In vivo measurements of multi-component T2 relaxation behaviour in guinea pig brain

Multi-echo Carr-Purcell-Meiboom-Gill (CPMG) imaging sequences were implemented on 1.5 T and 4.0 T imaging systems to test their ability to measure in vivo multi-component T-2 relaxation behavior in normal guinea pig brain. The known dependence of accurate T-2 measurements on the signal-to-noise ratio (SNR) was explored in vivo by comparing T, decay data obtained using three methods to increase SNR (improved RF coil design, signal averaging and increased magnetic field strength). Good agreement between T-2 values of nickel-doped agarose phantoms was found between imaging and spectroscopic methods. T-2 values were determined for gray matter (GM) and white matter (WM) locations from images of guinea pig brain in vivo, T-2 measurements of GM were found to be monoexponential at both field strengths. The mean T, times for GM were 71 ms at 1.5 T, and 53 ms at 4.0T. The highest average SNR was achieved using an improved RF coil at 4.0T. In this case, two peaks were extracted in WM, a "short" T-2 peak at approximately 6 ms, and a "medium" T-2 peak at approximately 48 ms. T-2 values in GM and the major component of WM were significantly decreased at 4.0T compared to 1.5 T, The improved SNR attained with this optimized imaging protocol at 4.0T has allowed for the first time extraction of the myelin-sensitive T-2 component of WM in animal brain in vivo. (C) 1999 Elsevier Science Inc.