The effect of clinical history on diagnostic performance of endodontic cone-beam CT interpretation

AIM

To assess the effect of clinical history on the interpretation of endodontic disease in dental cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

A reader performance study of an image test-set was undertaken using a factorial, free-response, crossover design, accounting for the independent variables: case type, case severity, reader type, and reading modality. Twenty-three readers interpreted 60 CBCT images twice over two reading sessions using a balanced design, once with access to clinical history and once without, where 30 in each session included history. Lesion localisations, specificity, false-positive marks and the weighted alternative free-response receiver operating characteristic (wAFROC1) figure of merit were calculated.

RESULTS

Clinical history had no significant effect on specificity and false-positive rates in non-diseased cases (p>0.05), but improved lesion localisation in subtle and obvious diseased cases (p<0.01). wAFROC1 values were higher with clinical history for subtle (0.58 versus 0.48; p<0.001) and obvious (0.77 versus 0.71; p=0.006) diseased categories. No associations were observed between clinical history and both readers' years of experience and reading volume in the non-diseased categories. Readers with fewer (p=0.03) and moderate (p=0.008) years of experience and low (p=0.002) CBCT reading volume demonstrated better lesion localisation in subtle diseased cases when clinical history was available.

CONCLUSIONS

Clinical history improved the interpretation of CBCT images with disease without affecting the interpretation of images without disease. Less and moderately experienced readers and low-volume readers benefitted more from availability of clinical history.

Artificial intelligence-based computer-aided system for knee osteoarthritis assessment increases experienced orthopaedic surgeons' agreement rate and accuracy

PURPOSE

The aims of this study were to (1) analyze the impact of an artificial intelligence (AI)-based computer system on the accuracy and agreement rate of board-certified orthopaedic surgeons (= senior readers) to detect X-ray features indicative of knee OA in comparison to unaided assessment and (2) compare the results to those of senior residents (= junior readers).

METHODS

One hundred and twenty-four unilateral knee X-rays from the OAI study were analyzed regarding Kellgren-Lawrence grade, joint space narrowing (JSN), sclerosis and osteophyte OARSI grade by computerized methods. Images were rated for these parameters by three senior readers using two modalities: plain X-ray (unaided) and X-ray presented alongside reports from a computer-assisted detection system (aided). After exclusion of nine images with incomplete annotation, intraclass correlations between readers were calculated for both modalities among 115 images, and reader performance was compared to ground truth (OAI consensus). Accuracy, sensitivity and specificity were also calculated and the results were compared to those from a previous study on junior readers.

RESULTS

With the aided modality, senior reader agreement rates for KL grade (2.0-fold), sclerosis (1.42-fold), JSN (1.37-fold) and osteophyte OARSI grades (3.33-fold) improved significantly. Reader specificity and accuracy increased significantly for all features when using the aided modality compared to the gold standard. On the other hand, sensitivity only increased for OA diagnosis, whereas it decreased (without statistical significance) for all other features. With aided analysis, senior readers reached similar agreement and accuracy rates as junior readers, with both surpassing AI performance.

CONCLUSION

The introduction of AI-based computer-aided assessment systems can increase the agreement rate and overall accuracy for knee OA diagnosis among board-certified orthopaedic surgeons. Thus, use of this software may improve the standard of care for knee OA detection and diagnosis in the future.

LEVEL OF EVIDENCE

Level II.

The Effect of Clinical History on Diagnostic Imaging Interpretation - A Systematic Review

RATIONALE AND OBJECTIVES

To provide updated information on the effect of clinical history on diagnostic image interpretation and to provide study methodology and design recommendations for future studies assessing the effect of clinical history on diagnostic image performance.

MATERIALS AND METHODS

A literature search of Medline, Embase, Scopus, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases was conducted from database inception to July 21, 2020. Studies comparing diagnostic imaging performance with and without clinical history, using observers reading images under both conditions that used an independent reference standard were included.

RESULTS

Twenty-two studies met the inclusion criteria, with 15 showing clinical history improved diagnostic performance. One study reported a decrease in diagnostic performance with clinical history and the remaining six studies found no significant change in performance. Two studies used the free response paradigm with both reporting clinical history increased location sensitivity, decreased specificity and had no overall change in diagnostic performance. The disease spectrum of included cases was largely unreported and a balanced reading design was not used in 19 studies.

