False Positive and False Negative Diagnosis

Most studies using low dose CT without IV contrast report upon hepatic or renal cysts that were further evaluated. False positives are thus caused by a low dose technique without IV contrast. For example, in the study of Hellstrom et al. (Hellstrom et al. 2004), there were four false positives two cases of renal cysts, one normal pancreas, and one case of focal fatty infiltration. The contrary is reflected in the results of the study of Spreng et al. (Spreng et al. 2005), and focus on the group...

Preoperative Assessment

The assessment of colon proximal to an obstructing colonic mass has been a shortcoming of conventional colonoscopy. In the past, inter-operative palpation or post-operative colonoscopy was performed with the possibility of a second surgery required for a missed synchronous cancer or adenoma. The sensitivity of hand palpation is fairly low and intraoperative insufflation of the colon increases the risk of peritoneal contamination. Double contrast barium enema remains in the algorithm for work-up...

Detection and Extraction of Colorectal Masses

Despite the importance of the detection of cancers, only a very small number of CAD schemes have been developed for detection of colorectal masses that are likely to be cancers. This is probably because colorectal masses are generally considered to be easily seen by radiologists due to their size and invasiveness. On the contrary, it is not easy for CAD to detect and accurately delineate entire mass regions instead, CAD tends erroneously to report local surface bumps of a mass as several...

References

Cotton PB, Durkalski VL, Pineau BC, Palesch YY, Mauldin PD, Hoffman B, Vining DJ, Small WC, Affronti J, Rex D, Kopecky KK, Ackerman S, Burdrick JS, Brewington C, Turner MA, Zfass A, Wright AR, Iyer RB, Lynch P, Sivak MV, Butler H (2004) Computed tomographic colonography (virtual coloscopy) a multicentre comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA 291 1713-1719 Fenlon HM (2002) CT colonography pitfalls and interpretation. Abdominal Imaging 27(3) 284-291...

The Alternative Faecal Tagging

Philippe Lefere and Stefaan Gryspeerdt 4.3 The Rationale of Performing Faecal Tagging 36 4.3.2 Improving Patient Compliance 36 4.4.1.2 Faecal Tagging with Barium 37 4.4.1.3 Mild Cathartic Cleansing 37 4.5.4 Miscellaneous Findings 45 4.7 The Future Laxative-Free CT Colonography 48 4.8 Conclusion 48 References 48

Perforation Risk

The morbidity and mortality of colonoscopy are well recognised and described (Vallera and Bailie 1996 Bowles et al. 2004 Waye et al. 1992 Muhldorfer et al. 1992), and larger series report perforation rates in the region of approximately 0.2 (i.e. 1 500). Since its introduction, proponents of CT colonography have proclaimed an excellent safety profile in comparison to endoscopy, assumptions based on its relatively non-invasive nature and the ability to perform the investigation without a need...

Technical Requirements

Progress made in the clinical implementation of CT colonography would not have been possible without significant advances that have been made in CT imaging technology over the past 10 years. Avail- Department of Radiology, Mater Misericordiae University Hospital, Eccles Street, Dublin 7, Ireland ability and ease of access to this technology is crucial for any CT colonography service to allow rapid acquisition, processing and reading of CT colonography datasets. Technologically, there are three...

Effect of Fecal Tagging and Digital Bowel Cleansing

Tagging of feces, especially fluid, by an oral contrast agent such as a barium suspension or water-soluble iodinated contrast material, is a promising method for differentiating residual feces from polyps and thus improving the accuracy in the detection of polyps (Bielen et al. 2003 Lefere et al. 2002, 2004a, b, PickhARDt et al. 2003 ThOMEER et al. 2003). Fig. 11.9a,b. Region-based supine-prone correspondence method for reduction of false-positive detections. (Reprint, with permission, from...

Use of Correspondence Between Supine and Prone Views

Use of both supine and prone data sets of a patient is important for improving the specificity in the detection of polyps, because the mobility of a suspicious lesion between supine and prone views can differentiate polyps from stool (Chen et al. 1999 Morrin et al. 2002). A real polyp tends to stay at the same location in the supine and prone views of the colon, whereas a piece of stool tends to move around in the colon, and thus, the stool can be found in different locations when supine and...

Colonic Preparation

Proper cleansing of the colon is essential if the radiologist is to identify colonic lesions accurately on CT colonography. Remaining pools of fluid in the colon can hide polyps and cancer both on two-dimensional axial and reformatted images and on the three-dimensional endoluminal views (Figs. 3.3, 3.4). Residual solid stool may be misdiagnosed as a polyp, particularly if homogeneous and non-mobile. Large amounts of residual stool can obscure true colorectal polyps and even cancer. Bowel...

History

The development of computed tomography (CT) independently by both Godfrey N Hounsfield and Allan M Cormack in 1972 has forever changed the practice of medicine in the detection, surveillance and treatment of disease. In the past three decades, we have seen an explosion in technological innovation, particularly in the field of CT. As CT has become more sophisticated, so has the radiologist in the detection and diagnosis of disease. In 1994, Vining and Gelfand introduced computed tomographic...

CAD for Rapid Interpretation First Reader Paradigm

Some researchers proposed that CAD can reduce the interpretation time if radiologists focus on a small number of regions indicated by a CAD scheme. A reduction in time is most likely to occur when CAD is used as a first reader. Such a paradigm, often called CAD as a first reader (Evancho 2002 Mani et al. 2004), can possibly be used for separating out negative CTC cases even before radiologists read the cases. However, such a separation is likely to come with an increased number of missed...

