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LE Magazine November 2001


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A comparison of virtual and conventional colonoscopy for the detection of colorectal polyps.

BACKGROUND: Virtual colonoscopy is a new method of imaging the colon in which thin-section, helical computed tomography (CT) is used to generate high-resolution, two-dimensional axial images. Three-dimensional images of the colon simulating those obtained with conventional colonoscopy are then reconstructed off-line. We compared the performance of virtual and conventional colonoscopy for the detection of colorectal polyps. METHODS: We prospectively studied 100 patients at high risk for colorectal neoplasia (60 men and 40 women; mean age, 62 years). We performed virtual colonoscopy immediately before conventional colonoscopy. We inserted a rectal tube and insufflated the colon with air to the maximal level that the patient could tolerate. We administered 1 mg of glucagon intravenously immediately before CT scanning to minimize the degree of smooth-muscle spasm and peristalsis and to reduce the patient’s discomfort. RESULTS: The entire colon was clearly seen by virtual colonoscopy in 87 patients and by conventional colonoscopy in 89. Fifty-one patients had normal findings on conventional colonoscopy. In the other 49, we identified a total of 115 polyps and 3 carcinomas. Virtual colonoscopy identified all 3 cancers, 20 of 22 polyps that were 10 mm or more in diameter (91 percent), 33 of 40 that were 6 to 9 mm (82 percent), and 29 of 53 that were 5 mm or smaller (55 percent). There were 19 false positive findings of polyps and no false positive findings of cancer. Of the 69 adenomatous polyps, 46 of the 51 that were 6 mm or more in diameter (90 percent) and 12 of the 18 that were 5 mm or smaller (67 percent) were correctly identified by virtual colonoscopy. Although discomfort was not specifically recorded, none of the patients requested that virtual colonoscopy be stopped because of discomfort or pain. CONCLUSIONS: In a group of patients at high risk for colorectal neoplasia, virtual and conventional colonoscopy had similar efficacy for the detection of polyps that were 6 mm or more in diameter.

N Engl J Med 1999 Nov 11;341(20):1496-1503

Technique factors and image quality as functions of patient weight at abdominal CT.

PURPOSE: To investigate how changes in kilovolt peak and milliampere second settings, and patient weight affect transmitted x-ray energy fluence and the image contrast-to-noise ratio (CNR) at abdominal computed tomography (CT). MATERIALS AND METHODS: Cylinders of water were used as patient models, and x-ray spectra, including x-ray tube potentials of 80-140 kVp, were investigated. The mean photon energy and energy fluence transmitted through water cylinders with varying diameters and the image contrast for fat, muscle, bone, and iodine relative to water were determined. The effect of changing the x-ray tube potential on CNR also was investigated. RESULTS: At a constant kVp, increasing patient weight from 10 kg to 120 kg reduced the transmitted energy fluence by two orders of magnitude. Changing the x-ray tube potential from 80 kVp to 140 kVp increased the mean photon energy from approximately 52 keV to approximately 72 keV and thus reduced the image contrast relative to water by 12% for muscle, 21% for fat, 39% for bone, and 50% for iodine (approximate reduction values). Increasing the x-ray tube potential from 80 kVp to 140 kVp increased the CNR by a factor of 2.6 for muscle and by a factor of 1. 4 for iodine. CONCLUSION: With changes in patient weight at abdominal CT, x-ray tube potentials must be varied to maintain a constant detector energy fluence. Increasing the x-ray tube potential generally improves CNR.

Radiology 2000 Nov;217(2):430-435

Use of colonoscopy to screen asymptomatic adults for colorectal cancer.

