Preliminary investigation of the clinical usefulness of super-high-resolution LCDs with 9 and 15 mega-sub-pixels: Observation studies with phantoms

金沢大学附属病院放射線部Our purpose in this study was to evaluate the preliminary clinical efficacy of soft-copy reading of digital mammography, for a 15-mega-sub-pixel (MsP) and a 9-MsP super-high-resolution liquid-crystal display (SHR-LCD) by use of an independent sub-pixel driving technology. We performed three kinds of phantom observation studies by six radiological technologists. Detectability of a contrast-detail phantom and simulated small objects (SSOs) resembling microcalcifications (MCLs), and shape discrimination ability of SSOs with round and square shapes, were examined and compared with a 5-MP conventional LCD (5-MP LCD). In each study, four types of display magnification ratio were used. The detectability and the shape discrimination ability of the 15-MsP SHR-LCD were highest among the three LCDs of most of the display magnification ratios. The 9-MsP SHR-LCD indicated a higher or equal performance as compared with the 5-MP LCD in the SSO detection and shape studies. The results of our study demonstrated that the SHR-LCDs had good potential to detect MCLs and to evaluate the shape in high-resolution digital mammography. © 2009 Japanese Society of Radiological Technology and Japan Society of Medical Physics

Using breast radiographers\u27 reports as a second opinion for radiologists\u27 readings of microcalcifications in digital mammography

Objective: The aim of this study was to investigate a practical method for incorporating radiographers\u27 reports with radiologists\u27 readings of digital mammograms. Methods: This simulation study was conducted using data from a free-response receiver operating characteristic observer study obtained with 75 cases (25 malignant, 25 benign and 25 normal cases) of digital mammograms. Each of the rating scores obtained by six breast radiographers was utilized as a second opinion for four radiologists\u27 readings with the radiographers\u27 reports. A logical "OR" operation with various criteria settings was simulated for deciding an appropriate method to select a radiographer\u27s report in all combinations of radiologists and radiographers. The average figure of merit (FOM) of the radiologists\u27 performances was statistically analysed using a jackknife procedure (JAFROC) to verify the clinical utility of using radiographers\u27 reports. Results: Potential improvement of the average FOM of the radiologists\u27 performances for identifying malignant microcalcifications could be expected when using radiographers\u27 reports as a second opinion. When the threshold value of 2.6 in Breast Imaging-Reporting and Data System (BI-RADS®) assessment was applied to adopt/ reject a radiographer\u27s report, FOMs of radiologists\u27 performances were further improved. Conclusion: When using breast radiographers\u27 reports as a second opinion, radiologists\u27 performances potentially improved when reading digital mammograms. It could be anticipated that radiologists\u27 performances were improved further by setting a threshold value on the BIRADS assessment provided by the radiographers. Advances in knowledge: For the effective use of a radiographer\u27s report as a second opinion, radiographers\u27 rating scores and its criteria setting for adoption/ rejection would be necessary

Blurred digital mammography images : an analysis of technical recall and observer detection performance

Background: Blurred images in Full Field Digital Mammography (FFDM) are a problem in the UK Breast Screening Programme. Technical recalls may be due to blurring not being seen on lower resolution monitors used for review. Objectives: This study assesses the visual detection of blurring on a 2.3 megapixel (MP) monitor and a 5 MP report grade monitor and proposes an observer standard for the visual detection of blurring on a 5 MP reporting grade monitor. Method: Twenty-eight observers assessed 120 images for blurring; 20 had no blurring present whilst 100 had blurring imposed through mathematical simulation at 0.2, 0.4, 0.6, 0.8 and 1.0 mm levels of motion. Technical recall rate for both monitors and angular size at each level of motion were calculated. Chi-squared (X2) tests were used to test whether significant differences in blurring detection existed between 2.3 and 5 MP monitors. Results: The technical recall rate for 2.3 and 5 MP monitors are 20.3 % and 9.1% respectively. Angular size for 0.2 to 1 mm motion varied from 55 to 275 arc seconds. The minimum amount of motion for visual detection of blurring in this study is 0.4 mm. For 0.2 mm simulated motion, there was no significant difference X2 (1, N=1095) =1.61, p=0.20) in blurring detection between the 2.3 and 5 MP monitors. Conclusion: According to this study monitors equal or below 2.3 MP are not suitable for technical review of FFDM images for the detection of blur. Advances in knowledge: This research proposes the first observer standard for the visual detection of blurring. Key words: Simulated motion; technical recall; monitor resolution; observer standard; blurring detectio

The impact of simulated motion blur on breast cancer detection performance in full field digital mammography (FFDM)