Fecal Tagging and Electronic Cleansing

A 3D evaluation will be less time-consuming and labor-intensive if the colon is empty colonic contents can hamper an efficient review as fecal material can resemble a polyp and fluid levels can hamper polyp detection. In principle an empty colon can be achieved in two different ways. The colon can be cathartically prepared with a laxative agent or its contents can be tagged after which it can be electronically cleansed. In the latter method patients are asked to ingest a contrast agent...

Does Patient Population Affect Extracolonic Findings

The studies of Gluecker et al. (Gluecker et al. 2003) and Pickhard et al. (Pickhard et al. 2003) are the only two studies evaluating a screening population, and are remarkably the two studies with the lowest incidence of highly important extracolonic findings, findings with additional investigation, or cancers. This indicates that significant extracolonic findings are lower in screening population settings. Looking at the age of patients, again, the study of Pickhard et al. (Pickhard et al....

Mild Cathartic Cleansing

Cathartic cleansing of the colon is based on the combination of magnesium citrate and bisacodyl tablets (Loso Prep , E-Z-EM). At 6 p.m. the patients have to ingest the magnesium citrate 16.5 g ( single dose) dissolved in one glass of cold water. At 7 p.m. they have to take four 5-mg tablets of bisacodyl. When used at this reduced dose, magnesium citrate is a milder cathartic when compared to sodium phosphate and polyethylene glycol (Vanner et al. 1990 Kolts et al. 1993 MacLeod et al. 1998...

Carcinomas

Carcinomas can assume a variety of shapes. Smaller cancers may be identical to large polyps and flat lesions, while semi-annular and annular, and scirrhous cancers have a unique CT appearance. Semi-annular and annular cancers are seen as a focal, segmental regions of luminal narrowing, accompanied by focal wall thickening, usually with proximal and distal shouldering (Fig. 14.26). The intraluminal margins of the mass are irregular. Extension of soft tissue into the pericolonic fat signals...

Current Reimbursable Indications

The first reimbursable indication for CT colonog-raphy was studying the colon following a failed colonoscopy. Currently, CT colonography is coded under the CPT category III code 0066T for screening and 0067T for diagnostic CT colonography. Reimbursement of CTC exams by Medicare and many third party payers is approved for diagnostic CTC only and only with specified ICD-9 codes. Medicare does not currently cover colon cancer screening and, therefore, patients have to pay out of pocket in the US....

Introduction

CT colonography (Virtual Colonoscopy) has rapidly evolved since its initial description just over a decade ago. It has gradually moved from being a research tool that was largely confined to academic teaching hospitals to a clinical test that is now widely available in many community-based hospitals. With its potential to become a credible tool for colon cancer screening many radiologists are interested in establishing CT colonography in their departments, physicians are requesting the test...

Low Residue Diet

The patients receive a dedicated low residue diet (Nutra Prep , E-Z-EM, Lake Success, NY, USA). This diet is provided in a box and supplies the patient with all the meals and drinks for the entire day before CT colonography (Fig. 4.2). This box contains powdered drinks with vanilla flavour, fruit drinks, soups, chips and nutrition bars. The diet reduces the fat intake and the faecal output. Patients are allowed to have breakfast (8 a.m.), lunch (noon) and dinner (5 p.m.). Breakfast consists of...

Folds

Colonic folds can be particularly complex, particularly in the flexures and rectum. Fused folds are common in these locations (Fig. 14.5). Fused folds are simply recognized by their three-dimensional shape. Occasionally one may visualize focal thickening within a fold. Folds can be distinguished from polyps due to the obtuse margins, internal attenuation (which will often contain some fat) and the non-focality of the lesion. Thickened folds are usually seen in regions of suboptimal colonic...

The Future Computer Aided Detection

11.3 CAD Techniques for Detection of Polyps 139 11.4 Performance in the Detection of Polyps 140 11.4.2 Improvement of Radiologists' Detection Performance 142 11.6 Current and Future Challenges 145 11.6.1 Detection and Extraction of Colorectal Masses 145 11.6.2 Use of Correspondence Between Supine and Prone Views 145 11.6.3 Effect of Fecal Tagging and Digital Bowel Cleansing 146 11.6.4 CAD for Rapid Interpretation First Reader Paradigm 148 11.7 Conclusion 148 References 149

Faecal Tagging with Barium

Faecal tagging is performed with a 40 weight volume barium suspension (Tagitol V , E-Z-EM). The patients only have to drink a total of 60 ml 20 ml at breakfast, lunch and dinner respectively. The patients are instructed to drink the barium at once after the meal. We use barium as sole tagging agent. Several authors advocate the use of iodine or a combination of barium and iodine to achieve fluid tagging (Zalis and Hahn 2001 Zalis et al. 2003 Pickhardt 2003 Iannaccone et al. 2004). Although its...

Reading Conditions

Reading conditions also impact on reader performance. CT colonography studies should ideally be batch-read in a quiet environment with each batch consisting of no more than five or six cases. This helps to reduce the impact of reader fatigue which adversely effects reader concentration and performance in terms of polyp detection. Although an experienced radiologist may take as little as 5 min to read a study in 2D format, interpretation requires a high level of concentration to maintain ones...

Conclusion

CAD techniques for CTC have advanced substantially during the last several years. As a result, a fundamental CAD scheme for the detection of polyps has been established, and commercial products are now appearing. Thus far, CAD shows the potential for detecting polyps and cancers with high sensitivity and with a clinically acceptable low false-positive rate. However, CAD for CTC needs to be improved further for more accurate and reliable detection of polyps and cancers. There are a number of...

The Preparation

The preparation takes one day and is performed the day before CT colonography. It consists of three Fig. 4.1. The residual stool in the ascending and descending colon is tagged and appears white on the two-dimensional images, facilitating diagnosis Fig. 4.1. The residual stool in the ascending and descending colon is tagged and appears white on the two-dimensional images, facilitating diagnosis main parts 1) a low residue diet 2) faecal tagging with barium 3) mild cathartic cleansing (LeferE et...

