[Current status of MRI diagnostics with liver-specific contrast agents. Gd-EOB-DTPA and Gd-BOPTA]

The contrast agents Gd-EOB-DTPA and Gd-BOPTA can be administered by bolus injection and are appropriate for use in MRI both as vascularization markers and markers of hepatobiliary excretion. This contribution presents an overview of the specific characteristics of contrast media and the status of clinical development. In comparison to CT and to MRI with unspecific extracellular Gd-chelates, liver-specific contrast agents offer advantages in differentiating unclear liver lesions, increasing the detection rate, and examining the bile duct system.

[Detection of airways stenoses: comparison of virtual and flexible bronchoscopy]

PURPOSE

To compare virtual with flexible bronchoscopy for the detection of bronchial stenoses.

MATERIALS AND METHODS

In a retrospective study, we compared the results of 26 patients, who had clinical suspected pathologies of the tracheobronchial airways and underwent both flexible bronchoscopy and multislice CT with 3D surface rendering of the airways. Flexible bronchoscopy and virtual bronchoscopy were compared as to the rate of detecting bronchial stenoses. For statistical analysis, we divided the tracheobronchial tree in the following sections: trachea, 2 main bronchi, 6 lobar bronchi, 18 segmental bronchi and 36 subsegmental bronchi, corresponding to 63 bronchial sections for each patient (on average) and a total of 1638 bronchial sections for all 26 patients. We graded the bronchial stenosis as less than 50 %, as 50 to 95 % and as complete obstruction.

RESULTS

Virtual bronchoscopy detected 25 bronchial stenoses, while flexible bronchoscopy only revealed 17 stenoses. Stenoses with a diameter less than 50 % were found with virtual bronchoscopy 14 times and with flexible bronchoscopy 10 times. Stenoses with a diameter between 50 and 95 % were detected 7 and 4 times, respectively, and complete obstructions 4 and 3 times, respectively. Tracheobronchial stenoses were well recognized with virtual bronchoscopy. Moreover, the virtual method enabled the visualization of high-grade stenoses and post-stenotic areas that could not be passed by the fiberoptic bronchoscope. Virtual bronchoscopy detected stenoses at a higher rate but the difference was not statistically significant (stenoses < 50 %: p = 0.352, 50 - 95 %: p = 0.339, complete obstruction: p = 0.696).

CONCLUSION

Virtual bronchoscopy is a useful non-invasive method for the diagnostic evaluation of the tracheobronchial tree. In comparison with flexible bronchoscopy, virtual bronchoscopy is superior in revealing high-grade stenoses and visualizing post-stenotic areas.

CT-Kolonographie mit dem 16-Zeilen-Detektor zur Diagnostik kolorektaler Neoplasien und entzündlicher Kolonerkrankungen

PURPOSE

Comparison of the performance of virtual and conventional colonoscopy for the detection of colorectal polyps and inflammatory colon diseases using a 16-slice spiral CT scanner. Furthermore, presentation of the first experiences with a new three-dimensional reconstruction mode ("colon-dissection") that dissects the colonic wall like a pathologic-anatomic preparation to increase the sensitivity.

MATERIALS AND METHODS

Forty patients were studied using a 16-slice spiral CT (Lightspeed 16, General Electric Medical Systems, Milwaukee, Wisconsin 53201, USA). The examination was performed after standard oral preparation for colonoscopy. The colonic distension was achieved with room air and intravenous butylscopolamine. Images were obtained in supine and prone position using a detector configuration of 16 x 0.625 mm, pitch 1.7, rotation time 0.5 s, 160 mAs and 120 kV. Axial reconstruction with a slice thickness of 0.625 mm. The CT data were assessed by two radiologists on an Advantage Workstation (Volume Analysis 2, USA) using a software with the capabilities of axial, multiplanar and volume rendering, virtual endoscopy, and colon dissection. Conventional colonoscopy was used to determine the sensitivity.

RESULTS

A total of 30 polyps were found in 8 patients and a carcinoma was detected in two patients. Colonography identified 4 polyps with a diameter of 10 mm or more, 6 polyps with a diameter of 5 mm to 9.9 mm, 11 polyps with a diameter of 3 to 4.9 mm and 9 polyps with a diameter of 3.0 mm or less. There were two false negative findings (one polyp of 3 mm and one of 4 mm had been overseen) and two false positive findings for polyps (polyps of 4 mm and 6 mm). The sensitivity and specificity for the detection of colonic polyps were 93% and 94% with the "colonic-dissection" mode, 87 % and 94 % with the "virtual-endoscopy" mode and 63 % and 97 % with multi-planar reconstruction, respectively. Depending on the diameter of the colonic polyps, the "colon-dissection" mode ("virtual-coloscopy") had a sensitivity and specificity of 100 % and 100 % for polyps with a diameter over 5.0 mm, 91 % and 82 % for polyps with a diameter from 3.0 to 4.9 mm and 89 % and 78 % for polyps with a diameter under 3.0 mm, respectively. Inflammatory colon diseases presented as thickening of the colon wall over 5 mm.

CONCLUSIONS

Virtual colonoscopy with 16-slice spiral CT allows accurate detection of colonic polyps, including small polyps below a diameter of 3 mm. In comparison with the 2D- and 3D-"virtual-endoscopic" reconstruction, the 3D-reconstruction software "colon-dissection" achieves the highest sensitivity for the detection of colonic masses. Therefore, the combination of a 16-slice spiral CT and the "colon-dissection" reconstruction software provides a high resolution in the z-axis for detecting colonic masses and polyps down to a diameter of less than 2 mm, with a sensitivity of about 90 %. This sensitivity is much higher than the sensitivity achievable with 4-slice spiral CT and without "colon-dissection" mode. A thickened colon wall over 5 mm indicates inflammatory colon disease.