TY - JOUR
T1 - Sodium ion apparent diffusion coefficient in living rat brain
AU - Goodman, James A.
AU - Kroenke, Christopher D.
AU - Larry Bretthorst, G.
AU - Ackerman, Joseph J.H.
AU - Neil, Jeffrey J.
PY - 2005/5
Y1 - 2005/5
N2 - The apparent diffusion coefficient (ADC) of Na+ was determined in live rat brain. The brain extracellular-to-intracellular Na+ content ratio is ∼8:2, which is the inverse of that for water in these spaces. Consequently, the ADC of Na+ is primarily affected by motion in the extracellular space, and Na+ can be viewed as a reporter molecule for motion in that space. Likewise, water ADC is dominated by intracellular motion. The brain Na+ ADC was 1.15 ± 0.09 μm2/ms, which is 61% of the aqueous Na+ free diffusion coefficient (Dfree) at 37°C (1.9 μm2/ms), while the ADC for brain water is 28% of the water Dfree at 37°C (3 μm2/ms). This suggests that the ADC of molecular species within the extracellular space is roughly twofold that within the intracellular space. In postmortem brain, both Na+ and water decrease to 17% of the respective Dfree values. These results are consistent with Na + and water ADC values sharing the same biophysical determinants in postmortem brain. The observed difference between Na+ and water ADC/Dfree ratios in living brain tissue may be attributable to the extracellular environment hindering molecular displacements twofold less than the intracellular environment.
AB - The apparent diffusion coefficient (ADC) of Na+ was determined in live rat brain. The brain extracellular-to-intracellular Na+ content ratio is ∼8:2, which is the inverse of that for water in these spaces. Consequently, the ADC of Na+ is primarily affected by motion in the extracellular space, and Na+ can be viewed as a reporter molecule for motion in that space. Likewise, water ADC is dominated by intracellular motion. The brain Na+ ADC was 1.15 ± 0.09 μm2/ms, which is 61% of the aqueous Na+ free diffusion coefficient (Dfree) at 37°C (1.9 μm2/ms), while the ADC for brain water is 28% of the water Dfree at 37°C (3 μm2/ms). This suggests that the ADC of molecular species within the extracellular space is roughly twofold that within the intracellular space. In postmortem brain, both Na+ and water decrease to 17% of the respective Dfree values. These results are consistent with Na + and water ADC values sharing the same biophysical determinants in postmortem brain. The observed difference between Na+ and water ADC/Dfree ratios in living brain tissue may be attributable to the extracellular environment hindering molecular displacements twofold less than the intracellular environment.
KW - Brain
KW - Compartmental diffusion
KW - In vivo MRS
KW - Na NMR
KW - Sodium diffusion
UR - http://www.scopus.com/inward/record.url?scp=18344389399&partnerID=8YFLogxK
U2 - 10.1002/mrm.20444
DO - 10.1002/mrm.20444
M3 - Article
C2 - 15844159
AN - SCOPUS:18344389399
VL - 53
SP - 1040
EP - 1045
JO - Magnetic Resonance in Medicine
JF - Magnetic Resonance in Medicine
SN - 0740-3194
IS - 5
ER -