CONCLUSION

Most published studies found that clinical history improved diagnostic performance. More recent studies accounting for abnormality location and multiple abnormalities showed an increase in false positives and no significant change in overall diagnostic performance with clinical history.

Radiologists and Clinical Trials: Part 2: Practical Statistical Methods for Understanding and Monitoring Independent Reader Performance

Though many clinical trials rely on medical image evaluations for primary or key secondary endpoints, the methods to monitor reader performance are all too often mired in the legacy use of adjudication rates. If misused, this simple metric can be misleading and sometimes entirely contradictory. Furthermore, attempts to overcome the limitations of adjudication rates using de novo or ad hoc methods often ignore well-established research conducted over the last half-century and can lead to inaccurate conclusions or variable interpretations. Underperforming readers can be missed, expert readers retrained, or worse, replaced. This paper aims to standardize reader performance evaluations using proven statistical methods. Additionally, these methods will describe how to discriminate between scenarios of concern and normal medical interpretation variability. Statistical methods are provided for inter-reader and intra-reader variability and bias, including the adjudicator's bias. Finally, we have compiled guidelines for calculating correct sample sizes, considerations for intra-reader memory recall, and applying alternative designs for independent readers.

How to support dental students in reading radiographs: effects of a gaze-based compare-and-contrast intervention

In dental medicine, interpreting radiographs (i.e., orthopantomograms, OPTs) is an error-prone process, even in experts. Effective intervention methods are therefore needed to support students in improving their image reading skills for OPTs. To this end, we developed a compare-and-contrast intervention, which aimed at supporting students in achieving full coverage when visually inspecting OPTs and, consequently, obtaining a better diagnostic performance. The comparison entailed a static eye movement visualization (heat map) on an OPT showing full gaze coverage from a peer-model (other student) and another heat map showing a student's own gaze behavior. The intervention group (N = 38) compared five such heat map combinations, whereas the control group (N = 23) diagnosed five OPTs. Prior to the experimental variation (pre-test) and after it (post-test), students in both conditions searched for anomalies in OPTs while their gaze was recorded. Results showed that students in the intervention group covered more areas of the OPTs and looked less often and for a shorter amount of time at anomalies after the intervention. Furthermore, they fixated on low-prevalence anomalies earlier and high-prevalence anomalies later during the inspection. However, the students in the intervention group did not show any meaningful improvement in detection rate and made more false positive errors compared to the control group. Thus, the intervention guided visual attention but did not improve diagnostic performance substantially. Exploratory analyses indicated that further interventions should teach knowledge about anomalies rather than focusing on full coverage of radiographs.

How massed practice improves visual expertise in reading panoramic radiographs in dental students: An eye tracking study

The interpretation of medical images is an error-prone process that may yield severe consequences for patients. In dental medicine panoramic radiography (OPT) is a frequently used diagnostic procedure. OPTs typically contain multiple, diverse anomalies within one image making the diagnostic process very demanding, rendering students’ development of visual expertise a complex task. Radiograph interpretation is typically taught through massed practice; however, it is not known how effective this approach is nor how it changes students’ visual inspection of radiographs. Therefore, this study investigated how massed practice–an instructional method that entails massed learning of one type of material–affects processing of OPTs and the development of diagnostic performance. From 2017 to 2018, 47 dental students in their first clinical semester diagnosed 10 OPTs before and after their regular massed practice training, which is embedded in their curriculum. The OPTs contained between 3 to 26 to-be-identified anomalies. During massed practice they diagnosed 100 dental radiographs without receiving corrective feedback. The authors recorded students’ eye movements and assessed the number of correctly identified and falsely marked low- and high prevalence anomalies before and after massed practice. Massed practice had a positive effect on detecting anomalies especially with low prevalence (p < .001). After massed practice students covered a larger proportion of the OPTs (p < .001), which was positively related to the detection of low-prevalence anomalies (p = .04). Students also focused longer, more frequently, and earlier on low-prevalence anomalies after massed practice (p_s < .001). While massed practice improved visual expertise in dental students with limited prior knowledge, there is still substantial room for improvement. The results suggest integrating massed practice with more deliberate practice, where, for example, corrective feedback is provided, and support is adapted to students’ needs.

