Feasibility of MDCT Colonography in ultra-low-dose technique in the detection of colorectal lesions: comparison with high-resolution video colonoscopy

Technical Note: Increased photon starvation artifacts at low helical pitch in ultra-low-dose CT

PURPOSE

The aim of this study was to demonstrate that a low helical pitch causes increased photon starvation artifacts at ultra-low-dose CT.

METHODS

A cylindrical water phantom with a diameter of 30 cm was scanned on two different generation CT scanners: a 64-slice scanner (Sensation 64, Siemens Healthcare) and a 192-slice scanner (Somatom Force, Siemens Healthcare) at multiple effective mAs levels (mAs/pitch = 200, 100, 50, 25, and 12). The corresponding CTDI_vol values were 4.1, 2.0, 1.0, 0.5 mGy, on the 64-slice scanner and 3.8, 1.9, 1.0, 0.5 mGy on the 192-slice scanner, for the selected effective mAs values. For each dose setting, the scan was repeated at four helical pitches: 1.2, 0.9, 0.6, and the lowest achievable pitch on each scanner. The tube current was automatically adjusted by the scanner so that the effective mAs, and thus CTDI_vol , were kept the same for different pitches. All CT data sets were reconstructed with a slice thickness of 3mm and a medium smooth kernel. Images acquired at the same dose level but different helical pitches were visually inspected to assess photon starvation artifacts and noise levels.

RESULTS

At the same radiation dose, image noise increased with the decreasing helical pitch. The increase was more severe on the old-generation 64-slice scanner. Photon starvation artifacts were evident at 200 effective mAs on the 64-slice scanner at 80 kV. On the 192-slice scanner there was no visible photon starvation artifacts at both 200 and 50 effective mAs (CTDI_vol  = 4.1 mGy and 1.0 mGy, respectively); nor was there a visible impact from the lower helical pitch. Only when the dose was lowered to be extremely low (~0.26 mGy, achievable at 70 kV), did photon starvation artifacts become evident.

CONCLUSIONS

A low helical pitch may increase image noise and photon starvation artifacts compared to a higher pitch for the same dose level, particularly at ultra-low dose CT.

Ultra-low dose CT colonography with automatic tube current modulation and sinogram-affirmed iterative reconstruction: Effects on radiation exposure and image quality

Objective

To assess the radiation dose and image quality of ultra‐low dose (ULD)‐CT colonography (CTC) obtained with the combined use of automatic tube current (mAs) modulation with a quality reference mAs of 25 and sinogram‐affirmed iterative reconstruction (SAFIRE), compared to low‐dose (LD) CTC acquired with a quality reference mAs of 55 and reconstructed with filtered back projection (FBP).

Methods

Eighty‐two patients underwent ULD‐CTC acquisition in prone position and LD‐CTC acquisition in supine position. Both ULD‐CTC and LD‐CTC protocols were compared in terms of radiation dose [weighted volume computed tomography dose index (CTDI_vol) and effective dose], image noise, image quality, and polyp detection.

Results

The mean effective dose of ULD‐CTC was significantly lower than that of LD‐CTC (0.98 and 2.69 mSv respectively, P < 0.0001) with an overall dose reduction of 63.2%. Image noise was comparable between ULD‐CTC and LD‐CTC (28.6 and 29.8 respectively, P = 0.09). There was no relevant difference when comparing image quality scores and polyp detection for both 2D and 3D images.

Conclusion

ULD‐CTC allows to significantly reduce the radiation dose without meaningful image quality degradation compared to LD‐CTC.

Low-Dose Computed Tomography Colonography Technique

Significant anxiety has been expressed by some over the radiation risks associated with computed tomography (CT), particularly when it applies to a screening examination such as CT colonography. These theoretic risks are far outweighed by the significant benefits colorectal cancer screening offers. Regardless of how significant the theoretic risk of CT radiation is in the older population, the ALARA principle maintains that radiation dose should be reduced to As Low As Reasonably Achievable. This article will discuss various strategies that may be utilized to reduce radiation dose and mitigate any increase in image noise that may occur.

Sub-milliSievert ultralow-dose CT colonography with iterative model reconstruction technique

Purpose. The purpose of this study was to evaluate the technical and diagnostic performance of sub-milliSievert ultralow-dose (ULD) CT colonograpy (CTC) in the detection of colonic and extracolonic lesions.

Materials and Methods. CTC with standard dose (SD) and ULD acquisitions of 64 matched patients, half of them with colonic findings, were reconstructed with filtered back projection (FBP), hybrid (HIR) and iterative model reconstruction techniques (IMR). Image noise in six colonic segments, in the left psoas muscle and aorta were measured. Image quality of the left adrenal gland and of the colon in the endoscopic and 2D view was rated on a five point Likert scale by two observers, who also completed the reading of CTC for colonic and extracolonic findings.

Results. The mean radiation dose estimate was 4.1 ± 1.4 mSv for SD and 0.86 ± 0.17 mSv for ULD for both positions (p < 0.0001). In ULD-IMR, SD-IMR and SD-HIR, the endoluminal noise was decreased in all colonic segments compared to SD-FBP (p < 0.001). There were 27 small (6–9 mm) and 17 large (≥10 mm) colonic lesions that were classified as sessile polyps (n = 38), flat lesions (n = 3), or as a mass (n = 3). Per patient sensitivity and specificity were 0.82 and 0.93 for ULD-FBP, 0.97 and 0.97 for ULD-HIR, 0.97 and 1.0 for ULD-IMR. Per polyp sensitivity was 0.84 for ULD-FBP, 0.98 for ULD-HIR, 0.98 for ULD-IMR. Significantly less extracolonic findings were detected in ULD-FBP and ULD-HIR, but in the E4 category by C-RADS (potentially important findings), the detection was similar.

Conclusion. Both HIR and IMR are suitable for sub-milliSievert ULD CTC without sacrificing diagnostic performance of the study.

Submilisievert ultralow-dose CT colonography using iterative reconstruction technique: a feasibility study

BACKGROUND

Computed tomography (CT) colonography is a well established modality for the examination of symptomatic patients as well as in screening. Recent technical advances in improving image quality by iterative reconstruction contribute to the reduction of the radiation dose which is a major concern in CT imaging.

PURPOSE

To evaluate image quality of ultralow-dose submilisievert CT colonography using hybrid iterative reconstruction technique.

