Helical CT colonography (virtual colonoscopy): the challenge that exists between advancing technology and generalizability

Virtual Colonoscopy in Colorectal Cancer Screening

Colorectal cancer is the third most commonly diagnosed tumor in both males and females in the United States. Current modalities for colorectal cancer screening include fecal occult blood testing, flexible sigmoidoscopy, double-contrast barium enema, and colonoscopy. Virtual colonoscopy is a promising new method for assessing the entire colon. Vining and Gelfand first described this technique in 1994. Since then, virtual colonoscopy has been shown to be extremely safe and well tolerated by patients. Indications for virtual colonoscopy include screening for polyps, incomplete or failed colonoscopy, and preoperative assessment of the colon proximal to an occlusive cancer or even redundant fixed or stenotic colon that cannot be endoscopically traversed. Virtual colonoscopy may dramatically increase patient participation in screening programs, leading to early diagnosis of colorectal cancer. Although virtual colonoscopy seems a potentially attractive screening method for colorectal cancer, the cost-effectiveness of this method is yet to be determined.

A study on the usefulness of methylcellulose in rectal CT based on the analysis of the differences in absorption of radiation-permeable and radiation-impermeable materials

PURPOSE

The purpose of this study was to use various radiation-permeable and radiation-impermeable materials, used to facilitate the observation of a lesion during a rectal computed tomography (CT) scan, in order to determine the best material to use.

MATERIALS AND METHODS

In regard to the study method, the radiation-permeable and radiation-impermeable materials of physiological saline, methylcellulose, contrast medium, ultrasound gel, and air were used to perform scanning with scan parameters that were used in general abdominal scanning. The GSI mode was used for material analysis.

RESULTS

According to the results of the phantom study, the average CT value was 25.5 ± 5.9 HU for physiological saline, 77.6 ± 7.3 HU for methylcellulose, 3,070 ± 0.1 HU for contrast medium, 74.1 ± 11.9 HU for ultrasound gel, and -954.1 ± 10.3 HU for air. According to the analysis of materials by energy, contrast medium and physiological saline showed a dramatic decrease in the CT value as energy increased. Methylcellulose showed a gradual decrease in CT value, whereas air showed a small change in CT value according to the graph.

CONCLUSIONS

Out of these materials, methylcellulose had the advantage of reducing discomfort in patients, and was more convenient for examiners before and after the rectal CT scan.

Screening of patients after colectomy: virtual colonography

BACKGROUND

Virtual colonography is a powerful new method of imaging the entire colon and is useful to assess polyps and diagnose colon cancer. We evaluated virtual colonography in the postoperative screening of patients who had colon cancer.

METHODS

Fifty-three patients were examined with virtual colonography 12 to 48 months postoperatively. Forty-four patients had received segmental colectomy with restoration of the gastrointestinal tract, and nine patients underwent abdominoperineal resection and permanent colostomy. After proper cleaning of the colon and distention with air, spiral computed tomographic examination of the abdomen with a slice thickness of 5 mm (table speed [TS] 10 mm, reconstruction interval [RI] 2.5 mm) was performed in the supine and prone positions (including intravenous contrast medium infusion). Images were transferred to a separate workstation (Philips Easy Vision) for postprocessing, three-dimensional rendering, and endoluminal viewing.

RESULTS

Eleven recurrences (16.41%) were identified in 10 patients by virtual colonography, but one recurrence was missed. Conventional colonoscopy was incomplete in six cases, and two patients with colostomy refused colonoscopy. In these eight cases (15%), virtual colonoscopy was completed without problems. A second tumor in one patient who had received abdominoperineal resection was demonstrated by virtual colonography, but conventional colonoscopy failed to demonstrate the lesion. Liver metastases were identified in only one patient.

CONCLUSIONS

Virtual colonography seems to provide a good alternative in the follow-up of patients after colectomy. The technique is effective in the diagnosis of locoregional recurrences and distant metastases and is well accepted by patients, and results are equal to those of the conventional colonoscopy.

Digital subtraction bowel cleansing for CT colonography using morphological and linear filtration methods

We describe a method to perform postacquisition processing of computed tomography colonography (virtual colonoscopy) datasets that results in electronic removal of opacified, ingested bowel contents while reconstructing natural appearing boundaries of colon lumen and thereby permitting three-dimensional visual analyses of the resulting colon models.

