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Magnetic resonance measurement of tetramethylammonium diffusion in rat brain: Comparison of magnetic resonance and ionophoresis in vivo diffusion measurements
Author(s) -
Kroenke Christopher D.,
Ackerman Joseph J.H.,
Neil Jeffrey J.
Publication year - 2003
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10579
Subject(s) - tetramethylammonium , displacement (psychology) , diffusion , nuclear magnetic resonance , chemistry , effective diffusion coefficient , in vivo , magnetic resonance imaging , mean squared displacement , analytical chemistry (journal) , ion , physics , chromatography , molecular dynamics , biology , medicine , psychology , microbiology and biotechnology , organic chemistry , radiology , psychotherapist , thermodynamics , computational chemistry
Magnetic resonance (MR) and ionophoresis are two experimental methods that provide measurements of molecular diffusion in living tissue. Typical experimental settings yield MR studies that are sensitive to mean molecular displacements of ∼5 μm, and ionophoresis experiments to displacements of ≥100 μm. An assessment of the correspondence between the methods is hampered by the fact that no common probe molecule has been used. One of the most frequently utilized probe molecules in ionophoresis measurements is the tetramethylammonium (TMA) ion. In the current work the diffusion properties of TMA were studied in rat brain in vivo with localized 1 H MR spectroscopy (MRS). Standard treatment of the MR data yielded a 3.6‐fold lower apparent diffusion coefficient (ADC) compared to ionophoresis. To explore the source of this discrepancy, a separate data processing scheme was applied to the MR data to monitor individual elapsed displacement‐distance subpopulations of TMA molecules. This analysis revealed a dependence of the ADC estimation on a given subpopulation's elapsed displacement distance. The MR‐derived ADC approached the ionophoresis‐derived value as the elapsed displacement distance increased to 15 μm. These observations demonstrate that MR and ionophoresis studies provide complementary information, and that ADC estimates obtained from the two techniques are sensitive to different biophysical determinants. Magn Reson Med 50:717–726, 2003. © 2003 Wiley‐Liss, Inc.