MR Colonography at 3 Tesla: Comparison with 1.5 Tesla in vivo and in a colon model

Purpose: In a retrospective study MR colonography images were compared in routine examinations of patients screened for polyps and in a colon model with the question whether and to which degree image quality was improved at the higher field strength of 3.0 compared to 1,5 T.

Methods: 128 MR colonography images of 40 patients, of whom 20 each had been scanned at 1,5 and 3,0 T using a 4 element phased array torso coil, respectively. At both fieldstrenghts imaging included T1-weighted fat-supressed spoiled gradient echo (T1w-fs-GE), T2/T1-weighted fast imaging employing steady state acquisition (FIESTA) and T2-weighted steady state fast spinecho sequence (T2SSFSE) in breath-hold technique. Using ROC analysis with seven readers the three types of images were compared from the colon model and from 20 patients each at 1,5 T and 3,0 T. While a time window of 20s was allowed for picture assessment in a chance-generated succession of images on a monitor, image quality was rated with a score of 1 to 5 (1,very good;5, very bad). Statistical significance was calculated with the Mann-Whitney-U test.

Results: At both field strengths the T2SSFSE images received the best ratings followed by the FIESTA images [p=0,001]. Although overall the 3.0T images obtained worser scores compared to 1,5T, a better detection of phantom polyps was noted in the colon model [p=0,001].

Conclusion: While MR-colonography in breath-hold using the same 4-element phased-array coil technique at 3.0 T and 1,5 T does not perform better at the higher fieldstrenght in general, an improved detection of small polyps may be obtained when air-related artifacts can be excluded.