Darren Boone

Surface Visualization at CT Colonography Simulated Colonoscopy: Effect of Varying Field of View and Retrograde View

OBJECTIVES:Colonoscopy is the gold standard for diagnosis of mucosal disease, but has a recognized “miss rate” for polyps probably because some lesions lie in areas of the colonic surface that do not enter the field of view. Using CT colonography (CTC) simulation this pilot study aimed to determine how much colonic surface is visualized with a standard, modern optical colonoscope (field of view 140°) with or without the addition of a retrograde viewing auxiliary imaging device (RVAID; 135°) and of a wide-angle (170°) colonoscope.METHODS:Supine CTC datasets for 20 patients were reviewed with customized CTC software that calculated the percentage of colonic surface seen and number and area of nonvisualized “missed” areas at a unidirectional three-dimensional (3D) endoluminal flythrough, approximating the view obtained at optical colonoscopy. The field of view could be varied from 0–180°. The combination of a colonoscope with RVAID was simulated by an additional flythrough facing the rectum.RESULTS:Mean colonic surface area was 2,743 ± 759 cm2. Percentage colonic surface visualized at simulated optical colonoscopy with a 90°, 140°, and 170° field of view was 68.0 ± 5.2%, 86.6 ± 3.3%, and 92.2 ± 3.3%, respectively, P < 0.001. Simulation of a 140° colonoscope with an RVAID resulted in almost complete surface visualization, 98.7 ± 0.5%, with total missed area reduced 10-fold compared with a 170° colonoscope, P < 0.001.CONCLUSIONS:CTC simulated 140° optical colonoscopy visualizes over 85% of the colonic surface. 170° colonoscopy provides a modest reduction in missed surface and the simulated addition of RVAIDs appears beneficial.

Registration of the endoluminal surfaces of the colon derived from prone and supine CT colonography

PURPOSE Computed tomographic (CT) colonography is a relatively new technique for detecting bowel cancer or potentially precancerous polyps. CT scanning is combined with three-dimensional (3D) image reconstruction to produce a virtual endoluminal representation similar to optical colonoscopy. Because retained fluid and stool can mimic pathology, CT data are acquired with the bowel cleansed and insufflated with gas and patient in both prone and supine positions. Radiologists then match visually endoluminal locations between the two acquisitions in order to determine whether apparent pathology is real or not. This process is hindered by the fact that the colon, essentially a long tube, can undergo considerable deformation between acquisitions. The authors present a novel approach to automatically establish spatial correspondence between prone and supine endoluminal colonic surfaces after surface parameterization, even in the case of local colon collapse. METHODS The complexity of the registration task was reduced from a 3D to a 2D problem by mapping the surfaces extracted from prone and supine CT colonography onto a cylindrical parameterization. A nonrigid cylindrical registration was then performed to align the full colonic surfaces. The curvature information from the original 3D surfaces was used to determine correspondence. The method can also be applied to cases with regions of local colonic collapse by ignoring the collapsed regions during the registration. RESULTS Using a development set, suitable parameters were found to constrain the cylindrical registration method. Then, the same registration parameters were applied to a different set of 13 validation cases, consisting of 8 fully distended cases and 5 cases exhibiting multiple colonic collapses. All polyps present were well aligned, with a mean (+/- std. dev.) registration error of 5.7 (+/- 3.4) mm. An additional set of 1175 reference points on haustral folds spread over the full endoluminal colon surfaces resulted in an error of 7.7 (+/- 7.4) mm. Here, 82% of folds were aligned correctly after registration with a further 15% misregistered by just onefold. CONCLUSIONS The proposed method reduces the 3D registration task to a cylindrical registration representing the endoluminal surface of the colon. Our algorithm uses surface curvature information as a similarity measure to drive registration to compensate for the large colorectal deformations that occur between prone and supine data acquisitions. The method has the potential to both enhance polyp detection and decrease the radiologists interpretation time.