Quality Assurance

Establishing a CT colonography service requires a major investment in time, cost and personal commitment. However maintaining a quality service and insuring high quality clinical standards is equally important, particularly when considering screening populations. This will involve setting standards, measuring competence, continuous medical education, clinical audit and quality control. Appropriate audit and quality control will assess the various systems involved in a CT colonography service...

Patient Positioning

Despite unanimous consensus in favour of dual position scanning amongst 27 international experts in 2003 (Barish et al. 2005), a minority still promulgate single position scanning. However, the evidence in support of dual position scanning is strong (Yee et al. 2003 Fletcher et al. 2000 Chen et al. 1999 Morrin et al. 2002). These studies have found that colonic segments obscured by either faecal residue fluid or poor distension will be revealed by redistribution in the complementary position...

Does the Scanning Technique Influence Extra Colonic Findings

Most studies use a low dose technique, without additional use of IV contrast. The reasons are the care of radiation dose in a technique requiring prone-supine imaging, and the fear of adverse reaction using IV contrast. The low dose technique capitalizes on the high contrast that exists between the air-filled lumen and the soft tissue density wall. Polyps protruding into air-filled lumen can be detected using these low-dose technique. Solid organ contrast however requires higher radiation dose...

D vs 3D

McFarland et al. (2001) compared three specific 2D and 3Dimage-display techniques. First a 2D MPR image display, secondly a 3D MPR image display (10 mm slab) and thirdly a 3D endoscopic view display. This was done in 30 colon segments. McFarland et al. concluded that among experienced abdominal radiologists, similar diagnostic performance in polyp detection was found among 2D MPR and the two 3D display techniques, although individual cases showed improved characterization with 3D display...

Principles

As with faecal tagging more residue can be left over in the colon without decreasing the accuracy of polyp detection, performing CT colonography after a preparation without cathartic cleansing is the obvious next step. Indeed, eliminating the need for cathartic cleansing prior to CT colonography would dramatically increase the adherence of an asymptomatic patient population to a colon cancer screening program (Rex 2000). This method has been called laxative-free CT colonography (Lefere et al....

Foreword

Modern spiral multidetector computed tomography enables isotropic voxel data acquisition and has opened up the way for superb multiplanar reconstruction, resulting in exquisite pathologic radiological correlation. CT angiography and CT colonography are examples of the clinical applications of this new technology. Both new radiological procedures have already secured their specific role in everyday radiological practice. During the previous decade, radiologists made fundamental contributions to...

Improving Diagnosis

Despite an intensive cleansing of the colon using regular preparations without faecal tagging, both residual stool and fluid in the colon not infrequently cause diagnostic difficulties (Johnson and Dachman 2000) (see also Chap. 8). Residual stool may appear isodense to the colonic wall and cause pseudopolypoid images, mimicking lesions and possibly resulting in false positive findings (FeNloN 2002 MAcAri and Megibow 2001a). Residual fluid is also isodense to the colonic wall and tumoral...

Frequency and Importance of Extracolonic Findings

The results of the major studies published after 2000, and reporting upon extracolonic findings and their follow-up, are tabulated in Tables 10.1-10.3 and Figs. 10.1 and 10.2. The reported percentages of incidental lesions is high, but shows a rather high inter-study variability, with a median of 68.9 of patients with incidental extracolonic findings. The reported percentages of highly important lesions also show great inter-study variability, but is also high, with a median of 12.5 of...

Clinical Results

CTC researchers have developed several conventions for standardizing result reporting (Fenlon et al. 1999 Dachman and Zalis 2004). Results are reported on a per polyp as well as a per patient basis. Results based on per poly analysis are the most rigorous as they imply direct comparison to colonoscopy. Per patient analysis, however, is the more clinically relevant parameter in terms of referral of the patient for therapeutic optical colonoscopy. Polyp detection rates are usually grouped...

Reading and Training

After image acquisition and transfer of datasets, studies should be read and reported in a timely fashion. The following discussion will address aspects of image interpretation including who should read the datasets, how much training is required, how many readers are required and when and where studies should be read. The primary aim of CT colonography is accurate identification of significant colorectal polyps and cancers in a minimally invasive manner. For CT colonography to be a safe,...

Interpretation Method

The method of interpretation will undoubtedly affect reading time and probably diagnostic exam performance. Over the history of CTC, a wide range of software packages with varying capabilities have been used. In fact, software for CTC is still advancing rapidly and it is not uncommon to find that by time a peer-reviewed manuscript is in press, the software version used has been updated or is even no longer available. For this reason software platforms should be specified by vendor, version and...

Synchronous Lesions Reporting of Data ByPolyp

The presence of synchronous polyps in the same patient could be handled in a variety of ways that could bias reported results. For example, in clinical practice, one might argue that the observation of even a single significant sized lesion on CTC will result in a colonoscopy follow-up examination. Hence, one could argue that, in order to decrease reading time and reader fatigue, a detailed search for synchronous lesion is unnecessary if a significant lesion has already been detected. However,...

What is Faecal Tagging

Faecal tagging means labelling of faecal residue in the colon. Stool tagging refers to labelling of residual stool, while fluid tagging refers to labelling of residual fluid. The technique is based on the oral ingestion of positive contrast material (barium and or iodine) as part of the preparation prior to CT colonography. The orally ingested contrast material impregnates the residual stool and mixes with the residual fluid in the colon. By doing so the residual stool and fluid, remaining in...

