A decrease in cerebral glucose metabolic uptake is an early and characteristic sign of Alzheimer's disease (AD). Streptozotocin (STZ) is a bacterial toxin which damages insulin-producing cells and insulin receptors. Intracerebroventricular (icv) application of STZ in rats has been found to chronically decrease cerebral glucose uptake and produce other effects that bear a resemblance to several other molecular and pathological features of AD. In the present experiments in vivo (1)H MR Spectroscopy with short echo time (3 ms) was used to non-invasively obtain a neurochemical profile of rat brains, 3 weeks and 2 months after double icv injections of STZ or vehicle. Seventeen metabolites were quantified from 27 microL tissue volume which included hippocampus and a part of cerebral cortex, using the LCModel and unsuppressed water signal as an internal reference. Three weeks after icv STZ several metabolites were significantly decreased, the most prominent changes noted in glycerophosphocholine and phosphocholine (-38 +/- 5%), glutathione (-37 +/- 4%), taurine (-30 +/- 19%), glutamate (-26 +/- 14%), phosphocreatine (-23 +/- 15%) and N-acetylaspartate (-16 +/- 6%). On the contrary, the concentration of N-acetylaspartylglutamate was found significantly increased (+38 +/- 18%). After 2 months some of these changes were even more pronounced. We conclude that in vivo (1)H MRS of rat brain following icv STZ injections provides a new input into a better understanding of the critical dependency of neural function and structure on brain glucose consumption, and may be of relevance in further studies of AD pathomechanism.
The engineering of a novel intra‐operative MRI system is described. A movable, 1.5 Tesla MRI magnet was placed in a neurosurgical operating room without affecting established neurosurgical procedure. The system allows fast, high‐quality MR intra‐operative imaging of the brain and spine without the necessity of patient transportation. A neuro‐navigational device capable of displaying and updating spatially referenced MR images in the operating room was integrated with the MRI system. Over 100 procedures have been carried out with this system without limiting surgical access and without compromising traditional neurosurgical, nursing or anesthetic techniques. J. Magn. Reson. Imaging 2001;13:78–86. © 2001 Wiley‐Liss, Inc.
There is a need for non-invasive diagnostic tools to detect and monitor the occurrence of diseases. Ideally, this can be done without resorting to ionizing radiation, especially when multiple rounds of imaging are required. Magnetic resonance imaging (MRI), a form of three-dimensional nuclear magnetic resonance, has become a common tool of choice for diagnosticians. Due to the low contrast difference between healthy and diseased tissue, contrast agents—magnetic species administered to the patient prior to imaging—are routinely used for contrast improvement. High-field (B0 ≥ 4.7 T, 1H Larmor frequency ≥ 200 MHz) MRI offers advantages in terms of better signal-to-noise ratio, as well as improved spectral resolution for certain applications. New contrast agents are being developed for high-field MRI, the topic of this review. After discussing the purpose of contrast agents and the advantages and potential issues of high-field MRI, we discuss recent developments in the field of contrast agent design, synthesis, and applications, citing examples of high-field MRI-ready molecular contrast agents, as well as nanoparticulate contrast agents based on various inorganic materials (e.g., coordination polymers, transition metal oxides, or lanthanide halides). We will discuss how certain aspects (composition, shape, ligands) affect the contrasting abilities of these agents. Finally, we highlight recent developments in the promising field of multifunctional probes, wherein multiple imaging and/or therapeutic modalities are combined in a single species. As high-field MRI becomes more commonplace in the clinical setting, such new contrast agents are needed to provide optimized imaging. This will facilitate the clinician's task in resolving pathologies for more efficient diagnosis and patient treatment.
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