BACKGROUND AND METHODS: The role of colonoscopy in screening for colorectal cancer is uncertain. At 13 Veterans Affairs Medical Centers, we performed colonoscopy to determine the prevalence and location of advanced colonic neoplasms and the risk of advanced proximal neoplasia in asymptomatic patients (age range, 50 to 75 years) with or without distal neoplasia. Advanced colonic neoplasia was defined as an adenoma that was 10 mm or more in diameter, a villous adenoma, an adenoma with high-grade dysplasia, or invasive cancer. In patients with more than one neoplastic lesion, classification was based on the most advanced lesion. RESULTS: Of 17,732 patients screened for enrollment, 3196 were enrolled; 3121 of the enrolled patients (97.7 percent) underwent complete examination of the colon. The mean age of the patients was 62.9 years, and 96.8 percent were men. Colonoscopic examination showed one or more neoplastic lesions in 37.5 percent of the patients, an adenoma with a diameter of at least 10 mm or a villous adenoma in 7.9 percent, an adenoma with high-grade dysplasia in 1.6 percent, and invasive cancer in 1.0 percent. Of the 1765 patients with no polyps in the portion of the colon that was distal to the splenic flexure, 48 (2.7 percent) had advanced proximal neoplasms. Patients with large adenomas (> or = 10 mm) or small adenomas (< 10 mm) in the distal colon were more likely to have advanced proximal neoplasia than were patients with no distal adenomas (odds ratios, 3.4 [95 percent confidence interval, 1.8 to 6.5] and 2.6 [95 percent confidence interval, 1.7 to 4.1], respectively). However, 52 percent of the 128 patients with advanced proximal neoplasia had no distal adenomas. CONCLUSIONS: Colonoscopic screening can detect advanced colonic neoplasms in asymptomatic adults. Many of these neoplasms would not be detected with sigmoidoscopy.

N Engl J Med 2000 Jul 20;343(3):162-168

Associations of ankle-brachial index with clinical coronary heart disease, stroke and preclinical carotid and popliteal atherosclerosis: the Atherosclerosis Risk in Communities (ARIC) Study.

The resting ankle-brachial index (ABI) is a non-invasive method to assess the patency of the lower extremity arterial system and to screen for the presence of peripheral occlusive arterial disease. To determine how the ABI is associated with clinical coronary heart disease (CHD), stroke, preclinical carotid plaque and far wall intimal-medial thickness (IMT) of the carotid and popliteal arteries, we conducted analyses in 15 106 middle-aged adults from the baseline examination (1987-1989) of the Atherosclerosis Risk in Communities (ARIC) Study. The prevalence of clinical CHD, stroke/transient ischemic attack (TIA) and preclinical carotid plaque increased with decreasing ABI levels, particularly at those of < 0.90. Individuals with ABI < 0.90 were twice as likely to have prevalent CHD as those with ABI > 0.90 (age-adjusted odds ratio (OR) ranging from 2.2 (95% CI: 1.0-5.1) in African-American men to 3.3 (95% CI: 2.1-5.0) in white men). Men with ABI < 0.90 were more than four times as likely to have stroke/TIA as those with ABI > 0.90 (age-adjusted OR: 4.2 (95% CI: 1.8-9.5) in African-American men and 4.9 (95% CI: 2.6-9.0) in white men). In women the association was weaker and not statistically significant. Among those free of clinical cardiovascular disease, individuals with ABI < or = 0.90 had statistically significantly higher prevalence of preclinical carotid plaque compared to those with ABI > 0.90 (age-adjusted ORs ranging from 1.5 (95% CI: 1.0-1.9) in white women to 2.6 (95% CI: 1.0-6.6) in african-american men). The ABI was also inversely associated with far wall IMT of the carotid arteries (in both men and women) and the popliteal arteries (in men only). The associations of ABI with clinical CHD, stroke, preclinical carotid plaque and IMT of the carotid and popliteal arteries were attenuated and often not statistically significant after further adjustment for LDL cholesterol, cigarette smoking, hypertension and diabetes. These data demonstrate that low ABI levels, particularly those of < 0.90, are indicative of generalized atherosclerosis.

Atherosclerosis 1997 May;131(1):115-125

Correlation of homocytsteine levels with the extent of coronary atherosclerosis in patients with low cardiovascular risk profiles.

Elevation of homocysteine is now known as an independent risk factor for vascular diseases. However, influences of homocysteine to the extent of coronary atherosclerosis in patients with different coronary risk profiles have not been studied. In this study, we used angiographic “diffuse score” and “clinical vessel score” to evaluate the extent of coronary atherosclerosis, and examined the correlation between levels of serum total homocysteine and angiographic scores among patients with high- and low-risk profiles. Seventy consecutive patients (58 men and 12 women, mean age 50 years) undergoing selective coronary angiography for the first time were recruited for this study. Patients were divided into high-risk (risk factor > or =3, n = 35) and low-risk (risk factor <3, n = 35) groups. Linear regression analysis revealed that levels of serum homocysteine were only significantly correlated with diffuse (r = 0.217, p = 0.007) and clinical vessel (r = 0.078, p = 0.037) scores in low-risk patients. These correlations could not be observed in diffuse (r = 0.070, p = 0.319) and clinical vessel (r = -0.001, p = 0.970) scores in the high-risk group. In conclusion, levels of homocysteine correlated with the extent of coronary atherosclerosis only among patients with low cardiovascular risk profiles.