Contraindications

The contraindications to CTC are few and, in general, different than these encountered with conventional colonoscopy (Rex et al. 1987). Weight and girth limitations of the scanner, artifacts from metal prosthesis and claustrophobia are examples of contraindications unique to CT. Absolute contraindications to instrumentation of the colon include presence of an acute abdomen, recent abdominal or pelvic surgery, colonic hernia, and acute diverticu-litis (Fig. 2.3). Relative contra-indications...

Room

Currently room air is used most frequently to manually insufflate the colon for CT colonography. Its ease of use and familiarity to radiologists and technologists because of a similar route of administration per rectum for double-contrast barium enema examinations have made it easily adaptable for CT colonography. It is also readily available at no additional cost. A large component of room air is nitrogen, which is inert, so that there is no active diffusion across the bowel wall when the...

I

MEDICAL RADIOLOGY Diagnostic Imaging Editors A. L. Baert, Leuven K. Sartor, Heidelberg F. Booya D. Burling A. H. Dachman A. H. de Vries H. Fenlon J. T. Ferrucci J. G. Fletcher S. Gryspeerdt S. Halligan A. Laghi P. Lefere A. Maier T. Mang B. G. McFarland K. J. Mortele A. S. Odulate A. O'Hare P. Paolantonio P. Pokieser W. Schima J. Stoker S. Taylor R. E. van Gelder J. Yee H. Yoshida M. E. Zalis With 173 Figures in 407 Separate Illustrations, 115 in Color and 11 Tables Philippe Lefere, MD...

Technical Artifacts

Technical artifacts are easy to recognize. Breath-hold and motion artifacts are usually best seen with sagittal or coronal oblique planes which better display the motion along the z-axis (Fig. 14.22). Metallic artifacts cause beam-hardening artifacts, and can obscure the colon lumen. Stairstep artifacts are usually not seen with thin slice thickness, but with thicker slice thicknesses (such as 5 mm), and are seen on 3D endoluminal images and 2D MPR images, most commonly within the rectum and...

Postoperative Colorectal Cancer Surveillance

The American Society of Clinical Oncology developed in 1999 a set of guidelines for the surveillance of the post-operative patient with colorectal cancer after thorough review of the literature of common surveillance protocols. Protocols were reviewed on the basis of reduction in morbidity and five-year disease free survival. Monitoring carcino-embryonic antigen (CEA) levels and colonoscopy were found to be the most effective in many protocols, with liver function evaluation, fecal occult blood...

CT Colonography Protocols

Specific CT colonography protocols should be established at a local level and should be based on the currently available published evidence. Protocols should address the method of bowel preparation (clean colon vs fluid or faecal tagging), use or not of intravenous contrast, use or not of spasmolytics, method of colon distension, scanning parameters, and methods of interpretation. The specifics of many of these options are discussed in subsequent chapters. The basic equipment required for the...

Future Indications

The need for colon cleansing with bowel cathartics may be a technique of the past with further development of electronic bowel cleansing software and prep-less fecal tagging protocols. This promises to significantly increase the overall percentage of patients willing to participate in colorectal cancer screening and, therefore, reduce morbidity and ultimately mortality related to colorectal cancer. Polyp surveillance with CTC may be further refined and some patients ultimately spared from...

Instruction Folder

It is accepted that availability of written information improves patient compliance (Murphy and Coster 1997). In order to proceed fluently with the preparation and to avoid misinterpretation of the instructions and or misuse of the provided items, the patients receive an information folder. This folder provides them with all the practical information necessary to bring this preparation to a good end by 1) showing all different ingredients on a picture 2) explaining how to proceed with the meals...

Contents

1 Starting CT Colonography in Your Department 2 The Eligible Patient Indications and Contraindications Ayodale S. Odulate and Koenraad J. Mortele 13 3 Patient Preparation for CT Colonography 4 The Alternative Faecal Tagging 5 How to Get the Colon Distended David Burling, Stuart Taylor, and Steve Halligan 51 6 The Right Scanner Parameters to Use 7 How to Interpret the Data Sets 8 How to Avoid Pitfalls in Imaging. Causes and Solutions to Overcome False Negatives and False Positives Stefaan...

Acceptance of CTC

Several factors will likely converge in the very near future to precipitate wide-spread acceptance of CTC Continued excellent results from single center trials will add to existing cumulative data of its efficacy. Evidence-based comparisons with existing approved screening tests (FOBT, flexible sigmoid-oscopy, double contrast barium enema, colonos-copy) will show that none is perfect and that CTC has a sufficient number of benefits and unique attractions to make it a legitimate addition....

Incomplete Conventional Colonoscopy

CTC has been shown to be superior to double contrast barium enema following incomplete conventional colonoscopy and, in fact, failed colonoscopy was the first established indication for CTC. An incomplete colonoscopy is defined as failure to intu-bate up to the cecum. The reported rate of failed colonoscopy ranges from 8 to as high as 35 . Patients with a history of an incomplete colonos-copy have a significantly increased risk of failing a second attempt. A multitude of reasons contribute to a...

The Examination

On the day of CT colonography the patients remain sober until the examination is performed. Whenever necessary we advise the patients to take their regular medication shortly before CT colonography. CT colonography is preferably performed in the morning. Prior to the exam the patient is instructed to visit the restroom to empty the rectum. Smooth muscle relaxation is achieved using scopolamine butylbromide (Buscopan Boehringer Ingelheim) (Taylor et al. 2003a). After distending the colon with...