Tracking Eye Gaze during Interpretation of Endoluminal Three-dimensional CT Colonography: Visual Perception of Experienced and Inexperienced Readers

PURPOSE To identify and compare key stages of the visual process in experienced and inexperienced readers and to examine how these processes are used to search a moving three-dimensional ( 3D three-dimensional ) image and their relationship to false-negative errors. MATERIALS AND METHODS Institutional review board research ethics approval was granted to use anonymized computed tomographic (CT) colonographic data from previous studies and to obtain eye-tracking data from volunteers. Sixty-five radiologists (27 experienced, 38 inexperienced) interpreted 23 endoluminal 3D three-dimensional CT colonographic videos. Eye movements were recorded by using eye tracking with a desk-mounted tracker. Readers indicated when they saw a polyp by clicking a computer mouse. Polyp location and boundary on each video frame were quantified and gaze data were related to the polyp boundary for each individual reader and case. Predefined metrics were quantified and used to describe and compare visual search patterns between experienced and inexperienced readers by using multilevel modeling. RESULTS Time to first pursuit was significantly shorter in experienced readers (hazard ratio, 1.22 [95% confidence interval: 1.04, 1.44]; P = .017) but other metrics were not significantly different. Regardless of expertise, metrics such as assessment, identification period, and pursuit times were extended in videos where polyps were visible on screen for longer periods of time. In 97% (760 of 787) of observations, readers correctly pursued polyps. CONCLUSION Experienced readers had shorter time to first eye pursuit, but many other characteristics of eye tracking were similar between experienced and inexperienced readers. Readers pursued polyps in 97% of observations, which indicated that errors during interpretation of 3D three-dimensional CT colonography in this study occurred in either the discovery or the recognition phase, but rarely in the scanning phase of radiologic image inspection.

Polyp Characteristics Correctly Annotated by Computer-aided Detection Software but Ignored by Reporting Radiologists during CT Colonography

PURPOSE To retrospectively describe the characteristics of polyps incorrectly dismissed by radiologists despite appropriate computer-aided detection (CAD) prompting during computed tomographic (CT) colonography. MATERIALS AND METHODS Ethics committee approval and patient informed consent were obtained from institutions that provided the data sets used in this HIPAA-compliant study. A total of 111 polyps that had a diameter of at least 6 mm and were detected with CAD were collated from three previous studies in which researchers investigated radiologist performance with and without CAD (total, 25 readers). Two new observers graded each polyp with predefined criteria, including polyp size, morphology, and location; data set quality; ease of visualization; tagging use and polyp coating; colonic curvature; CAD mark obscuration; and number of false-positive findings. The 86 polyps that were missed before CAD (those that were unreported by one or more original readers) were divided into those that remained unreported after CAD (no CAD gain, n = 36) and those that were reported correctly by at least one additional reader (CAD gain, n = 50). Logistic-regression analysis and the Fisher exact and Mann-Whitney tests were used to compare the results of both groups with each other and with a control group of 25 polyps, all of which were detected by readers without CAD. RESULTS Before CAD, polyps 10 mm in diameter or larger, those that were rated easy to visualize, and those that were uncoated by tagged fluid were less likely to be missed (72%, 76%, and 80% of control polyps vs 43%, 43%, and 59% of missed polyps, respectively; P < .001, P < .01, and P < .03, respectively). After CAD, the odds of CAD gain decreased with increasing polyp size (odds ratio, 0.92; 95% confidence interval: 0.85, 1.00; P = .04) and irregular morphology (odds ratio, 0.28; 95% confidence interval: 0.08, 0.92; P = .04). CONCLUSION Larger irregular polyps are a common source of incorrect radiologist dismissal, despite correct CAD prompting.

Detection of Extracolonic Pathologic Findings with CT Colonography: A Discrete Choice Experiment of Perceived Benefits versus Harms

