CT Colonography (Virtual Colonoscopy): A Practical Approach for Population Screening

Value of Virtual Colonoscopy with 64 Row CT in Evaluation of Colorectal Cancer

Background

Virtual colonoscopy (VC) enables three-dimensional view of walls and internal lumen of the colon as a result of reconstruction of multislice CT images. The role of VC in diagnosis of the colon abnormalities systematically increases, and in many medical centers all over the world is carried out as a screening test of patients with high risk of colorectal cancer.

Material/Methods

We analyzed results of virtual colonoscopy of 360 patients with clinical suspicion of colorectal cancer. Sensitivity and specificity of CT colonoscopy for detection of colon cancers and polyps were assessed.

Results

Results of our research have shown high diagnostic efficiency of CT colonoscopy in detection of focal lesions in large intestine of 10 mm or more diameter. Sensitivity was 85.7%, specificity 89.2%.

Conclusions

Virtual colonoscopy is noninvasive and well tolerated by patients imaging method, which permits for early detection of the large intestine lesions with specificity and sensitivity similar to classical colonoscopy in screening exams in patients suspected for colorectal cancer. Good preparation of the patients for the examination is very important for proper diagnosis and interpretation of this imaginge procedure.

Abdominal computed tomography, colonography and radiation exposure: what the surgeon needs to know

AIM

Abdominal computed tomography (CT) improves the accuracy of clinical diagnosis and facilitates patient management. Radiation exposure must be considered by requesting clinicians and is especially relevant owing to the increasing use of CT colonography for diagnosis and screening of colorectal disorders. This review describes the radiation dose of abdominopelvic CT and colonography and attempts to quantify the risk for the clinician.

METHOD

Articles were searched in the PubMed and Medline databases using combinations of the MeSH terms 'radiation', 'abdominal computed tomography' and 'colonography'. Electronic English language abstracts were read by two reviewers and the full article was retrieved if relevant to the review.

RESULTS

Abdominopelvic CT and CT colonography convey significant radiation dose to the patient but also have considerable diagnostic potential. In the right clinical context, the radiation risk should not be overestimated. Techniques to reduce the dose should be used. Repeated imaging in certain patients is a concern and should be monitored.

CONCLUSION

Radiation risk can be quantified and presented simply in a manner that both patients and doctors can comprehend and evaluate. This approach will diminish misconceptions and allow a rational choice of diagnostic test.

CT colonography: pitfalls in interpretation

As with any radiologic imaging test, there are several potential interpretive pitfalls at CT colonography that need to be recognized and handled appropriately. Perhaps the single most important step in learning to avoid most of these diagnostic traps is simply to be aware of their existence. With a little experience, most of these potential pitfalls are easily recognized. This article systematically covers the key pitfalls confronting the radiologist at CT colonography interpretation, primarily dividing them into those related to technique and those related to underlying anatomy. Tips and pointers for how to effectively handle these potential pitfalls are included.

Minimising medically unwarranted computed tomography scans

As computed tomography (CT) is such a superb diagnostic tool and individual CT risks are small, whenever a CT scan is clinically warranted, the CT benefit/risk balance is by far in the patient's favour. However, if a CT scan is not clinically warranted, this balance shifts dramatically. It is likely that at least 25% of CT scans fall into this latter category, in that they could either be replaced with alternative imaging modalities or could be avoided entirely. Use of clinical decision rules for CT usage represents a powerful approach for slowing down the increase in CT usage, because they have the potential to overcome some of the major factors that result in some CT scans being undertaken when they may not be clinically helpful.

Performing an additional decubitus series at CT colonography

PURPOSE

To determine the rate and associated factors for acquiring a decubitus series at CT colonography (CTC), in addition to the standard supine and prone series.

MATERIALS AND METHODS

CTC examinations read centrally at one institution but performed at three different centers in 6,380 adults were reviewed to determine the frequency of an additional decubitus series. Results were analyzed according to study indication (primary screening vs. diagnostic for incomplete colonoscopy), practice site (academic vs. community), patient age, gender, body mass index (BMI), and temporal variation. At all sites, the CT technologist determined the need for an additional decubitus series, with infrequent radiologist input in select cases.

