Delayed progression of cytotoxic oedema in focal cerebral ischemia after treatment with a torasemide derivative: a diffusion-weighted magnetic resonance imaging study.

Diffusion-weighted magnetic resonance imaging (MRI) was used to assess the effect of an astrocytic Na+2Cl-K+ cotransporter inhibitor, a novel torasemide derivative, on the time course and spatial evolution of a focal cerebral ischemia in the rat. The drug (1 mg/ kg, i.p.) was injected 30 min before middle cerebral artery occlusion and diffusion-weighted images were acquired at various times thereafter. The results showed that the drug reduced the size of the hyperintensity during the first hours, but did not affect the time constant of growth or the final size. The temporary reduction of the cytotoxic oedema induced by the torasemide derivative, demonstrates an antioedematous activity.

Methods for reconstructing phase sensitive slice profiles in magnetic resonance imaging.

The experimental determination of slice profiles excited by applying radiofrequency pulses in the presence of a gradient generally results in magnitude profiles. The conditions necessary to obtain a phase-sensitive picture of the profile of a slice are discussed. A distinction is made between the "excitation profile" (distribution of the transverse magnetization immediately after the RF pulse) and the "slice profile" (distribution after refocusing by gradient reversal and/or imperfect gradient switching). Methods are presented that allow one to obtain either the excitation profile or the slice profile. It is shown that phase encoding along the direction of the slice selection gradient provides a convenient protocol for obtaining the distribution of both the real and imaginary parts of the slice profile. The phase sensitive excitation profile can be obtained by frequency encoding. These methods were used to evaluate the performance of various shaped pulses.

Two-dimensional 1H spectroscopic imaging for evaluating the local metabolic response to focal ischemia in the conscious rat.

Two-dimensional 1H spectroscopic imaging and magnetic resonance imaging were used to study focal ischemia induced by middle cerebral artery occlusion in rats. A water suppressing spin-echo sequence was used at 4.7 T. Phase encoding during the spin-echo delay (TE = 272 ms) yielded an 8 x 8 array of 35 microL voxels. The injured area of the brain had a higher lactate level and markedly lower N-acetyl aspartate, creatine and choline levels than did the non-ischemic regions. The spectroscopic imaging data clearly showed the localization of the infarct, which agreed well with both magnetic resonance imaging and the histological data obtained post-mortem. This study demonstrates the potential usefulness of combining magnetic resonance imaging and 1H spectroscopic imaging for studying animal models of stroke, and indicates the suitability of the technique for further pharmacological approaches.

Proton spectroscopic imaging: a tool for studying intracerebral tumor models in rat.

Water-suppressed 2D 1H spectroscopic imaging was used with surface coils to study in vivo the cerebral metabolism changes in rat brain induced by a glial tumor growing in situ. To achieve slice selection without a chemical-shift artifact, we exploited the depth pulse properties of a spin-echo sequence. In order to give a spectral response which is independent of the position, the water suppression was achieved by using a spin-locking excitation and a binomial refocusing pulse. Spectroscopic images were obtained with an in-plane resolution of 1.1 X 1.1 mm and a slice thickness of roughly 3 mm. The growing of the tumor induced dramatic modifications in the proton spectra, including a nearly complete loss of N-acetyl aspartate, an increase of the 1.3-ppm peak, an increase in choline, and a decrease in creatine. The results demonstrate the potential of spectroscopic imaging in the study of intracranial tumor models in rats.