Efficient self-refocusing zero echo time MR imaging

A computer-implemented method of magnetic resonance (MR) imaging of an object positioned in an examination volume of a MR device, the method comprising:

• specifying a set of radial k-space spokes to cover a spherical k-space volume, such that spokes of the set of radial k-space spokes extend from a k-space origin in the spherical k-space volume to end points distributed on a surface of the spherical k-space volume;
• automatically selecting subsets of spokes from the specified set of radial k-space spokes, with each subset comprising a predetermined number of spokes from the specified set of radial k-space spokes so that concatenation of the spokes in each of the subsets forms a closed trajectory in k-space, wherein selecting the subsets involves determining a sequence in which the spokes in each of the subsets are acquired, and wherein selecting the subsets is based on optimizing a cost function favouring (i) minimizing a maximum angle between subsequently acquired spokes within the same subset, and (ii) maximizing a uniformity of the distribution of the end points of the spokes on the surface of the spherical k-space volume, while ensuring that the concatenation of the spokes of each of the subsets forms the closed trajectory in k-space;
• performing a zero echo time imaging sequence of the object, wherein each of the subsets is acquired as a sequence of gradient echo signals;
• reconstructing an MR image from the acquired spokes;
• and
• providing a human-readable display of reconstructed MR image.

A computer-implemented method of magnetic resonance (MR) imaging of an object positioned in an examination volume of a MR device, the method comprising:

• specifying a set of radial k-space spokes to cover a spherical k-space volume, wherein the set of radial k-space spokes consists of pairs of spokes having anti-parallel orientations;
• automatically selecting subsets of spokes from the specified set of radial k-space spokes, with each subset comprising a predetermined number of spokes from the specified set of radial k-space spokes so that concatenation of the spokes in each of the subsets forms a closed trajectory in k-space, wherein selecting the subsets is based on optimizing a cost function favouring (i) minimizing a maximum angle between subsequently acquired spokes within the same subset, and (ii) maximizing a uniformity of distribution of end points of the spokes on a surface of the spherical k-space volume, while ensuring that the concatenation of the spokes of each of the subsets forms the closed trajectory in k-space;
• performing a zero echo time imaging sequence of the object, wherein each of the subsets is acquired as a sequence of gradient echo signals;
• reconstructing an MR image from the acquired spokes;
• and
• providing a human-readable display of reconstructed MR image.

A magnetic resonance (MR) device comprising:

• at least one main magnet coil for generating a uniform, static magnetic field within an examination volume;
• a number of gradient coils for generating switched magnetic field gradients in different spatial directions within the examination volume;
• at least one RF coil for generating RF pulses within the examination volume and/or for receiving MR signals from an object positioned in the examination volume;
• a control unit for controlling a temporal succession of RF pulses and switched magnetic field gradients, wherein the control unit is configured to:
• specify a set of radial k-space spokes to cover a spherical k-space volume, such that spokes of the set of radial k-space spokes are between a k-space origin and end points distributed on a surface of the spherical k-space volume;
• select subsets of a predetermined number of spokes from the specified set radial k-space spokes so that concatenation of the spokes in each of the subsets forms a closed trajectory in k-space, wherein selecting the subsets is based on a cost function is based on optimizing a cost function favouring (i) minimizing a maximum angle between subsequently acquired spokes within the same subset, (ii) maximizing the uniformity of the distribution of the end points of the spokes on the surface of the spherical k-space volume, while ensuring that the concatenation of the spokes of the subsets forms the closed trajectory in k-space;
• and
• perform a zero echo time imaging sequence of the object, wherein each of the subsets is acquired as a sequence of gradient echo signals;
• a reconstruction unit configured to reconstruct an MR image from the acquired spokes;
• and
• a video monitor configured to provide a human-readable display of the reconstructed MR image.

A non-transitory computer readable medium storing instructions that, when executed by at least one computer, cause the at least one computer to:

• specify a set of radial k-space spokes to cover a spherical k-space volume, such that spokes of the set of radial k-space spokes are between a k-space origin and end points distributed on a surface of the spherical k-space volume;
• select subsets of a predetermined number of spokes from the specified set of radial k-space spokes so that concatenation of the spokes contained in each of the subsets forms a closed trajectory in k-space, wherein selecting the subsets is based on a cost function favouring (i) minimizing a maximum angle between subsequently acquired spokes within the same_subset, (ii) maximizing a uniformity of the distribution of the end points of the spokes on the surface of the spherical k-space volume, while ensuring that the concatenation of the spokes of each of the subsets forms the closed trajectory in k-space;
• generate a zero echo time imaging sequence, wherein each of the subsets is acquired as a sequence of gradient echo signals;
• reconstruct an MR image from the acquired spokes;
• and
• cause the reconstructed MR image to be displayed on a video monitor.