The effect of a digital training tool to aid chest image interpretation: Hybridising eye tracking technology and a decision support tool

INTRODUCTION

Eye tracking technology, checklists and search strategies have been demonstrated as useful aids in image interpretation. A training tool was developed, by the research team, which included these features. This study aimed to evaluate the effect of the training tool on participant image interpretation performance.

METHODS

The study was carried out with reporting radiographers who had either commenced training in chest image interpretation (n = 12) or were trained in musculoskeletal image interpretation (n = 23) (total n = 35). Participants were allocated to a control or intervention group. Participants completed an initial assessment at recruitment and re-attended nine months later for a follow-up assessment. The intervention group were given unlimited access to a digital training tool. During assessments participants interpreted 20 chest images whilst using eye tracking technology (total of 1400 images were interpreted). A confidence level was obtained from participants on their diagnosis and a questionnaire, to obtain demographic data, was completed following the assessment.

RESULTS

Improvements were seen in the confidence of intervention group participants (p < 0.05). False Positive (FP) scores decreased for both the control and intervention group (p < 0.05), this decrease was from 4.20 to 3.20 for the control group and from 5.87 to 3.27 for the intervention group. True Negative (TN) scores increased, from 5.13 to 6.73 for the intervention group (p < 0.05). Mean decision time decreased for both the control and intervention group.

CONCLUSION

The tool led to positive effects on participant performance and could be a useful aid in chest image interpretation learning.

IMPLICATIONS FOR PRACTICE

Improvements in performance were observed with a digital tool. The tool could improve image interpretation methods and training.

Detection of the intimal tear in aortic dissection and ulcer-like projection in intramural hematoma: usefulness of full-phase retrospective ECG-gated CT angiography

PURPOSE

To compare the accuracy of non-electrocardiogram (ECG)-gated CT angiography (CTA), single-diastolic-phase ECG-gated CTA, and full-phase ECG-gated CTA in detecting the intimal tear (IT) in aortic dissection (AD) and ulcer-like projection (ULP) in intramural hematoma (IMH).

MATERIALS AND METHODS

A total of 81 consecutive patients with AD and IMH of the thoracic aorta were included in this single-center retrospective study. Non-ECG-gated CTA, single-diastolic-phase ECG-gated CTA, and full-phase ECG-gated CTA were used to detect the presence of the IT and ULP in thoracic aortic regions including the ascending aorta, aortic arch, and proximal and distal descending aorta.

RESULTS

The accuracy of detecting the IT and ULP was significantly greater using full-phase ECG-gated CTA (88% [95% CI: 100%, 75%]) than non-ECG-gated CTA (72% [95% CI: 90%, 54%], P = 0.001) and single-diastolic-phase ECG-gated CTA (76% [95% CI: 93%, 60%], P = 0.008).

CONCLUSION

Full-phase ECG-gated CTA is more accurate in detecting the IT in AD and ULP in IMH, than non-ECG-gated CTA and single-diastolic-phase ECG-gated CTA.

The pop-up research centre - Challenges and opportunities

OBJECTIVES

This article sets out to describe the concept of the "pop-up" research centre as a means to promote and develop radiography research locally, nationally and internationally, and to empower professional colleagues to set up similar initiatives in the future.

KEY FINDINGS

A detailed overview of the development and management of "pop-up" research is provided based on the experiences of the authors, including specific examples. Matters such as study design, approvals, equipment and software, environment, participant recruitment and management, research teams and activity costs are discussed. Quantifiable benefits of "pop-up" research such as resultant peer reviewed publications, development of researchers' skills and potential collaborations are described. A number of "soft skill" benefits are also apparent and include enhanced organisational profiles, team building and the development of leadership skills.

CONCLUSIONS

"Pop-up" research centres are a valuable option for conducting research and offer the radiography profession an achievable mechanism to increase and enhance research activity. However, careful planning and execution are essential.

