density using areometric and volumetric automatic measurements to best match Breast Imaging-Reporting and Data System (BI-RADS) density scores, and determine which technique best agrees with BI-RADS. Second, this study aimed to provide a set of threshold values for areometric and volumetric density to estimate BI-RADS categories. MATERIALS AND METHODS: We randomly selected 537 full-field digital mammography examinations from a population-based screening program. Five radiologists assessed breast density using BI-RADS with all views available. A commercial program calculated areometric and volumetric breast density automatically. We compared automatically calculated density to all BI-RADS density thresholds using area under the receiver operating characteristic curve, and used Youden's index to estimate thresholds in automatic densities, with matching sensitivity and specificity. The 95% confidence intervals were estimated by bootstrapping. RESULTS: Areometric density correlated well with volumetric density (r(2) = 0.76, excluding outliers, n = 2). For the BI-RADS threshold between II and III, areometric and volumetric assessment showed about equal area under the curve (0.94 vs. 0.93). For the threshold between I and II, areometric assessment was better than volumetric assessment (0.91 vs. 0.86). For the threshold between III and IV, volumetric assessment was better than areometric assessment (0.97 vs. 0.92). CONCLUSIONS: Volumetric assessment is equal to or better than areometric assessment for the most clinically relevant thresholds (ie, between scattered fibroglandular and heterogeneously dense, and between heterogeneously dense and extremely dense breasts). Thresholds found in this study can be applied in daily practice to automatic measurements of density to estimate BI-RADS classification.

Classification of fatty and dense breast parenchyma: comparison of automatic volumetric density measurement and radiologists' classification and their inter-observer variation.

BACKGROUND: Automatically calculated breast density is a promising alternative to subjective BI-RADS density assessment. However, such software needs a cutoff value for density classification. PURPOSE: To determine the volumetric density threshold which classifies fatty and dense breasts with highest accuracy compared to average BI-RADS density assessment, and to analyze radiologists' inter-observer variation. MATERIAL AND METHODS: A total of 537 full field digital mammography examinations were randomly selected from a population based screening program. Five radiologists assessed density using the BI-RADS density scale, where BI-RADS I-II were classified as fatty and III-IV as dense. A commercially available software (Quantra) calculated volumetric breast density. We calculated the cutoff (threshold) values in volumetric density that yielded highest accuracy compared to median and individual radiologists' classification. Inter-observer variation was analyzed using the kappa statistic. RESULTS: The threshold that best matched the median radiologists' classification was 10%, which resulted in 87% accuracy. Thresholds that best matched individual radiologist's classification had a range of 8-15%. A total of 191 (35.6 %) cases were scored both dense and fatty by at least one radiologist. Fourteen (2.6 %) cases were unanimously scored by the radiologists, yet differently using automatic assessment. The agreement (kappa) between reader's median classification and individual radiologists was 0.624 to 0.902, and agreement between median classification and Quantra was 0.731. CONCLUSION: The optimal volumetric threshold of 10% using automatic assessment would classify breast parenchyma as fatty or dense with substantial accuracy and consistency compared to radiologists' BI-RADS categorization, which suffers from high inter-observer variation.

A proposed protocol for acceptance and constancy control of computed tomography systems: a Nordic Association for Clinical Physics (NACP) work group report.

BACKGROUND: Quality assurance (QA) of computed tomography (CT) systems is one of the routine tasks for medical physicists in the Nordic countries. However, standardized QA protocols do not yet exist and the QA methods, as well as the applied tolerance levels, vary in scope and extent at different hospitals. PURPOSE: To propose a standardized protocol for acceptance and constancy testing of CT scanners in the Nordic Region. MATERIAL AND METHODS: Following a Nordic Association for Clinical Physics (NACP) initiative, a group of medical physicists, with representatives from four Nordic countries, was formed. Based on international literature and practical experience within the group, a comprehensive standardized test protocol was developed. RESULTS: The proposed protocol includes tests related to the mechanical functionality, X-ray tube, detector, and image quality for CT scanners. For each test, recommendations regarding the purpose, equipment needed, an outline of the test method, the measured parameter, tolerance levels, and the testing frequency are stated. In addition, a number of optional tests are briefly discussed that may provide further information about the CT system. CONCLUSION: Based on international references and medical physicists' practical experiences, a comprehensive QA protocol for CT systems is proposed, including both acceptance and constancy tests. The protocol may serve as a reference for medical physicists in the Nordic countries.

Step back from the patient: reduction of radiation dose to the operator by the systematic use of an automatic power injector for contrast media in an interventional angiography suite.

BACKGROUND: During arterial interventional procedures, power injectors allow the operator to step back from the patient or exit the angiography suite during digital subtraction angiography (DSA) acquisitions. Increasing the distance to the radiation source reduces exposure to the operator and staff. PURPOSE: To systematically investigate the effect of increasing the distance between the radiation source and the operator during DSA acquisitions in a daily clinical setting, regarding radiation exposure to the operator and patient, as well as the duration of the procedure using a power injector to deliver contrast media. MATERIAL AND METHODS: Patients scheduled for arterial interventional procedures in the pelvis or lower extremities were consecutively included. In phase one (duration 6 weeks, 44 patients) contrast media were injected manually. In phase two (duration until the total dose area product [DAP] was equal to phase 1, 41 patients) the operator used a power injector and exited the suite whenever possible. Patient, procedure, and examination data were recorded. Collective dose to the operator's collar, lead apron, and hands was recorded using thermo luminescent dosimetry (TLD). RESULTS: Our results showed a dose reduction of 50% to the operator's hands, lead apron, and thyroid collar when using a power injector during DSA, with no significant increase in DAP or procedure time when performing pelvic procedures. For lower extremity procedures there was a small but significant increase in procedure time and DAP. Pelvic procedures yielded substantially higher DAP than lower extremity procedures during both phases. CONCLUSION: Utilization of a power injector, thus allowing the operator to step back from the patient, facilitates a radiation dose reduction to the operator of approximately 50% with no significant increase in patient dose or procedure time during pelvic procedures.

EPR dosimetry of radiotherapy photon beams in inhomogeneous media using alanine films.

In the current work, EPR (electron paramagnetic resonance) dosimetry using alanine films (134 microm thick) was utilized for dose measurements in inhomogeneous phantoms irradiated with radiotherapy photon beams. The main phantom material was PMMA, while either Styrofoam or aluminium was introduced as an inhomogeneity. The phantoms were irradiated to a maximum dose of about 30 Gy with 6 or 15 MV photons. The performance of the alanine film dosimeters was investigated and compared to results from ion chamber dosimetry, Monte Carlo simulations and radiotherapy treatment planning calculations. It was found that the alanine film dosimeters had a linear dose response above approximately 5 Gy, while a background signal obscured the response at lower dose levels. For doses between 5 and 60 Gy, the standard deviation of single alanine film dose estimates was about 2%. The alanine film dose estimates yielded results comparable to those from the Monte Carlo simulations and the ion chamber measurements, with absolute differences between estimates in the order of 1-15%. The treatment planning calculations exhibited limited applicability. The current work shows that alanine film dosimetry is a method suitable for estimating radiotherapeutical doses and for dose measurements in inhomogeneous media.