Proton magnetic resonance in myelin deficient brains of mutant mice

The role of myelin in determining the magnetic resonance (MR) characterization of the central nervous system (CNS) was investigated in unmyelinated brains of normal fetal mice, as well as myelin-deficient adult mutant mice ( shi, qk, mld) and their age-matched controls. In vitro NMR relaxation time measurements at 10 MHz for whole brains showed consistently longer T 1 (range 558 ± 8 to 580 ± 27 msec) and T 2 (range 81 ± 3 to 89 ± 3 msec) values for the adult myelin-deficient animals than the age-matched controls ( T 1 = 496 ± 31, T 2 = 79 ± 4 msec). The fetal brains exhibited even more prolonged relaxation times ( T 1 = 976 ± 60, T 2 = 158 ± 7 msec). MR images obtained at 81 MHz using spin echo (SE) sequences, which unlike the in vitro approach allowed discrimination between white and gray matter areas, revealed an absence of gray-white matter contrast in the brains of mutant mice, consistent with longer than normal relaxation of the myelin-deficient white matter. While larger tissue water components such as those present in the immature brain and edematous white matter contribute a greater effect, myelin and its associated bound water may still play an important role in the MR characterization of normal gray and white matter.