Double-contrast barium enema examination technique

Real-time detection of gastrointestinal leaks via bismuth chelate-enhanced X-ray gastroenterography

Anastomotic leaks are among the most dreaded complications following gastrointestinal (GI) surgery, and contrast-enhanced X-ray gastroenterography is considered the preferred initial diagnostic method for GI leaks. However, from fundamental research to clinical practice, the only oral iodinated contrast agents currently available for GI leaks detection are facing several challenges, including low sensitivity, iodine allergy, and contraindications in patients with thyroid diseases. Herein, we propose a cinematic contrast-enhanced X-ray gastroenterography for the real-time detection of GI leaks with an iodine-free bismuth chelate (Bi-DTPA) for the first time. The Bi-DTPA, synthesized through a straightforward one-pot method, offers distinct advantages such as no need for purification, a nearly 100 % yield, large-scale production capability, and good biocompatibility. The remarkable X-ray attenuation properties of Bi-DTPA enable real-time dynamic visualization of whole GI tract under both X-ray gastroenterography and computed tomography (CT) imaging. More importantly, the leaky site and severity can be both clearly displayed during Bi-DTPA-enhanced gastroenterography in a rat model with esophageal leakage. The proposed movie-like Bi-DTPA-enhanced X-ray imaging approach presents a promising alternative to traditional GI radiography based on iodinated molecules. It demonstrates significant potential in addressing concerns related to iodine-associated adverse effects and offers an alternative method for visually detecting gastrointestinal leaks.

Imaging of Gastrointestinal Tract Ailments

Gastrointestinal (GI) disorders comprise a diverse range of conditions that can significantly reduce the quality of life and can even be life-threatening in serious cases. The development of accurate and rapid detection approaches is of essential importance for early diagnosis and timely management of GI diseases. This review mainly focuses on the imaging of several representative gastrointestinal ailments, such as inflammatory bowel disease, tumors, appendicitis, Meckel's diverticulum, and others. Various imaging modalities commonly used for the gastrointestinal tract, including magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT), and photoacoustic tomography (PAT) and multimodal imaging with mode overlap are summarized. These achievements in single and multimodal imaging provide useful guidance for improved diagnosis, staging, and treatment of the corresponding gastrointestinal diseases. The review evaluates the strengths and weaknesses of different imaging techniques and summarizes the development of imaging techniques used for diagnosing gastrointestinal ailments.

Classification of rectal cancer according to recurrence types - comparison of Japanese guidelines and Western guidelines

BACKGROUND

Rectal cancer is characterized by more local recurrence (LR) and lung metastasis than colon cancer. However, the diagnosis of rectal cancer is not standardized as there is no global consensus on its definition and classification. The classification of rectal cancer differs between Japanese and Western guidelines.

AIM

To clarify the characteristics of rectal cancer by comparing the tumor location and characteristics of rectal cancer with those of colon cancer according to each set of guidelines.

METHODS

A total of 958 patients with Stage II and III colorectal cancer were included in the analysis: 607 with colon cancer and 351 with rectal cancer. Localization of rectal cancers was assessed by enema examination and rigid endoscopy. According to Japan guidelines, rectal cancer is classified as Rb (below the peritoneal inversion), Ra (between the inferior margin of second sacral vertebrae and Rb) or RS (between Ra and sacral promontory).

RESULTS

There were no significant differences between RS rectal cancer and colon cancer in the rates of liver and lung metastasis or LR. Lung metastasis and LR were significantly more common among Rb rectal cancer (in Japan) than in colon cancer (P = 0.0043 and P = 0.0002, respectively). Lung metastases and LR occurred at significantly higher rates in rectal cancer measuring ≤ 12 cm and ≤ 10 cm than in colon cancers (P = 0.0117, P = 0.0467, P = 0.0036, P = 0.0010). Finally, the rates of liver metastasis, lung metastasis, and LR in rectal cancers measuring 11 cm to 15 cm were 6.9%, 2.8%, and 5.7%, respectively. These were equivalent to the rates in colon cancer.

