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 radiologist's interpretation time. (C) 2011 American Association of Physicists in Medicine. [DOI: 10.1118/1.3577603

Fundamental Elements for Successful Performance of CT Colonography (Virtual Colonoscopy)

There are many factors affecting the successful performance of CT colonography (CTC). Adequate colonic cleansing and distention, the optimal CT technique and interpretation with using the newest CTC software by a trained reader will help ensure high accuracy for lesion detection. Fecal and fluid tagging may improve the diagnostic accuracy and allow for reduced bowel preparation. Automated carbon dioxide insufflation is more efficient and may be safer for colonic distention as compared to manual room air insufflation. CT scanning should use thin collimation of ≤3 mm with a reconstruction interval of ≤1.5 mm and a low radiation dose. There is not any one correct method for the interpretation of CTC; therefore, readers should be well-versed with both the primary 3D and 2D reviews. Polyps detected at CTC should be measured accurately and reported following the "polyp size-based" patient management system. The time-intensive nature of CTC and the limited resources for training radiologists appear to be the major barriers for implementing CTC in Korea

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

Feature extraction to aid disease detection and assessment of disease progression in CT and MR colonography

Computed tomographic colonography (CTC) is a technique employed to examine the whole colon for cancers and premalignant adenomas (polyps). Oral preparation is taken to fully cleanse the colon, and gas insufflation maximises the attenuation contrast between the enoluminal colon surface and the lumen. The procedure is performed routinely with the patient both prone and supine to redistribute gas and residue. This helps to differentiate fixed colonic pathology from mobile faecal residue and also helps discover pathology occluded by retained fluid or luminal collapse. Matching corresponding endoluminal surface locations with the patient in the prone and supine positions is therefore an essential aspect of interpretation by radiologists; however, interpretation can be difficult and time consuming due to the considerable colonic deformations that occur during repositioning. Hence, a method for automated registration has the potential to improve efficiency and diagnostic accuracy. I propose a novel method to establish correspondence between prone and supine CT colonography acquisitions automatically. The problem is first simplified by detecting haustral folds which are elongated ridgelike endoluminal structures and can be identified by curvature based measurements. These are subsequently matched using appearance based features, and their relative geometric relationships. It is shown that these matches can be used to find correspondence along the full length of the colon, but may also be used in conjunction with other registration methods to achieve a more robust and accurate result, explicitly addressing the problem of colonic collapse. The potential clinical value of this method has been assessed in an external clinical validation, and the application to follow-up CTC surveillance has been investigated. MRI has recently been applied as a tool to quantitatively evaluate the therapeutic response to therapy in patients with Crohn's disease, and is the preferred choice for repeated imaging. A primary biomarker for this evaluation is the measurement of variations of bowel wall thickness on changing from the active phase of the disease to remission; however, a poor level of interobserver agreement of measured thickness is reported and therefore a system for accurate, robust and reproducible measurements is desirable. I propose a novel method which will automatically track sections of colon, by estimating the positions of elliptical cross sections. Subsequently, estimation of the positions of the inner and outer bowel walls are made based on image gradient information and therefore a thickness measurement value can be extracted

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

Virtualna kolonoskopija i 3d rekonstrukcije u bolesnika s karcinomom kolona i rektuma