MATERIAL AND METHODS

Sixteen patients underwent contrast-enhanced CT colonography with standard protocol in supine position and ultralow-dose protocol in prone position. Ultralow-dose datasets were reconstructed with filtered back projection and an advanced hybrid iterative reconstruction technique. Two radiologists independently evaluated 96 colonic segments for image quality in the endoluminal view and axial thin sections. Colonic distension, smoothness of colonic wall and distortion of folds in the endoluminal view, sharpness of colonic wall delineation, perceived image noise, and presence of photon starvation artifact were rated on a five-point scale. Intraluminal noise expressed as standard deviation of Hounsfield density was measured in all segments.

RESULTS

The mean radiation dose was 0.42 mSv and 5.48 mSv in prone and supine scans, respectively. All distended segments were rated evaluable in standard dose and ultralow-dose series reconstructed with the iterative reconstruction technique, whereas in 61% segments image quality was rated poor or unacceptable in ultralow-dose series where filtered back projection was used with worst ratings in the rectum and the sigmoid colon.

CONCLUSION

This pilot study shows that iterative reconstruction technique is a feasible method to decrease the radiation dose from CT colonography for both positions below 1mSv. Further investigations of larger scale need to be done to clarify, whether such a low radiation dose would influence the detection of polyps.

Pilot study on image quality and radiation dose of CT colonography with adaptive iterative dose reduction three-dimensional

Objective

To investigate image quality and radiation dose of CT colonography (CTC) with adaptive iterative dose reduction three-dimensional (AIDR3D).

Methods

Ten segments of porcine colon phantom were collected, and 30 pedunculate polyps with diameters ranging from 1 to 15 mm were simulated on each segment. Image data were acquired with tube voltage of 120 kVp, and current doses of 10 mAs, 20 mAs, 30 mAs, 40 mAs, 50 mAs, respectively. CTC images were reconstructed using filtered back projection (FBP) and AIDR3D. Two radiologists blindly evaluated image quality. Quantitative evaluation of image quality included image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Qualitative image quality was evaluated with a five-score scale. Radiation dose was calculated based on dose-length product. Ten volunteers were examined supine 50 mAs with FBP and prone 20 mAs with AIDR3D, and image qualities were assessed. Paired t test was performed for statistical analysis.

Results

For 20 mAs with AIDR3D and 50 mAs with FBP, image noise, SNRs and CNRs were (16.4 ± 1.6) HU vs. (16.8 ± 2.6) HU, 1.9 ± 0.2 vs. 1.9 ± 0.4, and 62.3 ± 6.8 vs. 62.0 ± 6.2, respectively; qualitative image quality scores were 4.1 and 4.3, respectively; their differences were all not statistically significant. Compared with 50 mAs with FBP, radiation dose (1.62 mSv) of 20 mAs with AIDR3D was decreased by 60.0%. There was no statistically significant difference in image noise, SNRs, CNRs and qualitative image quality scores between prone 20 mAs with AIDR3D and supine 50 mAs with FBP in 10 volunteers, the former reduced radiation dose by 61.1%.

Conclusion

Image quality of CTC using 20 mAs with AIDR3D could be comparable to standard 50 mAs with FBP, radiation dose of the former reduced by about 60.0% and was only 1.62 mSv.

Model-based vs hybrid iterative reconstruction technique in ultralow-dose submillisievert CT colonography

OBJECTIVE

To compare image quality of different reconstruction techniques in submillisievert ultralow-dose CT colonography (CTC) and to correlate colonic findings with subsequent optical colonoscopy.

METHODS

58 patients underwent ultralow-dose CTC. The images were reconstructed with filtered back projection (FBP), hybrid iterative reconstruction (HIR) or model-based iterative reconstruction (MBIR) techniques. In each segment, endoluminal noise (expressed as standard deviation of endoluminal density) was measured and image quality was rated on a five-point Likert scale by two independent readers. Colonic lesions were evaluated in consensus and correlated with subsequent optical colonoscopy where possible.

RESULTS

The estimated radiation dose was 0.41 ± 0.05 mSv for the supine and 0.42 ± 0.04 mSv for the prone acquisitions. In the endoluminal view, the image quality was rated better in HIR, whereas better scores were obtained in MBIR in the cross-sectional view, where the endoluminal noise was the lowest (p < 0.0001). Five (26%) polyps were not identified using both computer-aided detection and endoluminal inspection in FBP images vs only one (5%) in MBIR and none in HIR images.

CONCLUSION

This study showed that in submillisievert ultralow-dose CTC, the image quality for the endoluminal view is better when HIR is used, whereas MBIR yields superior images for the cross-sectional view. The inferior quality of images reconstructed with FBP may result in decreased detection of colonic lesions.

ADVANCES IN KNOWLEDGE

Radiation dose from CTC can be safely reduced <1 mSv for both positions when iterative reconstruction is used. MBIR provides better image quality in the cross-sectional view and HIR in the endoluminal view.

Ultra-low peak voltage CT colonography: effect of iterative reconstruction algorithms on performance of radiologists who use anthropomorphic colonic phantoms

PURPOSE

To analyze the effect of a decrease in computed tomographic (CT) colonographic voltage, from 100 and 120 kVp to 80 kVp and reconstructed with filtered back projection ( FBP filtered back projection ), on radiation dose, image noise, and diagnostic performance in anthropomorphic phantoms and to assess the effect of iterative reconstruction ( IR iterative reconstruction ) algorithms on radiologists' performance for 80-kVp CT colonography.

MATERIALS AND METHODS

Seven colon phantoms with 68 simulated polyps (≥6 mm) were scanned at three peak voltage settings (80, 100, 120 kVp) and 10 mAs. Images were reconstructed by using FBP filtered back projection , hybrid statistic-based IR iterative reconstruction , and knowledge-based IR iterative reconstruction algorithms. Effective radiation dose, image noise, and per-polyp sensitivity were recorded and compared by two reviewers with Friedman test, repeated measures analysis of variance, and McNemar test.