Computed Tomography Colonography

OBJECTIVE

: To determine the feasibility of a computer-aided detection (CAD) algorithm as the "first reader" in computed tomography colonography (CTC).

METHODS

: In phase 1 of a 2-part blind trial, we measured the performance of 3 radiologists reading 41 CTC studies without CAD. In phase 2, readers interpreted the same cases using a CAD list of 30 potential polyps.

RESULTS

: Unassisted readers detected, on average, 63% of polyps > or =10 mm in diameter. Using CAD, the sensitivity was 74% (not statistically different). Per-patient analysis showed a trend toward increased sensitivity for polyps > or =10 mm in diameter, from 73% to 90% with CAD (not significant) without decreasing specificity. Computer-aided detection significantly decreased interobserver variability (P = 0.017). Average time to detection of the first polyp decreased significantly with CAD, whereas total reading case reading time was unchanged.

CONCLUSION

: Computer-aided detection as a first reader in CTC was associated with similar per-polyp and per-patient detection sensitivity to unassisted reading. Computer-aided detection decreased interobserver variability and reduced the time required to detect the first polyp.

Detection of colorectal lesions: lower-dose multi-detector row helical CT colonography compared with conventional colonoscopy

PURPOSE

To compare the performance of lower-dose multi-detector row helical computed tomographic (CT) colonography with that of conventional colonoscopy in the detection of colorectal lesions.

MATERIALS AND METHODS

One hundred fifty-eight patients underwent multi-detector row helical CT colonography (beam collimation, 4 x 2.5 mm; table feed, 17.5 mm/sec; voltage, 140 kV; and effective dose, 10 mAs) followed by conventional colonoscopy. Conventional colonoscopy served as the reference standard. Two radiologists interpreted CT colonographic images to assess the presence of polyps or carcinomas. Sensitivity was calculated on both a per-polyp and a per-patient basis. In the latter, specificity and positive and negative predictive values were also calculated. Weighted CT dose index was calculated on the basis of measurements obtained in a standard body phantom. Effective dose was estimated by using commercially available software.

RESULTS

CT colonography correctly depicted all 22 carcinomas (sensitivity, 100%) and 52 of 74 polyps (sensitivity, 70.3%). Sensitivity for detection was 100% in all 13 polyps 10 mm or larger in diameter, 83.3% in 20 of 24 polyps 6-9 mm, and 51.3% in 19 of 37 lesions 5 mm or smaller. With regard to the per-patient analysis, CT colonography had a sensitivity of 96.0%, a specificity of 96.6%, a positive predictive value of 94.1%, and a negative predictive value of 97.7%. The total weighted CT dose index for combined prone and supine acquisitions was 2.74 mGy. The simulated effective doses for complete CT colonography were 1.8 mSv in men and 2.4 mSv in women.

CONCLUSION

Lower-dose multi-detector row helical CT colonography ensures substantial dose reduction while maintaining excellent sensitivity for detection of colorectal carcinomas and polyps larger than 6 mm in diameter.

CT- and MR colonography

BACKGROUND

Colorectal cancer is the second most frequent cancer and adenomas are widely accepted as precursors to colorectal cancer. Diagnosis and removal of adenomas are recommended to reduce cancer incidence and mortality. The current diagnostic methods include sigmoidoscopy and colonoscopy. Lately, CT- and MR colonography have emerged as non-invasive methods for colon imaging.

METHODS

At present, CTC and MRC require bowel preparation. However, preliminary studies have been carried out without colon preparation. After the colon has been filled with air or contrast, the patient is scanned in the supine and prone positions. Data are then downloaded to a workstation for post processing and image-analysis.

RESULTS

Results have shown a high sensitivity and specificity for polyps > or = 10 mm, comparable to the sensitivity of conventional colonoscopy and superior to double contrast barium enema.

CONCLUSIONS

With the exponential development in computer processing power, CT- and MR colonography holds the promise for future colon examination with the advantages of non-invasiveness, no need for sedation, and probably no bowel preparation. A major disadvantage, however, is the radiation dose during CT colonography. Future developments with the use of "intelligent" computers, better resolution and faster examinations will make CT and/or MR colonography realistic options to replace conventional diagnostic colonoscopy.

