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.

Can we improve trauma mortality in a state with a voluntary trauma system.

BACKGROUND: Arizona has no organized statewide trauma system. We looked at the 1997 and the 1998 Uniform Hospital Discharge Data Set (UHDDS) for the State of Arizona, and examined the trauma mortality data at both trauma hospitals and nontrauma hospitals. METHODS: All qualifying mortalities based on hospital data from 1997 through 1998 were reviewed for the State of Arizona. Trauma deaths from 32 nontrauma hospitals were examined and compared with that of 7 level 1 trauma centers within the state. RESULTS: In this time period, there were 375 qualified mortalities from nontrauma centers and 761 qualified mortalities from level 1 trauma facilities. Only 29 (8%) of nontrauma hospital deaths were found to be due to motor vehicle accidents. Only 8 (4%) mortalities at nontrauma centers were due to firearms. CONCLUSION: The data suggest that patients are arriving at the appropriate facility for definitive care despite the absence of a formal statewide trauma system.

Evaluation of JPEG and wavelet compression of body CT images for direct digital teleradiologic transmission.

PURPOSE: To determine acceptable levels of JPEG (Joint Photographic Experts Group) and wavelet compression for teleradiologic transmission of body computed tomographic (CT) images. MATERIALS AND METHODS: A digital test pattern (Society of Motion Picture and Television Engineers, 512 x 512 matrix) was transmitted after JPEG or wavelet compression by using point-to-point and Web-based teleradiology, respectively. Lossless, 10:1 lossy, and 20:1 lossy ratios were tested. Images were evaluated for high- and low-contrast resolution, sensitivity to small signal differences, and misregistration artifacts. Three independent observers who were blinded to the compression scheme evaluated these image quality measures in 20 clinical cases with similar levels of compression. RESULTS: High-contrast resolution was not diminished with any tested level of JPEG or wavelet compression. With JPEG compression, low-contrast resolution was not lost with 10:1 lossy compression but was lost at 3% modulation with 20:1 lossy compression. With wavelet compression, there was loss of 1% modulation with 10:1 lossy compression and loss of 5% modulation with 20:1 lossy compression. Sensitivity to small signal differences (5% and 95% of the maximal signal) diminished only with 20:1 lossy wavelet compression. With 10:1 lossy compression, misregistration artifacts were mild and were equivalent with JPEG and wavelet compression. Qualitative clinical findings supported these findings. CONCLUSION: Lossy 10:1 compression is suitable for on-call electronic transmission of body CT images as long as original images are subsequently reviewed.

Influence of image acquisition parameters on CT artifacts and polyp depiction in spiral CT colonography: in vitro evaluation.

PURPOSE: To quantify the effects of spiral computed tomographic (CT) acquisition parameters on the magnitude of three-dimensional (3D) rippling artifacts and polyp depiction. MATERIALS AND METHODS: An in vitro colon phantom was constructed with air-filled acrylic cylinders that contained synthetic polyps of 3-13 mm. The phantom was submerged in fluid and positioned at four angles of inclination relative to the z axis. Image data were acquired at collimation and pitch combinations of 3 mm and 1.67 and 5 mm and 1.6, respectively. Rippling artifacts were quantified by measuring the longitudinal variation of in-plane phantom edge width, and the influence of these artifacts on the depiction of pedunculated and sessile polyps was assessed qualitatively. RESULTS: The in-plane magnitude of the rippling artifact was a function of the angle of inclination relative to the longitudinal axis and the table increment. The through-plane periodicity of the artifact was equal to one-half the table increment. CONCLUSION: The table increment and angle of inclination of the surface of the object relative to the z axis determine the periodicity and magnitude of the rippling artifact at 3D spiral CT colonography. Although the depiction of small pedunculated polyps was not compromised, some sessile polyps were degraded by the artifact.

A single naturally processed measles virus peptide fully dominates the HLA-A*0201-associated peptide display and is mutated at its anchor position in persistent viral strains.