RESULTS

Median size-specific dose estimate and effective radiation dose of 80-kVp CT colonography was 0.231 mGy and 0.167 mSv, respectively, which was lower than with 100- and 120-kVp CT colonography, with significant difference between 80 and 120 kVp (P = .0005). Image noise (202.0 HU) at 80-kVp FBP filtered back projection CT colonography was significantly higher than at 100-kVp FBP filtered back projection (139.1 HU) and 120-kVp FBP filtered back projection (120.4 HU) (P < .0001). Per-polyp sensitivity (reviewer 1, 14.7% [10 of 68]; reviewer 2, 7.4% [five of 68]) at 80-kVp FBP filtered back projection was significantly lower than at 100-kVp FBP filtered back projection (reviewer 1, 57.4% [39 of 68]; reviewer 2, 39.7% [27 of 68]) and 120-kVp FBP filtered back projection (reviewer 1, 85.3% [58 of 68]; reviewer 2, 83.8% [57 of 68]) (P < .0001). With statistic-based IR iterative reconstruction , image noise at 80 kVp decreased significantly (52.8% [106.7 HU of 202.0 HU]) compared with that at 80-kVp FBP filtered back projection (P < .0001), but per-polyp sensitivity (reviewer 1, 79.4% [54 of 68]; reviewer 2, 66.2% [45 of 68]) at 80-kVp statistic-based IR iterative reconstruction remained significantly lower than at 100-kVp statistic-based IR iterative reconstruction (reviewer 1, 95.6% [65 of 68]; reviewer 2, 86.8% [59 of 68]) (P = .001) and 120-kVp statistic-based IR iterative reconstruction (reviewer 1, 98.5% [67 of 68]; reviewer 2, 89.7% [61 of 68]) (P < .001). For knowledge-based IR iterative reconstruction , per-polyp sensitivity at 80 kVp was improved to 98.5% (67 of 68) and 94.1% (64 of 68), not significantly different from that at 100 kVp (reviewer 1, 100% [68 of 68]; reviewer 2, 95.6% [65 of 68]) and 120 kVp (reviewer 1, 100% [68 of 68]; reviewer 2, 95.6% [65 of 68]) (P > .999).

CONCLUSION

A decrease in tube voltage to 80 kVp caused reduction in radiation dose (0.166 mSv) with deterioration in image noise and per-polyp sensitivity. By using a knowledge-based IR iterative reconstruction algorithm, radiologists' performance of 80-kVp CT colonography was acceptable and on par with that at 100- or 120-kVp CT colonography.

In vivo CT dosimetry during CT colonography

OBJECTIVE

The purpose of this study was to develop a method of measuring rectal radiation dose in vivo during CT colonography (CTC) and assess the accuracy of size-specific dose estimates (SSDEs) relative to that of in vivo dose measurements.

MATERIALS AND METHODS

Thermoluminescent dosimeter capsules were attached to a CTC rectal catheter to obtain four measurements of the CT radiation dose in 10 volunteers (five men and five women; age range, 23-87 years; mean age, 70.4 years). A fixed CT technique (supine and prone, 50 mAs and 120 kVp each) was used for CTC. SSDEs and percentile body habitus measurements were based on CT images and directly compared with in vivo dose measurements.

RESULTS

The mean absorbed doses delivered to the rectum ranged from 8.8 to 23.6 mGy in the 10 patients, whose mean body habitus was in the 27th percentile among American adults 18-64 years old (range, 0.5-67th percentile). The mean SSDE error was 7.2% (range, 0.6-31.4%).

CONCLUSION

This in vivo radiation dose measurement technique can be applied to patients undergoing CTC. Our measurements indicate that SSDEs are reasonable estimates of the rectal absorbed dose. The data obtained in this pilot study can be used as benchmarks for assessing dose estimates using other indirect methods (e.g., Monte Carlo simulations).

The time has arrived for national reimbursement of screening CT colonography

OBJECTIVE

CT colonography (CTC) has been fully validated as an accurate screening test for colorectal carcinoma and is being disseminated globally. There is an abundance of new literature addressing the prior concerns of the U.S. Preventive Services Task Force and the Centers for Medicare & Medicaid Services. Specific areas related to radiation dose, extracolonic findings, and generalizability of CTC to senior patients are discussed.

CONCLUSION

The time has arrived for national reimbursement of CTC in the United States.

Dose reduction methods for CT colonography

Patients, referring physicians, the media, and government agencies have all expressed concern over the risks of medical radiation, particularly as it relates to CT. This concern is particularly paramount when associated with a screening examination such as CT colonography. These theoretical risks must be weighed realistically against the substantial benefits of colon cancer screening as well as against the risks inherent in the major alternative screening option, optical colonoscopy. When put into perspective, the risk-benefit ratio is highly in favor of the performance of CT colonography. Nevertheless, in following the ALARA principle, there is an ever increasing armamentarium of options that can be employed in the pursuit of CT radiation dose reduction, all of which can be used in many synergistic combinations allowing for dose reduction while simultaneously preserving image quality and minimizing image noise. After a brief tutorial on estimating radiation dose, various strategies will be discussed including reductions in tube current and tube voltage as well as the use of automatic dose modulation and iterative reconstruction. Other practical considerations will also be reviewed including proper patient isocentering, optimization of colonic insufflation to minimize additional decubitus scans, proper choice of scan volumes to avoid overranging, and variation of slice thickness and window width to minimize perceived image noise. Finally, a strategy for how to incrementally introduce these methods as well as a way to compare dose reduction efforts across institutions throughout the country will be offered.

Effective radiation dose in CT colonography: is there a downward trend?

RATIONALE AND OBJECTIVES

Radiation dose is an important drawback of computed tomography (CT) colonography, especially for its use as a screening tool for colorectal cancer. It is therefore important to know the present radiation dose. Our objective is to assess the effective radiation doses used for CT colonography and its trend over time.

MATERIALS AND METHODS

Institutions performing CT colonography research were asked to provide their CT colonography protocols. Median effective doses were calculated and compared with a 2007 inventory. Separate analyses were performed for protocols using intravenous contrast medium and for academic versus nonacademic institutions. Differences in effective dose were tested for significance, using Wilcoxon rank-sum or Wilcoxon signed-rank test.

RESULTS

Sixty-two of 109 (57%) institutions responded, providing protocols for 58 institutions. Median effective dose for daily practice protocols was 7.6 mSv (4.3 mSv and 2.0 mSv for supine and prone, respectively) and for screening 4.4 mSv (2.6 mSv and 2.0 mSv, respectively; P = .01). For daily practice with and without contrast medium, the median effective doses were 10.5 mSv and 4.0 mSv (P < .001), respectively. Academic and nonacademic institutions used similar doses (all comparisons P > .05). For institutions also participating in the 2007 inventory, effective dose for both daily practice and screening protocols were similar (P > .05).