Extracolonic Findings in CT Colonography

Stefaan Gryspeerdt and Philippe LeferE 10.3 Frequency and Importance of Extracolonic Findings 130 10.4 Nature of Extracolonic Findings 132 10.5 Does Patient Population Affect Extracolonic Findings 132 10.6 Does the Scanning Technique Influence Extra-Colonic Findings 132 10.7 False Positive and False Negative Diagnosis 134 10.9 Impact on Patient Care and Well-Being and Ethical Impact 135 10.10 Conclusion 135 References 135

Results

Several studies using a preparation based on faecal tagging have been performed. The results of polyp detection of these studies are listed in Table 4.1. Thomeer et al. (2003) examined 150 patients and performed colonic cleansing using 3-5 L of an electrolyte solution on the day of CT colonography. Faecal tagging was obtained with 90-150 ml of iodi-nated contrast. As they were starting CT colonogra-phy in their department the results of polyp detection were clearly influenced by the learning...

Reading the Data Sets

After scanning the patient the images are sent to a dedicated workstation with regular endoluminal software. Although possible (Pickhardt and Choi 2003) it is important to stress that no dedicated software (stool subtraction) is needed to read and interpret the tagged data sets adequately. Reading is performed using a primary 2D read with 3D problem solving method (Dachman et al. 1998) (Fig. 4.4). In case of a clean colon, primary 3D read is possible. However if the colon is not clean, the...

Screening vs Non Screening Cohorts

The diagnostic performance in a screening cohort might be poorer than in a cohort with a high prevalence of disease. It is useful to know what percentage of cases are truly screening, meaning average risk for colorectal cancer (CRC), the risk factor being age 50 years or older, vs above average risk patients. Above average risk patients are those with a family history of CRC (particularly in a first degree relative), a personal history of CRC or colonic adenomas, or signs or symptoms suggestive...

CAD False Positives

False positives may lead to unnecessary further workups such as polypectomy by colonoscopy therefore, knowledge about the pattern of CAD false positives is important for dismissing them. Studies showed that most of the false positives detected by CAD tend to exhibit polyp-like shapes, and the major causes of CAD false positives are the following (Yoshida et al. 2002a,b). Approximately half (45 ) of the false positives are caused by folds or flexural pseudotumors. They consist of sharp folds at...

Indications

The indications for CTC closely follow the indications for conventional optical colonoscopy with few exceptions. These indications include screening asymptomatic high- and average-risk patient populations, pre-operative assessment of the colon proximal to an obstructing mass, evaluation of patients with change in bowel habits, surveillance of patients post colorectal cancer surgery, and incomplete or failed colonoscopy. Patients with bleeding diathesis, contraindications to sedation, and frail...

Discussion

In this section on accuracy, a distinction between high and low prevalence has been made. The difference that is made in this spectrum is of course arbitrary and is not absolute. However by drawing this line, a difference in performance of both methods is apparent. In studies with a high prevalence for colorectal polyps or cancer, primary 2D reviewing performed well (Pineau et al. 2003 Johnson et al. 2003b Iannaccone et al. 2004a) and in comparative studies (primary 2D vs primary 3D) (McFarland...

Carbon Dioxide or

As mentioned above, many practitioners promulgate carbon dioxide as superior to air, largely based on barium enema and colonoscopy literature, which suggests it causes less discomfort because of its rapid mucosal absorption (Grant et al. 1986 Church and Delaney 2003). A recent study (Iafrate et al. 2004) also showed improved patient tolerance using automated carbon dioxide administration vs manually administered room air, although it is not clear whether the benefit was derived from using the...

Patient Information Referral and FollowUp

For patients and the population in general, particularly those considering a screening test, easy access to information regarding the procedure and clear communication with the providers are also important. There should exist within a department a means by which patients can be informed of the procedure, the necessary preparation, potential risks and complications, implications of a normal and abnormal result and what mechanism for follow-up exists. The most practical way of achieving this...

Summary

Virtual colonoscopy, now ten years old, has made substantial progress in the detection of adenomas and colorectal cancer. Recent studies report comparable sensitivities and specificities to conventional colonoscopy for polyps 10 mm or larger on a per polyp basis. CTC is currently approved by Medicare as a diagnostic study in patients with positive symptoms and after failed colonoscopy. Work continues to approve CTC as a colorectal cancer screening exam. Many experts believe CTC is also ready to...

Without CAD gain using CAD

Improvement of detection performance of human reader by use of CAD in the detection of polyps those encountered by radiologists (Yoshida et al. 2002a,b). Most of the CAD techniques depend on a shape analysis that assumes that polyps appear to have a cap-like shape, i.e., they appear as polypoid lesions. Therefore, polyps that do not protrude sufficiently into the lumen (e.g., diminutive polyps and flat lesions), whose shape deviates significantly from polypoid (e.g., infiltrating...

Primary 2D and Primary 3D Difference in Accuracy

The accuracy of a diagnostic tool can vary with the prevalence of a disease or disorder. This may apply for the accuracy of both display methods as well. As a consequence a differentiation between high and low prevalence studies is made in this paragraph. The sensitivity per polyp is used as a criterion for the functioning of the review methods different diagnostic modes, since it is a more precise way to measure the visibility of a polyp. However, in a screening setting the sensitivity per...

Colonic Insufflation Methods

Colonic distension prior to CT colonography entails gently administering gas (air or carbon dioxide) via a rectal catheter using either manual or automated insufflation techniques. Both gases and insufflation methods are widely used and all have their advocates some favour the least expensive and simplest method, i.e. room air insufflation by manual compression of a plastic insufflator bulb, while others prefer carbon dioxide delivered by automated insufflation devices. Until recently, there...

Single vs Multidetectorrow Scanners

Multidetector row scanners allow considerably reduced scan times, facilitating single breath hold studies for the majority of patients. As a consequence, image misregistration is practically eliminated and respiratory artefact significantly reduced (Hara et al. 2001). Moreover, distension also seems to be improved with a study by Hara et al. (2001) showing that suboptimal distension in at least one colonic segment was significantly more common with single detector row CT (40 of 77 patients, 52...