Computed tomography gastrography with volume-rendering technique: correlation with double-contrast barium study and conventional gastroscopy

The volume-rendering technique uses computed tomography data to produce simulated images of conventional barium and endoscopic studies of the stomach. Various gastric lesions are detected on volume-rendered images, and submucosal tumors are easily differentiated from mucosal lesions by means of the overlying bridging fold. Lesions that are only manifested by a change of mucosal color (early gastric cancer type 2b) or a loss of mucosal detail (gastritis) are difficult to detect from volume-rendered images, however. In cases of gastric neoplasm and varix, both the extraluminal pathologies of the lesion and the relation between the intraluminal and extraluminal components can be evaluated simultaneously.

Patient preferences for CT colonography, conventional colonoscopy, and bowel preparation

OBJECTIVES

The aim of this study was to determine patient pre-examination expectations and postexamination appraisals for CT colonography, conventional colonoscopy and bowel preparation.

METHODS

Prospective evaluation of 120 patients at defined risk for colorectal neoplasia was performed with CT colonography followed by colonoscopy on the same day. Subjects were stratified by age and sex (67 women and 53 men) and were randomized to receive either manual air (n = 61) or CO(2) (n = 59) insufflation during CT colonography. Patients' expectations were assessed just before the two examinations, and appraisals were assessed 2 to 3 days afterward regarding pain/discomfort, embarrassment, difficulty, overall assessment, preference for future testing, and bowel preparation.

RESULTS

No significant differences were found in appraisals of manual air versus CO(2) insufflation techniques. For both CT colonography and colonoscopy, patients' appraisals after the procedure were significantly more positive than prior expectations. Patients expressed more favorable appraisals of colonoscopy for pain (p < 0.001) and embarrassment (p < 0.001), with most responses being "none" to "a little" for both examinations. Overall appraisals of the tests were favorable and similar between CT and colonoscopy: patients mainly expressed "not unpleasant" to "a little unpleasant" (95%, 114/120 for both examinations). Overall, appraisal of the bowel preparation was the most negative. Preferences for future testing were more favorable toward CT: of the patients, 58% (69/120) preferred CT, 14% (17/120) preferred colonoscopy, and 28% (34/120) had no preference.

CONCLUSIONS

Overall appraisals were similar and positive for both CT colonography and colonoscopy, with less favorable appraisals of the bowel preparation. Most patients stated that they would prefer CT for future evaluation.

CT colonography: digital subtraction bowel cleansing with mucosal reconstruction initial observations

The authors evaluated a computed tomography (CT) colonographic technique with a combination of preexamination orally ingested positive contrast material and postacquisition image processing to subtract out the ingested opacified bowel contents. With this technique, rigorous physical purging of the bowel was not necessary before structural examination of the colon. With images obtained in 20 patients, two readers were able to correctly identify the majority of polyps confirmed at colonoscopy. Their performance for detection of lesions larger than 1 cm was similar to that with conventional CT colonography.

The current status of multidetector row CT and three-dimensional imaging of the small bowel

Radiologists have played an important role in evaluation of patients with small bowel pathology. The small bowel series and, later, enteroclysis were the mainstays in radiologic diagnosis of many small bowel diseases, because the resolution and speed of CT was limited. Continued improvements in CT technology over the last 2 decades have resulted in a expanding role of CT for evaluation of the gastrointestinal tract, including the small intestine. Many conditions, such as small bowel obstruction and ischemia, that would traditionally be imaged with other modalities (small bowel series or angiography) are now routinely imaged with CT. The development of MDCT and improvements in 3D imaging systems have greatly improved the ability to examine the small bowel and mesenteric vasculature. With the introduction of new CT oral contrast agents and faster 32-detector row CT scanners, the diagnosis and evaluation of patients with small bowel disease will continue to improve.

Magnetic resonance colonography with fecal tagging: an innovative approach without bowel cleansing

To date, virtual colonography mandates bowel cleansing in a manner similar to colonoscopy. Because more than half of patients undergoing bowel preparation complain about negative side effects, patient acceptance is negatively impacted. To assure high patient acceptance of MR colonography, bowel cleansing needs to be eliminated. This can be accomplished by fecal tagging, a concept based on altering the signal intensity of stool by adding contrast-modifying substances to regular meals. This article describes different fecal tagging approaches and points out both advantages and limitations of these strategies.

CT colonography: multiobserver diagnostic performance

PURPOSE

To prospectively evaluate multiobserver diagnostic performance and reader agreement for colorectal polyp detection in a well-characterized cohort of patients with increased number of polyps, compared with an average-risk patient, with colonoscopy as the reference standard.