Am J Cardiol 2000 Jan 1;85(1):49-52

Effect of plasma homocysteine concentration on early and late events in patients with acute coronary syndromes.

BACKGROUND: Although a raised plasma homocysteine is a risk factor for vascular disease, it is not known whether it is associated with an adverse cardiac outcome in patients admitted with acute coronary syndromes. We evaluated the relationship between plasma homocysteine and short-term (28 days) and long-term (median 2.5 years) prognosis in acute coronary syndromes. METHODS AND RESULTS: We evaluated the relationship of quintiles of homocysteine to fatal and nonfatal coronary disease early (28 days) and late (29 days to a median of 2. 5 years) after admission to a single unit of patients with unstable angina (n=204) and myocardial infarction (n=236). The end points studied were cardiac death (n=67) and/or myocardial (re)infarction (n=30). Cox regression and logistic regression were used to estimate the relationship of homocysteine to coronary events. The event rate within the first 28 days (22 cardiac deaths and 5 nonfatal infarctions) was not related to the admission homocysteine level. In the 203 unstable angina and 214 myocardial infarction survivors, an apparent threshold effect was seen on long-term follow-up, with a significant step-up in the frequency of events between the lowest 3 quintiles (14 cardiac deaths and 11 nonfatal infarctions) and the upper 2 quintiles (31 fatal and 12 nonfatal events). Patients in the upper 2 quintiles (>12.2 micromol/L) had a 2.6-fold increase in the risk of a cardiac event (95% CI, 1.5 to 4.3, P<0.001). CONCLUSIONS: Elevated total homocysteine levels on admission strongly predict late cardiac events in acute coronary syndromes.

Circulation 2000 Aug 8;102(6):605-610

Computed tomographic colonography and conventional colonoscopy for colon diseases: a prospective, blinded study.

OBJECTIVES: Computed tomographic (CT) colonography or virtual colonoscopy is a new diagnostic method for the colon and rectum, developed on the basis of spiral computed axial tomography and employing virtual reality technology. The aim of this study was to determine the sensitivity, specificity, and diagnostic accuracy of CT colonography compared with colonoscopy in a prospective, blinded study in one single institution in Italy. METHODS: Ninety-nine patients randomly selected among those attending the open-access endoscopy unit for diagnostic colonoscopy underwent colonoscopy and spiral CT. The images obtained were transmitted to generate the virtual colonoscopy pictures. A supervisor compared the results with the findings of conventional colonoscopy. RESULTS: CT colonography diagnosed seven of eight tumors, one being missed because the patient had been inadequately prepared. In 28 patients, CT colonography identified 26 polyps of 45 (57.8% sensitivity, 92.6% specificity, 86.7% positive predictive value), regardless of their size. The sensitivity in detecting colonic polyps was 31.8% (7/22) in the first 25 cases and 91.6% (11/12) in the last 20 patients. CT colonography missed one flat adenoma, some angioectasias and colonic lesions because of portal hypertension in one patient, Crohn’s disease ulcers in two patients, and ulcerative colitis lesions in three. CONCLUSIONS: CT colonography shows poor sensitivity for identifying colonic polyps and does not always detect neoplastic lesions. Flat lesions are impossible to see by this method.

Am J Gastroenterol 2001 Feb;96(2):394-400

An initial experience with screening for colon polyps using spiral CT with and without CT colography (virtual colonoscopy).

