2D locally focused MRI: Applications to dynamic and spectroscopic imaging

Abstract

Conventional magnetic resonance images have uniform spatial resolution across the entire field of view. A method of creating MR images with user-specified spatial resolution along one dimension of the field of view was described recently by the authors. This paper presents the 2D generalization of this technique, which allows the user to specify arbitrary spatial resolution in arbitrary 2D regions. These images are reconstructed from signals that sparsely sample the k-space representation of the image. Therefore, locally focused images can be acquired in less time than that required by Fourier imaging with uniformaly high resolution. In this paper the authors show how to increase the temporal resolution of dynamic imaging (e.g., interventional imaging) by using high resolution in areas of expected change and lower resolution elsewhere. Alternatively, by matching the local spatial resolution to the expected edge content of the image, it is possible to avoid the localized truncation artifacts that mark Fourier images reconstructed from the same number of signals. For example, the authors show how proton spectroscopic images of the head may be improved by using high resolution in the neighborhood of scalp lipids that might otherwise cause truncation artifacts.

BSLIM: Spectral Localization by Imaging With Explicit $B_{0}$ Field Inhomogeneity Compensation

“…Next, the spatial-domain discrete Fourier transform (DFT) is applied to obtain the low-resolution space samples . Finally, the temporal-domain inverse DFT is applied after zero padding of the spectral samples, up to length , to obtain the BSLIM kernels (21) In Fig. 1, we show a schematic overview of the computation of the kernels.…”

“…These methods include: imposing a limited spatial support on the reconstruction to limit the effect of the SRF [15], [16]; optimizing space trajectories [17]- [19]; adjusting the SRF using higher-order gradients [20]; sampling partial space data [21]; and, applying sensitivity encoding (SENSE) [22].…”

Extension of finite-support extrapolation using the generalized series model for MR spectroscopic imaging

“…In MR elastography (MRE), two fundamental approaches have been demonstrated. Static [5] and quasi-static deformation [6] techniques fall into one broad category, while shear wave imaging with oscillatory [7], [8] stresses applied mechanically at the object surface, or remotely by other means such as ultrasound [9] fall into another. Common to many of these methods is the use of displacement-encoding by phase contrast [10].…”

Locally focused 3D coronary imaging using volume-selective RF excitation

“…Locally focused MRI is a technique first proposed by Cao et al (2)(3)(4) for providing non-uniform spatial resolution within the imaging field of view (FOV). It differs from the conventional Fourier imaging approach in that it uses basis functions that have variable spatial characteristics depending on regional object details.…”