Screening for colon cancer.

Colorectal cancer screening reduces mortality in individuals 50 years and older. Each of the screening tests currently available has advantages and limitations, and there is no consensus as to which test or combination of tests is best. What is clear, however, is that the rates of colorectal cancer screening remain low. This review summarizes the clinical evidence supporting colorectal cancer screening in the average risk population and in high risk groups, discusses the advantages and disadvantages of the available screening tests, outlines the currently recommended guidelines for screening based on risk category, and discusses new and emerging technologies for colorectal cancer screening.

Late recurrence of malignant melanoma presenting as peritoneal "carcinomatosis".

Malignant melanoma is a relatively rare malignancy that arises from melanocytes and accounts for approximately 1% of all malignancies reported in the United States. Malignant melanoma can develop in any part of the skin or mucosal membranes. It metastasizes to all organs of the body and often demonstrates unpredictable metastatic behavior. Late recurrence of malignant melanoma, defined as occurring 10 or more years after diagnosis and treatment, is a rare but characteristic metastatic behavior of malignant melanoma. We present a case of a late recurrence of malignant melanoma presenting with diffuse peritoneal studding.

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

PURPOSE: To assess the diagnostic performance and reader agreement with two-dimensional (2D) and three-dimensional (3D) display techniques for detecting colorectal polyps with spiral computed tomographic (CT) colonography. MATERIALS AND METHODS: A test set of 30 colonic segments was developed from spiral CT colonographic studies (12 with polyps and 18 without). The 12 segments with polyps contained 22 lesions (11 polyps <10 mm, 11 polyps or cancers >/=10 mm), with all findings verified with colonoscopy. Three specific 2D and 3D image-display techniques were tested. Three experienced abdominal radiologists independently analyzed each test case and were retested 6 weeks later. RESULTS: The results of readings 1 and 2 were similar for all image-display techniques among the readers. Pooled segment results were sensitivity of 89%-92% and specificity of 72%-83%. Pooled polyp size results for sensitivity and positive predictive value were 77%-86% and 74%-86% (all polyps, n = 22), 91%-100% and 85%-100% (polyps or cancers >10 mm, n = 11), and 61%-73% and 61%-80% (polyps 5-9 mm, n = 11), respectively. Overall intraobserver agreement was good for the three display techniques (kappa, 0.60-1.00); however, interobserver agreement for 2D multiplanar reformation was lower (kappa, 0.53-0.80). CONCLUSION: Among experienced abdominal radiologists, similar diagnostic performance in polyp detection was found among 2D multiplanar reformation and 3D display techniques, although individual cases showed improved characterization with 3D display techniques. Evaluation of reader agreement demonstrated good intraobserver agreement, with variable interobserver agreement.

Quantitative and qualitative evaluation of volume of low osmolality contrast medium needed for routine helical abdominal CT.

OBJECTIVE: The purpose of our study was to determine the minimum optimal dose of IV contrast medium for helical CT that can preserve image quality while reducing cost. SUBJECTS AND METHODS: Four hundred sixty-three patients from six centers were enrolled in a prospective trial in which patients were randomized into one of four weight-based dose categories of iopromide, 300 mg I/mL: 1.25, 1.50, 1.75, and 2.0 mL/kg. Six of 463 patients were excluded from analysis. A radiologist at each center who was unaware of the volume of contrast medium administered determined whether the scans were acceptable. The responses were analyzed by dose, in aggregate, and by weight. Enhancement values (in Hounsfield units) in regions of interest in the liver, pancreas, aorta, and kidneys were obtained at a single time during the scan. The participating radiologist was unaware of these values. Finally, three additional nonparticipating site observers assessed the images for acceptability, diagnostic quality, and overall level of confidence. A cost model comparing incurred charges in using 150 or 100 mL, or 1.5 mL/kg, of low osmolality contrast medium was developed from experience in an additional 303 patients. RESULTS: We found no clinically significant difference in acceptability of scans at doses greater than 1.5 mL/kg. However, significant variability occurred among the centers. The use of 1.5 mL/kg led to a savings of $9927.16 for 303 patients when compared with the use of 150 mL at list price. The cost is the same for 1.5 mL/kg or use of 100 mL of contrast medium. CONCLUSION: A weight-based dose at 1.5 mL/kg of low osmolality contrast medium can provide acceptable scans in most patients, with a significant cost savings.

Renal cysts: is attenuation artifactually increased on contrast-enhanced CT images?