PURPOSE To determine the maximum rate of false-positive diagnoses that patients and health care professionals were willing to accept in exchange for detection of extracolonic malignancy by using computed tomographic (CT) colonography for colorectal cancer screening. MATERIALS AND METHODS After obtaining ethical approval and informed consent, 52 patients and 50 health care professionals undertook two discrete choice experiments where they chose between unrestricted CT colonography that examined intra- and extracolonic organs or CT colonography restricted to the colon, across different scenarios. The first experiment detected one extracolonic malignancy per 600 cases with a false-positive rate varying across scenarios from 0% to 99.8%. One experiment examined radiologic follow-up generated by false-positive diagnoses while the other examined invasive follow-up. Intracolonic performance was identical for both tests. The median tipping point (maximum acceptable false-positive rate for extracolonic findings) was calculated overall and for both groups by bootstrap analysis. RESULTS The median tipping point for radiologic follow-up occurred at a false-positive rate greater than 99.8% (interquartile ratio [IQR], 10 to >99.8%). Participants would tolerate at least a 99.8% rate of unnecessary radiologic tests to detect an additional extracolonic malignancy. The median tipping-point for invasive follow-up occurred at a false-positive rate of 10% (IQR, 2 to >99.8%). Tipping points were significantly higher for patients than for health care professionals for both experiments (>99.8 vs 40% for radiologic follow-up and >99.8 vs 5% for invasive follow-up, both P < .001). CONCLUSION Patients and health care professionals are willing to tolerate high rates of false-positive diagnoses with CT colonography in exchange for diagnosis of extracolonic malignancy. The actual specificity of screening CT colonography for extracolonic findings in clinical practice is likely to be highly acceptable to both patients and health care professionals. Online supplemental material is available for this article.

Method for Tracking Eye Gaze during Interpretation of Endoluminal 3D CT Colonography: Technical Description and Proposed Metrics for Analysis

PURPOSE To develop an eye-tracking method applicable to three-dimensional (3D) images, where the abnormality is both moving and changing in size. MATERIALS AND METHODS Research ethics committee approval was granted to record eye-tracking data from six inexperienced readers who inspected eight short (<30 seconds) endoluminal fly-through videos extracted from computed tomographic (CT) colonography examinations. Cases included true-positive and false-positive polyp detections from a previous study (polyp diameters, 5-25 mm). Eye tracking was performed with a desk-mounted tracker, and readers indicated when they saw a polyp with a mouse click. The polyp location on each video frame was quantified subsequently by using a circular mask. Gaze data related to each video frame were calculated relative to the visible polyp boundary and used to identify eye movements that pursue a polyp target as it changes size and position during fly-through. Gaze data were then related to positive polyp detections by readers. RESULTS Tracking eye gaze on moving 3D images was technically feasible. Gaze was successfully classified by using pursuit analysis, and pursuit-based gaze metrics were able to help discriminate different reader search behaviors and methods of allocating visual attention during polyp identification. Of a total of 16 perceptual errors, 15 were recognition errors. There was only one visual search error. The largest polyp (25 mm) was seen but not recognized by five of six readers. CONCLUSION Tracking a readers gaze during endoluminal interpretation of 3D data sets is technically feasible and can be described with pursuit-based metrics. Perceptual errors can be classified into visual search errors and recognition errors. Recognition errors are more frequent in inexperienced readers.

Public perceptions and preferences for CT colonography or colonoscopy in colorectal cancer screening

OBJECTIVES To examine public perceptions of and preferences for colonoscopy vs. CT colonography (CTC) as technologies for colorectal cancer (CRC) screening. METHODS Six discussion groups were carried out with 30 adults aged 49-60 years (60% female). Information about different aspects of the tests (e.g. sensitivity, practical issues) was presented sequentially using a semi-structured, step-by-step topic guide. Discussions were recorded and analyzed using framework analysis. RESULTS CTC was favored on the parameters of invasiveness, extra-colonic evaluation and interference with daily life, whereas sensitivity, avoiding false-positives and the capacity to remove polyps immediately were perceived to be important advantages of colonoscopy. Ultimately, there was no strong preference for either test: with 46% preferring colonoscopy vs. 42% for CTC. CONCLUSION With comprehensive information, colonoscopy and CTC were seen as having different advantages and disadvantages, yielding no clear preferences between the two. The sensitivity of colonoscopy was a decisive factor for some people, but the lower invasiveness of CTC was seen as an asset in the screening context. PRACTICE IMPLICATIONS CTC may be an acceptable alternative to colonoscopy in CRC screening. Healthcare professionals working in the screening context should be sensitive to the range of characteristics that can determine preferences for CRC screening tests.

Systematic review: bias in imaging studies - the effect of manipulating clinical context, recall bias and reporting intensity.