CONCLUSION

High rectal cancer may be treated with the same treatment strategies as colon cancer. There was no difference in the classification of colorectal cancer between Japan and Western countries.

IDEAL study: magnetic resonance imaging for suspected deep endometriosis assessment prior to laparoscopy is as reliable as radiological imaging as a complement to transvaginal ultrasonography

OBJECTIVE

To compare the value of using one-stop magnetic resonance imaging (MRI) vs standard radiological imaging as a supplement to transvaginal ultrasonography (TVS) for the preoperative assessment of patients with endometriosis referred for surgery in a tertiary care academic center.

METHODS

This prospective observational study compared the diagnostic value of the standard preoperative imaging practice of our center, which involves expert TVS complemented by intravenous urography (IVU) for the evaluation of the ureters and double-contrast barium enema (DCBE) for the evaluation of the rectum, sigmoid and cecum, with that of expert TVS complemented by a 'one-stop' MRI examination evaluating the upper abdomen, pelvis, kidneys and ureters as well as rectum and sigmoid on the same day, for the preoperative triaging of 74 women with clinically suspected deep endometriosis. The findings at laparoscopy were considered the reference standard. Patients were stratified according to their need for monodisciplinary surgical approach, carried out by gynecologists only, or multidisciplinary surgical approach, involving abdominal surgeons and/or urologists, based on the extent to which endometriosis affected the reproductive organs, bowel, ureters, bladder or other abdominal organs.

RESULTS

Our standard preoperative imaging approach and the combined findings of TVS and MRI had similar diagnostic performance, resulting in correct stratification for a monodisciplinary or a multidisciplinary surgical approach of 67/74 (90.5%) patients. However, there were differences between the estimation of the severity of disease by DCBE and MRI. The severity of rectal involvement was underestimated in 2.7% of the patients by both TVS and DCBE, whereas it was overestimated in 6.8% of the patients by TVS and/or DCBE.

CONCLUSIONS

Complementary to expert TVS, 'one-stop' MRI can predict intraoperative findings equally well as standard radiological imaging (IVU and DCBE) in patients referred for endometriosis surgery in a tertiary care academic center. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

A comparison of the localization of rectal carcinomas according to the general rules of the Japanese classification of colorectal carcinoma (JCCRC) and Western guidelines

PURPOSE

The aim of this study was to compare the localization of rectal cancers as classified according to the general rules of the Japanese classification of colorectal carcinoma (JCCRC) and also according to the European Society for Medical Oncology (ESMO) and the National Comprehensive Cancer Network (NCCN) guidelines, which are based on rigid endoscopic measurements.

METHODS

The medical records of patients scheduled to receive curative surgery for histologically proven rectal adenocarcinoma during 2009-2015 were investigated (n = 230). Rigid proctoscopy was performed in patients with rectal cancer located in the upper (Ra) or lower (Rb) division using double-contrast barium enema.

RESULTS

The median values of height from the anal verge were 7.5 cm (range 2-12) and 3 cm (0-9.5) on rigid proctoscopy for cancers assigned as Ra and Rb, respectively. All 159 cancers at Ra or Rb were located within 12 cm from the anal verge by rigid proctoscopy, while only 79.7% of Ra or 82.1% of Rb cancers were located in the mid (5.1-10 cm) or low (≤5 cm) rectum, respectively.

CONCLUSION

Ra and Rb cancers are deemed to be rectal cancers according to NCCN guidelines, but these classifications are not interchangeable with mid- and low-rectal cancers, respectively, according to the ESMO guidelines.