Left myocardial wall measurements on postmortem imaging compared to autopsy

PURPOSE

The aims of this study were, firstly, to determine the relationship of left ventricular wall thickness (LVWT) measurements between postmortem computed tomography (PMCT) and postmortem magnetic resonance imaging (PMMR) and, secondly, to assess the utility of postmortem imaging for LVWT measurements compared to autopsy.

MATERIALS AND METHODS

All cases ≥18years old, with postmortem interval ≤4days, cardiac PMCT, PMMR, and full forensic autopsy, were reviewed in our database retrospectively. Exclusion criteria were gas accumulations in the myocardial wall and cardiac trauma. LVWT on PMCT and PMMR was assessed. The measurements were repeated by the same rater after 2months. Autopsy reports were reviewed, and LVWT and pericardial fluid volume measured at autopsy were noted. Pericardial fluid volume >50ml was determined positive for pericardial effusion.

RESULTS

A total of 113 cases were included in the study. Twelve cases had pericardial effusion. Intrarater reliability for imaging based LVWT was excellent. LVWT (free wall) was significantly larger on PMCT (18.3mm) compared to PMMR (17.6mm), but these measurements correlated positively. LVWT (anterior wall) was significantly larger on PMMR (15mm) than at autopsy (14mm), and these measurements also correlated positively. Pericardial effusions led to larger differences between PMMR and autopsy measurements, however without statistical significance.

DISCUSSION

There exist discrepancies between LVWT as measured on postmortem imaging and at autopsy. Specialists should be aware in order to not misinterpret imaging measurements.

Memory bias in observer-performance literature

The objective of our study was to determine how authors of published observer–performance experiments dealt with memory bias in study design. We searched American Journal of Roentgenology online and Radiology using “observer study” and “observer performance.” We included articles from 1970 or later that reported an observer performance experiment using human observers. We recorded the methods used by the authors to order presentation of the conditions being tested and images within sets for viewing. We recorded use and length of any time gap between viewings. We included 110 experiments. Forty-five used methods not subject to memory bias. Of 68 remaining experiments, 30 (44.1%) ordered the viewing of tested conditions to decrease memory bias. Fifteen (22.1%) ordered the tested conditions in ways that may create memory bias. Eleven (16.2%) intermixed the tested conditions. Forty-three (63.2%) used random or pseudorandom ordering of images within sets. Forty-six (67.6%) used a time gap (median 14 days) between viewings. Six (8.8%) did not use a time gap. Thirty-six (52.9%) did not indicate what methods they used in at least one studied parameter. Therefore, we conclude that 22.1% of the experiments could improve their methods of ordering tested conditions. Completeness of reporting could be improved by including more details regarding methods of ameliorating memory bias.

Intercountry analysis of breast density classification using visual grading

OBJECTIVE

Disagreement in mammographic breast density (MBD) assessment can impact breast cancer risk stratification, choices of further breast cancer screening intervals and pathways. This study examines whether intercountry MBD expectations and assessment approaches are associated with differences in MBD assessment.

METHODS

20 American Board of Radiology (ABR) examiners and 24 UK practitioners using the 4th edition BI-RADS^® lexicon assessed 40 mammogram cases of 20 females. 26 Royal Australian and New Zealand College of Radiologists (RANZCR) registered radiologists also assessed the same cases. Interobserver correlation and agreement were assessed using Spearman's correlation (ρ) and weighted kappa (κ_w), respectively.

RESULTS

Strong positive correlation was observed between the study cohorts on a binary scale (1-2 vs 3-4) [ABR examiners and RANZCR radiologists (ρ = 0.950); ABR examiners and UK practitioners (ρ = 0.940); and RANZCR radiologists and UK practitioners (ρ = 0.958)]. ABR and RANZCR radiologists demonstrated slight agreement [κ_w = 0.10; 95% confidence interval (CI) = -1.13-0.43], whereas ABR and UK practitioners showed a fair agreement [κ_w = 0.25; 95% CI = -0.42-0.61], and an almost perfect agreement was observed between RANZCR radiologists and UK practitioners [κ_w = 0.95; 95% CI = 0.91-0.97].

CONCLUSION

Findings demonstrate wide international and interobserver variability in MBD assessment. This level of variability underscores the need for automation and standardization of MBD assessment. Advances in knowledge: Intercountry analysis of MBD assessment shows variations, with less variation on the binary scale than on the 4-point scale. With this level of variation, automation and standardization of MBD assessment becomes more appropriate.

