A general linear relaxometry model of R1 using imaging data.
OBJECTIVE
The longitudinal relaxation rate (R1 ) measured in vivo depends on the local microstructural properties of the tissue, such as macromolecular, iron, and water content. Here, we use whole brain multiparametric in vivo data and a general linear relaxometry model to describe the dependence of R1 on these components. We explore a) the validity of having a single fixed set of model coefficients for the whole brain and b) the stability of the model coefficients in a large cohort.


METHODS
Maps of magnetization transfer (MT) and effective transverse relaxation rate (R2 *) were used as surrogates for macromolecular and iron content, respectively. Spatial variations in these parameters reflected variations in underlying tissue microstructure. A linear model was applied to the whole brain, including gray/white matter and deep brain structures, to determine the global model coefficients. Synthetic R1 values were then calculated using these coefficients and compared with the measured R1 maps.


RESULTS
The model's validity was demonstrated by correspondence between the synthetic and measured R1 values and by high stability of the model coefficients across a large cohort.


CONCLUSIONS
A single set of global coefficients can be used to relate R1 , MT, and R2 * across the whole brain. Our population study demonstrates the robustness and stability of the model.
Wellcome Trust Centre for Neuroimaging, Institute of Neurology, University College London, London, United Kingdom.
Martina F
MF
Callaghan
Gunther
G
Helms
Antoine
A
Lutti
Siawoosh
S
Mohammadi
Nikolaus
N
Weiskopf
D000328:Adult; D000368:Aged; D000465:Algorithms; D003198:Computer Simulation; D017097:Electric Impedance; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D016014:Linear Models; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult
3T; MT; PD; PD*; R1; R2*; T1; T2*; longitudinal relaxation; magnetization transfer; quantitative; relaxometry; transverse relaxation; water content