CONCLUSION

In 2011 the median effective radiation dose for daily practice protocols was 7.6 mSv and for screening 4.4 mSv. Median effective doses have not decreased as compared to 2007. Academic and nonacademic institutions use similar radiation dose.

Evaluation of ultra-low dose CT in the diagnosis of pediatric-like fractures using an experimental animal study

Objective

The aim of this prospective study was to evaluate the performance of ultra-low dose CT for the diagnosis of pediatric-like fractures and ascertain the lowest dose level sufficient for diagnostics.

Materials and Methods

Fifty-one bones of young pig cadavers were artificially fractured and subsequently examined by using a 64 multi-detector CT with 36 various dose levels down to a dose comparable with that of X-rays. Two pediatric radiologists analysed the CT scans according to the presence or absence of a fracture, determination of the fracture type and the displacement as well as the diagnostic certainty. For each dose protocol, a success rate for the correct determination of the above-mentioned CT analyses was calculated. A success rate of at least 95% was considered sufficient for diagnostics.

Results

All but the lowest dose levels were sufficient to identify the fracture. Only the two lowest dose levels were insufficient to detect the fracture type. All dose levels were adequate for the identification of the displacement. The lowest dose level sufficient for diagnostics was 120 kVp, 11 mAs, and pitch 1.5, with a CTDIvol of 10% of a standard dose and an effective dose three times as large as that of X-rays.

Conclusion

Ultra-low dose CT provides the feasibility of a significant dose reduction, still allowing sufficient diagnostics of pediatric-like fractures.

Colon distension and scan protocol for CT-colonography: an overview

This article reviews two important aspects of CT-colonography, namely colonic distension and scan parameters. Adequate distension should be obtained to visualize the complete colonic lumen and optimal scan parameters should be used to prevent unnecessary radiation burden. For optimal distension, automatic carbon dioxide insufflation should be performed, preferably via a thin, flexible catheter. Hyoscine butylbromide is - when available - the preferred spasmolytic agent because of the positive effect on insufflation and pain/burden and its low costs. Scans in two positions are required for adequate distension and high polyp sensitivity and decubitus position may be used as an alternative for patients unable to lie in prone position. The great intrinsic contrast between air or tagging and polyps allows the use of low radiation dose. Low-dose protocol without intravenous contrast should be used when extracolonic findings are deemed unimportant. In patients suspected for colorectal cancer, normal abdominal CT scan protocols and intravenous contrast should be used in supine position for the evaluation of extracolonic findings. Dose reduction can be obtained by lowering the tube current and/or voltage. Tube current modulation reduces the radiation dose (except in obese patients), and should be used when available. Iterative reconstructions is a promising dose reducing tool and dual-energy CT is currently evaluated for its applications in CT-colonography. This review also provides our institution's insufflation procedure and scan parameters.

Reducing the radiation dose for CT colonography using adaptive statistical iterative reconstruction: A pilot study

OBJECTIVE

The purpose of our study was to evaluate the feasibility of preserving image quality during CT colonography (CTC) using a reduced radiation dose with adaptive statistical iterative reconstruction (ASIR).

MATERIALS AND METHODS

A proven colon phantom was imaged at standard dose settings (50 mAs) and at reduced doses (10-40 mAs) using six different ASIR levels (0-100%). We assessed 2D and 3D image quality and noise to determine the optimal dose and ASIR setting. Eighteen patients were then scanned with a standard CTC dose (50 mAs) in the supine position and at a reduced dose of 25 mAs with 40% ASIR in the prone position. Three radiologists blinded to the scanning techniques assessed 2D and 3D image quality and noise at three different colon locations. A score difference of > or = 1 was considered clinically important. Actual noise measures were compared between the standard-dose and low-dose acquisitions.

RESULTS

The phantom study showed image noise reduction that correlated with a higher percentage of ASIR. In patients, no significant image quality differences were identified between standard- and low-dose images using 40% ASIR. Overall image quality was reduced for both image sets as body mass index increased. Measured image noise was less with the low-dose technique using ASIR.

CONCLUSION

The results of this pilot study show that the radiation dose during CTC can be reduced 50% below currently accepted low-dose techniques without significantly affecting image quality when ASIR is used. Further evaluation in a larger patient group is warranted.

CT colonography: perforation rates and potential radiation risks

Computed tomographic colonography (CTC) has emerged as an alternative screening tool for colorectal cancer due to the potential to provide good efficacy combined with greater acceptability than optical colonoscopy or fecal occult blood testing. However, some organizations have raised concerns about the potential harms, including perforation rates and radiation-related cancer risks, and have not recommended that it currently be used as a screening tool in the general population in the US. In this article the authors review the current evidence for these potential harms from CTC and compare them to the potential harms from the alternatives including colonoscopy and double-contrast barium enema.

Innovations in CT dose reduction strategy: application of the adaptive statistical iterative reconstruction algorithm

OBJECTIVE

The purpose of this article is to discuss the application of a new CT reconstruction algorithm, adaptive statistical iterative reconstruction (ASIR), to reduce radiation dose at body CT and to provide imaging examples in comparison with low-dose and standard-dose filtered back projection CT.

CONCLUSION

The ASIR reconstruction algorithm is a promising technique for providing diagnostic quality CT images at significantly reduced radiation doses.

ACR Colon Cancer Committee white paper: status of CT colonography 2009

PURPOSE

To review the current status and rationale of the updated ACR practice guidelines for CT colonography (CTC).

METHODS

Clinical validation trials in both the United States and Europe are reviewed. Key technical aspects of the CTC examination are emphasized, including low-dose protocols, proper insufflation, and bowel preparation. Important issues of implementation are discussed, including training and certification, definition of the target lesion, reporting of colonic and extracolonic findings, quality metrics, reimbursement, and cost-effectiveness.

