CT colonography (virtual colonoscopy) for the detection of colorectal polyps and neoplasms. current status and future developments

PET/CT colonography in patients with colorectal polyps: a feasibility study

PURPOSE

To examine: (1) the feasibility of PET/CT colonography (PET/CTc) in patients with colorectal polyps; (2) the impact of metabolic information on CTc interpretation and, conversely, the impact of morphological information on PET characterisation of focal colorectal uptake.

METHODS

Ten patients with colorectal polyps underwent PET/CTc, followed within 3 h by therapeutic conventional colonoscopy (CC). A radiologist and a nuclear medicine physician analysed the PET/CTc images. The agreement of morphological and metabolic information in the colon and rectum was evaluated. The sensitivity and specificity of PET, CT and PET/CT were calculated for colorectal polyps.

RESULTS

Seventeen polypoid lesions were identified at CC: six< or =5 mm, six between 6 and 9 mm, and five > or =10 mm (four hyperplastic polyps, 11 tubular adenomas, one adenocarcinoma and one submucosal lipoma). A total of 20 scans (supine and prone) were performed in the ten patients: the agreement of morphological and metabolic information was excellent in 17 scans, good in two and moderate in one. PET/CTc showed a sensitivity of 91% for lesions > or =6 mm and a specificity of 100%. The metabolic information did not disclose any further polyps missed on CTc. The morphological information permitted correct classification of all eight instances of focal radiotracer uptake.

CONCLUSION

PET/CTc is a feasible study. Adding a colonographic protocol to PET/CT images seems to allow correct characterisation of all cases of colorectal focal radiotracer uptake. The metabolic information does not seem to increase the accuracy of CTc.

Accuracy of single phase contrast enhanced multidetector CT colonography in the preoperative staging of colo-rectal cancer

AIM

The optimal acquisition time for staging colo-rectal carcinoma with a contrast enhanced multidetector CT colonography (CE CTC) has not yet been established. A dual phase with both arterial and portal venous acquisition has been proposed. The purpose of our study is to assess the value of single portal venous phase CE CTC in the preoperative staging of colo-rectal carcinoma.

MATERIALS AND METHODS

Fifty two (30 M, 22 F; aged 35-82 years) consecutive patients with a histologically proven diagnosis of colo-rectal adenocarcinoma or a highly suspected colo-rectal cancer on conventional colonoscopy underwent a four-slice CE CTC. The procedure was performed 70s (portal phase) after the intravenous bolus (3 ml/s) administration of 120 ml iodinated non-ionic contrast agent (370 mg iodine/ml). Scans were performed using the following parameters: 2.5mm beam collimation, pitch 1.25, 120 kV, 200 mAs, rotation time 0.75 s. Images were reconstructed with an effective thickness of 3.2mm at intervals of 1.6mm. Two radiologists independently evaluated the depth of tumour invasion into the colo-rectal wall (T), regional lymph node involvement (N), and extracolonic metastases (M). Disagreement was resolved by means of a consensus decision. The pathological results served as the standard of reference. Assessment was made of sensitivity, specificity and accuracy, as well as positive and negative predictive values were assessed.

RESULTS

CE CTC correctly staged the pT of 52/56 (93%) and the N of 40/56 (71%) lesions, as well as properly identifying 13/14 (93%) extracolonic findings.

CONCLUSION

The single portal venous phase CE CTC scanning protocol enables satisfactory preoperative assessment of T, N and M staging in patients with colo-rectal cancer.

Rectal perforations after barium enema: a review

PURPOSE

Rectal injuries during barium enema are rare but life-threatening complications. The last review about this subject was published more than ten years ago. In the present review, we present an overview on the subject and especially focus on changes in treatment strategies and developments of less risky visualization techniques.

METHODS

A literature search was performed in the PubMed library using the key words-barium enema, complications, peritonitis, and rectal perforation-as well as related articles and other references obtained from these articles.

RESULTS

The most frequent cause of perforation is iatrogenic and catheter-related. Other causes are related to weakness of the colorectal wall or obstruction. Five types of perforations have been described: 1) perforations of the anal canal below the levator; 2) incomplete perforations; 3) perforations into the retroperitoneum; 4) transmural perforations into adjacent viscera; 5) perforations into the free intraperitoneal cavity. Most incomplete perforations and one-half of the retroperitoneal perforations have minimal clinical signs. Intraperitoneal perforations lead to the most catastrophic course, starting with rectal bleeding and mild abdominal complaints. This is rapidly followed by progressive sepsis and peritonitis, and leads to a high mortality rate. Surgery is not always required for intramural or small retroperitoneal perforations. These can be treated conservatively and require surgical debridement only in case of large amounts of extravasation or abscesses. Surgical repair of large rectal mucosal lesions or anal sphincter lesions is advised. Perirectal abscesses require drainage. Intraperitoneal perforations with gross extravasation need immediate aggressive surgical treatment in a critical care setting, because the threat of shock is high. Intraperitoneal perforations, neglected perforations, gross barium extravasation, poorly prepared colon, and venous intravasation of barium are prognostically unfavorable. The severest late complication in intraperitoneal perforations is ileus. Meticulous technical performance of the barium enema is the most important factor in prevention.

