Relaxivity and magnetization transfer of white matter lipids at MR imaging: importance of cerebrosides and pH

Abstract

Purpose: To measure the effect of the major lipid components of white matter on the relaxation times and magnetization transfer (MT) of water protons.

Materials and methods: Multilamellar vesicle (MLV) suspensions of pure phosphatidylcholine (PC) and PC with varying proportions of cholesterol (CHOL), sphingomyelin (SPH), and galactocerebroside (GC) were produced at varying pH. T1, T2, and MT were measured.

Results: Suspensions consisting of PC with CHOL or SPH caused greater shortening of T1 and T2 and slightly greater MT effects than did PC alone. Suspensions consisting of GC and PC caused the greatest decrease in relaxation times, and the MT effect was two to three times greater than with either CHOL-PC or SPH-PC suspensions. At acidic pH, the relaxation time changes and the MT effects with CHOL-PC, SPH-PC, and GC-PC suspensions were greater than the effects of the same MLVs at physiologic pH.

Conclusion: GC has the strongest effect on relaxivity and MT of all the major white matter lipids. The relaxivity and MT observed with white matter lipids is pH dependent, indicating that chemical exchange of protons likely contributes to relaxivity and MT.