MATERIALS AND METHODS

A cohort of 70 patients suspected of having polyps was examined with spiral computed tomographic (CT) colonography, with colonoscopy performed the same day. After air insufflation per rectum, supine and prone images were obtained with single-detector row CT (5-mm collimation, 8-mm table increment, 2-mm reconstruction interval). Images were analyzed independently by four experienced abdominal radiologists using two-dimensional multiplanar reformation followed by selective use of three-dimensional endoscopic volume-rendered images. Data were analyzed both per polyp and per patient.

RESULTS

Analysis per polyp demonstrated a pooled sensitivity of 0.68 for lesions 10 mm or larger (n = 40), with 75% agreement among the four readers. Analysis per patient demonstrated improved detection and agreement, with a pooled sensitivity of 0.88 for patients with polyps or cancers 10 mm or larger (n = 28), with 94% agreement. When sensitivity and receiver operating characteristic analyses were analyzed per polyp size threshold, results among readers converged and peaked at polyp diameters of approximately 10 mm.

CONCLUSION

In this patient cohort, diagnostic performance and interobserver agreement with single-detector row CT colonography was sufficient for detection of patients with lesions 10 mm or larger, with more variable results for smaller polyps.

Optimization of scanning parameters for CT colonography

To determine the optimal collimation, pitch and reconstruction interval for CT colonography, 10 spherical polyps between 1 mm and 10 mm diameter and made of tissue equivalent material with a CT number of 40 Hounsfield units (HU) were placed in the colon of an anthropomorphic phantom. The phantom was scanned at slice thicknesses of 3 mm, 5 mm and 7 mm and pitches of 1.0, 1.3, 1.5, 1.7 and 2.0 on an IGE Hispeed advantage system. Images were reconstructed for each scanning parameter at the minimum intervals allowed along the z-axis. The optimum scanning protocol was assessed by measuring maximum contrast between the polyp and air, sensitivity for detection of each polyp along the z-axis, and relative radiation dose. In addition, images were reviewed separately by two radiologists who graded polyp conspicuity as: 0, not seen; 1, faintly seen; 2, well seen. It was found that varying the scanning parameters caused a marked alteration in the maximum contrast between each polyp and air. For example, for the 5 mm polyp, the range of contrasts from best to worst case was 910-490 HU. It was noted that with contrasts of less than 500 HU, polyps were only faintly seen. A slice thickness of 3 mm with a pitch of 2 offers optimal polyp conspicuity with a relatively low radiation dose, we conclude that scanning parameters can be optimized for threshold contrast, radiation dose and subjective conspicuity. We propose an optimal parameter of 3 mm slice thickness and pitch 2.

Virtual colonoscopy

Computerized tomographic colonography (CT colonography) is a new, non-invasive technique that has been developed over the last few years; it looks at the large bowel in detail. In this chapter we look at how the examination is performed and we consider how the images are displayed. We describe the normal features of the colon, as seen using this technique, as well as the features of common pathological conditions. We will discuss screening for colorectal cancer and the performance of CT colonography; we compare the latter with other procedures currently employed in the screening and diagnosis of colorectal pathology. We consider the difficulties in interpreting these CT colonographic images and look at ways to overcome such difficulties. Finally we discuss future developments of this exciting, new technique.

Detection of colorectal lesions with virtual computed tomographic colonography

BACKGROUND

The aim of our study was to compare the performance of virtual computed tomographic colonography with that of conventional colonoscopy in a blinded, prospective study in 165 patients with suspected colorectal lesions.

METHODS

There were 165 patients, all referred for conventional colonoscopy, who underwent preliminary virtual computed tomographic colonography. Computed tomograhic images of all suspected lesions were analyzed and subsequently compared with conventional colonoscopy findings.

RESULTS

There were 30 colorectal cancers and 37 polyps identified at conventional colonoscopy. Virtual computed tomographic colonography correctly detected all cancers, as well as 11 of 12 polyps of 10 mm in diameter or larger (sensitivity, 92%); 14 of 17 polyps between 6 and 9 mm (sensitivity, 82%); and 4 of 8 polyps of 5 mm or smaller (sensitivity, 50%). The per-patient sensitivity and specificity were 92% and 97%, respectively.

CONCLUSIONS

Virtual computed tomographic colonography has a diagnostic sensitivity similar to that of conventional colonoscopy for the detection of colorectal lesions larger than 6 mm in diameter.

