CT colonography: size reduction of submerged colorectal polyps due to electronic cleansing and CT-window settings.

OBJECTIVES: To assess whether electronic cleansing (EC) of tagged residue and different computed tomography (CT) windows influence the size of colorectal polyps in CT colonography (CTC). METHODS: A database of 894 colonoscopy-validated CTC datasets of a low-prevalence cohort was retrospectively reviewed to identify patients with polyps ≥6 mm that were entirely submerged in tagged residue. Ten radiologists independently measured the largest diameter of each polyp, two-dimensionally, before and after EC in colon, bone, and soft-tissue-windows, in randomised order. Differences in size and polyp count before and after EC were calculated for size categories ≥6 mm and ≥10 mm. Statistical testing involved 95% confidence interval, intraclass correlation and mixed-model ANOVA. RESULTS: Thirty-seven patients with 48 polyps were included. Mean polyp size before EC was 9.8 mm in colon, 9.9 mm in bone and 8.2 mm in soft-tissue windows. After EC, the mean polyp size decreased significantly to 9.4 mm in colon, 9.1 mm in bone and 7.1 mm in soft-tissue windows. Compared to unsubtracted colon windows, EC, performed in colon, bone and soft-tissue windows, led to a shift of 6 (12,5%), 10 (20.8%) and 25 (52.1%) polyps ≥6 mm into the next smaller size category, thus affecting patient risk stratification. CONCLUSIONS: EC and narrow CT windows significantly reduce the size of polyps submerged in tagged residue. Polyp measurements should be performed in unsubtracted colon windows. KEY POINTS: • EC significantly reduces the size of polyps submerged in tagged residue. • Abdominal CT-window settings significantly underestimate 2D sizes of submerged polyps. • Size reduction in EC is significantly greater in narrow than wide windows. • Underestimation of polyp size due to EC may lead to inadequate treatment. • Polyp measurements should be performed in unsubtracted images using a colon window

The role of optical and virt ual colonoscopy in colorectal neoplasms

Purpose: High prevalence of colon carcinoma explains the continued high mortality rate of this disease.Utilizing a strategy of virtual colonoscopy (VC) in patients aged over 50 years with optical colonoscopy (OC) following-up for removal of detected adenomatous polyps may result in lowering the colon cancer death rate. However, VC diagnostic potential has not been widely recognized yet.Material and methods: This article reviews the currently available in diagnostic options in colorectal neoplasms and discusses their advantages and drawbacks.Results: VC has many advantages over the existing options and its several drawbacks can be mitigated so that it would become a valuable diagnostic modality. A strategy that utilizes VC for screening of patients over the age of 50 years and OC for screening high-risk individuals and those with positive VC findings would result in a significantly reduced colon cancer mortality rate.Conclusion: Both OC and VC (i.e., CTC and MRC) progress toward the clinical needs as new technologies are developed and applied to overcome the drawbacks of these diagnostic methods. Each of them plays a unique role for colon cancer prevention

Eye-tracking the moving medical image: Development and investigation of a novel investigational tool for CT Colonography

Colorectal cancer remains the third most common cancer in the UK but the second leading cause of cancer death with >16,000 dying per year. Many advances have been made in recent years in all areas of investigation for colorectal cancer, one of the more notable being the widespread introduction of CT Colonography (CTC). CTC has rapidly established itself as a cornerstone of diagnosis for colonic neoplasia and much work has been done to standardise and assure quality in practice in both the acquisition and interpretation of the technique. A novel feature of CTC is the presentation of imaging in both traditional 2D and the ‘virtual’ 3D endoluminal formats. This thesis looks at expanding our understanding of and improving our performance in utilizing the endoluminal 3D view. We present and develop novel metrics applicable to eye-tracking the moving image, so that the complex dynamic nature of 3D endoluminal fly-through interpretation can be captured. These metrics are then applied to assess the effect of important elements of image interpretation, namely, reader experience, the effect of the use Computer Aided Detection (CAD) and the influence of the expected prevalence of abnormality. We review our findings with reference to the literature of eye tracking within medical imaging. In the co-registration section we apply our validated computer-assisted registration algorithm to the matching of 3D endoluminal colonic locations between temporally separate datasets, assessing its accuracy as an aid to colonic polyp surveillance with CTC

Facilitating Colorectal Cancer Diagnosis with Computed Tomographic Colonography

Computed tomographic colonography (CTC) is a diagnostic technique involving helical volume acquisition of the cleansed, distended colorectum to detect colorectal cancer or potentially premalignant polyps. This Thesis summarises the evidence base, identifies areas in need of further research, quantifies sources of bias and presents novel techniques to facilitate colorectal cancer diagnosis using CTC. CTC literature is reviewed to justify the rationale for current implementation and to identify fruitful areas for research. This confirms excellent diagnostic performance can be attained providing CTC is interpreted by trained, experienced observers employing state-of-the-art implementation. The technique is superior to barium enema and consequently, it has been embraced by radiologists, clinicians and health policy-makers. Factors influencing generalisability of CTC research are investigated, firstly with a survey of European educational workshop participants which revealed limited CTC experience and training, followed by a systematic review exploring bias in research studies of diagnostic test accuracy which established that studies focussing on these aspects were lacking. Experiments to address these sources of bias are presented, using novel methodology: Conjoint analysis is used to ascertain patients‘ and clinicians’ attitudes to false-positive screening diagnoses, showing that both groups overwhelmingly value sensitivity over specificity. The results inform a weighted statistical analysis for CAD which is applied to the results of two previous studies showing the incremental benefit is significantly higher for novices than experienced readers. We have employed eye-tracking technology to establish the visual search patterns of observers reading CTC, demonstrated feasibility and developed metrics for analysis. We also describe development and validation of computer software to register prone and supine endoluminal surface locations demonstrating accurate matching of corresponding points when applied to a phantom and a generalisable, publically available, CTC database. Finally, areas in need of future development are suggested

Registration of prone and supine CT colonography images and its clinical application

Computed tomographic (CT) colonography is a technique for detecting bowel cancer and potentially precancerous polyps. CT imaging is performed on the cleansed and insufflated bowel in order to produce a virtual endoluminal representation similar to optical colonoscopy. Because fluids and stool can mimic pathology, images are acquired with the patient in both prone and supine positions. Radiologists then match endoluminal locations visually between the two acquisitions in order to determine whether pathology is real or not. This process is hindered by the fact that the colon can undergo considerable deformation between acquisitions. Robust and accurate automated registration between prone and supine data acquisitions is therefore pivotal for medical interpretation, but a challenging problem. The method proposed in this thesis reduces the complexity of the registration task of aligning the prone and supine CT colonography acquisitions. This is done by utilising cylindrical representations of the colonic surface which reflect the colon's specific anatomy. Automated alignment in the cylindrical domain is achieved by non-rigid image registration using surface curvatures, applicable even when cases exhibit local luminal collapses. It is furthermore shown that landmark matches for initialisation improve the registration's accuracy and robustness. Additional performance improvements are achieved by symmetric and inverse-consistent registration and iteratively deforming the surface in order to compensate for differences in distension and bowel preparation. Manually identified reference points in human data and fiducial markers in a porcine phantom are used to validate the registration accuracy. The potential clinical impact of the method has been evaluated using data that reflects clinical practise. Furthermore, correspondence between follow-up CT colonography acquisitions is established in order to facilitate the clinical need to investigate polyp growth over time. Accurate registration has the potential to both improve the diagnostic process and decrease the radiologist's interpretation time. Furthermore, its result could be integrated into algorithms for improved computer-aided detection of colonic polyps