PURPOSE: To determine if the attenuation values of simple renal cysts are artifactually increased on contrast material-enhanced, clinically acquired spiral computed tomographic (CT) images. MATERIALS AND METHODS: Dual-phase renal spiral CT studies (5-mm collimation; pitch, 1.0) were retrospectively analyzed in 24 consecutive patients who had ultrasonographic (US) documentation of simple renal cysts. Forty-eight cysts were identified. The attenuation values of each cyst were measured on nonenhanced, cortical phase, and nephrographic phase images. The size and the location of each cyst in relation to the renal parenchyma were also recorded. RESULTS: The cysts were 0.6-10.8 cm in diameter (mean, 2.6 cm; SD, 2.0). The mean attenuation change in the cysts from nonenhanced to contrast-enhanced images was statistically significant in a comparison of cortical phase and nephrographic phase images (P: <.01): +1.8 HU (SD, 3.8) for cortical phase and +3. 6 HU (SD, 5.6) for nephrographic phase images. Renal cysts 1.0 cm or smaller showed a higher attenuation increase (mean, +4.0 HU for cortical phase and +11.0 HU for nephrographic phase). None of the renal cysts larger than 1.0 cm demonstrated an increase greater than 10 HU (mean, +1.4 HU for cortical phase and +2.3 HU for nephrographic phase). Intraparenchymal cysts showed higher mean attenuation changes than the exophytic cysts. CONCLUSION: Attenuation values in the renal cysts increased artifactually on contrast-enhanced images, but this pseudoenhancement was not substantial and was less than 10 HU when the cyst was larger than 1. 0 cm in diameter.

Multiphasic injection method for uniform prolonged vascular enhancement at CT angiography: pharmacokinetic analysis and experimental porcine model.

PURPOSE: To determine if multiphasic injection provides uniform, prolonged vascular contrast medium enhancement at computed tomographic (CT) angiography. MATERIALS AND METHODS: With a computer-based, compartmental model of the cardiovascular system, theoretic analysis was performed to estimate an injection algorithm for uniform, prolonged vascular enhancement. For algorithm validation, four pigs were scanned after intravenous injection of 50 or 70 mL of contrast medium (282 mg of iodine per milliliter). Uni-, bi-, and multiphasic injection schemes were tested. In most cases, the initial injection rate was 2 mL/sec. In each CT study, 27 dynamic images were acquired every 2 seconds at a fixed mid-abdominal aortic level. Time-enhancement curves were calculated. Injection duration, peak aortic enhancement, and enhancement uniformity (duration of enhancement achieved within 90% of the peak [90% DCE]) were evaluated. RESULTS: Theoretic and experimental results agreed well. Compared with uniphasic injection, biphasic injection resulted in more prolonged enhancement but generated two enhancement peaks with a valley between, and multiphasic injection yielded more uniform and prolonged enhancement. With 50- and 70-mL multiphasic injections, respectively, injection duration increased by 32% and 51%, peak enhancement decreased by 19% and 18%, and 90% DCE increased by 81% and 94%. CONCLUSION: Uniform, prolonged vascular enhancement, which is desirable for CT angiography and essential for steady-state quantification of blood volume in organs, can be achieved with multiphasic injection.

Efficient correction for CT image artifacts caused by objects extending outside the scan field of view.

The purpose of this paper is to develop a method of eliminating CT image artifacts generated by objects extending outside the scan field of view, such as obese or inadequately positioned patients. CT projection data are measured only within the scan field of view and thus are abruptly discontinuous at the projection boundaries if the scanned object extends outside the scan field of view. This data discontinuity causes an artifact that consists of a bright peripheral band that obscures objects near the boundary of the scan field of view. An adaptive mathematical extrapolation scheme with low computational expense was applied to reduce the data discontinuity prior to convolution in a filtered backprojection reconstruction. Despite extended projection length, the convolution length was not increased and thus the reconstruction time was not affected. Raw projection data from ten patients whose bodies extended beyond the scan field of view were reconstructed using a conventional method and our extended reconstruction method. Limitations of the algorithm are investigated and extensions for further improvement are discussed. The images reconstructed by conventional filtered backprojection demonstrated peripheral bright-band artifacts near the boundary of the scan field of view. Images reconstructed with our technique were free of such artifacts and clearly showed the anatomy at the periphery of the scan field of view with correct attenuation values. We conclude that bright-band artifacts generated by obese patients whose bodies extend beyond the scan field of view were eliminated with our reconstruction method, which reduces boundary data discontinuity. The algorithm can be generalized to objects with inhomogeneous peripheral density and to true "Region of Interest Reconstruction" from truncated projections.