CONCLUSIONS

Rectal perforations after barium enema are rare. The overall mortality rate decreased in recent decades from approximately 50 to 35 percent as the result of advances in supportive and intensive care. Because of these advances, more aggressive surgical strategies were undertaken. With the advent of endoscopy, less barium enemas are performed. Consequently, the absolute incidence of complications has decreased. It is expected that in the future barium enemas will be replaced by more sensitive and less risky techniques, such as CT colonography and magnetic resonance colonography.

Multislice CT Colonography: Current Status and Limitations

CT colonography (CTC) is a promising method for colorectal cancer screening because it provides a full structural evaluation of the entire colon. It has a superior safety profile, a low rate of complications, and high patient acceptance. In addition, CTC offers the real possibility of eliminating the cathartic bowel preparation, one of the biggest obstacles to patient compliance with colorectal cancer screening. Results of CTC studies in recently published literature are extremely encouraging, demonstrating that this method of screening can detect lesions equal to or larger than 8 mm with few false-positive findings.

Spasmolysis at CT colonography: butyl scopolamine versus glucagon

PURPOSE

To retrospectively determine if the use of butyl scopolamine or glucagon in the supine patient improves colonic distention and reduces the number of collapsed intestinal segments at computed tomographic (CT) colonography.

MATERIALS AND METHODS

This study had institutional review board approval; subject informed consent was not required. CT colonography was performed without the administration of an intravenous spasmolytic in 80 asymptomatic subjects (group 1; 45 women, 35 men; age range, 48-77 years; mean, 61.9 years). These subjects were matched with two groups of 80 subjects who were similar in age but were premedicated with glucagon (group 2; 41 women, 39 men; age range, 43-76 years; mean, 63.1 years) or butyl scopolamine (group 3; 43 women, 37 men; age range, 34-77 years; mean, 63.4 years). All 240 subjects were examined in the supine position with multisection CT and a section thickness of 1 mm after intravenous contrast agent administration and rectal carbon dioxide insufflation. The colon was divided into seven segments, and the colon length, total volume, radial distensibility, and number of non-distended segments were calculated for each subject and compared among the three groups. Statistical analysis was performed with analysis of variance and chi2 testing.

RESULTS

Mean bowel length was not significantly different among the groups. Mean colon volumes and radial distensibilities, respectively, were 1.84 L and 3.69 cm in group 1, 2.14 L and 3.98 cm in group 2, and 2.35 L and 4.23 cm in group 3; differences in colon volume and radial distensibility were significant only between group 1 and group 3 (P < .001). At CT colonography, 29 segments in 20 group 1 subjects were collapsed, 23 segments in 12 group 2 subjects were collapsed, and 11 segments in six group 3 subjects were collapsed (P = .016).

CONCLUSION

Premedication with butyl scopolamine or, less effectively, glucagon improves colonic distention in the supine subject.

Automatic colon segmentation with dual scan CT colonography

We present a fully automated three-dimensional (3-D) segmentation algorithm to extract the colon lumen surface in CT colonography. Focusing on significant-size polyp detection, we target at an efficient algorithm that maximizes overall colon coverage, minimizes the extracolonic components, maintains local shape accuracy, and achieves high segmentation speed. Two-dimensional (2-D) image processing techniques are employed first, resulting in automatic seed placement and better colon coverage. This is followed by near-air threshold 3-D region-growing using an improved marching-cubes algorithm, which provides fast and accurate surface generation. The algorithm constructs a well-organized vertex-triangle structure that uniquely employs a hash table method, yielding an order of magnitude speed improvement. We segment two scans, prone and supine, independently and with the goal of improved colon coverage. Both segmentations would be available for subsequent polyp detection systems. Segmenting and analyzing both scans improves surface coverage by at least 6% over supine or prone alone. According to subjective evaluation, the average coverage is about 87.5% of the entire colon. Employing near-air threshold and elongation criteria, only 6% of the data sets include extracolonic components (EC) in the segmentation. The observed surface shape accuracy of the segmentation is adequate for significant-size (6 mm) polyp detection, which is also verified by the results of the prototype detection algorithm. The segmentation takes less than 5 minutes on an AMD 1-GHz single-processor PC, which includes reading the volume data and writing the surface results. The surface-based segmentation algorithm is practical for subsequent polyp detection algorithms in that it produces high coverage, has a low EC rate, maintains local shape accuracy, and has a computational efficiency that makes real-time polyp detection possible. A fully automatic or computer-aided polyp detection system using this technique is likely to benefit future colon cancer early screening.

Added value of CT colonography after a positive conventional colonoscopy: impact on treatment strategy

BACKGROUND

Conventional colonoscopy (CC) requires an experienced operator to avoid technical or interpretative errors, and an endoscopic error rate of 14% for tumor localization has been reported. We evaluated the impact of computed tomographic colonography (CTC) on surgical treatment strategy in patients with CC reported as having colorectal neoplasm.