Improved cancer detection in automated breast ultrasound by radiologists using Computer Aided Detection

OBJECTIVE

To investigate the effect of dedicated Computer Aided Detection (CAD) software for automated breast ultrasound (ABUS) on the performance of radiologists screening for breast cancer.

METHODS

90 ABUS views of 90 patients were randomly selected from a multi-institutional archive of cases collected between 2010 and 2013. This dataset included normal cases (n=40) with >1year of follow up, benign (n=30) lesions that were either biopsied or remained stable, and malignant lesions (n=20). Six readers evaluated all cases with and without CAD in two sessions. CAD-software included conventional CAD-marks and an intelligent minimum intensity projection of the breast tissue. Readers reported using a likelihood-of-malignancy scale from 0 to 100. Alternative free-response ROC analysis was used to measure the performance.

RESULTS

Without CAD, the average area-under-the-curve (AUC) of the readers was 0.77 and significantly improved with CAD to 0.84 (p=0.001). Sensitivity of all readers improved (range 5.2-10.6%) by using CAD but specificity decreased in four out of six readers (range 1.4-5.7%). No significant difference was observed in the AUC between experienced radiologists and residents both with and without CAD.

CONCLUSIONS

Dedicated CAD-software for ABUS has the potential to improve the cancer detection rates of radiologists screening for breast cancer.

Radiologists remember mountains better than radiographs, or do they?

Expertise with encoding material has been shown to aid long-term memory for that material. It is not clear how relevant this expertise is for image memorability (e.g., radiologists' memory for radiographs), and how robust over time. In two studies, we tested scene memory using a standard long-term memory paradigm. One compared the performance of radiologists to naïve observers on two image sets, chest radiographs and everyday scenes, and the other radiologists' memory with immediate as opposed to delayed recognition tests using musculoskeletal radiographs and forest scenes. Radiologists' memory was better than novices for images of expertise but no different for everyday scenes. With the heterogeneity of image sets equated, radiologists' expertise with radiographs afforded them better memory for the musculoskeletal radiographs than forest scenes. Enhanced memory for images of expertise disappeared over time, resulting in chance level performance for both image sets after weeks of delay. Expertise with the material is important for visual memorability but not to the same extent as idiosyncratic detail and variability of the image set. Similar memory decline with time for images of expertise as for everyday scenes further suggests that extended familiarity with an image is not a robust factor for visual memorability.

Observer Variability in BI-RADS Ultrasound Features and Its Influence on Computer-Aided Diagnosis of Breast Masses

Objective:

Computer classification of sonographic BI-RADS features can aid differentiation of the malignant and benign masses. However, the variability in the diagnosis due to the differences in the observed features between the observations is not known. The goal of this study is to measure the variation in sonographic features between multiple observations and determine the effect of features variation on computer-aided diagnosis of the breast masses.

Materials and Methods:

Ultrasound images of biopsy proven solid breast masses were analyzed in three independent observations for BI-RADS sonographic features. The BI-RADS features from each observation were used with Bayes classifier to determine probability of malignancy. The observer agreement in the sonographic features was measured by kappa coefficient and the difference in the diagnostic performances between observations was determined by the area under the ROC curve, A_z, and interclass correlation coefficient.

Results:

While some features were repeatedly observed, κ = 0.95, other showed a significant variation, κ = 0.16. For all features, combined intra-observer agreement was substantial, κ = 0.77. The agreement, however, decreased steadily to 0.66 and 0.56 as time between the observations increased from 1 to 2 and 3 months, respectively. Despite the variation in features between observations the probabilities of malignancy estimates from Bayes classifier were robust and consistently yielded same level of diagnostic performance, A_z was 0.772 – 0.817 for sonographic features alone and 0.828 – 0.849 for sonographic features and age combined. The difference in the performance, ΔA_z, between the observations for the two groups was small (0.003 – 0.044) and was not statistically significant (p < 0.05). Interclass correlation coefficient for the observations was 0.822 (CI: 0.787 – 0.853) for BI-RADS sonographic features alone and for those combined with age was 0.833 (CI: 0.800 – 0.862).