The abdominal compartment syndrome: CT findings.

OBJECTIVE: The abdominal compartment syndrome is a potentially fatal condition resulting from pathologic elevation of intraabdominal pressure. We evaluated preoperative abdominal CT scans of four patients with proven abdominal compartment syndrome to identify signs of increased intraabdominal pressure. CONCLUSION: CT findings common to all four patients included tense infiltration of the retroperitoneum out of proportion to peritoneal disease, extrinsic compression of the inferior vena cava by retroperitoneal hemorrhage or exudate, and massive abdominal distention with an increased ratio of anteroposterior-to-transverse abdominal diameter (positive round belly sign; ratio > .80; p < .001). Direct renal compression or displacement, bowel wall thickening with enhancement, and bilateral inguinal herniation were each present in two of the four patients. Radiologists should be aware of this life-threatening syndrome. In the appropriate clinical setting, CT findings of increased intraabdominal pressure should be swiftly communicated to other physicians involved in treating the patient because the abdominal compartment syndrome requires emergent surgical decompression.

Aortic and hepatic contrast medium enhancement at CT. Part I. Prediction with a computer model.

PURPOSE: To develop a physiologic model of contrast medium enhancement by incorporating available physiologic data and contrast medium pharmacokinetics and to predict organ-specific contrast medium enhancement at computed tomography (CT) with various contrast medium injection protocols in patients of variable height and weight. MATERIALS AND METHODS: A computer-based, compartmental model of the cardiovascular system was generated by using human physiologic parameters and more than 100 differential equations to describe the transport of contrast medium. Blood volume, extracellular fluid volume, and regional blood flow were estimated from available data. Local structures were modeled mathematically to describe the distribution and dispersion of intravascularly administered iodinated contrast medium. A global model was formed by integrating regional circulation parameters with the models of local structures. Aortic and hepatic CT contrast-enhancement curves were simulated for three protocols and were compared with mean enhancement curves in three groups of 25-28 patients (80 patients total; 28 in one group, 25 in one group, and 27 in one group) receiving the same protocols. The percent difference in maximum enhancement between the simulated and empiric curves and the enhancement difference index (sum of the area difference between the simulated and empiric curves divided by the total area under the empiric curve) were computed. RESULTS: The simulated and empiric enhancement curves closely agreed in maximum enhancement (the mean percent difference in the aorta was 7.4%; liver, 4.8%) and in variation over time (mean enhancement difference index in the aorta was 11.6%; liver, 12.7%). CONCLUSION: A computer-based, physiologic model that may help predict organ-specific CT contrast medium enhancement for different injection protocols was developed. Such a physiologic model may have many clinical applications.

Aortic and hepatic contrast medium enhancement at CT. Part II. Effect of reduced cardiac output in a porcine model.

PURPOSE: To investigate how reduction in cardiac output affects the magnitude and timing of aortic and hepatic contrast medium enhancement during abdominal computed tomography (CT). MATERIALS AND METHODS: Eight 20-30-kg pigs underwent CT before and after pharmacologic reduction of cardiac output (measured by means of thermodilution). Each CT study consisted of 53 dynamic images acquired every 5 seconds at a fixed level through the midliver after intravenous injection of contrast medium (concentration, 282 mg of iodine per milliliter; dose, 2 mL per kilogram of body weight; injection rate, 2 mL/sec). Curves of contrast medium enhancement versus time were measured. Changes in the magnitude and timing of aortic and hepatic enhancement were compared with the reduction in cardiac output. RESULTS: With reduction in cardiac output, the time from the injection start to the arrival of the contrast medium bolus in the aorta (P < .01) and the times from injection completion to peak aortic (P < .01) and peak hepatic (P < .01) enhancement increased. As cardiac output decreased, peak aortic enhancement increased proportionally (P < .01). Peak hepatic enhancement increased only slightly and correlated weakly with the decrease in cardiac output (P = .07). CONCLUSION: As cardiac output decreases, the times to the arrival of the contrast medium bolus in the aorta and to peak aortic and hepatic enhancement increase. Reduction in cardiac output results in a substantial increase in peak aortic enhancement but not in peak hepatic enhancement.

Aortic and hepatic peak enhancement at CT: effect of contrast medium injection rate--pharmacokinetic analysis and experimental porcine model.