RESULTS

The frequency for the CT technologist to obtain a decubitus series at screening was 9.7% (578/5,952), compared with 22.9% (98/428) following failed colonoscopy (P < 0.001). The decubitus rate for screening at the academic center (9.4%, 550/5,871) was significantly lower than the community hospitals (34.6% combined, 28/81) (P < 0.001). The rate progressively increased with age, from 5.0% under age 50 to 28.0% over age 80. No significant difference was seen between men and women (10.3 vs. 9.2%), but a strong correlation existed with increased BMI, rising to >25% for BMI over 40. Marked temporal variation existed at the academic center, with quarterly rates ranging from 0 to 17%.

CONCLUSIONS

The frequency for performing a third series at CTC varies considerably according to indication, practice site, patient age, BMI, and time. These results have important implications for clinical practice, including the need for improved training and feedback for CT technologists.

Polyp size measurement at CT colonography: what do we know and what do we need to know?

Polyp size is a critical biomarker for clinical management. Larger polyps have a greater likelihood of being or of becoming an adenocarcinoma. To balance the referral rate for polypectomy against the risk of leaving potential cancers in situ, sizes of 6 and 10 mm are increasingly being discussed as critical thresholds for clinical decision making (immediate polypectomy versus polyp surveillance) and have been incorporated into the consensus CT Colonography Reporting and Data System (C-RADS). Polyp size measurement at optical colonoscopy, pathologic examination, and computed tomographic (CT) colonography has been studied extensively but the reported precision, accuracy, and relative sizes have been highly variable. Sizes measured at CT colonography tend to lie between those measured at optical colonoscopy and pathologic evaluation. The size measurements are subject to a variety of sources of error associated with image acquisition, display, and interpretation, such as partial volume averaging, two- versus three-dimensional displays, and observer variability. This review summarizes current best practices for polyp size measurement, describes the role of automated size measurement software, discusses how to manage the measurement uncertainties, and identifies areas requiring further research.

Screening CT colonography in an asymptomatic average-risk Asian population: a 2-year experience in a single institution

OBJECTIVE

The purpose of our study was to report the results of screening CT colonography (CTC) in an asymptomatic average-risk Asian population.

MATERIALS AND METHODS

In 2005 and 2006, 1,015 Korean adults (609 men and 406 women; mean age, 51 years) underwent screening CTC using a 16-MDCT scanner and an automated CO2 delivery system. During the study period, the protocols were changed to use less vigorous purgation and lower radiation doses; fecal tagging (n = 890) and primary 3D interpretation (n = 966) were generally used. CTC results were categorized as C0, inadequate; C1, no significant polyp; C2, one or two 6- to 9-mm polyps; C3, polyps > or = 10 mm or > or = three 6- to 9-mm polyps; and C4, mass. Patients with positive CTC results were referred to gastroenterologists for follow-up or management planning.

RESULTS

Categories C0-C4 were assigned to 21 (2.1%), 916 (90.2%), 54 (5.3%), 23 (2.3%), and one (0.1%) patients, respectively. Fifty-four patients with C4 (n = 1), C3 (n = 20), or C2 (n = 33) underwent subsequent optical colonoscopy: complete (n = 53) and incomplete (n = 1). Per-patient positive predictive values (PPVs) for categories C3-C4 and C2-C4 were 90% (18/20) and 74% (39/53), respectively. Per-polyp PPVs at 10- and 6-mm thresholds were 92% (22/24) and 69% (45/65), respectively. The diagnostic yield for advanced neoplasm was 1.5% (15/1,015).

CONCLUSION

Our results seem comparable to Western experiences, showing that a successful screening CTC program can be reproduced in an Asian population.