Objective: Full-field Digital Mammography (FFDM) is employed in breast screening for the early detection of breast cancer. High quality, artefact free, diagnostic images are crucial to the accuracy of this process. Unwanted motion during the image acquisition phase and subsequent image blurring is an unfortunate occurrence in some FFDM images. The research detailed in this thesis seeks to understand the impact of motion blur on cancer detection performance in FFDM images using novel software to perform simulation of motion, an observer study to measure the lesion detection performance and physical measures to assess the impact of simulated motion blur on image characteristics of the lesions. Method: Seven observers (15±5 years’ reporting experience) evaluated 248 cases (62 containing malignant masses, 62 containing malignant microcalcifications and 124 normal cases) for three conditions: no motion blur (0.0 mm) and two magnitudes of simulated motion blur (0.7 mm and 1.5 mm). Abnormal cases were biopsy proven. A free-response observer study was conducted to compare lesion detection performance for the three conditions. Equally weighted jackknife alternative free-response receiver operating characteristic (wJAFROC) was used as the figure of merit. A secondary analysis of data was deemed important to simulate ‘double reporting’. In this secondary analysis, six of the observers are combined with the seventh observer to evaluate the impact of combined free-response data for lesion detection and to assess if combined two observers data could reduce the impact of simulated motion blur on detection performance. To compliment this, the physical characteristics of the lesions were obtained under the three conditions in order to assess any change in characteristics of the lesions when blur is present in the image. The impact of simulated motion blur on physical characteristics of malignant masses was assessed using a conspicuity index; for microcalcifications, a new novel metric, known as dispersion index, was used. Results: wJAFROC analysis found a statistically significant difference in lesion detection performance for both masses (F (2,22) = 6.01, P=0.0084) and microcalcifications (F(2,49) = 23.14, P<0.0001). For both lesion types, the figure of merit reduced as the magnitude of simulated motion blur increased. Statistical differences were found between some of the pairs investigated for the detection of masses (0.0mm v 0.7mm, and 0.0mm v 1.5mm) and all pairs for microcalcifications (0.0 mm v 0.7 mm, 0.0 mm v 1.5 mm, and 0.7 mm v 1.5 mm). No difference was detected between 0.7 mm and 1.5 mm for masses. For combined two observers’ data of masses, there was no statistically significant difference between single and combined free-response data for masses (F(1,6) = 4.04, p=0.1001, -0.031 (-0.070, 0.008) [treatment difference (95% CI)]. For combined data of microcalcifications, there was a statistically significant difference between single and combined free-response data (F(1,6) = 12.28, p=0.0122, -0.056 (-0.095, -0.017) [treatment difference (95% CI)]. Regarding the physical measures of masses, conspicuity index increases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=-6.158 (p<0.000); 0.0–1.5 mm t(22)=-6.273 (p<0.000); and 0.7–1.5 mm (t(22)=-6.231 (p<0.000). Lesion edge angle decreases as the magnitude of simulated motion blur increases. Statistically significant differences were demonstrated for 0.0–0.7 mm t(22)=3.232 (p<0.004); for 0.0–1.5 mm t(22)=6.592 (p<0.000); and 0.7–1.5mm t(22)=2.234 (p<0.036). For the grey level change there was no statistically significant difference as simulated motion blur increases to 0.7 and then to 1.5mm. For image noise there was a statistically significant difference, where noise reduced as simulated motion blur increased: 0.0–0.7 mm t(22)=22.95 (p<0.000); 0.0–1.5mm t(22)=24.66 (p<0.000); 0.7–1.5 mm t(22)=18.11 (p<0.000). For microcalcifications, simulated motion blur had a negative impact on the ‘dispersion index’. Conclusion: Mathematical simulations of motion blur resulted in a statistically significant reduction in lesion detection performance. This reduction in performance could have implications for clinical practice. Simulated motion blur has a negative impact on the edge angle of breast masses and a negative impact on the image characteristics of microcalcifications. These changes in the image lesion characteristics appear to have a negative effect on the visual identification of breast cancer

Eye Tracking Methods for Analysis of Visuo-Cognitive Behavior in Medical Imaging

Predictive modeling of human visual search behavior and the underlying metacognitive processes is now possible thanks to significant advances in bio-sensing device technology and machine intelligence. Eye tracking bio-sensors, for example, can measure psycho-physiological response through change events in configuration of the human eye. These events include positional changes such as visual fixation, saccadic movements, and scanpath, and non-positional changes such as blinks and pupil dilation and constriction. Using data from eye-tracking sensors, we can model human perception, cognitive processes, and responses to external stimuli. In this study, we investigated the visuo-cognitive behavior of clinicians during the diagnostic decision process for breast cancer screening under clinically equivalent experimental conditions involving multiple monitors and breast projection views. Using a head-mounted eye tracking device and a customized user interface, we recorded eye change events and diagnostic decisions from 10 clinicians (three breast-imaging radiologists and seven Radiology residents) for a corpus of 100 screening mammograms (comprising cases of varied pathology and breast parenchyma density). We proposed novel features and gaze analysis techniques, which help to encode discriminative pattern changes in positional and non-positional measures of eye events. These changes were shown to correlate with individual image readers' identity and experience level, mammographic case pathology and breast parenchyma density, and diagnostic decision. Furthermore, our results suggest that a combination of machine intelligence and bio-sensing modalities can provide adequate predictive capability for the characterization of a mammographic case and image readers diagnostic performance. Lastly, features characterizing eye movements can be utilized for biometric identification purposes. These findings are impactful in real-time performance monitoring and personalized intelligent training and evaluation systems in screening mammography. Further, the developed algorithms are applicable in other application domains involving high-risk visual tasks

