Purpose: To evaluate lesion contrast enhancement in brain magnetic resonance (MR) images with and without magnetization transfer pulse (MT) in patients affected with multiple sclerosis (MS).
Material and methods: Ten patients affected with relapsing-remitting MS underwent a 1.5-T (Magnetom Vision, Siemens) MR examination with T1-weighted spin-echo sequences without MT (TR/TE = 630/14 ms) and with MT (840/14 ms) using the following common parameters: 21 para-axial slices (thickness 5 mm, 10% gap); matrix 256 x 256; field of view 25 cm (rectangular 5/8); 2 excitations. The postcontrast sequences with and without MT were acquired in a randomized order, starting 5 minutes after the intravenous injection of 0.1 mmol/kg Gadoteridol (ProHance, Bracco). The images were blindly evaluated in four separate sessions: only the postcontrast images with MT (post-Gd with MT); only the postcontrast images without MT (post-Gd without MT); comparing the pre- and postcontrast images with MT (pre/post-Gd with MT); comparing the pre- and postcontrast images without MT (pre/post-Gd without MT). The number of hyperintense areas referred to contrast enhancement and the evaluation time were measured for each session. The Wilcoxon test was used for statistical analysis.
Results: The number of areas referred to lesion contrast enhancement per patient were as follows: post-Gd with MT, 6.9 +/- 6.8 (mean +/- standard deviation) (range 1-24); post-Gd without MT, 3.6 +/- 4.3 (0-14); pre/post-Gd with MT, 5.2 +/- 6.1 (1-21); pre/post-Gd without MT, 3.6 +/- 4.9 (0-16). A nonsignificant difference was found for the comparison between post-Gd without MT and pre/post-Gd without MT while significant differences were found between post-Gd with MT and pre/post-Gd with MT (p = .028), pre/post-Gd without MT and pre/post-Gd with MT (p = .012), as well as between post-Gd without and post-Gd with MT (p = .008). The mean evaluation time for the different sessions was always less than a minute, ranging from 33 seconds for pre/post-Gd without MT to 51 seconds for post-Gd with MT.
Conclusions: The postcontrast sequence obtained with the MT pulse detects more active lesions than the postcontrast sequence without MT. However, the comparison with the plain images with the MT pulse is mandatory to exclude pseudoenhancement foci, i.e. hyperintense areas already present in the precontrast images with the MT pulse, without disruption of the blood-brain barrier. The post-Gd without MT sequence needs not be compared with the precontrast images without MT. Differences in evaluation time are practically negligible.