Locally focused mri

Abstract

Conventional magnetic resonance images are reconstructed by Fourier transformation and have uniform spatial resolution across the entire field of view (FOV). This paper describes a way of creating MR images that have higher spatial resolution in some areas than in others. High resolution imaging can be confined to just those areas where it is necessary to resolve strong edges without truncation artifact. Such locally focused images can be acquired in less scan time than that required to image the entire FOV with uniformly high resolution. Images are reconstructed from a subset of the usual phase-encoded signals required to create a uniformly well-resolved image. The measured signals are usually nonuniformly scattered in k-space. Functional and interventional imaging may benefit from this technique, which makes it possible to acquire a rapid series of dynamical images that have high resolution in areas of expected change and lower resolution elsewhere. Spectroscopic images may be improved by using high resolution in the neighborhood of sharp edges (e.g., scalp lipids) that might otherwise cause truncation artifacts.

Acquisition and reconstruction of the principal components of an image: A novel MRI technique for reducing scanning time

“…For example, the usual sampling theorem can be applied to find the k-space measurements required to reconstruct each zone (HR, LR) separately. As reported elsewhere [20], the LF MRI method worked quite well when it was applied to the collection of all of these k-space points, taken together.…”

“…However, previous experiments [21] suggested that the SBS solutions produce L F reconstructions with reasonably small error.…”

On the Relationship Between Feature‐Recognizing MRI and MRI Encoded by Singular Value Decomposition

“…"Dynamic" features (i.e., the small structures in the "dynamic" image but not in the baseline image) are not depicted clearly in these projections, showing the inadequacy of these basis functions for dynamic imaging. The right panels of the second and third rows show the projections of the same "dynamic" image onto the first 12 and 16 basis functions, respectively, derived from the SVD of the baseline image in the upper right panel. Fewer artifacts are present, indicating that the second basis function expansion converges more rapidly to the "dynamic" features.…”

“…The upper left panel shows a simulated 64 x 64 "dynamic" image with a central void ("ventricle"), one large "lesion," and numerous small "dynamic" features. The left panels of the second and third rows are the projections of this image onto the first 12 and 16 basis functions, respectively, which were derived from the SVD (or principal components analysis) of a nearly structureless baseline image (upper middle panel). "Dynamic" features (i.e., the small structures in the "dynamic" image but not in the baseline image) are not depicted clearly in these projections, showing the inadequacy of these basis functions for dynamic imaging.…”

Strategies for inner volume 3D fast spin echo magnetic resonance imaging using nonselective refocusing radio frequency pulsesa)

“…Furthermore, these methods in fact shift sampling requirements to excitation, requiring RF pulses that are longer than desired. Methods that employ non-Fourier analyses via phase encoding [7,8] necessarily introduce data extrapolation errors.…”