RESULTS

Successful validation trials in screening cohorts both in the United States with ACRIN and in Germany demonstrated sensitivity > or = 90% for patients with polyps >10 mm. Proper technique is critical, including low-dose techniques in screening cohorts, with an upper limit of the CT dose index by volume of 12.5 mGy per examination. Training new readers includes the requirement of interactive workstation training with 2-D and 3-D image display techniques. The target lesion is defined as a polyp > or = 6 mm, consistent with the American Cancer Society joint guidelines. Five quality metrics have been defined for CTC, with pilot data entered. Although the CMS national noncoverage decision in May 2009 was a disappointment, multiple third-party payers are reimbursing for screening CTC. Cost-effective modeling has shown CTC to be a dominant strategy, including in a Medicare cohort.

CONCLUSION

Supported by third-party payer reimbursement for screening, CTC will continue to further transition into community practice and can provide an important adjunctive examination for colorectal screening.

Iterative reconstruction technique for reducing body radiation dose at CT: feasibility study

OBJECTIVE

The purpose of this study was to evaluate the image noise, low-contrast resolution, image quality, and spatial resolution of adaptive statistical iterative reconstruction in low-dose body CT.

MATERIALS AND METHODS

Adaptive statistical iterative reconstruction was used to scan the American College of Radiology phantom at the American College of Radiology reference value and at one-half that value (12.5 mGy). Test objects in low- and high-contrast and uniformity modules were evaluated. Low-dose CT with adaptive statistical iterative reconstruction was then tested on 12 patients (seven men, five women; average age, 67.5 years) who had previously undergone routine-dose CT. Two radiologists blinded to scanning technique evaluated images of the same patients obtained with routine-dose CT and low-dose CT with and without adaptive statistical iterative reconstruction. Image noise, low-contrast resolution, image quality, and spatial resolution were graded on a scale of 1 (best) to 4 (worst). Quantitative noise measurements were made on clinical images.

RESULTS

In the phantom, low- and high-contrast and uniformity assessments showed no significant difference between routine-dose imaging and low-dose CT with adaptive statistical iterative reconstruction. In patients, low-dose CT with adaptive statistical iterative reconstruction was associated with CT dose index reductions of 32-65% compared with routine imaging and had the least noise both quantitatively and qualitatively (p < 0.05). Low-dose CT with adaptive statistical iterative reconstruction and routine-dose CT had identical results for low-contrast resolution and nearly identical results for overall image quality (grade 2.1-2.2). Spatial resolution was better with routine-dose CT (p = 0.004).

CONCLUSION

These preliminary results support body CT dose index reductions of 32-65% when adaptive statistical iterative reconstruction is used. Studies with larger statistical samples are needed to confirm these findings.

Evaluation of image quality and lesion perception by human readers on 3D CT colonography: comparison of standard and low radiation dose

AIMS

We compared the prevalence of noise-related artefacts and lesion perception on three-dimensional (3D) CT colonography (CTC) at standard and low radiation doses.

METHODS

Forty-eight patients underwent CTC (64 x 0.625 mm collimation; tube rotation time 0.5 s; automatic tube current modulation: standard dose 40-160 mA, low dose 10-50 mA). Low- and standard-dose acquisitions were performed in the supine position, one after the other. The presence of artefacts (cobblestone and snow artefacts, irregularly delineated folds) and the presence of polyps were evaluated by five radiologists on 3D images at standard dose, the original low dose and a modified low dose, i.e. after manipulation of opacity on 3D.

RESULTS

The mean effective dose was 3.9 +/- 1.3 mSv at standard dose and 1.03 +/- 0.4 mSv at low dose. The number of images showing cobblestone artefacts and irregularly delineated folds at original and modified low doses was significantly higher than at standard dose (P < 0.0001). Most of the artefacts on modified low-dose images were mild. No significant difference in sensitivity between the dose levels was found for polyps > or =6 mm.

CONCLUSIONS

Reduction of the effective dose to 1 mSv significantly affects image quality on 3D CTC, but the perception of > or =6 mm lesions is not significantly impaired.

Virtual colonoscopy in paediatric patients Usefulness of a colon dissection technique

OBJECTIVE

To determine the usefulness of perspective-filet view for polypoid lesions in paediatric patients in comparison with conventional virtual colonoscopy (VC) analysis and optical colonoscopy.

METHODS

Sixty-one patients (mean age 5 years old) with a previous episode of rectal bleeding were studied using a 16 slices CT scanner. All patients underwent a colonic preparation. Two acquisitions were done in supine and prone positions with slices of 2mm thickness; increment 1mm, 30-50mA; 90-120kV. In a workstation an experienced radiologist reviewed images twice. The first read was done using the conventional virtual colonoscopy technique with the evaluation of two-dimensional (2D), three-dimensional (3D) and endoscopical images. Later, in a second session, perspective-filet view was used. It shows a 360 degrees unrolled visualization of the inner colon. The presence, size and location of the lesions were determined. A record of the reading time was made.

RESULTS

At per patient evaluation the conventional virtual colonoscopy analysis obtained a sensitivity of 86% and a specificity of 98%. The perspective-filet view obtained a sensitivity of 91% and a specificity of 99%. In the evaluation on a per lesion basis the conventional analysis had a sensitivity of 81% and a specificity of 88%. Perspective-filet view, had a sensitivity of 82% and specificity of 90%. The average total reading time using conventional colonoscopy technique was 18+/-3min, versus 4+/-1min using the perspective-filet view.

CONCLUSION

Virtual colon dissection with perspective-filet view is more time-efficient than conventional virtual colonoscopy evaluation with correct correlation in results.

Computed tomography colonography (virtual colonoscopy): climax of a new era of validation and transition into community practice

Colorectal cancer, which kills more than 50,000 patients every year in the United States and costs more than $6 billion in direct health costs, is a prime target for cancer prevention. Computed tomography colonography (CTC) has emerged as a minimally invasive, structural examination of the entire colon that can complement the current tools of cancer prevention and may improve patient compliance. Large trials have suggested a sensitivity of roughly 90% and specificity greater than 97% for CTC for patients with polyps >or= 10 mm. Bowel preparation by diet restriction, catharsis, and stool and fluid tagging are typically used. A prepless CTC protocol is an active area of research with a focus on improving patient compliance. Insurance coverage of CTC is a key factor affecting current dissemination and local and national coverage decisions are ongoing. CT examination of the abdomen allows visualization of extracolonic organs, where detection of additional disease must balance any unnecessary anxiety and testing. Estimates of CTC cost-effectiveness are generally favorable, but vary due to the high sensitivity of these models to costs, polyp sensitivity, compliance rates, and other parameters, which are difficult to accurately assess. Quality initiatives are being developed that will be key for implementation into community practice.

