Selective excitation of myelin water using inversion–recovery‐based preparations

Abstract

T 1 and T 2 relaxation of excised frog sciatic nerve water was characterized at 7 T. Based on these findings, optimal timings for multiple inversion-recovery magnetization preparations were determined to selectively excite the so-called myelinwater T 2 component. Subsequent double inversion-recovery and triple inversion-recovery preparations were used in combination with CPMG acquisitions to experimentally determine optimal timings and effect of the preparation. Using double inversion-recovery, optimal timings were found to excite magnetization that is predominantly (Ϸ93%) derived from the myelin-water component. Greater selectivity (Ϸ96%) was found by extending the preparation to triple inversion-recovery, at the price of decreasing SNR by a factor of Ϸ 2. Magn Reson Med 54:743-747, 2005.

Compartment‐specific enhancement of white matter and nerve ex vivo using chromium

“…Across samples, mean signal fractions were 20 ± 5, 34 ± 5, and 46 ± 5% for components with short ( T 1 = 60 ± 13 ms, T 2 = 9 ± 2 ms), intermediate ( T 1 = 132 ± 16 ms, T 2 = 15 ± 3 ms), and long relaxation times ( T 1 = 226 ± 20 ms, T 2 = 54 ± 7 ms), respectively. Interestingly, these spectra are similar to those previously observed in peripheral nerve (4, 8, 9). Also, the relative sizes of the spectral components (in order of increasing relaxation times) are in reasonable agreement with electron‐microscopy‐derived values of water content in the myelin, extra‐, and intra‐axonal spaces, respectively, of crayfish abdominal nerve (31), a model tissue for mammalian white matter.…”

“…Water from within myelin, intra‐, and extra‐axonal compartments of peripheral nerve can be isolated based upon multiexponential T 1 and/or T 2 (1–9). In cerebral white matter (10–12) and optic nerve (13, 14), however, only two relaxation components are generally found: a short relaxation time component arising from myelin water and a long relaxation time component arising from a combination of intra‐ and extra‐axonal water.…”

Myelin water weighted diffusion tensor imaging

“…minimize partial volume effects and also improve specificity. Finally, further sensitization to myelin water can be achieved by reducing the TR, as myelin water is believed to have the shortest T 1 compared to all other T 1 components in human white matter at 3T (Travis and Does, 2005;Labadie et al, 2008).…”

“…The DIR method is based on the short T 1 of myelin and requires a lengthy (e.g. 2 s) preparation pulse, making it impractical for a whole-brain clinical DTI scan (Travis and Does, 2005). The MT technique, which uses an off-resonance radiofrequency pulse to selectively excite and saturate bound hydrogen protons in non-aqueous molecules including macromolecules (hereafter referred to as macromolecules for simplicity), leads to reduced longitudinal magnetization of free water molecules after they exchange magnetization with the saturated protons.…”

Development, simulation, and validation of NMR relaxation-based exchange measurements

“…REXSY data were collected at 30 t m values linearly arrayed in 50 ms increments and 24 T 2 -weighting periods ͑t e1 ͒ pseudologarithmically arrayed from 2 to 512 ms. IR-REXSY data were collected using the same t m values with t e1 = 2 ms. The t i was experimentally determined-from IR-CPMG data using a previously described method 27 -to null water proton signal. REXSY and IR-REXSY sequences were repeated twice ͑NEX= 2͒ to accompany the two-part phase cycle previously described.…”