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Home Projects 1st call (2008) 1. Parallel imaging of the neurochemical profile in the mouse

1. Parallel imaging of the neurochemical profile in the mouse

 Dr. M. Rudin (ETHZ), Dr. R. Gruetter (EPFL)  - PhD student: Aline Seuwen 

Chemical shift imaging (CSI) on the rat and the mouse brain can be used to generate metabolic and neurotransmitter profiles in specific brain areas, which can be linked to the animal’s disease status, specific behavior and therapeutic treatment effects. Recent advances in improving the sensitivity, suggest that spatial resolution of 1μl can be achieved when mapping compounds of interest such as glucose, glutamine, glutamate and GABA (Mlynarik et al. 2006). However, the small size of the organ and high demands on shimming correction currents pose particular challenges in applying this measurement technique to the mouse brain. In fact, The CSI method is based on the averaging of phase encoding steps in two or three dimensions which can lead to very long acquisition times for high spatial resolutions. Several rapid CSI techniques have been proposed, ranging from echo-planar (Posse et al. 2001) and spiral sampling approaches (Adalsteinsson et al. 1998) to approaches on the steady state free precession of the magnetization (Althaus et al. 2006). These methods optimize sensitivity per unit of time resulting in a significant reduction of the total scan time, at the expense of amplitude distortions due to saturation effects and T2 decay, which renders the determination off metabolite concentrations difficult. Alternatively, complementary k-space sampling strategies, i.e. parallel imaging approaches might be used: in this case k-space is undersampled and missing information is retrieved by using multiple receiver coils.

The main goal of this project is to extend these measurement capabilities to high spatial resolutions by making use of parallel acquisition techniques, to improve the signal to noise ratio on the one hand, and to reduce the measurement time on the other hand, with the help of parallel acceleration techniques such as SENSE (Prüssman et al 1999) or GRAPPA (Griswold et al. 2002).

Adalsteinsson E et al. (1998). Volumetric spectroscopic imaging with spiral-based k-space trajectories. Magn Reson Med 39:889-98

Althaus, M., W.Dreher et al. (2006). Fast 3D echo planar SSFP-based 1H spectroscopic imaging: demonstration on the rat brain in vivo. Magn Reson imaging 24(5):549-55

Griswold MA et al. (2002) Generalized autocalibrating partially parallel acquisitions (GRAPPA). Magn. Reson. Med. 47(6): 12021210.

Mlynarik V et al. (2006). Localized short-echo-time proton MR spectroscopy with full signal-intensity acquisition. Magn Reson Med 56:965-970

Posse S et al. (1995). High speed 1H spectroscopic imaging in human brain by echo planar spatial-spectral encoding. Magn Renon Med 33:34-40

Pruessmann KP et al. (1999). SENSE: Sensitivity encoding for fast MRI. Magn Reson Med 42: 952-62

Contact: Aline Seuwen