METHODS

Fifty-three patients testing positive for colorectal neoplasm on CC underwent CTC: 32 patients had CC in our hospital (group A) and 21 had CC in area hospitals (group B). All CTC procedures were performed with a multidetector CT system. The results of CTC and CC were compared with that of surgery. The preoperative surgical planning evaluated on the basis of CC and CTC was compared with the actual surgical approach, and the percentage of patients in whom CTC modified the treatment strategy suggested by CC was calculated.

RESULTS

CTC changed the treatment strategy in four of 53 patients (7.5%) in whom CC showed technical or interpretative errors. Group analysis showed that CTC did not influence the surgical management in any patient in group A but did affect treatment strategy in four of 21 patients (19%) in group B. The effect of CTC on treatment strategy between groups was statistically significant (p < 0.05). CTC identified five adenomas and three adenocarcinomas localized proximally to an impassable stenosis.

CONCLUSION

CTC can be used to reevaluate the findings of a positive CC and can indicate a more correct therapeutic approach in patients with colorectal neoplasms who are candidates for surgery.

An analysis of the potential impact of computed tomographic colonography (virtual colonoscopy) on colonoscopy demand

BACKGROUND AND AIMS

There has been much speculation about the potential impact on the use of conventional colonoscopy if "virtual" computed tomographic colonography (CTC) became a widely accepted modality for colorectal cancer (CRC) screening. However, no formal analysis of the impact of CTC on colonoscopy demand has been reported.

METHODS

A mathematical model to predict colonoscopy demand based on several relevant input parameters was constructed. Current national colonoscopy practice, estimated using various published reports, was used as the foundation to project colonoscopy demand if CTC were implemented as the primary CRC screening modality.

RESULTS

In the base-case analysis, if CTC were used as the primary modality for CRC screening, 1.78 million colonoscopies could be eliminated from the total 6.47 million in 2003. Depending on the polyp size threshold used to define a CTC study as positive (6 or 10 mm), this loss would be partially offset by 1.21 million (6 mm) or .34 million (10 mm) follow-up colonoscopies for CTC examinations with positive findings, resulting in a net loss of .57 million (8.8% decrease) (6 mm) or 1.44 million (22.3% decrease) (10 mm). Extensive sensitivity analyses showed that the findings of this model were robust and insensitive to most parameters tested but were sensitive to a few parameters, including the percentage of CTC examinations with positive findings.

CONCLUSIONS

Wide-scale implementation of CTC for CRC screening would likely lead to a decrease in use of conventional colonoscopy. The percentage of CTC studies with positive findings seemed to be a pivotal variable, which would be determined in large part by the polyp size ultimately established to define a positive finding.

Molecular stool screening for colorectal cancer

BACKGROUND

Mass screening for colorectal cancer reduces mortality and, with recent advances in molecular genetics, molecular stool-based tests have produced promising results. This article reviews this innovation and discusses its clinical significance.

METHODS

Medline searches were used to identify recent key articles relating to stool-based testing. Further articles were obtained by manual scanning of the reference lists of identified papers.

RESULTS

Current screening methods are based on endoscopic, radiological and stool-based testing. Recent recognition of the adenoma-carcinoma sequence and pathophysiological studies of colonic epithelium have enabled tumour markers to be used in the screening setting. Non-invasive molecular stool testing has now been shown to have a high sensitivity and specificity.

CONCLUSION

Recent studies on molecular stool-based testing have shown higher sensitivity and specificity than earlier studies, but larger clinical trials are required. Laboratory methods are still undergoing research, with the aim of improving sensitivity to allow large-scale testing.

Multislice CT colonography: current status and limitations

CT colonography (CTC) is a promising method for colorectal screening providing a full structural evaluation of the entire colon and gaining in popularity due to a superior safety profile, a low rate of complications, and high patient acceptance. Multislice CT (MSCT) has further improved the diagnostic potential of CTC by generating high-resolution CT images of the abdomen and pelvis in shorter acquisition times than was previously possible. Over the past year, multiple studies have been published on every aspect of CTC including techniques, image display, image reconstruction, and clinical trial results assessing the feasibility of CTC as a screening tool. Yet despite increasing clinical use, the appropriate role of CTC in colorectal cancer screening remains undefined and barriers to widespread adoption remain. In particular, though the test is generally regarded as easy to perform, accurate interpretation requires a steep learning curve. While several large studies have found high sensitivity and specificity, the accuracy of CTC in a screening population has yet to be verified and almost no health insurance plans reimburse for its use in colorectal screening. Ongoing research in computer-aided detection and new software tools, however, have the potential to increase accuracy and ease of interpretation significantly, accelerating its acceptance as a colorectal screening tool.

PET scan imaging in oncology

With the emergence of positron emission tomography (PET) from research laboratories into routine clinical use, it is important to redefine the most appropriate use of each imaging technique. The aim of this review article is to show the potential of PET in oncology. We discuss the most promising indications and the perspectives for the future. We will also point out the shortcomings and the important questions to be answered before fully considering PET as a necessary tool in the day-to-day practice of oncology. Although many studies have documented the high accuracy of 18F-FDG PET for the detection and staging of malignant tumours and for the monitoring of therapy results in these patients, it is very important to assess the impact of the technique on patient outcome and to show cost-effectiveness from the societal viewpoint.