Performances of a protector against scattered radiation during intraoperative use of a C-arm fluoroscope

The scattered radiation protector for mobile x-ray systems, Creative Valuable Protector-2, has been recently developed. However, there have been no studies investigating the effects of this device. We aim to investigate the effects of the scattered radiation protector on the equivalent doses from scattered radiation delivered to radiosensitive organs while simulating spine surgery using a C-arm fluoroscope. Chest and rando phantoms were used to simulate a patient and a surgeon in this study. The equivalent dose from scattered radiation to radiosensitive organs was measured in four different situations according to the use of the scattered radiation protector and the C-arm configuration. To compare the quality of the images with and without the scattered radiation protector, an acryl step phantom with five steps was used, and the contrast resolution of each step was calculated. The equivalent dose from the scattered radiation to the surgeon's eye, thyroid, and gonad decreased significantly by using the scattered radiation protector for both the Posteroanterior (PA) (p  <  0.001) and Anteroposterior (AP) (p  <  0.001) C-arm configurations. The installation of the scattered radiation protector also reduced the direct radiation dose to the chest phantom. A scattered map showed that scattered radiation doses decreased by approximately 50% for the PA configuration and 75% for the AP configuration by using the scattered radiation protector. Before and after installation of the scattered radiation protector, the contrast resolution of each adjacent step area was 0.025-0.404 and 0.216-0.421. The scattered radiation protector was effective in reducing not only the equivalent dose from scattered radiation to the surgeon's radiosensitive organs, but also the direct radiation dose to the patient. This was all achieved without decreasing the quality of the C-arm fluoroscopic images.

Comparison between CT colonography and double-contrast barium enema for colonic evaluation in patients with renal insufficiency

Objective

To compare the CT colonography (CTC) and double-contrast barium enema (DCBE) for colonic evaluation in patients with renal insufficiency.

Materials and Methods

Two sequential groups of consecutive patients with renal insufficiency who had a similar risk for colorectal cancer, were examined by DCBE (n = 182; mean ± SD in age, 51 ± 6.4 years) and CTC (n = 176; 50 ± 6.7 years), respectively. CTC was performed after colon cleansing with 250-mL magnesium citrate (n = 87) or 4-L polyethylene glycol (n = 89) and fecal tagging. DCBE was performed after preparation with 250-mL magnesium citrate. Patients with colonic polyps/masses of ≥ 6 mm were subsequently recommended to undergo a colonoscopy. Diagnostic yield and positive predictive value (PPV) for colonic polyps/masses, examination quality, and examination-related serum electrolyte change were retrospectively compared between the two groups.

Results

Both the CTC and DCBE were positive for colonic polyps/masses in 28 (16%) of 176 and 11 (6%) of 182 patients, respectively (p = 0.004). Among patients with positive findings, 17 CTC and six DCBE patients subsequently underwent a colonoscopy and yielded a PPV of 88% (15 of 17 patients) and 50% (3 of 6 patients), respectively (p = 0.089). Thirteen patients with adenomatous lesions were detected in the CTC group (adenocarcinoma [n = 1], advanced adenoma [n = 6], and non-advanced adenoma [n = 6]), as compared with two patients (each with adenocarcinoma and advanced adenoma) in the DCBE group (p = 0.003). Six (3%) of 176 CTC and 16 (9%) of 182 DCBE examinations deemed to be inadequate (p = 0.046). Electrolyte changes were similar in the two groups.

Conclusion

In patients with renal insufficiency, CTC has a higher diagnostic yield and a marginally higher PPV for detecting colorectal neoplasia, despite a similar diagnostic yield for adenocarcinoma, and a lower rate of inadequate examinations as compared with DCBE.

Identification of cancer-associated proteins by proteomics and downregulation of β-tropomyosin expression in colorectal adenoma and cancer

Elucidating the molecular mechanism underlying the development of adenoma, the major precursor lesion of colorectal cancer (CRC), would provide a basis for early detection, prevention as well as treatment of CRC. Using the highly sensitive 2-D DIGE method coupled with MS, we identified 24 differentially expressed proteins in adenoma tissues compared with matched normal colonic mucosa and CRC tissues. Fifteen proteins were downregulated and three proteins were upregulated in adenoma tissues when compared with individual-matched normal colonic mucosa. Five proteins were downregulated, while one protein was upregulated in adenoma tissues when compared with matched CRC tissues. A protein, β-tropomyosin (TM-β), recently suggested to be a biomarker of esophageal squamous carcinoma, was downregulated in both adenoma and CRC tissues. Additionally, the reduction in the level of TM-β in adenoma and CRC tissues was further validated by Western blotting (p<0.05) and RT-PCR (p<0.001). Our findings suggest that downregulation of TM-β is involved in the early development of CRC and that differentially expressed proteins might serve as potential biomarkers for detection of CRC.

