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AJNR - American Journal of Neuroradiology

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A Comparison of Magnetization Transfer Ratio, Magnetization Transfer Rate, and the Native Relaxation Time of Water Protons Related to Relapsing-remitting Multiple Sclerosis

Stefan Ropele^a, Siegried Strasser-Fuchs^a, Michael Augustin^a, Rudolf Stollberger^a, Christian Enzinger^a, Hans-Peter Hartung^a and Franz Fazekas^a,b

^a From the Department of Neurology (S.R., S.S-F., M.A., C.E., H-P.H. F.F.), Magnetic Resonance Institute (S.R., R.S., F.F.), Karl-Franzens University of Graz, Austria.
^b Address reprint requests to Franz Fazekas, MD, Department of Neurology, Karl-Franzens University, Auenbruggerplatz 22, A-8036 Graz, Austria.

View larger version (26K): [in a new window]   FIG 1. The FastPACE sequence, as used for quantitative magnetization transfer imaging. Two phase-alternated acquisitions for a single phase-encoding step are shown. These two acquisitions are necessary to remove the background phase, because T1 is obtained from the phase of the composite echo. Each TR interval can be exploited for excitation of additional slices. MT saturation is achieved by performing a short binomial pulse before 1. Owing to multislice acquisition, a high saturation level can be achieved

View larger version (83K): [in a new window]   FIG 2. NAWM (circle) and "dirty white matter" (square) in MS on spin-echo proton density–weighted (2060/20/1) image (A). No corresponding changes are seen on the postcontrast T1-weighted (510/14/2) image (B). In the calculated image showing the transfer rate kfor, the area of dirty white matter is clearly visible (C)

View larger version (18K): [in a new window]   FIG 3. MTR, kfor, and T1free of different lesion types. The whiskers represent the range, the box represents the SD, and the line indicates the mean value. The mean value for NWM is marked by the solid line across the graph

View larger version (95K): [in a new window]   FIG 4. Ring-enhancing lesion surrounded by edema (arrows) and multiple non-active lesions. Proton density–weighted (2060/20/1) (A), postcontrast T1-weighted (510/14/2) (B), kfor (C), and T1free (D) images. The quantitative analysis in the acute lesions yielded the following results: ring-enhancing lesion: MTR = 16.4 %, kfor = 0.13 s-1, T1free = 1.5 s; edema: MTR = 41.1 %, kfor = 0.56 s-1, T1free = 1.2 s. Proton density–weighted (E) and postcontrast T1-weighted (F) images acquired 6 weeks later. Disappearance of perifocal signal abnormality supports the assumption of edema

View larger version (34K): [in a new window]   FIG 5. MTR versus kfor for different lesion types. The open squares show NWM. The filled circles show areas with diffuse changes. Non- active lesions are represented by the open circles, and active lesions are represented by the filled squares. The clustered groups show a good correlation between MTR and kfor; however, the overall relationship is non-linear