Acute abdominal pain: value of non-contrast enhanced ultra-low-dose multi-detector row CT as a substitute for abdominal radiographs

The aim of this study was to evaluate a non-enhanced ultra-low-dose (ULD) abdominal-pelvic multi-detector row computerized tomography (MDCT) to assess patients with acute abdominal pain who would otherwise undergo three-view abdominal X-ray series. Institutional review board approval was obtained with waiver of informed consent. This study was Health Insurance Portability and Accountability Act-compliant. One hundred and sixty-three patients (mean age, 51 years; range, 19-82 years, M/F = 110:53) who underwent ULD MDCT were included in the study. Two subspecialty radiologists independently reviewed the images for abnormal findings and image quality parameters. The effective radiation dose was calculated for each patient and compared to standard-dose computed tomography (CT) scans of 50 matched controls. Findings were confirmed by reviewing the patients' medical records, and statistical analysis was performed. ULD MDCT showed a high sensitivity (100%), specificity (98.5%), and positive predictive value (91.7%) for detection of free air, stones, and intestinal obstruction. For other sources of abdominal pain, the overall sensitivity, specificity, and positive predictive value were 86%, 96%, and 95%, respectively. Mean effective radiation dose from this study was 2.10 mSv (range of 0.67 to 6.64 mSv) with a 78% mean dose reduction compared to standard-dose CT. There was good inter-observer agreement (=0.4 to 0.81). ULD abdominal-pelvic MDCT provides rapid and reasonably accurate diagnostic information in patients with acute abdominal pain at a very low radiation dose.

Radiation dose in CT colonography--trends in time and differences between daily practice and screening protocols

The purpose of this study was to evaluate the currently used effective doses in CT colonography (CTC) and to search for trends in time. A Pubmed search for articles and a search for congress abstracts concerning CTC was performed. Research institutions were sent a CTC dose questionnaire concerning the type of CT system employed and the CT parameters used. With the ImPACT CT Dosimetry Spreadsheet effective doses were calculated. Of 83 institutions, 34 returned a complete questionnaire; 21 (62%) used 64-detector row CT and 17 (50%) used dose modulation. The median effective dose per institution was 5.7 mSv (2.8 mSv supine; 2.5 mSv prone) for screening protocols and 9.1 mSv (5.2 and 3.0 mSv, respectively) for daily practice protocols (p<0.05). Doses did not differ significantly between CT machines with different numbers of detector rows. In 17 institutions incorporated in a study in 2004 as well, the median dose for daily practice protocols changed from 11 mSv in 2004 to 9.7 mSv now (n.s.). Median effective dose for CTC is significantly lower for screening than for daily practice protocols. Although the number of CTC protocols with dose modulation increased substantially since 2004, no significant decrease in effective dose was found.

Critical analysis of the performance of double-contrast barium enema for detecting colorectal polyps > or = 6 mm in the era of CT colonography

OBJECTIVE

The purpose of our study was to perform a meta-analysis comparing the performance of double-contrast barium enema (DCBE) with CT colonography (CTC) for the detection of colorectal polyps > or = 6 mm using endoscopy as the gold standard.

MATERIALS AND METHODS

Prospective DCBE and CTC studies were identified. Percentages of polyps and of patients with polyps > or = 10 mm and 6-9 mm were abstracted. The performance of DCBE versus CTC was determined by separately evaluating each technique's performance versus that of endoscopy, and contrasting the techniques. The I-squared statistic and Fisher's exact test were used for heterogeneity, the Cochran-Mantel-Haenszel and the Kruskal-Wallis tests for correlation, and the A(z) test for comparing pooled weighted estimates of performance.

RESULTS

Eleven studies of DCBE (5,995 patients, 1,548 polyps) and 30 studies of CTC (6,573 patients, 2,348 polyps) fulfilled inclusion criteria. For polyps > or = 10 mm, a 0.121-per-patient sensitivity difference favored CTC (p < 0.0001; DCBE, 0.702 [95% CI, 0.687-0.715]; CTC, 0.823 [0.809-0.836]). For polyps > or = 10 mm, a 0.031-per-polyp sensitivity difference favored CTC (p < 0.0001; DCBE, 0.715 [0.703-0.726]; CTC, 0.746 [0.735-0.757]). For polyps > or = 10 mm, a specificity difference of 0.104 favored CTC (p = 0.001; DCBE, 0.850 [0.847-0.855]; CTC, 0.954 [0.952-0.955]). DCBE was also significantly less sensitive for 6- to 9-mm polyps (p < 0.001).

CONCLUSION

DCBE has statistically lower sensitivity and specificity than CTC for detecting colorectal polyps > or = 6 mm.

CT colonography: an update

Computed tomographic (CT) colonography (CTC)--also known as "virtual colonoscopy"--was first described more than a decade ago. As advancements in scanner technology and three-dimensional (3D) postprocessing helped develop this method to mature into a potential option in screening for colorectal cancer, the fundamentals of the examination remained the same. It is a minimally invasive, CT-based procedure that simulates conventional colonoscopy using 2D and 3D computerized reconstructions. The primary aim of CTC is the detection of colorectal polyps and carcinomas. However, studies reveal a wide performance variety in regard to polyp detection, especially for smaller polyps. This article reviews the available literature, discusses established indications as well as open issues and highlights potential future developments of CTC.

MR colonography

Combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, MR imaging of the gastrointestinal tract has become increasingly used clinically. Both bowel inflammation and tumor disease of the large bowel can be well visualized by means of MR colonography (MRC). This article describes current techniques of MRC and gives an overview of its clinical outcome. Special focus is directed toward the evaluation of patients' acceptance of MRC.

The evolving role of CT colonography

Colorectal cancer (CRC) screening is widely recommended as part of standard preventive care. All average risk persons over the age of 50 y are eligible. Various authorities have advocated fecal occult blood testing, flexible sigmoidoscopy, barium enema and colonoscopy at varying intervals as acceptable screening options. Despite the array of choices, CRC screening lags in frequency behind other cancer screening maneuvers like mammography or Pap smear. Of late, there is growing interest in CT colonography (CTC) as another screening option. CTC, or virtual colonoscopy, may represent an attractive, non-invasive method of CRC screening that provides images akin to traditional colonoscopy. Improvements in CTC performance, especially when coupled with declining costs, suggest that CTC's role in average risk screening will increase in the future. This review summarizes available data about the efficacy of CTC in average and high risk screening populations. Current indications as well as limitations to this technology are discussed, as are practical issues like the cost-effectiveness of CTC for widespread use.