Mammography machine compression paddle movement andobserver performance analysis

Full field digital mammography (FFDM) was introduced into the United Kingdom (UK) as a replacement for screen-film mammography (SFM) in 2005. Since then, individual breast screening centres have begun to report blurred images through local audits. Blurring was probably present in SFM as well, however the improvement in contrast resolution in FFDM may have made it more apparent. The sources of blurring include improper imaging techniques, patient movement caused by breathing and heart motion,the viscoelastic motion of the breast, and paddle motion. This thesis aims to test the hypothesis that paddle motion might cause image blur. It investigates whether blurring can be detected visually on technical review monitors and reporting grade monitors.The thesis presents a method to minimise paddle motion during X-ray exposure. Six papers have been published. Two of these (papers 1 and 2) investigated paddle displacement using linear potentiometers. Three investigated the influence of paddle motion on image quality. Paper 3 investigated whether paddle motion can cause image blur; paper 4 determined the minimum amount of simulated motion required for the visual detection of blurring; and paper 5 evaluated the practitioner’s ability to identify blurring on monitors with different resolutions (2.3 MP and 5 MP). The final research paper (paper 6) investigated a way to reduce paddle displacement settling time; this involved the use of a closed-loop control system.Results: In papers 1 and 2 paddle displacement followed a bi-exponential function with a settling time of approximately 40 s. The use of average paddle displacement to estimate the amount of paddle motion would underestimate the worst case of the threedifferent runs of the experiment. The estimated paddle motion would be greatly reduced if the time of exposure is delayed from 5 to 10 s. In paper 3 all metal ball bearings shown increased in diameters and the range of magnification varied from 1.04 to 1.21. T-test results shown that there was a significant difference (p < 0.05) in the ball bearing diameters between the intensity thresholding and the edge detection methods for all paddle/ compression force combinations. The ball bearing diameters calculated by the intensity thresholding method had higher variability than the edge detection method.In paper 4 the soft-edged mask method best represented the physical process that caused the blurring effect and was chosen as the standard simulation approach for motion blurring. The ratio between the vertical paddle motion and the horizontal breast motion estimated by the mathematical model is approximately 1:0.3.In paper 5 the angular size calculation shown that for a viewing distance of 75 cm the screen resolution for 5 MP and 12 MP monitors was better than the observer eyes' resolution. For a viewing distance of 30 cm the observer eyes' resolution was betterthan the screen resolution for 2.3 MP, 5 MP and 12 MP monitors. Among all three monitors, image displayed on the 12 MP monitor has the lowest loss in image quality after interpolation. In paper 6 the simulation results shown that force overshoot is possible for position control system. Force overshoot occurred almost instantaneously for step input and its magnitude is about 10 times larger than the ramp input. Force overshoot and steadystateerror can be eliminated by the use of force control system.Conclusion: The magnitude of calculated paddle motion is much lower than the minimum amount of simulated motion required for the visual detection of blurring. Mathematical models have shown that vertical paddle motion caused a smaller horizontal breast displacement when compressed. Therefore, there is no sufficientevidence to support the hypothesis that paddle motion is a cause of image blurring in FFDM

Towards greater clarity for the analysis of imaging studies: Development & validation of an alternative to the area under the receiver-operator characteristic curve.

This thesis arose from a 2006 study performed by the author and his collaborators that attempted to gain regulatory approval for computer-assisted detection (CAD) software. The USA Food & Drug Administration (FDA) obliged us to use the change in the area under the receiver-operator characteristic curve (ROC AUC) as our primary outcome. Despite its wide dissemination in radiology research, we found implementation of ROC AUC very problematic. This thesis explores the hurdles we encountered and argues for an alternative approach. Chapter 1 describes the rationale for and against ROC AUC as a measure of diagnostic performance. An alternative analysis based on net benefit is proposed on the basis that it is more transparent and simpler to interpret. Chapter 2 uses the net benefit method to analyse a multi-reader multi-case (MRMC) study of CAD for CT colonography. The analysis requires an estimate of relative misclassification costs for false-negative versus false-positive diagnoses; “W”. This study used a conservative value for W, arrived at via consensus. In Chapter 3 an evidence-based value for W in the context of screening for colorectal cancer and polyps by CT colonography is arrived at via a discrete choice experiment (DCE) of patients and healthcare workers. Chapter 4 uses the value for W obtained in Chapter 3 in a net benefit analysis to compare observer performance in two MRMC studies of CAD for CT colonography. Chapter 5 obtains W by DCE for a different clinical context – detection of extracolonic pathology by CT colonography. Chapter 6 describes a systematic review that aims to determine whether reporting of MRMC ROC AUC methods in the radiological literature is comprehensive. Chapter 7 then provides guidelines for the comprehensive reporting of MRMC ROC AUC studies. The thesis finishes with a summary of the work performed and suggestions for further research