[In vivo quantitative measurement of diffusion parameters in brain extracellular space of rat by using magnetic resonance imaging].
OBJECTIVE
To develop a novel method of quantitatively measuring the diffusion parameters of brain extracellular  space (ECS) by using gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) as the tracer.


METHODS
Six Sprague  Dawley male adult rats were subjected to magnetic resonance (MR) imaging before and after the introduction of 2 μL Gd-DTPA  into caudate nucleus (Cn). The enhancement on MR subtracted images was converted to the concentration of Gd-DTPA and an  average diffusion rate was calculated pixel by pixel based on the traditional diffusion model.


RESULTS
After the injection, the  tracer diffused frontally and laterally with an average diffusion rate of (3.38±1.07)×10(-4) mm(2)/s. It reached at the margin of cortex 2  hours later, and drained into the subarachnoid space 3 hours later. The tortuosity [Λ(Cn (agar))] was 1.31±0.31 with the reference  of free diffusion measured in agar gel, which was consistent with the result using real-time iontophoresis-tetramethylammonium method. A more feasible reference was acquired by using a routine MR diffusion weighed imaging and [Λ(Cn (MRI))] was  calculated as 3.12±0.73. The tracer was finally clearly out at the end of 12 hours on MR images with a clearance rate constant in Cn  of (7.60±4.18)×10(-5)/s.


CONCLUSIONS
The biophysical properties of brain ECS can be quantitatively characterized by this  newly developed method in living brain, which will enhance our understanding of the micro-environment of neuron and provide a  new way to understand cognition and encephalopathy.
Department of Radiology, Peking University Third Hospital, Beijing, China. hanhongbin@bjmu.edu.cn
Hong-bin
HB
Han
D000818:Animals; D055592:Biophysical Phenomena; D001921:Brain / Q000378:metabolism*; D002421:Caudate Nucleus / Q000378:metabolism; D003287:Contrast Media / Q000493:pharmacokinetics; D004058:Diffusion; D005110:Extracellular Space / Q000378:metabolism; D019786:Gadolinium DTPA / Q000493:pharmacokinetics; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D003287:Contrast Media; D019786:Gadolinium DTPA