Review Time

Although exposure fold characterization is easier (Fig. 9.11) when using the 3D display, the barriers to 3D evaluation as the primary strategy for review have been its time-consuming and labor-intensive nature (Macari et al. 2000 McFarland et al. 2001). Two matters underlie its time consuming nature. First, additional processing time is needed in order to create a 3D rendered view. In order to create a 3D view the CT-data files need additional processing by a computer. The speed of this process...

Lesion Morphology

Polyps should be reported with morphologic data in addition to size, as lesions with sessile or flat morphology are thought to confer a different risk of harboring carcinoma. Another important area of interest is the diagnostic performance of CTC for detecting flat lesions-polyps that primarily infiltrate along the colon mucosa and hence do not markedly impinge into the colon lumen (Fidler et al. 2002). A recent review of the National Polyp Study showed that flat lesions, as defined by...

Cost and Financial Implications

The economic implications of setting up a CT colonog-raphy service must also be considered. Each department must consider whether or not it is financially viable for them to provide this service. Estimates suggest that, when all factors are considered, the real cost of providing a CT colonography examination is in the order of 250 Euro. Balanced against this is the ongoing difficulty with reimbursement, which varies widely from country to country and even from state to state in North America....

Twodimensional Methods

Pineau et al. (2003) conducted a comparative study with optic colonoscopy assessing the diagnostic accuracy of virtual colonoscopy using oral contrast. The colonography examination was done with a primary 2D method with 3D problem solving. In a population of 205 patients the sensitivity for large (> 10 mm) colorectal polyps was 78 . The reported specificity was higher (95 ). This decreased for medium-sized (6-9 mm) polyps to 75 and 83 respectively. Johnson et al. (2003b) conducted a...

Low Prevalence Population

Pickhardt et al. (2003) studied the accuracy of CT colonography in an asymptomatic population of 1233 patients of average risk for colorectal cancer. A primary 3D endoluminal bidirectional fly-through was used for detection of polyps, after electronic cleansing. Non-visualized areas were presented to the observers after the fly-through (Fig. 9.3). Pickhardt reported a sensitivity and specificity for large adenomatous polyps of respectively 92 and 96 . For adenomatous polyps larger than 6 mm the...

Tagged Stool

Transverse Colon Yellow

With faecal tagging the residual stool appears as a bright hyperdense or white spot or mass in the colonic lumen with or without air inclusion (Fig. 4.7). This bright stool almost lights up when scrolling through the 2D images simplifying interpretation as there is no likelihood of mistaking it for a lesion. In that way the time consuming comparison between supine and prone position to detect an eventual change in location of the residual stool becomes superfluous. This shortens the reading...

Imaging Invaluable for the Correct Diagnosis

Ayso H. de Vries, Rogier E. van Gelder, and Jaap StokeR 9.2 Three-dimensional Reconstruction 117 9.3 Three-dimensional Display Methods 118 9.3.1 Conventional 3D Display 118 9.3.2 Alternative 3D Display Methods 119 9.4 2D and 3D Reading are Complementary 120 9.5 Fecal Tagging and Electronic Cleansing 123 9.6 Primary 2D and Primary 3D Difference in Accuracy 123 9.6.1 High Prevalence Population 123 9.6.1.1 Two-dimensional Methods 123 9.6.2 Low Prevalence Population 124 9.8 Conclusion and Future...

X

Ileo-cecal valve with lobulated polypoid filling defects on a 2D view b 3D views (arrows) without symmetry c soft tissue windows revealed internal soft tissue attenuation (arrow). Endoscopy demonstrated an adenoma of ileo-cecal valve Fig. 14.12a-c. Lipomatous ileo-cecal valves retain benign features, only appearing more bulbous. They possess homogenous fatty internal attenuation and appear smoothly marginated without focal lesions on 3D endo-luminal views Fig. 14.12a-c....

Foam

Faecal residue with a foamy appearance is mostly detected in the cecum or ascending colon. It appears as an amorphous inhomogeneous mixture mostly of air bubbles and stool. They occur in both preparations without and with faecal tagging. In the latter case the foam is tagged or non-tagged. This foam may distract the reader's attention or cover a lesion making detection difficult (Fig 4.19). Fig. 4.16.a Non-tagged fluid covering 25-50 of the colonic lumen at the hepatic flexure in supine...

Screening CT Colonography

In the United States, 1 in 17 people will develop colorectal cancer. According to reports from the National Cancer Institute, colorectal cancer is the third most common cancer in US men and women. The overall incidence of colorectal cancer increased until 1985 and then began decreasing at an average rate of 1.6 per year. Approximately 75 of all colorectal cancers occur among persons of average risk, i.e., those without predisposing conditions, such as inflammatory bowel disease, familial...

Defining the Patient Preparation and CT Technique

The effect of preparation is important, not only in terms of cleansing of the colon of residual stool, but also of residual fluid. Most CTC reports have been done on consenting research patients who are already scheduled to undergo a non-research conventional colonoscopy. The preparation is often chosen by the gastroenterologist. A colonic lavage with 4 L of polyethylene glycol is know to leave significant residual fluid which can hide polyps unless a unique strategy is used to reveal polyps...

Hemorrhoids

Internal hemorrhoids can be seen as smoothly marginated and curved filling defects that project into the rectal vault, lying adjacent to the rectal tube tip (Fig. 14.1). In contradistinction, low rectal cancers will normally have shouldering, and arise some distance from the anus itself. Physical examination usually confirms the presence of internal hemorrhoids. If the remainder of the colorectum has been cleared of significant lesions, a limited proctoscopic or sigmoidoscopic examination can...