Quantification of distention in CT colonography: development and validation of three computer algorithms

Three bowel distention-measuring algorithms for use at computed tomographic (CT) colonography were developed, validated in phantoms, and applied to a human CT colonographic data set. The three algorithms are the cross-sectional area method, the moving spheres method, and the segmental volume method. Each algorithm effectively quantified distention, but accuracy varied between methods. Clinical feasibility was demonstrated. Depending on the desired spatial resolution and accuracy, each algorithm can quantitatively depict colonic diameter in CT colonography.

Colon cancer screening with virtual colonoscopy: promise, polyps, politics

Virtual colonoscopy (CT colonography) promises to become a primary method for colorectal cancer screening and return radiologists to a major role in colon cancer prevention. Results from major centers in the United States show accuracy to be comparable to conventional colonoscopy for detection of polyps of significant size--that is, greater than 10 mm--with few false-positives. The advent of virtual colonoscopy has also heightened awareness of the natural history of colonic polyps, particularly in terms of identifying an appropriate target size for detection in colorectal screening programs. Small polyps (<10 mm) are often either hyperplastic on histology or are unlikely to progress to frank cancer in the patient's lifetime and are therefore of little clinical significance for the average adult. Thus, the rationale for detecting and removing each and every colonic polyp regardless of size has come under increasing scrutiny in the context of cost-benefit analysis of various test strategies for colorectal cancer screening. Virtual colonoscopy may allow patients to obtain reliable information about the status of their colonic mucosa noninvasively and thus make a more informed decision as to whether to proceed to conventional colonoscopy for polypectomy.

Bile-tagged 3d magnetic resonance colonography after exclusive intravenous administration of gadobenate dimeglumine, a contrast agent with partial hepatobiliary excretion

RATIONALE AND OBJECTIVES

Imaging of the colon is an important diagnostic procedure. Endoscopic colonoscopy and x-ray barium enemas are currently the standard diagnostic procedures. Magnetic resonance (MR) and computed tomographic colonography have been recently introduced with true three-dimensional (3D) cross-sectional imaging. Up to now, all imaging techniques have required the use of oral and/or aboral contrast agents for luminal enhancement and commonly, a relaxation medication (glucagon or N-butylscopolamine). While performing several phase I, II, and III studies with a new partially hepatobiliary excreted gadolinium-based MR contrast agent, we noted substantial intraluminal enhancement within the colon and investigated its potential for imaging.

METHODS

Three-dimensional MR angiographic techniques enable imaging of large volumes. We have used these sequences to detect contrast enhancement within the hepatobiliary and gastrointestinal systems. A 3D volume of 40 x 32 x 12 cm with 42 images was acquired under breath-hold. Six volunteers were studied according to the protocol. No bowel preparation was performed and no medication given. Subsequent follow-ups of the abdomen were performed at 1, 12, 24, 36, 48, 70, and 105 hours postinjection. Gadobenate dimeglumine at 0.1 mmol/kg body weight was given intravenously. Images were assessed quantitatively and by blinded reader analysis.

RESULTS

Intense intraluminal contrast enhancement within the colon was seen within 24 hours in all subjects. The homogeneous enhancement was of sufficient intensity to enable 3D visualization and virtual endoscopy. The optimal time window for imaging was determined to be 16 to 50 hours postinjection.

CONCLUSIONS

We report for the first time the feasibility of exclusively bile-tagged MR colonography with the use of only an intravenous MR contrast that exhibits partial hepatobiliary excretion. This new diagnostic procedure will enable not only morphological assessment of the colon but also functional and pathophysiological studies on the transport kinetics of bile and stool without any preparation of the patient.

CT colonography with teleradiology: effect of lossy wavelet compression on polyp detection--initial observations

PURPOSE

To assess the consequences of lossy compression on the diagnostic accuracy of CT colonography for detecting colonic polyps.

MATERIALS AND METHODS

Helical CT images of cleansed colonic segments were evaluated. Source images were compressed to 1:1, 10:1, and 20:1 ratios with lossy wavelet compression. Two independent readers blinded to corresponding colonoscopic results analyzed 144 randomly ordered colonic segments in multiplanar and volume-rendered endoscopic views. Sensitivity, specificity, and receiver operating characteristic curves were generated for each compression ratio on the basis of expressed confidence in lesion presence. Similar analyses were performed to assess distention and bowel preparation adequacy and evaluation time required.

