Quantitative assessment of water pools by T 1 rho and T 2 rho MRI in acute cerebral ischemia of the rat.
The rotating frame longitudinal relaxation magnetic resonance imaging (MRI) contrast, T(1 rho), obtained with on-resonance continuous wave (CW) spin-lock field is a sensitive indicator of tissue changes associated with hyperacute stroke. Here, the rotating frame relaxation concept was extended by acquiring both T(1 rho) and transverse rotating frame (T(2 rho)) MRI data using both CW and adiabatic hyperbolic secant (HSn; n=1, 4, or 8) pulses in a rat stroke model of middle cerebral artery occlusion. The results show differences in the sensitivity of spin-lock T(1 rho) and T(2 rho) MRI to detect hyperacute ischemia. The most sensitive techniques were CW-T(1 rho) and T(1 rho) using HS4 or HS8 pulses. Fitting a two-pool exchange model to the T(1 rho) and T(2 rho) MRI data acquired from the infarcting brain indicated time-dependent increase in free water fraction, decrease in the correlation time of water fraction associated with macromolecules, and increase in the exchange correlation time. These findings are consistent with known pathology in acute stroke, including vasogenic edema, destructive processes, and tissue acidification. Our results show that the sensitivity of the spin-lock MRI contrast in vivo can be modified using different spin-lock preparation blocks, and that physicochemical models of the rotating frame relaxation may provide insight into progression of ischemia in vivo.
Jokivarsi
Kimmo T
KT
Biomedical Imaging Unit, Department of Neurobiology, A.I. Virtanen Institute for Molecular Sciences, University of Kuopio, Kuopio, Finland.
Niskanen
Juha-Pekka
JP
Michaeli
Shalom
S
Gröhn
Heidi I
HI
Garwood
Michael
M
Kauppinen
Risto A
RA
Gröhn
Olli H
OH
D000208:Acute Disease; D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D004058:Diffusion; D004195:Disease Models, Animal; D018450:Disease Progression; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D014867:Water / Q000032:analysis* / Q000378:metabolism*
D014867:Water