Economical Impact

Hara et al. (Hara et al. 2000) reported that the additional and recommended work-up added 28 to the examination cost per patient. If all highly important lesions would be further investigated, the added costs would be 36 per patient. Gluecker (Gluecker et al. 2003) reported an added costs of 34 to the average cost. Given the fact that in truly screening patient populations the total number of highly suspected findings is expected to be lower, as shown by Pickhard (Pickhard et al. 2003), both...

Mucous Filaments

Mucous filaments appear as thin threadlike structures crossing the colonic lumen or lying upon one or more semicircular folds. They can occur after a preparation without or with faecal tagging. In the latter case these filaments can be tagged or non-tagged. They can changed in shape with dual positioning. However they may simulate the stalk of a polyp. It is important not to misinterpret it as a polyp and vice versa. In the latter case they are not connected to the head of a polyp. However...

Intravenous Spasmolytics

There are two intravenous spasmolytics available for CT colonography hyoscine butylbromide and glucagon hydrochloride. Both produce hypotonia in smooth muscle within the colonic wall and are used widely to improve distension during double contrast barium enema. However, while both agents have been shown to improve patient perception during barium enema, only hyoscine butylbromide reliably improves distension (Goei et al. 1995 Bova et al. 1993). As a result, it is widely utilized for barium...

Absolute Contraindications

Many CT scanners have a weight limit of 300 to 400 pounds and a circumferential girth limit of 60 cm. A patient with an acute abdomen should not be inflated with room air or CO2, and a consultation with a surgeon is most appropriate. Patients with active diverticulitis should not be referred to CT colonography. If an abscess or free air is suspected, a CT of the abdomen and pelvis can be performed with oral and IV contrast. Insufflation of the colon is contraindicated and may cause perforation...

How to Interpret the Data Sets

Vulvar Lesion

7.2 Current and Future Image Display Techniques 73 7.2.1 2D Multiplanar Reformation (2D MPR) 74 7.2.2 3D Endoscopic Fly-Through 75 7.2.3 3D Transparency View (Edge-Enhanced View) 76 7.2.4 Future Advances in Image Display Techniques 76 7.3 Different Categories of Colorectal Morphologies 76 7.3.1 Focal Polypoid Lesions (r o stool) 76 7.3.4 Advanced Mural Lesions (r o collapse) 81 7.4 Standardization of Reporting of Clinically Significant Colorectal Findings 82 References 85 CT colonography (CTC)...

CAD Techniques for Detection of Polyps

To date, most of the CAD schemes developed in academia and in industry comprise of the following four fundamental steps (1) extraction of the colonic wall from the CTC images, (2) detection of polyp candidates in the extracted colon, (3) characterization of false positives, and (4) discrimination between false positives and polyps. A brief descrip tion of each of these steps is provided below. More technical details on the fundamental CAD scheme can be found in recent review articles (Yoshida...

Colonic Distension

Proper distension of the colon is necessary to allow the radiologist the ability to visualize polyps and cancers that may impinge upon the lumen on CT colonography (Figs. 3.5, 3.6). A segment of colon that is poorly distended or collapsed can simulate a malignant narrowing such as that caused by an annular carcinoma (Fig. 3.7). A well-trained technologist or nurse can assist in placing the rectal tube with care and performing the colonic insufflation, depending upon local guidelines. With the...

Colorectal Carcinoma

Adenocarcinomas are the most common colonic primary tumors. The peak incidence is between 50 and 70 years of age. Approximately 90 arise from benign adenomatous polyps. Most carcinomas show an exophytic, polypous type of growth with frequent central degeneration. Adenocarcinomas tend to infiltrate the bowel wall circumferentially and 50 are found in the rectum, and 25 in the sigmoid. In up to 5 of cases, a synchronous carcinoma is present (Fig. 13.18a,b). The main indication for CT colonography...

Stool

Stool is the most frequent cause of false positive findings at CT colonography (Fletcher et al. 2000). There are several imaging characteristics, which usually aid in the identification of stool. Stool has a heterogeneous internal attenuation, often with internal air (Fig. 14.16). Additionally, stool particles usually lie along the dependent colonic wall and change location with changes in patient positioning (Fig. 14.17). On 3D normal endoluminal images, Fig. 14.14a-c. Lipoma. Note the...

Conclusion and Future Development

Three-dimensional display is an integral part of reviewing of CT-colonography examinations and most likely a prerequisite for good sensitivity. The method can be used either primary or as adjunct to 2D evaluation. In populations with a high polyp prevalence the use of primary 3D does not seem advantageous compared to primary 2D, although comparative data are sparse and no optimized 3D methods have been used. The use of the later methods might prove to be valuable. The question which review...

Collapse and Contraction

Contraction Colon

Luminal collapse can be confused with malignant scirrhous tumors by radiologists learning CT colo-nography (Fidler et al. 2004). Imaging patients in two positions has been shown by multiple observers to result in complementary distension and can be employed to distend collapsed bowel (Chen et al. 1999 Fletcher et al. 2000 Yee et al. 2003). In general, the patient should be rolled such that the collapsed bowel loop is in the most nondependent location (Fig. 14.7). Contraction can appear as a...

Non Tagged Stool

In a minority of cases a small amount of stool remains non-tagged. Fig. 4.8. Patient with right sided sigmoid. There is tagged stool (arrowhead). There is also non-tagged material (arrow). This should be considered a lesion unless the contrary is proved. A correct diagnosis of an 8-mm sessile polyp was made Non-tagged stool < 6 mm is too small too cause any concern as it is generally accepted that polyps < 6 mm do not need to be removed. Hence pseudopol-ypoid lesions < 6 mm caused by...