RESULTS

Results based on video colonoscopy-confirmed lesions revealed 100% (four of four) sensitivity for lesions larger than 10 mm for compression ratios 1:1, 10:1, and 20:1 for both readers; sensitivities for all lesions smaller than 10 mm were 50%-78%, 38%-67%, and 38%-67% for respective ratios for both readers. Differences in diagnostic performance for each reader across ratios were not significant (P =.30-.99, McNemar test). The time required to evaluate and assess bowel preparation and distention adequacy did not change significantly across ratios.

CONCLUSION

On the basis of the patient sample, lossy compression of transverse source images to at least a 20:1 ratio did not adversely affect diagnostic performance or evaluation time for CT colonography.

Ultrasound virtual endoscopic imaging

Volume data acquisition, three dimensional (3D) imaging, and multiplanar reformatting have become widely used for computed tomography (CT) and magnetic resonance imaging (MRI). As an extension of this technology, virtual endoscopic visualization of hollow organs has become a reality that is now finding its way into clinical CT practice. The same methods of computer processing as are used for CT and MRI can be applied to an ultrasound (US) volume image data set with the same potential output; namely, 3D, multiplanar, and virtual endoscopic images. The use of this image processing technology for US applications has lagged behind the CT and MRI applications, but considerable progress in applying these methods to US has occurred in recent years. As a result, US virtual endoscopic imaging now can be performed on a clinical basis by using standard US instruments and commercially available computer software. The use of newer US imaging methods, such as tissue harmonic and power Doppler imaging, has enhanced the potential for US virtual endoscopy. This article reviews the technology of US virtual endoscopy. In addition, our preliminary experience of using this method for abdominal and vascular diagnosis is described. Finally, we speculate on technical improvements and potential applications that are likely in the future.

Spiral CT colonography: reader agreement and diagnostic performance with two- and three-dimensional image-display techniques

PURPOSE

To assess the diagnostic performance and reader agreement with two-dimensional (2D) and three-dimensional (3D) display techniques for detecting colorectal polyps with spiral computed tomographic (CT) colonography.

MATERIALS AND METHODS

A test set of 30 colonic segments was developed from spiral CT colonographic studies (12 with polyps and 18 without). The 12 segments with polyps contained 22 lesions (11 polyps <10 mm, 11 polyps or cancers >/=10 mm), with all findings verified with colonoscopy. Three specific 2D and 3D image-display techniques were tested. Three experienced abdominal radiologists independently analyzed each test case and were retested 6 weeks later.

RESULTS

The results of readings 1 and 2 were similar for all image-display techniques among the readers. Pooled segment results were sensitivity of 89%-92% and specificity of 72%-83%. Pooled polyp size results for sensitivity and positive predictive value were 77%-86% and 74%-86% (all polyps, n = 22), 91%-100% and 85%-100% (polyps or cancers >10 mm, n = 11), and 61%-73% and 61%-80% (polyps 5-9 mm, n = 11), respectively. Overall intraobserver agreement was good for the three display techniques (kappa, 0.60-1.00); however, interobserver agreement for 2D multiplanar reformation was lower (kappa, 0.53-0.80).

CONCLUSION

Among experienced abdominal radiologists, similar diagnostic performance in polyp detection was found among 2D multiplanar reformation and 3D display techniques, although individual cases showed improved characterization with 3D display techniques. Evaluation of reader agreement demonstrated good intraobserver agreement, with variable interobserver agreement.

Effect of different bowel preparations on residual fluid at CT colonography

The effect of different bowel preparations on residual fluid during computed tomographic (CT) colonography was evaluated. Forty-two patients received either a polyethylene glycol electrolyte solution preparation or a phospho-soda preparation the day prior to CT colonography. The amount of residual fluid was calculated for each patient. On average, a phospho-soda preparation provided significantly less residual fluid than a polyethylene glycol electrolyte solution preparation.

Virtual colonoscopy compared with conventional colonoscopy: a developing technology

AIM

To determine the accuracy of computed tomography colography (virtual colonoscopy) in detecting colorectal polyps and colorectal cancer.

DESIGN

Blinded comparison of virtual colonoscopy (initially supine-only scans and later supine plus prone scans) with the criterion standard of conventional colonoscopy.