Conclusion:

Despite the differences in the BI- RADS sonographic features between different observations, the diagnostic performance of computer-aided analysis for differentiating breast masses did not change. Through continual retraining, the computer-aided analysis provides consistent diagnostic performance independent of the variations in the observed sonographic features.

Consistency of response and image recognition, pulmonary nodules

OBJECTIVE

To investigate the effect of recognition of a previously encountered radiograph on consistency of response in localized pulmonary nodules.

METHODS

13 radiologists interpreted 40 radiographs each to locate pulmonary nodules. A few days later, they again interpreted 40 radiographs. Half of the images in the second set were new. We asked the radiologists whether each image had been in the first set. We used Fisher's exact test and Kruskal-Wallis test to evaluate the correlation between recognition of an image and consistency in its interpretation. We evaluated the data using all possible recognition levels-definitely, probably or possibly included vs definitely, probably or possibly not included by collapsing the recognition levels into two and by eliminating the "possibly included" and "possibly not included" scores.

RESULTS

With all but one of six methods of looking at the data, there was no significant correlation between consistency in interpretation and recognition of the image. When the possibly included and possibly not included scores were eliminated, there was a borderline statistical significance (p = 0.04) with slightly greater consistency in interpretation of recognized than that of non-recognized images.

CONCLUSION

We found no convincing evidence that radiologists' recognition of images in an observer performance study affects their interpretation on a second encounter.

ADVANCES IN KNOWLEDGE

Conscious recognition of chest radiographs did not result in a greater degree of consistency in the tested interpretation than that in the interpretation of images that were not recognized.

Can prevalence expectations drive radiologists' behavior?

RATIONALE AND OBJECTIVES

To measure the effect of explicit prevalence expectation on the performance of experienced radiologists during image interpretation of pulmonary lesions on chest radiographs.

MATERIALS AND METHODS

Each of 22 experienced radiologists was allocated to one of three groups to interpret a set of 30 (15 abnormal) posteroanterior chest images on two occasions to decide if pulmonary lesions were present. Before each viewing, the radiologists were told that the images contained a specific number of abnormal images: group 1, 9 versus 15; group 2, 22 versus 15; and group 3, not told versus 15, respectively. Eye position metrics and receiver operating characteristics confidence ratings were compared for normal and abnormal images. An analysis of false-positive and false-negative decisions was also performed.

RESULTS

For normal images, at higher prevalence expectation, significant increases were noted for duration of image scrutiny (group 1: P = .0004; group 2: P = .007; and group 3: P = .003) and number of fixations per image (group 1: P = .0006; group 2: P = .0004; and group 3: P = .0001). Also for normal images, group 1 demonstrated a significant increase (P = .038) in average confidence ratings when prevalence expectation increased. For abnormal images, at higher prevalence expectation, significant increases were noted for duration of image scrutiny in group 1 (P = .005) and number of fixations per image in group 1 (P = .01) and group 2 (P = .003).

CONCLUSIONS

Confidence ratings and visual search of the expert radiologists appear to be affected by changing prevalence expectations. The impact of prevalence expectation appears to be more apparent for normal images.

Mammography test sets: reading location and prior images do not affect group performance

AIM

To examine how the location where reading takes place and the availability of prior images can affect performance in breast test-set reading.

MATERIALS AND METHODS

Under optimized viewing conditions, 10 expert screen readers each interpreted a reader-specific set of images containing 200 mammographic cases. Readers, randomly divided into two groups read images under one of two pairs of conditions: clinical read with prior images and laboratory read with prior images; laboratory read with prior images and laboratory read without prior images. Region-of-interest (ROI) figure-of-merit (FOM) was analysed using JAFROC software. Breast side-specific sensitivity and specificity were tested using Wilcoxon matched-pairs signed rank tests. Agreement between pairs of readings was measured using Kendall's coefficient of concordance.

RESULTS

Group performances between test-set readings demonstrated similar ROI FOMs, sensitivity and specificity median values, and acceptable levels of agreement between pairs of readings were shown (W = 0.75-0.79, p < 0.001) for both pairs of reading conditions. On an individual reader level, two readers demonstrated significant decreases (p < 0.05) in ROI FOMs when prior images were unavailable. Reading location had an inconsistent impact on individual performance.