New technologies for human cancer imaging

Despite technical advances in many areas of diagnostic radiology, the detection and imaging of human cancer remains poor. A meaningful impact on cancer screening, staging, and treatment is unlikely to occur until the tumor-to-background ratio improves by three to four orders of magnitude (ie, 10(3)- to 10(4)-fold), which in turn will require proportional improvements in sensitivity and contrast agent targeting. This review analyzes the physics and chemistry of cancer imaging and highlights the fundamental principles underlying the detection of malignant cells within a background of normal cells. The use of various contrast agents and radiotracers for cancer imaging is reviewed, as are the current limitations of ultrasound, x-ray imaging, magnetic resonance imaging (MRI), single-photon emission computed tomography, positron emission tomography (PET), and optical imaging. Innovative technologies are emerging that hold great promise for patients, such as positron emission mammography of the breast and spectroscopy-enhanced colonoscopy for cancer screening, hyperpolarization MRI and time-of-flight PET for staging, and ion beam-induced PET scanning and near-infrared fluorescence-guided surgery for cancer treatment. This review explores these emerging technologies and considers their potential impact on clinical care. Finally, those cancers that are currently difficult to image and quantify, such as ovarian cancer and acute leukemia, are discussed.

The demise of the instant/unprepared contrast enema in large bowel obstruction

OBJECTIVE

Imaging the colon in suspected acute large bowel obstruction (LBO) is traditionally carried out with a supine abdominal X-ray (AXR) and erect chest X-ray. If there is no clinical or radiological evidence to suggest a perforation, then an unprepared barium or water-soluble contrast enema (CE) can be performed to confirm the presence of and demonstrate the site of obstruction. The advent of modern, fast multidetector CT (MDCT) scanners has changed management strategies for acute abdominal conditions including suspected LBO in all groups of patients especially the elderly, infirm and those on ITU/HDU.

METHOD

A retrospective case note analysis was carried over a 7-year period in a single centre. The study criteria involved investigation of suspected LBO with CE, CT and MDCT.

RESULTS

It showed a reduction in the number of contrast enemas performed.

CONCLUSION

MDCT was shown to be more accurate in the diagnosis of LBO, is usually available on a 24-h basis, and in many institutions has replaced the urgent CE in this group of patients. This also has the advantage of excluding incidental findings and in staging malignant disease.

Not your father's colonoscopy: a high-tech future for screening and surveillance of colorectal cancer

The 20-year technology slump in endoscopic innovation is finally giving way to a flurry of technologies, of which many are directed specifically at improving or even replacing traditional colonoscopy. These technologies include "smart" overtubes, electronically mapped and driven instruments, and completely self-propelled devices. In addition to nonendoscopic technologies such as CT, these innovations may dramatically alter the practice of colorectal cancer screening, the "bread and butter" of gastroenterologists in this country. There are multiple and complex forces driving these changes, including a mismatch between the supply and demand in colonoscopy, patient convenience and comfort, costs, and more recently, a growing concern about the miss rate of conventional colonoscopy.

Cancer risks from diagnostic radiology

In recent years, there has been a rapid increase in the number of CT scans performed, both in the US and the UK, which has fuelled concern about the long-term consequences of these exposures, particularly in terms of cancer induction. Statistics from the US and the UK indicate a 20-fold and 12-fold increase, respectively, in CT usage over the past two decades, with per caput CT usage in the US being about five times that in the UK. In both countries, most of the collective dose from diagnostic radiology comes from high-dose (in the radiological context) procedures such as CT, interventional radiology and barium enemas; for these procedures, the relevant organ doses are in the range for which there is now direct credible epidemiological evidence of an excess risk of cancer, without the need to extrapolate risks from higher doses. Even for high-dose radiological procedures, the risk to the individual patient is small, so that the benefit/risk balance is generally in the patients' favour. Concerns arise when CT examinations are used without a proven clinical rationale, when alternative modalities could be used with equal efficacy, or when CT scans are repeated unnecessarily. It has been estimated, at least in the US, that these scenarios account for up to one-third of all CT scans. A further issue is the increasing use of CT scans as a screening procedure in asymptomatic patients; at this time, the benefit/risk balance for any of the commonly suggested CT screening techniques has yet to be established.

Screening CT colonography: how I do it

OBJECTIVE

The purpose of this article is to detail an approach to CT colonographic screening that has evolved at one institution.

CONCLUSION

CT colonography is a rapidly advancing technology that has great potential for addressing a deadly but preventable disease-colorectal carcinoma. CT colonography is ideally suited for widespread screening of asymptomatic adults and has become an integral component of the screening efforts at my institution since local third-party coverage was initiated.