Synopsis
Cartesian sampling is widely used in conventional MRI,
however, non-Cartesian sampling schemes (e.g. radial or spiral sampling) offer
advantages over Cartesian schemes. Among them is flexibility and efficiency of
k-space sampling, motion insensitivity, and the ability to generate images with
high spatio-temporal resolution from limited data. The lecture will cover the
basic acquisition schemes of Cartesian and non-Cartesian sampling along with
the conventional and state-of-the-art reconstruction methods with an emphasis on
advantages and disadvantages.
Abstract:
Cartesian sampling is widely used in conventional MRI
acquisitions and its popularity has been based on the reconstruction speed
afforded by the Fast Fourier Transform (FFT) algorithm. Non-Cartesian sampling
schemes (e.g. radial or spiral sampling) offer advantages over Cartesian
schemes, among them is flexibility and efficiency of k-space sampling. A key
advantage of schemes that oversample the center of k-space is the intrinsic
insensitivity to motion and, as shown more recently, the ability to generate
images with high spatio-temporal resolution from limited data.
The lecture will cover the basic acquisition schemes of
Cartesian and Non-Cartesian sampling along with the conventional and
state-of-the-art reconstruction methods with an emphasis of their advantages
and disadvantages.
Target Audience:
Basic scientist and clinicians who want to better understand
the basic principles and practical issues of k-space sampling and
reconstruction in terms of the advantages and disadvantages for research and
clinical applications. Introduction:
This section will cover the basics of k-space and sampling
theory including the basic reconstruction schemes such as FFT and Non Uniform Fourier
Transform (NUFT). Cartesian acquisition strategies:
This section will cover the full Cartesian and partial
Fourier acquisition strategies, highlighting differences in terms of
acquisition efficiency as well as the benefits and limitations of partial
Fourier. It will cover Echo Planar Imaging (EPI) and the consequences of
imperfect Cartesian trajectories.Non-Cartesian acquisition strategies:
This section will cover 2D and 3D radial and spiral sampling
acquisition schemes with an emphasis on advantages and disadvantages of
non-uniform k-space sampling. Among the advantages the section will cover the
use of these trajectories in terms of motion insensitivity, efficient k-space
coverage, high spatio-temporal sampling including view ordering and its
implications in parametric imaging. Among the drawbacks of non-Cartesian
trajectories, it will cover artifacts such as off-resonance sensitivity, effect
of trajectory imperfections, and differences in aliasing artifacts relative to
the Cartesian counterpart.Hybrid trajectories:
This section will cover trajectories that mix Cartesian and
non-Cartesian schemes either by sampling on the Cartesian grid but with a
non-Cartesian trajectory or by employing non-Cartesian sampling in kx-ky and
Cartesian sampling along kz (e.g. radial and spiral stack of stars as well
trajectories with pseudo random k-space coverage like DISCO and TWIST).Reconstruction of non-Cartesian data:
Non-Cartesian acquisitions are best suited to extract unique
information from highly undersampled data. This section will provide an
overview of novel reconstruction algorithms for undersampled data including the
use of multi-coil information, model based reconstruction methods for
parametric imaging, and Magnetic Resonance Fingerprinting (MRF). The section will address status on the
clinical implementation of these more computationally demanding methods.Clinical Impact of non-Cartesian sampling:
This section will highlight applications where non-Cartesian
methods are preferred due to their intrinsic motion robustness. It will also
focus on applications where images with high spatio-temporal resolution are acquired
at accelerations not available with conventional Cartesian methods. These
include free breathing acquisitions, rapid parameter mapping (e.g., T1/T2
mapping), dynamic contrast enhancement MRI,
and other dynamic processes.The ideal scanner for optimal non-Cartesian scanning:
This section will address limitations of current scanners
for optimal non-Cartesian scanning and provide an insight on what changes in
hardware and software are needed to take full advantage of non-Cartesian MRI in
the clinic.Acknowledgements
No acknowledgement found.References
No reference found.