The microstructural correlates of T1 in white matter.
OBJECTIVE
Several studies have shown strong correlations between myelin content and T1 within the brain, and have even suggested that T1 can be used to estimate myelin content. However, other micro-anatomical features such as compartment size are known to affect longitudinal relaxation rates, similar to compartment size effects in porous media.


METHODS
T1 measurements were compared with measured or otherwise published axon size measurements in white matter tracts of the rat spinal cord, rat brain, and human brain.


RESULTS
In both ex vivo and in vivo studies, correlations were present between the relaxation rate 1/T1 and axon size across regions of rat spinal cord with nearly equal myelin content.


CONCLUSIONS
While myelination is likely the dominant determinant of T1 in white matter, variations in white matter microstructure, independent of myelin volume fraction, may also be reflected in T1 differences between regions or subjects.
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.
Kevin D
KD
Harkins
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.
Junzhong
J
Xu
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.
Adrienne N
AN
Dula
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.
Ke
K
Li
Department of Pathology, Vanderbilt University, Nashville, Tennessee, USA.
William M
WM
Valentine
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.|Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, USA.
Daniel F
DF
Gochberg
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.|Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.|Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA.
John C
JC
Gore
Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.|Department of Electrical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
Mark D
MD
Does
D000818:Animals; D001369:Axons / Q000648:ultrastructure; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000000981:diagnostic imaging*; D066127:White Matter / Q000033:anatomy & histology* / Q000166:cytology / Q000000981:diagnostic imaging* / Q000648:ultrastructure
MRI; T1; axon size; microstructure; rat; spinal cord