Inverted Appendiceal Stump and Appendiceal Intussusception

Inverted Appendix

An inverted appendiceal stump can appear identical to a polyp (Fig. 14.13), and is located at the site of prior appendectomy. Both the appendiceal stump and intraluminal neoplasm will enhance with intravenous contrast. Close correlation with the clinical history of incidental inversion-ligation appendectomy may be revealing , but in cases where clinical history is incomplete, endoscopic correlation may be required. Appendiceal intussusception can also occur. Barium enema has the advantage of...

Recommended Technique

It is clear form the above discussion that the practitioner has many options available when attempting to optimise colonic distension prior to scan acquisition. While some techniques have an established evidence-base, others are largely a matter of personal preference. Whatever regime is chosen, it is clear that good distension is absolutely pivotal to the success of any CTC examination. The follow section will provide the reader with details of the authors' preferred methods. Written patient...

Carbon Dioxide

Carbon dioxide (CO2) has been used instead of atmospheric air for insufflation of the colon for colonoscopy as well as for barium enema examination because it has been found to decrease patient discomfort. CO2 is readily resorbed through the colonic wall because of a steep diffusion gradient and it is then exhaled from the lungs. One hundred patients were randomized to undergo colonoscopy with insufflation with either air or CO2. Post-procedural pain was reported in 45 and 31 of patients...

The Right Scanner Parameters to

25mm Polyp During Colonoscopy

Andrea Laghi and Pasquale Paolantonio 6.5 Tube Current Setting and Low Dose Protocols 65 6.6 Practical Guidelines 68 Appendix. Glossary of Terms 69 References 70 The advent of CT colonography (CTC) (or, virtual colonoscopy) in 1994 was made possible by the development of spiral CT technology, which provides a volumetric coverage of a cleansed and air-distended colon within a single breath-hold (Vining et al. 1994). The introduction of multidetector row computed tomographic (MDCT) scanners in...

Performance of CAD

Several academic institutions have conducted clinical trials to demonstrate the performance of their CAD systems (Kiss et al. 2002 Nappi et al. 2004b Nappi and Yoshida 2003 Paik et al. 2004 Summers et al. 2001 Yoshida et al. 2002a, b Yoshida and Nappi 2001) that implement the full CAD scheme in the previous section or a part of it. In these studies, optical colonoscopy was used as the gold standard, i.e., the locations of the polyps detected by CAD were compared with the true locations of...

Choice of Rectal Catheter

There is wider scope for using more flexible and thinner catheters during CT colonography compared to barium enema because of the requirement to transmit only gas and because the consequences of anal incontinence are less dramatic. The choice of rectal catheter will mainly depend on local availability, method of insufflation, and individual patient but there is some evidence suggesting that thin tubes are adequate for most circumstances. Perhaps the simplest catheter is a thin plastic or rubber...

Ulcerative Colitis

Colonoscopy Ulcerative Colitis

Ulcerative colitis is an inflammatory bowel disease limited to the mucosa and submucosa of the colon. The disease typically begins in the rectum and continuously extends proximally to involve part of the colon or the entire colon (pancolitis). In 10-40 of cases, the distal ileum is also inflamed, which is referred to as backwash ileitis. The most severe Table 13.2. CTC features of inflammatory bowel disease Discrete irregular wall thickening (continuous vs. discontinuous) Flattening or...

Colorectal Lymphoma

Lymphoma involves the colon either as a primary neoplasm or as a part of a disseminated disease. In contrast to the small bowel, where lymphomas are the most frequent primary, lymphomas in the colon are rare. In secondary colonic lymphoma, the involvement of the gastrointestinal tract follows a previously diagnosed extraabdominal lymphoma (O'Connell and Thompson 1978 Megibow et al. 1983). The primary colonic lymphoma is usually found in middle-aged or elderly people. Males are twice as often...

Automated Insufflation

Enema Bags Used Hospitals

Automated insufflation devices are now widely utilised across Europe and the US, despite the additional equipment costs. Advocates suggest that insufflating carbon dioxide at controlled flow rates and pressures is convenient for the operator, and improves distension and patient compliance. Early experience comparing a crudely modified laparoscopic insufflator to manual bulb insufflation of room air showed equivocal effects on luminal distension (Ristvedt et al. 2003). More recently, two Fig....

Patient Preparation for CT Colonography

Scopolamine Butylbromide Synthesis

3.3.2 Hyoscine n-Butylbromide 31 References 32 CT colonography or virtual colonoscopy has increasing support as a screening tool for colorectal polyps and carcinoma. This radiologic examination uses the patient data acquired from a helical CT scanner and combines it with computer software that post-processes the data to generate both two- and three-dimensional images of the colon for analysis. However, before the patient undergoes the CT scan, there are initial steps that must be taken to help...

Manual Insufflation

The easiest and cheapest method for distending the colon is to use room air, insufflated via a hand held plastic bulb. Typically patients lie on the CT scanner table in a left lateral position facing away from the operator. A lubricated rectal catheter attached to an insufflator bulb via a connecting tube is then inserted into the rectum and taped to the patient's buttocks. The patient is encouraged to retain any gas and avoid passing flatus by clenching the anal sphincter. Colonic insufflation...

Glucagon

Glucagon is a polypeptide hormone normally produced by the pancreatic islets of Langerhans. It causes an increase in blood glucose, but is perhaps better known for its clinical use as a hypotonic agent for the stomach, small bowel, and colon. Glucagon relaxes the smooth muscle of the gastrointestinal tract and is thought to improve bowel distension and decrease patient discomfort due to spasm. The effectiveness of glucagon is dependent upon location, and it has been found to be most effective...