Dynamic imaging with multiple resolutions along phase‐encode and slice‐select dimensions

Abstract

An implementation is reported of an imaging method to obtain MUltiple Resolutions along Phase-encode and Slice-select dimensions (MURPS), which enables dynamic imaging of focal changes using a graded, multiresolution approach. MURPS allows one to trade spatial resolution in part of the volume for improved temporal resolution in dynamic imaging applications. A unique method of Hadamard slice encoding is used, enabling the varying of the phase encode and slice resolution while maintaining a constant effective TR throughout the entire 3-D volume. MURPS was implemented using a gradient-recalled echo sequence, and its utility was demonstrated for MR temperature monitoring. In this preliminary work, it has been shown that changes throughout a large volume can be effectively monitored in times that would normally only permit dynamic imaging in one or a very few slices. Magn Reson Med 45:940 -947, 2001.

Non‐Fourier‐encoded parallel MRI using multiple receiver coils

“…Based on Eq. [6], Hadamard-, wavelet-, and SVD-based input vector sets have been studied (7,10,17) and used in MRI (8,9). For example, Hadamard encoding derives the matrix P from the M ϫ M Hadamard matrix H M (c.f.…”

“…NF encoding has been used to achieve effective interview motion compensation (7) or volume imaging of the heart (8), to increase effective relaxation times (7), and for imaging with multiple resolutions along the phase-encode and slice-select dimensions (MURPS) (9). NF spatial encoding can be derived from well-known fixed mathematical basis sets, such as the Hadamard (10) and wavelet (7) bases that are popular in signal processing.…”

Enhancing the acquisition efficiency of fast magnetic resonance imaging via broadband encoding of signal content

“…This encodes g consecutive portions of the FOV identically, as reflected by the subsampled k-space in each linear system of Eq. (22). Acquired signals can thus only recover the identically encoded portions of Once the SMASH combinations are applied to the (non-Fourier) signals acquired from the receiver coils after each RF-encoding excitation (Eq.…”

“…Alternatively, it can be designed to possess features that are not otherwise readily attainable, such as variable-resolution imaging, enhanced edge definition and reduced motion susceptibility [20][21][22][23][24]. Despite its robustness, non-Fourier encoding is largely underdeveloped compared to fast Fourier MRI methods, partially due to the unique limitations it poses.…”

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

“…The error minimization necessary to achieve image reconstruction in the presence of these inaccuracies (e.g., regularization in parallel imaging) inadvertently results in unresolved image subspaces wherein diagnostically significant information may exist. Non-Fourier methods avoid signal sampling limitations altogether [4,5] by replacing gradient encoding with RF-induced encoding [6]. This requires specialized imaging sequences and typically results in reduced SNR.…”