In vivo chlorine-35, sodium-23 and proton magnetic resonance imaging of the rat brain.

In this study we demonstrate the feasibility of combined chlorine-35, sodium-23 and proton magnetic resonance imaging (MRI) at 9.4 Tesla, and present the first in vivo chlorine-35 images obtained by means of MRI. With the experimental setup used in this study all measurements could be done in one session without changing the setup or moving the subject. The multinuclear measurement requires a total measurement time of 2 h and provides morphological (protons) and physiological (sodium-23, chlorine-35) information in one scanning session. Chlorine-35, sodium-23 and high resolution proton images were acquired from a phantom, a healthy rat and from a rat displaying a focal cerebral infarction. Compared to the healthy tissue a signal enhancement of a factor of 2.2 +/- 0.2 in the chlorine-35 and a factor of 2.9 +/- 0.6 in the sodium-23 images is observed in the areas of infarction. Exemplary unlocalized measurement of the in vivo longitudinal and transversal relaxation time of chlorine-35 in a healthy rat showed multi-exponential behaviour. A biexponential fit revealed a fast and a slow relaxing component with T(1,a) = (1.7 +/- 0.4) ms, T(1,b) = (25.1 +/- 1.4) ms, amplitudes of A = 0.26 +/- 0.02, (1-A) = 0.74 +/- 0.02 and T(2,a) = (1.3 +/- 0.1) ms, T(2,b) = (11.8 +/- 1.1) ms, A = 0.64 +/- 0.02, (1-A) = 0.36 +/- 0.02. Combined proton, sodium-23 and chlorine-35 MRI may provide a new approach for non-invasive studies of ionic regulatory processes under physiological and pathological conditions in vivo.