High Spatial Resolution Spectroscopy

The ability of improved MRI technologies to detect smaller lesions may involve a greater need for higher spatial resolution in single-voxel spectroscopy and CSI experiments. Whereas the poor SNR of 1.5 T magnets prevented the acquisition of single-voxel spectra with a spatial resolution significantly below 4 - 8 ml or chemical shift images with a spatial resolution of less than 2 ml, lower spatial resolutions are becoming feasible at 3.0 T.

A specific application requiring lower resolution is the MR spectroscopic study of small animals. These studies are usually performed on dedicated animal systems, which offer ideal conditions. However, given their increasing diffusion, researchers are interested in using whole-body high-field MR systems for animal studies both for reasons of cost reduction and to perform direct comparisons of animal and human data. This requires new techniques that allow to achieve the highest possible spatial resolution and obtain conclusive data from brain structures that are several orders of magnitude smaller than the human brain while keeping examination times short to minimize animal mortality [59].

Recent studies have shown that proton spectrosco-py, for instance of newborn rat brain in a 3.0 T whole-body scanner using a standard clinical spectroscopy protocol is feasible. Irrespective of field strength, the RF resonator for signal transmission and reception plays a major role in the quality that can be achieved. A coil with a size close to that of the object to be studied is usually appropriate, like the small birdcage resonator shown in Fig. 6.10 designed for brain studies of new

Fig. 6.10. Dedicated linear volume resonator (Flick Engineering Solutions, The Netherlands) designed for newborn rat brain MR studies in a conventional clinical 3.0 T MR scanner. (Image courtesy of University Children's Hospital, Zurich, Switzerland)

Fr&quency (ppm)

Fig. 6.11. High-resolution single-voxel spectrum (a) with a spatial resolution of 0.2 ml and high-resolution CSI (b) with a spatial resolution of 0.04 ml acquired from a newborn rat brain in a conventional clinical whole-body 3.0 T scanner

Fr&quency (ppm)

Fig. 6.11. High-resolution single-voxel spectrum (a) with a spatial resolution of 0.2 ml and high-resolution CSI (b) with a spatial resolution of 0.04 ml acquired from a newborn rat brain in a conventional clinical whole-body 3.0 T scanner born rats. If the transfer of results from animal experiments to human in vivo studies is going to be explored, similar acquisition protocols would be appropriate to achieve comparable results. While maintaining these prerequisites, single-voxel spectra can be acquired of volumes as small as about 0.2 ml, or CSI spectra with a spatial resolution of 0.04 ml, both with an acquisition time of less than 10 min (Fig. 6.11).

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