Dose reduction for cardiac CT using a registration-based approach

Two reasons for the recent rise in radiation exposure from CT are increases in its clinical applicability and the desire to maintain high SNR while acquiring smaller voxels. To address this emerging dose problem, several strategies for reducing patient exposure have already been proposed. One method employed in cardiac imaging is ECG-driven modulation of the tube current between 100% at one time point in the cardiac cycle and a reduced fraction at the remaining phases. In this paper, we describe how images obtained during such acquisition can be used to reconstruct 4D data of consistent high quality throughout the cardiac cycle. In our approach, we assume that the middiastole (MD) phase is imaged with full dose. The MD image is then independently registered to lower dose images (lower SNR) at other frames, resulting in a set of transformations. Finally, the transformations are used to warp the MD frame through the cardiac cycle to generate the full 4D image. In addition, the transformations may be interpolated to increase the temporal sampling or to generate images at arbitrary time points. Our approach was validated using various data obtained with simulated and scanner-implemented dose modulation. We determined that as little as 10% of the total dose was required to reproduce full quality images with a 1 mm spatial error and an error in intensity values on the order of the image noise. Thus, our technique offers considerable dose reductions compared to standard imaging protocols, with minimal effects on the quality of the final data.

CT-guided intervention with low radiation dose: feasibility and experience

OBJECTIVE

The purpose of this study was to evaluate the feasibility of performing CT-guided interventional procedures with a very low radiation dose.

MATERIALS AND METHODS

We performed 291 CT-guided interventional procedures using a low dose of radiation. The subjects were 165 men and 126 women 22-89 years old with a mean age of 65 years. CT fluoroscopy was not used. The procedures were 201 percutaneous biopsies and 90 percutaneous aspiration or drainage procedures. Before the procedure, images were obtained with standard mAs of 175-250 mAs. All subsequent CT was performed at a reduced mAs. Technical success of catheter placement and biopsy was calculated, and the results were compared with those of procedures performed over the previous 12 months with standard radiation doses. Patient weight, lesion size, and number of CT acquisitions needed to complete the procedure were recorded.

RESULTS

All but three aspiration or drainage procedures performed at 30 mAs were successful, for a success rate of 96.7%. The technical success rate of biopsy performed at 30 mAs was 93.5%. In the cases of 13 patients undergoing biopsy, the masses were not identified with low-dose technique, and these procedures were completed at a higher dose. Results were independent of patient weight and lesion size. The technical success rate was 98% for percutaneous drainage performed at a standard radiation dose in the 12 months before introduction of the low-dose technique. The technical success rate was 87.5% for biopsy performed at a standard radiation dose in the 12 months before introduction of the low-dose technique. The complication rate of the low-dose technique was comparable to that of the standard-dose technique.

CONCLUSION

Low-dose radiation technique using 30 mAs results in technical success for both catheter placement and percutaneous biopsy comparable to standard radiation dose.

CT colonography versus colonoscopy in the follow-up of patients after diverticulitis - a prospective, comparative study

AIM

To assess whether computed tomography colonography (CTC) is a viable alternative to colonoscopy or double contrast barium enema in the follow-up of patients after diverticulitis.

MATERIAL AND METHODS

Fifty patients underwent CTC followed immediately by colonoscopy. Results were blinded to the examiners. Findings of diverticular disease and patient acceptance were evaluated.

RESULTS

Bowel preparation and distension were good in the majority of CTC and colonoscopy examinations. Diverticular disease was found in 96% of patients at CTC and in 90% at colonoscopy. The rate of agreement between CTC and colonoscopy for diverticular findings in the sigmoid colon was good (kappa=0.64). No complications were seen. Patients found colonoscopy more uncomfortable (p<0.03), more painful (p<0.001), and more difficult (p<0.01) than CTC. Of the patients favouring one examination, 74% preferred CTC.

CONCLUSION

CTC appears to have a better diagnostic potential for imaging of diverticular disease-specific findings, when compared with colonoscopy. Also, CTC was less uncomfortable and was preferred by a majority of patients. CTC seems to be a reasonable alternative in follow-up of patients with symptomatic diverticular disease.

Pitfalls in Multi–Detector Row CT Colonography: A Systematic Approach

Thin-section multi-detector row computed tomographic (CT) colonography is a powerful tool for the detection and classification of colonic lesions. However, each step in the process of a CT colonographic examination carries the potential for misdiagnosis. Suboptimal patient preparation, CT scanning protocol deficiencies, and perception and interpretation errors can lead to false-positive and false-negative findings, adversely affecting the diagnostic performance of CT colonography. These problems and pitfalls can be overcome with a variety of useful techniques and observations. A relatively clean, dry, and well-distended colon can be achieved with careful patient preparation, thereby avoiding the problem of residual stool and fluid. Knowledge of the morphologic and attenuation characteristics of common colonic lesions and artifacts can help identify bulbous haustral folds, impacted diverticula, an inverted appendiceal stump, or mobile polyps, any of which may pose problems for the radiologist. A combined two-dimensional and three-dimensional imaging approach is recommended for each colonic finding. A thorough knowledge of the various pitfalls and pseudolesions that may be encountered at CT colonography, along with use of dedicated problem-solving techniques, will help the radiologist differentiate between definite colonic lesions and pseudolesions.

Meta-analysis comparing CT colonography, air contrast barium enema, and colonoscopy

INTRODUCTION

Published studies have reported a wide range of sensitivities and specificities for computed tomographic (CT) colonography for polyp detection, generating controversy regarding its diagnostic accuracy.

METHODS

A meta-analysis of published studies comparing the accuracies of CT colonography and colonoscopy for polyp detection was performed. The pooled per-patient sensitivities and specificities were calculated at various thresholds for polyp size. Summary receiver operating characteristic (sROC) curves were also constructed.