Double-contrast barium enema and transrectal endoscopic ultrasonography in the diagnosis of intestinal deeply infiltrating endometriosis

STUDY OBJECTIVE

To evaluate the sensitivity, specificity, negative predictive value, positive predictive value, association, and agreement of double-contrast barium enema (DCBE) and transrectal endoscopic ultrasonography (Tr EUS) in the diagnosis of rectosigmoid colon endometriosis.

DESIGN

Prospective nonrandomized (Canadian Task Force classification II-2).

SETTING

University hospital.

PATIENTS

We evaluated 37 patients with clinically suspected deeply infiltrating endometriosis (DIE) from January 2004 through January 2005.

INTERVENTIONS

Clinical examination, DCBE, Tr EUS, and laparoscopy for histologic confirmation.

MEASUREMENTS AND MAIN RESULTS

Deeply infiltrating endometriosis was confirmed by laparoscopic visualization and by histopathologic examination in all patients. Intestinal endometriosis was observed in 27 patients (72.9%). DCBE showed abnormalities suggestive of bowel endometriosis in 24 patients (64.9%) and Tr EUS in 28 patients (75.7%). Considering the DCBE findings we observed among the 24 abnormal examination results, 16 (42.3%) had spiculation, 16 (42.3%) had circumferential narrowing of the bowel, and 4 (10.8%) had the mass effect sign. For DCBE the sensitivity was 88%, the specificity was 54%, the negative predictive value (NPV) was 70%, and the positive predictive value (PPV) was 78%. For Tr EUS the sensitivity, specificity, NPV, and PPV were 96%, 100%, 90%, and 100%. A significant association of the DCBE and the Tr EUS in the diagnosis of intestinal DIE (p = .017) and a moderate agreement of the methods (kappa = 0.44) was also observed.

CONCLUSION

Our data, although limited by sample size, confirmed that DCBE has a good sensitivity and a low specificity in the diagnosis of intestinal DIE. The Tr EUS proved to have a higher sensitivity and specificity with elevated NPV and PPV. A significant association of the DCBE and the Tr EUS in the diagnosis of intestinal DIE and a moderate agreement of the methods was also observed.

Teniae coli-based circumferential localization system for CT colonography: feasibility study

This HIPAA-compliant study, with institutional review board approval and informed patient consent, was conducted to retrospectively develop a teniae coli-based circumferential localization method for guiding virtual colon navigation and colonic polyp registration. Colonic surfaces (n = 72) were depicted at computed tomographic (CT) colonography performed in 36 patients (26 men, 10 women; age range, 47-72 years) in the supine and prone positions. For 70 (97%) colonic surfaces, the tenia omentalis (TO), the most visible of the three teniae coli on a well-distended colonic surface, was manually extracted from the cecum to the descending colon. By virtually dissecting and flattening the colon along the TO, the authors developed a localization system involving 12 grid lines to estimate the circumferential positions of polyps. A sessile polyp would most likely (at 95% confidence level) be found within +/-1.2 grid lines (one grid line equals 1/12 the circumference) with use of the proposed method. By orienting and positioning the virtual cameras with use of the new localization system, synchronized prone and supine navigation was achieved. The teniae coli are extractable landmarks, and the teniae coli-based circumferential localization system helps guide virtual navigation and polyp registration at CT colonography.

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.

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.

An update on imaging of colorectal cancer

Screening of asymptomatic average-risk patients for presence of colon cancer and early detection in precursor stages is of great interest to general population. Comprehensive evaluation of symptomatic or high-risk patients represents another important clinical focus. Available techniques for total colon imaging, rectal cancer staging and the role of positron emission tomography are discussed.