SUBJECTS AND SETTING

100 patients aged 55 years or over referred to a public teaching hospital for colonoscopy, July 1997 to January 2000, because of colonic symptoms or a family history of bowel cancer.

MAIN OUTCOME MEASURES

Presence and size of polyps and other lesions; certainty of polyp identification on virtual colonoscopy (on 100-point visual analogue scale); sensitivity and predictive values of virtual colonoscopy.

RESULTS

Conventional colonoscopy identifed 121 polyps in 47 patients; 28 of these polyps, in 19 patients, were identified by virtual colonoscopy. Sensitivity of virtual colonoscopy for detecting polyps (using supine plus prone scans) was 73% for polyps with diameter > or = 10 mm (95% CI, 39%-94%) and 19% for smaller polyps (95% CI, 10%-31%) (P < 0.001); corresponding figures for supine-only scans were 57% (95% CI, 18%-90%) and 11% (95% CI, 4%-24%), respectively. Ten polyps identified at virtual colonoscopy were considered false-positive findings (8%). The value of finding a polyp on virtual colonoscopy (with thresholds of 5 mm for diameter and 30 points for certainty score) was assessed as a predictor of finding a polyp (diameter > 5 mm) on conventional colonoscopy. Positive and negative predictive values were 88% and 89%, respectively, for supine plus prone scans.

CONCLUSION

Although virtual colonoscopy shows potential as a diagnostic tool for colorectal neoplasia, it is currently not sufficiently sensitive for widespread use.

CT colonography: the next colon screening examination?

Computed tomographic (CT) colonography is a new-generation technique for detecting colorectal neoplasms by using volumetric CT data combined with specialized imaging software. Patient examinations require full colonic preparation, insufflation, and data acquisition with the patient in the supine and prone positions. Current CT technology allows a single image of the colon to be acquired in as little as 20 seconds with a minimum of patient discomfort. Specialized computer software for interpretation usually combines transverse, multiplanar reformation, and three-dimensional endoluminal images for the optimal visualization of the colon and rectum. As of the time this article was written, CT colonography was competitive as a full structural colonic examination for the detection of polyps and cancer. To the authors' knowledge, no study results have yet been reported in a screening population. The unique capabilities of CT colonography include the display of the proximal colon that is inaccessible at colonoscopy because of obstructing colonic lesions or because of incomplete endoscopic examinations and the assessment of extracolonic abdominal and pelvic organs. This abdominopelvic survey potential provides radiologists with an opportunity to discover other potentially life-threatening, asymptomatic conditions. Further technologic developments and validation studies are in progress. CT colonography is an exciting and promising technique with an enormous potential for colorectal screening in the future.

Gastrointestinal radiology in the United States: An overview of the past 50 years

Gastrointestinal radiology has expanded its scope beyond conventional abdominal radiography, barium studies, and cholecystography. Ultrasonography allows imaging of solid abdominal organs and the intestine without the use of radiation. Computed tomography now allows comprehensive assessment of abdominal and pelvic inflammatory and infectious processes, obstruction, tumor detection and staging, and display of vasculature and blunt trauma effects that were not possible 50 years ago. Magnetic resonance imaging provides multiplanar imaging to the same degree, without the use of radiation. Barium studies of the gastrointestinal tract, enteroclysis for small-bowel assessment, and conventional radiography still have a role, despite the extensive use of fiberoptic endoscopy. Fluoroscopy is still important, but great advances in technologies have changed gastrointestinal radiology irrevocably.

Developments in imaging. An historical review

Following the discovery of X-rays by Roentgen in 1895, it was 70 years later that the specialty of imaging really took off, with ultrasound, CT, Nuclear medicine, and MRI now an integral part of all large departments. The recent progress has been accelerated by advances in computer technology which aided the development of imaging techniques that do not use ionising radiation. Some imaging techniques are replacing other more hazardous diagnostic procedures, (e.g. MRCP v ERCP, and MRA v catheter angiography) while some are able to provide almost perfect anatomical detail e.g. brain MRI. Techniques using radioisotopes provide more functional information which can be used to complement the morphological studies. We have witnessed the birth and maturation of Interventional Radiology. This is a highly skilled subspecialty enabling some surgical procedures to be replaced by minimally invasive methods using image guidance. These range from simple drainage procedures and guided biopsies to complex aortic bifurcation stent graft insertions. The potential for digital storage of all images is already established and the filmless radiology department in the more developed countries could be the norm by 2020.