BACKGROUND: Computed tomographic (CT) colography (virtual colonoscopy) is a new imaging method for detection of colon polyps and cancer. OBJECTIVE: To evaluate the sensitivity of CT colography for polyp detection in a population without symptoms that included persons without colon neoplasia and with radiologists blinded to colonoscopic findings. METHODS: Forty-six persons without symptoms underwent spiral CT followed by same-day colonoscopy with subsequent inspection of two-dimensional axial CT images, interactive multiplanar images, and surfaced and volume-rendered images of the colon (three-dimensional CT colography). RESULTS: Three-dimensional CT colography was superior to two-dimensional axial imaging for detection of colon polyps. Three-dimensional CT colography depicted 1 of 4 (25%) adenomas 2 cm in diameter or larger, 6 of 10 (60%) adenomas 1 to 1.9 cm, 6 of 14 (43%) 6 to 9 mm, and 7 of 65 (11%) 5 mm in diameter or smaller. Three-dimensional CT colography showed a polyp that might have led to colonoscopy in 3 of 4 (75%) patients whose largest adenoma was 2 cm or larger, 5 of 6 (83%) patients with largest adenoma 1 to 1.9 cm, 3 of 7 (43%) patients with largest adenoma 6 to 9 mm, and 4 of 16 patients (25%) with largest adenoma 5 mm or smaller. Large, flat adenomas of the right colon were difficult to identify with three-dimensional CT colography. The specificity of three-dimensional CT colography for patients with adenomas 1 cm in diameter or larger was 89%. Examination of patients with missed adenomas after unblinding indicated that meticulous bowel preparation and adequate distention are critical to accurate interpretation. Perceptual errors were common. CONCLUSIONS: CT colography as performed in this study is not adequate as a colorectal cancer screening test. Several technical factors that appear critical to accurate performance of CT colography are defined.

Gastrointest Endosc 1999 Sep;50(3):309-313

Increased plasma homocysteine is an independent predictor of new coronary events in older persons.

A prospective study investigated the association of plasma homocysteine and other risk factors with the incidence of new coronary events at 31 +/- 9 month follow-up in 153 men and 347 women, mean age 81 +/- 9 years. The stepwise Cox regression model showed that significant independent predictors of new coronary events in older persons were age (risk ratio 1.041), plasma homocysteine (risk ratio 1.073), current cigarette smoking (risk ratio 2.524), hypertension (risk ratio 2.032), diabetes mellitus (risk ratio 2.022), serum total cholesterol (risk ratio 1.013), serum high-density lipoprotein cholesterol (risk ratio 0.925), and serum triglycerides (risk ratio 1.004).

Am J Cardiol 2000 Aug 1;86(3):346-347

Mammograms obtained with rhodium vs molybdenum anodes: contrast and dose differences.

OBJECTIVE: A mammography unit with both a molybdenum anode and a rhodium anode, filtered with molybdenum and rhodium, respectively, was evaluated to determine which types of women would benefit from the dose savings of the rhodium combination despite some loss of contrast. SUBJECTS AND MATERIALS: In 100 women, the molybdenum anode and molybdenum filtration (Mo/Mo) were used to obtain mammograms of the right breast, and the rhodium anode and rhodium filtration (Rh/Rh) were used for mammograms of the left breast. All mammograms were obtained at 26 kVp. All milliampere-second values used to radiograph the breasts of these women were recorded. Mammograms of 54 women (30 with previous mammograms available), representing the four types of breasts as defined by the American College of Radiology, were interpreted by three radiologists. Each mammogram was assigned a grade for breast type, preference (Rh/Rh, Mo/Mo, or previous mammograms), contrast, and sharpness. RESULTS: Overall, mammograms obtained by using the Mo/Mo combination were preferred. However, for images of types 3 and 4 breasts, Rh/Rh was preferred twice as often as it had been for mammograms of types 1 and 2 breasts. The mean glandular dose for all breast types when the Rh/Rh combination was used was 42% of the dose used for the Mo/Mo combination. For a 6-cm-thick dense breast, the Rh/Rh combination required 40% of the dose required for the Mo/Mo combination. CONCLUSION: Mammograms obtained with the Rh/Rh combination carried an overall decrease in contrast and mean glandular dose. However, for young women and some women with large dense breasts, the Rh/Rh mammograms were equivalent to or better than the mammograms obtained with the Mo/Mo combination. Effective use of Rh/Rh units requires careful selection of women based on age or the amount of glandular tissue seen on previous mammograms.

AJR Am J Roentgenol 1994 Jun;162(6):1313-1317

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