Multi-slice CT-colonography in low-dose technique -: Preliminary results

Purpose: Assessment of Multi-Slice CT-colonography (MSCTC) with standard and low-dose technique in comparison to conventional colonoscopy (CC). Materials and Methods: After standardized bowel cleansing, 28 men and 24 women (mean age 60.3 years) underwent CC within two hours after MSCTC had been performed (4 x 2.5 mm collimation, 3 mm slice width, 17.5 mm table feed, 120 kVp). In 19 patients, MSCTC was performed with 120 mAs (CTDIw,eff: 11.28 mGy), and in 33 patients with 10 mAs (CTDIw,eff: 0.94 mGy), respectively. After noise reduction using mathematical algorithms by a dedicated software (ECCET), images were analyzed by two blinded readers in simultaneously displayed 2D- and 3D-modes. Findings in MSCTC were compared to the results obtained with CC. Results: Calculated effective doses ranged between 9 and 12 mSv for 120 mAs, and between 0.75 and 1 mSv for the low-dose technique. In standard dose MSCTC, 20 of 25 lesions (80%) were found: all 7 tumors (100%), one large polyp (>10 mm; 100%), 6 of 7 medium sized polyps (9.9 to 5 mm; 86%) and 6 of 10 small polyps (< 5 mm; 60%). In low-dose MSCTC, 32 of 44 lesions (73%) were seen: all three large polyps (100%), 13 of 14 medium sized polyps (93%) and 16 of 27 small polyps (59%). An overall sensitivity of 78% with a specificity of 68% was calculated. False positive findings were seen mostly for small lesions (12 for standard dose, 11 for low-dose). Conclusion: Despite a 12-fold reduction of radiation exposure, MSCTC in low-dose technique performs comparably well to standard dose MSCTC. After mathematical noise reduction, more than 90% of polyps larger than 5 mm can be detected.