ObjectivesTo perform a systematic review of diagnostic test accuracy studies which manipulate or investigate the context of interpretation. In particular, those which modify or conceal sample characteristics (e.g. disease prevalence or reporting intensity) or research setting (“laboratory” versus “field”). We also investigated recall bias.MethodsWe searched the biomedical literature to March 2010 using 3 complementary strategies. Inclusion criteria were: imaging studies quantifying the effect on diagnosis of modifying the context of observers’ interpretations, varying disease prevalence, concealing sample characteristics, reporting intensity and recall bias.Results11247 abstracts were reviewed, 201 full texts examined and 12 ultimately included. There were 5 to 9520 patients and 2 to 129 observers per study. Nine studies investigated clinical review bias of sample level information. Only 3 studies investigated prevalence, 2 of which investigated maximum enrichment well below the levels often used by researchers. We identified no research specifically directed at concealing disease prevalence. Available research found no evidence of recall bias or “washout” on study results.ConclusionsSeveral sources of bias central to the design of diagnostic test accuracy studies are poorly researched; the implications for evidence-based-practice remain uncertain. Research is suggested to guide methodological design, particularly in the context of screening.Key PointsImaging research studies often ignore the possible effect of disease prevalenceIt is unclear how the expectation of disease influences radiological interpretationThe potential effect of observer recall bias is poorly researchedSuch factors might introduce bias into radiological research methodologyThis systematic review attempts to illustrate these points

Public preferences for colorectal cancer screening tests: a review of conjoint analysis studies

A wide range of screening technologies is available for colorectal cancer screening. There is demand to discover public preferences for these tests on the rationale that tailoring screening to preferences may improve uptake. This review describes a type of study (conjoint analysis) used to assess people’s preferences for colorectal cancer screening tests and critically evaluates research quality using a recently published set of guidelines. Most primary studies assessed preferences for colonoscopy and fecal occult blood testing but newer technologies (e.g., capsule endoscopy) have not yet been evaluated. Although studies often adhered to guidelines, there was limited correspondence between stated preferences and actual screening behavior. Future research should investigate how studies can go beyond the guidelines in order to improve this and also explore how test preferences may differ by important population subgroups.

Quantifying public preferences for different bowel preparation options prior to screening CT colonography: a discrete choice experiment

Objectives CT colonography (CTC) may be an acceptable test for colorectal cancer screening but bowel preparation can be a barrier to uptake. This study tested the hypothesis that prospective screening invitees would prefer full-laxative preparation with higher sensitivity and specificity for polyps, despite greater burden, over less burdensome reduced-laxative or non-laxative alternatives with lower sensitivity and specificity. Design Discrete choice experiment. Setting Online, web-based survey. Participants 2819 adults (45–54 years) from the UK responded to an online invitation to take part in a cancer screening study. Quota sampling ensured that the sample reflected key demographics of the target population and had no relevant bowel disease or medical qualifications. The analysis comprised 607 participants. Interventions After receiving information about screening and CTC, participants completed 3–4 choice scenarios. Scenarios showed two hypothetical forms of CTC with different permutations of three attributes: preparation, sensitivity and specificity for polyps. Primary outcome measures Participants considered the trade-offs in each scenario and stated their preferred test (or chose neither). Results Preparation and sensitivity for polyps were both significant predictors of preferences (coefficients: −3.834 to −6.346 for preparation, 0.207–0.257 for sensitivity; p<0.0005). These attributes predicted preferences to a similar extent. Realistic specificity values were non-significant (−0.002 to 0.025; p=0.953). Contrary to our hypothesis, probabilities of selecting tests were similar for realistic forms of full-laxative, reduced-laxative and non-laxative preparations (0.362–0.421). However, they were substantially higher for hypothetical improved forms of reduced-laxative or non-laxative preparations with better sensitivity for polyps (0.584–0.837). Conclusions Uptake of CTC following non-laxative or reduced-laxative preparations is unlikely to be greater than following full-laxative preparation as perceived gains from reduced burden may be diminished by reduced sensitivity. However, both attributes are important so a more sensitive form of reduced-laxative or non-laxative preparation might improve uptake substantially.