Phosphate salt bowel preparation regimens alter perioperative acid-base and electrolyte balance

BACKGROUND

Hyperphosphatemic acidosis and severe electrolyte disturbances caused by phosphate salts (PO) used for mechanical bowel preparation have been described in occasional case reports prior to bowel resection surgery. We hypothesized that PO used preoperatively for bowel preparation may cause more pronounced acid base and electrolyte changes than polyethylene glycol (PG).

METHODS

Forty American Society of Anesthesiologists physical status II-III patients were randomly allocated to receive either PO or PG for bowel preparation before intra-abdominal surgery (bowel resection or other major elective intra-abdominal surgeries). Measurements of pH, base deficit, blood gases, lactate, hemoglobin, calcium, magnesium, potassium and phosphorus were undertaken before the laxative administration, intraoperatively, and postoperatively.

RESULTS

Preoperative demographic, hemodynamic and laboratory data were similar in the two groups. Intraoperative calcium (8.4 [0.6] vs 9 [0.5] mg x dL(-1)) and pH (7.35 [0.04] vs 7.41 [0.03]) were lower, while lactate (1.3 [0.4] vs 0.9 [0.3] mmol x L(-1)) was higher with PO. Postoperative calcium, magnesium and potassium were lower (8 [0.5] vs 8.9 [0.2] mg x dL(-1), 1.68 [0.3] vs 1.8 [0.4] and 3.5 [0.36] vs 3.7 [0.33] mEq x L(-1) respectively) while phosphorus (4.1 [0.3] vs 3.3 [0.2] mEq x L(-1)) was higher with PO. A higher percentage of abnormal values for calcium, potassium, phosphorus and base deficit (66% vs 33%, 25% vs 10%, 19% vs 2% and 28.3% vs 5% respectively) were observed with PO.

CONCLUSIONS

Calcium and magnesium changes were more pronounced in patients who received PO for bowel preparation.

Supine/left decubitus scanning: a valuable alternative to supine/prone scanning in CT colonography

The purpose was to evaluate supine/left decubitus as an alternative to supine/prone scanning in computed tomographic colonography (CT colonography). Fifty patients were randomised to supine/prone, another 50 to supine/left decubitus scanning. Patients were scanned using a single-slice CT scanner. The colon was divided into eight segments. Comparisons of distension, breathing artefacts, residus and polyp detection were made between the two groups as well as between the different positions. Adequate distension was found in approximately 85, 97 and 95% of segments in the supine, prone and left decubitus positions, respectively. Combined scanning increased the percentage of adequate distension to 98.5% for prone-supine and 97.7% for left decubitus-supine scanning ( P<0.0005 compared to supine, P=0.001 compared to left decubitus and P=0.046 compared to prone scanning). Absence of residual material was found in approximately 62.7, 69.7 and 64% of segments in the supine, prone and left decubitus positions, respectively. Combined scanning increased this percentage to approximately 99% for both groups. No significant differences towards distension or residual material were found between combined supine-prone or supine-left decubitus scanning. In the supine-prone group, combined scanning additionally revealed four lesions and improved conspicuity in two cases of stalked polyps. In the supine-left decubitus group, combined scanning additionally revealed two lesions and improved conspicuity in one stalked polyp. There were significantly fewer breathing artefacts with left decubitus scanning than prone scanning ( P=0.005). A strong positive correlation was found between breathing artefacts and the age of patients in both patient groups. Colonic distension and preparation is improved by using supine and prone or supine and left decubitus scanning in combination, with a subsequent improved polyp detection. There were no significant differences between the two scanning protocols. Prone scanning, however, is hampered by breathing artefacts, especially in the elderly. Therefore, supine-left decubitus scanning is considered a valuable alternative to supine-prone scanning for the elderly.

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MR colonography: How does air compare to water for colonic distention?

PURPOSE

To prove the feasibility of air-distended magnetic resonance colonography (MRC) and compare it with water-based distention.

MATERIALS AND METHODS

In five volunteers, the colon was imaged twice: once after distending the colon with air and a second time after distending the colon with water. A total of 50 patients, who had been referred to colonoscopy for a suspected colorectal pathology were randomized into water-distention (N = 25) and air-distention (N = 25) groups. A contrast-enhanced T1-weighted three-dimensional volume interpolated breath-hold (VIBE) sequence was collected. Comparative analysis was based on qualitative ratings of image quality and bowel distention, as well as contrast-to-noise ratio (CNR) measurements for the colonic wall with respect to the colonic lumen. In addition, patient acceptance was evaluated.