PURPOSE: To investigate the effect of injection rate of contrast medium on aortic and hepatic peak enhancement at computed tomography. MATERIALS AND METHODS: Early pharmacokinetics of contrast enhancement was analyzed theoretically and simulated with a compartment model. Contrast enhancement curves were generated from the model at different injection rates (0.5-10.0 mL/sec). Time-enhancement curves were measured. The effect of contrast medium injection rate on the time and magnitude of peak enhancement was evaluated and validated empirically in pigs. RESULTS: Theoretic predictions and experimental results were in good agreement. Time to aortic peak enhancement was the sum of injection duration and bolus transfer time of contrast medium from the injection site to the aorta. Time to hepatic peak enhancement was the sum of injection duration and time to equilibrium. The magnitude of peak enhancement increased with the injection rate, but the increase was different in the aorta and liver. CONCLUSION: Use of injection rates above 2 mL/sec did not substantially increase hepatic peak enhancement but helped increase the magnitude of arterial enhancement and temporal separation of arterial and venous phases of enhancement for dual-phase spiral CT.

Visualization of colorectal polyps with spiral CT colography: evaluation of processing parameters with perspective volume rendering.

PURPOSE: To evaluate two key processing steps for detection of colon polyps with spiral computed tomographic (CT) colography with perspective volume rendering (PVR): image reconstruction and opacity assignment of the attenuation data. MATERIALS AND METHODS: Spiral CT was performed in 10 patients with known polyps confirmed at colonoscopy, and detailed quantitative analyses were performed of data obtained in four. First, anatomic fidelity of three-dimensional (3D) images generated from two-dimensional (2D) source images with equal voxel dimensions (87%-90% overlap) was compared with 3D images generated from 2D source images with unequal voxel dimensions (0%-80% overlap). Next, the relative dimensions of colorectal polyps to adjacent structures were evaluated for various opacity threshold settings. Then, step and sigmoidal opacity functions were compared with respect to image smoothness and edge sharpness. RESULTS: PVR images generated after interpolation of image data reconstructed with at least 60% overlap were equivalent in image quality to PVR images generated from source images with equal voxel dimensions. Relative polyp-to-haustral fold dimensions demonstrated substantial distortions with opacity thresholds below -700 HU. The 3D PVR images generated with the sigmoidal opacity function were significantly smoother than those generated with the step opacity function (paired t test, P < .02), with small differences noted in edge sharpness. CONCLUSION: Use of highly overlapping source images (87%-90%) was not necessary to generate 3D PVR images of colorectal polyps. Image artifacts were suppressed with use of an appropriate opacity threshold and a sigmoidal opacity function without substantial loss in edge sharpness.

CT of cystic renal masses: analysis of diagnostic performance and interobserver variation.

OBJECTIVE: Our objective was to assess the clinical usefulness and interobserver variability of the Bosniak classification scheme for characterizing a series of pathologically proven cystic renal lesions imaged with CT. MATERIALS AND METHODS: Seventy pathologically proven cystic renal masses (38 benign, 32 malignant) in 46 patients were reviewed independently by three radiologists. The cystic masses were categorized by each reviewer according to both the Bosniak classification and the receiver operating characteristic (ROC) analysis. Both the individual results for each reader and the pooled results for all three readers were analyzed. Interobserver agreement and discordance in classifying lesions as Bosniak categories I-II or III-IV were assessed. RESULTS: The distribution of the 70 lesions (based on the average of the three readers) was 22 Bosniak I (0% malignant), eight Bosniak II (13% malignant), 11 Bosniak III (45% malignant), and 29 Bosniak IV (90% malignant). All readers agreed on the Bosniak classification in 59%, or 41 of the 70 lesions (I, 17; II, one: III, four: and IV, 19). Eleven (16%) of the 70 lesions were classified as Bosniak I or II by one reader and as Bosniak III or IV by at least one other reader. The area under the curve for the pooled ROC analysis was calculated to be 0.957. Individual reader values ranged from 0.914 to 0.981. The sensitivities, specificities, and accuracies for the three readers ranged from 94% to 100%, 71% to 92%, and 84% to 93%. Assessment of interobserver variability by kappa analysis yielded scores of .571 and .477 for the Bosniak and ROC analyses, respectively. CONCLUSION: Overall, the Bosniak classification scheme is useful for evaluating renal masses: however, interobserver variation in distinguishing. Bosniak II and Bosniak III lesions may present difficulties in recommending surgical versus conservative management.

Depiction of pulmonary emboli with spiral CT: optimization of display window settings in a porcine model.