Introduction: Virtual endoscopy of the colon or virtual colonoscopy (VC) is a technique for postprocessing high resolution helical CT datasets. 3D surface rendering volume reconstruction that simulates endoscopic views of the inner surface of the colon was performed in real time by means of computer generated ray casting. VC may be performed together with 3D volume rendering (3DVR). VC can be applied in teaching, diagnostics, intervention planning or intraoperative navigation and as a non-invasive technique it is particularly useful when the patient cannot tolerate classical fiberoptic endoscopy. Objectives: To implement VC as a new technique of high resolution helical CT data postprocessing in screening, preoperative diagnostics and management and to discuss advantages and disadvantages of the method. Methods: VC and 3DVR in space analysis were performed using Syngo 2006G platform by Siemens Medical Systems in: a 46-year-old man with a spastic colon and some intestinal diverticula and polyps, a 65-year-old man who underwentendoscopic removal of a large colorectal polyp, a 64-year-old women with large circular cancer stenosis of the rectum and right hepatic lobe metastatic lesion, and a 52-year-old man with a large endoluminal cancer mass in the sigmoid colon. Virtual colonoscopy was performed in real time using ray casting algorithm with space leaping acceleration method. Siemens Somatom Emotion 16 scanner was used for image acquisition. Postprocessing of the images stored in DICOM format was done by dual Xeon workstation. Results: Fly through algorithm and 3DVR were performed on data sets created from axial CT images collected from multislice helical CT scanner archived in DICOM format. Fly through and 3DVR postprocessing produced a series of images that were analyzed by one radiologist, two surgeons and two physicians experienced in virtual endoscopy. Conclusion: VC is a useful non-invasive method in the assessment of malignant and benign lesions of colon. It may provide useful additional information for a surgeon during preoperative management. Furthermore, it allows three dimensional visualization in the lumen beyond areas of narrowing or stenosis and it gives a highly accurate representation of colorectal lesions. Its disadvantages are that it does not provide histology, it requires an air-mucosa interface to produce an image and it cannot identify functional lesions. Using VC, clinicians can appreciate not only the intraluminal proliferation of the tumor but also the extraluminal extension of the mass and its relation to the surrounding organs.Uvod: Virtualna endoskopija kolona ili virtualna kolonoskopija (VC) je metoda postprocesiranja podataka dobivenih kompjutoriziranom tomografijom visoke razlučivosti. VC simulira pogled pravog endoskopa na unutrašnju površinu debelog crijeva, a izvodi se u realnom vremenu na računalnim radnim stanicama s pomoću računalnog algoritma “ray casting”. VC se može izvoditi zajedno sa trodimenzionalnim volumnim renderiranjem (3DVR) koje daje 3D prikaz promatranog dijela tijela. VC se može koristiti u edukaciji, dijagnostici, planiranju endoskopskih zahvata ili operacija, te intraoperacijskoj navigaciji. Kao neinvazivna tehnika VC je naročito korisna ako bolesnik ne može podnijeti klasičnu fiberoptičku endoskopiju ili je ova kontraindicirana.. Ciljevi rada: Uvođenje VC kao nove metode postprocesiranja podataka dobivenih spiralnom kompjutoriziranom tomografijom visoke razlučivosti u ranu dijagnostiku (screening), prijeoperacijsku dijagnostiku i obradu bolesnika, te prikaz prednosti i nedostataka ove metode. Metode rada: VC i 3DVR učinjene su s pomoću specijaliziranog programskog paketa Syngo 2006G Platform proizvođača Siemens Medical Systems u: četrdesetšestogodišnjeg muškarca sa spastičnim kolonom te nekoliko intestinalnih divertikula i polipa, šezdesetpetogodišnjeg muškarca koji je podvrgnut endoskopskom uklanjanju velikog kolorektalnog polipa, šezdesetčetverogodišnje žene s opsežnom cirkularnom stenozom rektuma i metastazama u desnom hepatalnom režnju, te pedesetdvogodišnjeg muškarca s velikom endoluminalnim karcinomom u sigmoidnom kolonu. Virtualna kolonoskopija napravljena je u realnom vremenu s pomoću “ray casting” algoritma uz “space leaping” metodu akceleracije. Siemens Somatom Emotion 16 CT uređaj primijenjen je za prikupljanje podataka. Postprocesiranje slikovnih CT prikaza pohranjenih u DICOM formatu napravljeno je na radnoj stanici s dva Xeon procesora. Rezultati: “Fly through” algoritam i 3DVR primijenjeni su nad skupom slikovnih podataka iz aksijalnih CT prikaza dobivenih višeslojnim CT uređajem i pohranjenim u DICOM formatu. VC i 3DVR postprocesiranje rezultiralo je serijom slikovnih prikaza koje su analizirali jedan radiolog, dva kirurga i dva liječnika s iskustvom u virtualnoj endoskopiji. Zaključak: VC je korisna neinvazivna tehnika za probir i procjenu benignih i malignih lezija kolona. VC može pružiti korisne dodatne informacije kirurgu prilikom prijeoperacijske obrade bolesnika. Nadalje, virtualna kolonoskopija pruža mogućnost trodimenzionalne vizualizacije lumena crijeva iza područja suženja ili stenoze te pruža vrlo pouzdan prikaz kolorektalnih lezija. Njezin nedostatak je da nije moguće napraviti biopsiju, zahtijeva granicu zrak-sluznica za generiranje slikovnog prikaza te ne može identificirati funkcionalne lezije. Primjenom ovih tehnika kliničari mogu procijeniti ne samo intraluminalnu proliferaciju tumora već i ekstraluminalno širenje tumorske mase te odnos prema okolnim anatomskim strukturama