RESULTS

Thirty studies were included in the meta-analysis of CT colonography. The pooled per-patient sensitivity of CT colonography was higher for polyps greater than 10 mm (0.82, 95% confidence interval [CI], 0.76-0.88) compared with polyps 6 to 10 mm (0.63, 95% CI, 0.52-0.75) and polyps 0 to 5 mm (0.56, 95% CI, 0.42-0.70). Similarly, the exact area under the sROC curve (area +/- standard error) was higher using a threshold greater than 10 mm (0.898 +/- 0.063) compared with thresholds of greater than 5 mm and any size (0.884 +/- 0.033 and 0.822 +/- 0.059, respectively). There were no significant differences in the diagnostic characteristics of 2-dimensional versus 3-dimensional CT colonography. At a threshold greater than 5 mm, the exact area under the sROC curve was significantly higher for endoscopic colonoscopy compared with CT colonography (0.998 +/- 0.006 vs 0.884 +/- 0.033, P < .005).

CONCLUSIONS

CT colonography has a reasonable sensitivity and specificity for detecting large polyps but was less accurate than endoscopic colonoscopy for smaller polyps. Thus, CT colonography may not be a reasonable alternative in situations in which a small polyp may be clinically relevant.

Update on Colorectal Cancer Imaging

Colorectal cancer remains a leading cancer killer worldwide. The disease is both curable and preventable, and yet the importance of widespread screening is only now starting to be appreciated. This article reviews the variety of diagnostic tests, imaging procedures and endoscopic examinations available to detect colorectal cancer and polyps in their early stage and also presents details on various screening options. The critical role of the radiologist is elaborated on including accurate assessment of the tumor extent within the bowel wall and beyond and the detection of lymph node and distant metastases. Staging with CT, MR imaging, endorectal ultrasound, and positron emission tomography are of paramount importance in determining the most appropriate therapy and the risk of tumor recurrence and overall prognosis.

Effective radiation doses in CT colonography: results of an inventory among research institutions

The purpose of this study was to estimate the effective dose that is currently used in CT colonography using scan parameters that were collected for this purpose, and to investigate trends in time. PubMed was systematically searched from 1996 until January 2004 for studies investigating CT colonography. Research institutions were contacted and asked for their current scan protocol. Thirty-six institutions published 74 studies. Twenty-eight of the 36 institutions provided their current protocol. The median effective dose in 2004 was 5.1 mSv (range 1.2-11.7 mSv) per position. Most institutions (93%) scan in both the supine and prone positions. The median mAs value was 67 mAs (range 20-200), median collimation was 2.5 mm (range 0.75-5). From 1996 until 2004 a significant decrease in mAs and collimation (P=0.006, P<0.0001, respectively) was observed, while institutions that used a multislice scanner increased (P<0.0001). The effective dose remained constant (P=0.76). In 2004 the median effective dose for a complete CT colonography was 10.2 mSv. Despite the increasing use of multislice scanners, which are slightly less dose-efficient, the median effective dose remained approximately constant between 1996 and 2004. This is mainly caused by the use of lower mAs settings.

Multi-detector CT-colonography in inflammatory bowel disease: prospective analysis of CT-findings to high-resolution video colonoscopy

AIM

Prospective analysis of multi-detector CT-colonography (MDCTC) in patients with inflammatory bowel disease (IBD) compared to high-resolution video-endoscopy (HRVC).

MATERIALS AND METHODS

Twenty-one patients (mean age 49.6 years) with Crohn's disease or ulcerative colitis underwent MDCTC (Somatom Volume Zoom, Siemens, Erlangen; 1mm collimation, Pitch 8, 100 mAs, 120 kVp). HRVC was performed within 2 h after MDCTC. MDCTC was analyzed by two blinded readers. MDCTC-findings including bowel wall alterations and extraintestinal changes were compared to results of HRVC.

RESULTS

Over-all-sensitivity was 100% for endoluminal lesions with correct diagnosis of two cancers. Acute and chronic IBD were correctly identified by MDCTC in 63.6%, and 100%, respectively, with a specificity of 75%, and 100%. Sensitivity, specificity, positive and negative predictive values of MDCTC for diagnosis of acute and chronic disease were best for chronic disease. Sensitivity was worst for acute ulcerative colitis and specificity was worst for acute Crohn's disease. Haustral loss was seen only in ulcerative colitis. Pseudopolyps and fistulae were findings exclusive to Crohn's disease. Particularly extraintestinal findings as increased vascularization and local lymphadenopathy correlated well with endoscopic definition of acute disease. Because of the possibly more vulnerable colonic wall in acute inflammatory bowel disease, the air inflation for MDCTC should be performed most carefully to avoid any risk of colonic perforation.

CONCLUSION

MDCTC may help to distinguish between patients with acute and chronic IBD. Especially extraintestinal complications, tumorous as well as pseudo-tumorous lesions can be detected with high sensitivity and specificity.

Virtual colonoscopy for colorectal cancer screening: current status

Computed tomography colonography (CTC) (also known as ‘virtual colonoscopy’) is a noninvasive method of imaging the colon using helical CT. Although CTC has been shown to be useful for certain clinical indications, it has not yet been endorsed as a colorectal cancer screening test. The purpose of this article is to review the current status of CTC for colorectal cancer screening. CTC is an accurate method to detect colonic polyps and to select patients who would benefit from colonoscopy. The major advantages of CTC over conventional colonography include its relatively low risk and greater tolerance by patients. In this article, the CTC procedure and results of clinical trials are reviewed, as well as potential pitfalls related to CTC performance and interpretation. Finally, radiation dose, the discovery of incidental extracolonic findings with CTC, bowel preparation methods, and computer-aided diagnosis are addressed.

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.

The role of CT colonography in colorectal cancer screening

Computed tomographic colonography (CTC) is a relatively noninvasive technique for large bowel imaging that has the ability to detect colorectal neoplasia. Already well established as a reliable diagnostic tool in symptomatic patients who are unable to undergo complete colonoscopy, it is now being considered as a viable method for population screening. Advances in technique over the past 10 yr make this an attractive alternative, including reduced bowel preparation and stool tagging, three-dimensional (3D) image reconstruction, computer-aided detection software, and low-radiation dose protocols. CTC may be favored by patients compared to other available screening tests due to the ease of performance and comfort. Although published studies vary in relation to the sensitivity of this test for the detection of polyps, in the best hands a sensitivity of greater than 90% for detection of polyps at least 10 mm in diameter may be obtained. Although not yet endorsed for widespread use by major gastroenterological societies, CTC shows promise as a screening tool.