PURPOSE: To determine optimal spiral computed tomographic (CT) image display for depiction of pulmonary emboli (PE). MATERIALS AND METHODS: Autologous PE detected in 10 pigs with contrast material-enhanced spiral CT were displayed with six display window settings (standard mediastinal window and five modified windows referenced to attenuation values in pulmonary artery [PA] branches). The thrombus gray level and gray level contrast and separability of PE versus those of the local PA branch were computed for each window setting; results were compared with repeated measured analysis of variance. RESULTS: Of 114 PE detected pathologically, 28 were visible with spiral CT. Two of the 28 PE were not detectable with standard mediastinal windows. Statistically significantly improved gray level contrast and separability were noted with modified windows referenced to the second-order PA branch and the local PA branch than with the standard mediastinal and other modified window settings (P < .05). However, thrombus gray level was statistically significantly higher with the standard mediastinal window (P < .05). CONCLUSION: PE are best depicted as filling defects when displayed with a modified window referenced to the right or left main PA attenuation. Standard mediastinal windows are useful for identifying vessels that are occluded completely with PE.

Spiral computed tomographic colonography: determination of the central axis and digital unraveling of the colon.

RATIONALE AND OBJECTIVES: The authors developed and tested automated and semiautomated bowel-lumen tracking and colon-unraveling techniques for determining the central axis of the bowel. METHODS: A computer-simulated gastrointestinal tract phantom was used to test the accuracy of an automated algorithm for central axis determination and bowel unraveling. Variations in cross-sectional features between straight and unraveled formats were compared in a canine bowel segment in vitro and a human colon in vivo by using spiral computed tomography. Three readers each performed three semiautomated evaluations. RESULTS: Accuracy of the automated algorithm was confirmed by the high degree of correlation in the cross-sectional feature measurements (length error, < 1%). For the canine colon segment, accuracy of the semiautomated algorithm was confirmed by comparison with the automated tracing. For the human colon, readings were reproducible with 3.3% (+/- 1.9 standard deviation) mean variation in length. CONCLUSION: An automated algorithm for central axis deterioration and unraveling the colon has been validated in a gastrointestinal tract phantom. A semiautomated algorithm has been shown to be reproducible and time-efficient.

Radical resection of tumors of the inferior vena cava with vascular reconstruction and kidney autotransplantation.

BACKGROUND: Tumors of the inferior vena cava (IVC) are rare tumors. Although often locally confined, juxtaposed vital structures usually limit the extent of resection. However, complete surgical resection has been shown to be the most important positive prognostic factor. METHODS: Four patients had resection of primary vena caval tumors. In two patients with locally extensive vena caval tumors the limits of conventional resection were extended by means of complete resection of the involved infrahepatic IVC, aorta, and both kidneys. The IVC and aorta were reconstructed with synthetic grafts, and the uninvolved kidney was autotransplanted for both patients. RESULTS: Of the two patients treated with more extensive resection, one patient had no evidence of disease 26 months after operation, and the second patient died of recurrent disease 23 months after operation. CONCLUSIONS: Primary tumors of the IVC may extend locally without distant metastasis. Radical surgical excision as the primary mode of treatment provides the best chance for prolonged survival in appropriately selected patients with tumors of the IVC. After surgical excision the patient with the leiomyosarcoma was treated with radiation therapy and the patient with rhabdomyosarcoma by chemotherapy. Although leiomyosarcomas of the IVC are rare tumors, the first patient is only the third reported case of the even rarer rhabdomyosarcoma of the IVC.

Adrenal adenomas: relationship between histologic lipid and CT and MR findings.

PURPOSE: To assess the relationship between the quantity of lipid in resected adrenal adenomas and the unenhanced computed tomographic (CT) attenuation number and the relative change in signal intensity on chemical shift magnetic resonance (MR) images. MATERIALS AND METHODS: The percentage of lipid-rich cortical cells in histologic sections from 20 resected adrenal adenomas was assessed. The results were correlated with the corresponding unenhanced CT attenuation number or the relative change in signal intensity on chemical shift MR images, or both. RESULTS: There was an inverse linear relationship between the percentage of lipid-rich cortical cells in the adrenal adenomas and the unenhanced CT attenuation number (R2 = .68, P = .0005). There was a similar inverse linear relationship to the relative change in MR signal intensity on chemical shift images by using both quantitative (R2 = .83, P = .004) and qualitative (R2 = .70, P = .019) assessment. CONCLUSION: The presence and amount of histologic lipid in many adrenal adenomas accounts for their low attenuation on unenhanced CT scans and their loss in relative signal intensity on chemical shift MR images.