RESULTS

Inflammatory changes and colorectal masses were correctly identified on MRC in eight patients each. One 4-mm polyp identified at colonoscopy was missed on water-distended MRC. There were no false positive findings. No significant differences were found between air- and water-distention regarding discomfort levels and image quality. The presence of air in the colonic lumen was not associated with susceptibility artifacts. CNR of the contrast-enhanced colonic wall, as well as bowel distention, were superior on air-distended three-dimensional data sets.

CONCLUSION

MRC can be performed using either water or air for colonic distention. Both techniques permit assessment of the colonic wall and identification of colorectal masses. While discomfort levels are similar for both agents, MRC with air provides higher CNR and better colonic distention.

CT and MR colonography: scanning techniques, postprocessing, and emphasis on polyp detection

In the last decade, computed tomographic (CT) and magnetic resonance (MR) colonography, two new cross-sectional techniques for imaging of the colon, emerged. Both techniques show promising initial results in the detection of polyps equal to or greater than 1 cm in diameter in symptomatic patients. Imaging protocols are still mostly under development and prone to change. Both CT and MR colonography generate a large number of source images, which have to be read carefully for filling defects and, if intravenous contrast material is used, enhancing lesions. An important postprocessing technique is multiplanar reformatting, which allows the viewer to see potential lesions in an orientation other than that of the source images. Virtual endoscopy, a volume rendering technique that generates images from within the colon lumen, is used for problem solving. CT and MR colonography have potential advantages over colonoscopy and double-contrast barium enema examination: multiplanar capabilities, detection of enhancing lesions that make the distinction between fecal residue and true lesion possible, and ante- and retrograde virtual colonoscopy. Currently, a number of studies suggest that patients have a preference for CT colonography over colonoscopy. Patients consider bowel cleansing the most uncomfortable part of any colon examination; hence, from the acceptance point of view, fecal tagging techniques are promising. Before CT and MR colonography can be implemented in daily practice, they must show approximately the same accuracy as colonoscopy for polyp detection in both symptomatic and screening patients.

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Double-contrast barium enema technique

During a double-contrast barium enema the radiologist interacts with the patient, the controls of the fluoroscope, and the image on the television monitor. The radiologist paints an image of the colon; the barium is the paint, the colon is the canvas. The radiologist manipulates the barium pool, the air column, and the patient to create images. Although the radiologist may have a plan going into the examination, the game plan is altered by the patient's ability to tolerate and perform the study, the length of the colon, and pathology encountered. If the radiologist understands the goals to be achieved, the studied can be tailored to fit what is happening in the fluoroscopic suite.

Investigation of colonic disease

Bowel cancer awareness among the general public has heightened in recent years. The promotion of prompt referral and the pressure on early diagnosis will alter our previous strategies on colonic evaluation. This article gives an overview of the colonic investigations currently available.

Diagnosis of colorectal neoplasms at double-contrast barium enema examination

The double-contrast barium enema examination has been recognized as an option for colorectal cancer screening in Americans with average risk who are greater than 50 years of age. The purpose of this article is to review the principles for diagnosing colorectal neoplasms on double-contrast images and the spectrum of findings associated with these lesions. Colonic polyps can be sessile or pedunculated; their appearance depends on whether they are located on the dependent or nondependent wall of the bowel. Villous tumors may be flat, lobulated lesions, also known as "carpet" lesions, that are characterized by a finely nodular or reticular surface pattern, without a discrete mass. Colonic carcinomas may manifest as plaquelike, polypoid, semiannular ("saddle") or annular lesions. Colonic neoplasms sometimes are more difficult to detect in the region of the ileocecal valve or the distal rectum or in patients with severe diverticulosis. Careful double-contrast technique and meticulous scrutiny of the images therefore are required to optimize detection of these lesions.