We studied the natural MHC class I display of measles virus (MV) epitopes. Peptide ligands associated with HLA-A*0201 were purified from a B lymphoblastoid cell line prior to and after infection with MV. Infection-induced peptides were revealed using microcapillary reversed phase high performance liquid chromatography electrospray ionization/mass spectrometry (microLC-ESI/MS) by subtraction of the "infected" and "uninfected" ion traces. Three naturally processed viral epitopes derived from different MV proteins were identified through tandem MS sequencing. These peptides were expressed at widely divergent levels of HLA-peptide complexes, but had similar binding capacities to HLA-A*0201. The most abundant viral peptide species, identified as residues 84-92 (KLWESPQEI) of the MV nonstructural C protein, was expressed at an unprecedented high density (> 10(5) copies per cell) and was immunogenic in HLA-A2/Kb-transgenic mice. Furthermore, natural mutants of this epitope, occurring in persistent lethal MV strains, were shown to have lost their HLA-A*0201 binding capacity. Thus, here we report for the first time the direct discovery through microLC-ESI/MS of a uniquely dominant viral HLA class I ligand, KLWESPQEI, with features eligible for immune selection pressure.

Optimal section spacing in single-detector helical CT.

To define the section spacing that maximizes longitudinal resolution without needless section overlap, the optimal percentage of overlap was computed theoretically and expressed as a constant relative to the effective section thickness. For imaging applications that require maximal longitudinal resolution, single-detector helical computed tomographic images should be reconstructed with at least 60% overlap relative to the effective section thickness.

Laparoscopic hernias: two case reports and a review of the literature.

Laparoscopic operations are becoming more common and replacing more traditional surgical procedures. As a result, radiologists should be aware of some of the unique complications that may occur from these types of procedures. We report two cases of incarcerated bowel hernias in lateral trocar sites.

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.

Retrospective analysis of the effect of crossing vessels on successful retrograde endopyelotomy outcomes using spiral computerized tomography angiography.

PURPOSE: Using spiral computerized tomography (CT) angiography, we sought to evaluate the incidence of a crossing vessel in a group of adults with primary ureteropelvic junction obstruction who had previously undergone successful retrograde endopyelotomy. MATERIALS AND METHODS: A total of 16 patients who had undergone successful Acucise balloon incision endopyelotomy for ureteropelvic junction obstruction, all with followup greater than 2 years, underwent a spiral CT angiogram with intravenous contrast material to identify those with a crossing vessel. Contrast enhanced CT was performed with dual phase technique on a Somatom-Plus-S CT scanner using prototype software. After 180-degree linear interpolation of the projection data, transaxial images of the affected kidney were reconstructed. In addition, at the time of the study all patients completed analog followup pain scales and quality of life assessment questionnaires. RESULTS: Among the 16 patients 6 (38%) had anterior or posterior crossing vessels based on spiral CT angiography. No patient had both types. By analog pain scale patients had 80% mean improvement in pain (range 63 to 100). CONCLUSIONS: In our series nearly 40% of patients with anterior or posterior crossing vessels had a long-term (greater than 2 years) successful outcome with retrograde endopyelotomy. Endopyelotomy continues to be our initial mode of therapy among adults with primary ureteropelvic junction obstruction. In our opinion the adverse influence of the crossing vessel is not sufficient to justify the added expense of preoperative angiography, spinal CT or endoluminal ultrasound.

Digital subtraction versus film-screen angiography for detecting acute pulmonary emboli: evaluation in a porcine model.

PURPOSE: To compare the diagnostic performance of digital subtraction angiography (DSA) to that of film-screen angiography (FSA) for detecting acute pulmonary embolism (PE) in a porcine model. MATERIALS AND METHODS: DSA and FSA were performed in 13 pigs before and after central venous administration of autologous emboli. Results were compared to findings at necropsy with use of ex vivo pulmonary angiography to guide pathologic sectioning. The sensitivity and predictive value of a positive case for detecting each embolus were computed for each pulmonary artery branch order and compared with use of 95% confidence intervals. Interobserver variability among three readers for individual PE detection was calculated. RESULTS: Pathologic examination of the lungs revealed 100 total PEs (location by vessel order: 1st = 1, 2nd = 0, 3rd = 15, 4th = 32, > 5th = 52). On average, FSA review identified 72 (72%) emboli and DSA review, 65 (65%). There was no significant difference in sensitivity or predictive value of a positive case between DSA and FSA for detecting emboli (P > .05). There was similar agreement among readers for individual PE detection with DSA (mean, 84%) and FSA (mean, 80%). CONCLUSION: The diagnostic performance of DSA is equivalent to that of FSA for detecting emboli in porcine PA branches. Interobserver agreement for individual PE detection is similar for both imaging techniques.

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.