CONCLUSION

Reading location and availability of prior images did not significantly alter group performance.

Memory for previously viewed radiographs and the effect of prior knowledge of memory task

RATIONALE AND OBJECTIVES

To investigate the effect of being forewarned that they would be asked to identify repeated images on radiologists' recognition of previously interpreted versus new chest radiographs.

MATERIALS AND METHODS

Thirteen radiologists viewed 60 posterior-anterior chest radiographs, 31 with and 29 without nodules, in two sets of 40 images each. Eight radiologists were forewarned and five radiologists were not forewarned of the memory task. Twenty images in each of the two sets were unique to each set and 20 images occurred in both sets. The readers indicated the presence or absence of any nodules during both readings, and in the second reading session they also indicated whether they thought each image had also occurred in the first reading.

RESULTS

There was no significant difference in recognition memory performance between forewarned and not-forewarned readers. Overall accuracy in distinguishing previously-viewed from new images was 60.7%.

CONCLUSIONS

Being forewarned of the memory task did not improve recognition memory.

Bone Windows for Distinguishing Malignant from Benign Primary Bone Tumors on FDG PET/CT

Objective. The default window setting on PET/CT workstations is soft tissue. This study investigates whether bone windowing and hybrid FDG PET/CT can help differentiate between malignant and benign primary bone tumors. Materials and methods. A database review included 98 patients with malignant (n=64) or benign primary bone (n=34) tumors. The reference standard was biopsy for malignancies and biopsy or >1 year imaging follow-up of benign tumors. Three radiologists and/or nuclear medicine physicians blinded to diagnosis and other imaging viewed the lesions on CT with bone windows (CT-BW) without and then with PET (PET/CT-BW), and separate PET-only images for malignancy or benignity. Three weeks later the tumors were viewed on CT with soft tissue windows (CT-STW) without and then with PET (PET/CT-STW). Results. Mean sensitivity and specificity for identifying malignancies included: CT-BW: 96%, 90%; CT-STW: 90%, 90%; PET/CT-BW: 95%, 85%, PET/CT-STW: 95%, 86% and PET-only: 96%, 75%, respectively. CT-BW demonstrated higher specificity than PET-only and PET/CT-BW (p=0.0005 and p=0.0103, respectively) and trended toward higher sensitivity than CT-STW (p=0.0759). Malignant primary bone tumors were more avid than benign lesions overall (p<0.0001) but the avidity of benign aggressive lesions (giant cell tumors and Langerhans Cell Histiocytosis) trended higher than the malignancies (p=0.08). Conclusion. Bone windows provided high specificity for distinguishing between malignant and benign primary bone tumors and are recommended when viewing FDG PET/CT.

If you don't find it often, you often don't find it: why some cancers are missed in breast cancer screening

Mammography is an important tool in the early detection of breast cancer. However, the perceptual task is difficult and a significant proportion of cancers are missed. Visual search experiments show that miss (false negative) errors are elevated when targets are rare (low prevalence) but it is unknown if low prevalence is a significant factor under real world, clinical conditions. Here we show that expert mammographers in a real, low-prevalence, clinical setting, miss a much higher percentage of cancers than are missed when the mammographers search for the same cancers under high prevalence conditions. We inserted 50 positive and 50 negative cases into the normal workflow of the breast cancer screening service of an urban hospital over the course of nine months. This rate was slow enough not to markedly raise disease prevalence in the radiologists' daily practice. Six radiologists subsequently reviewed all 100 cases in a session where the prevalence of disease was 50%. In the clinical setting, participants missed 30% of the cancers. In the high prevalence setting, participants missed just 12% of the same cancers. Under most circumstances, this low prevalence effect is probably adaptive. It is usually wise to be conservative about reporting events with very low base rates (Was that a flying saucer? Probably not.). However, while this response to low prevalence appears to be strongly engrained in human visual search mechanisms, it may not be as adaptive in socially important, low prevalence tasks like medical screening. While the results of any one study must be interpreted cautiously, these data are consistent with the conclusion that this behavioral response to low prevalence could be a substantial contributor to miss errors in breast cancer screening.

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.