Method and apparatus for recording of diffusion-weighted magnetic resonance image data with anisotropic diffusion directions

A method for acquiring diffusion-weighted MR raw data along anisotropic diffusion directions, determined by diffusion vectors, which respectively define diffusion gradients to be generated by a gradient coil arrangement of a magnetic resonance (MR) data acquisition scanner, said method comprising:

• providing a computer with an electronic designation of maximum gradient amplitudes of respective gradients to be generated by said gradient coil arrangement in respective directions of physical gradient axes of said gradient coil arrangement, said physical gradient axes intersecting at an origin;
• in said computer, dependent on said maximum gradient amplitudes, defining a space of achievable diffusion gradient vectors as a cuboid with edges respectively oriented along said physical gradient axes, and with said edges of said cuboid respectively having an extent corresponding to the maximum gradient amplitude along the physical gradient axes of the respective edge;
• in said computer, selecting a value range for an effective gradient amplitude, said value range having a minimum value and a maximum value for the effective gradient amplitude;
• in said computer, determining a spherical shell around said origin, said spherical shell having an inside radius having said minimum value and an outside radius having said maximum value;
• in said computer, determining a plurality of sub-regions of said spherical shell that lie inside said cuboid and that represent end points of a plurality of candidate origin vectors that each originate at said origin and proceed to the respective end points;
• in said computer, selecting a set of at least six diffusion gradient vectors, which additionally satisfy directional constraints for tensors, from said set of candidate origin vectors;
• making an electronic designation of said at least six diffusion gradient vectors available from said computer as an output;
• from said computer, operating said MR data acquisition scanner to acquire said diffusion-weighted MR raw data with said gradient coil arrangement being operated to produce diffusion gradients in respective directions corresponding to the determined at least six diffusion gradient vectors;
• in a reconstruction computer, reconstructing diffusion encoded image data from the acquired raw data;
• and
• from said reconstruction computer, presenting said diffusion-encoded image data in a visualization that shows diffusion behavior in said region.

A computer for determining diffusion vectors, which respectively define diffusion gradients to be generated by a gradient coil arrangement of a magnetic resonance (MR) data acquisition scanner in order to acquire diffusion-weighted MR image data along anisotropic diffusion directions, said computer comprising:

• an input interface configured to receive an electronic designation of maximum gradient amplitudes of respective gradients to be generated by said gradient coil arrangement in respective directions of physical gradient axes of said gradient coil arrangement, said physical gradient axes intersecting at an origin;
• a processor configured to define, dependent on said maximum gradient amplitudes, a space of achievable diffusion gradient vectors as a cuboid with edges respectively oriented along said physical gradient axes, and with said edges of said cuboid respectively having an extent corresponding to the maximum gradient amplitude along the physical gradient axes of the respective edge;
• said processor being configured to select a value range for an effective gradient amplitude, said value range having a minimum value and a maximum value for the effective gradient amplitude;
• said processor being configured to determine a spherical shell around said origin, said spherical shell having an inside radius having said minimum value and an outside radius having said maximum value;
• said processor being configured to determine a plurality of sub-regions of said spherical shell that lie inside said cuboid and that represent end points of a plurality of candidate origin vectors that each originate at said origin and proceed to the respective end points;
• said processor being configured to select a set of at least six diffusion gradient vectors, which additionally satisfy directional constraints for tensors, from said set of candidate origin vectors;
• and
• an output interface configured to make an electronic designation of said at least six diffusion gradient vectors available from said processor as an output.

A magnetic resonance (MR) apparatus comprising:

• an MR data acquisition scanner having a gradient coil arrangement with physical gradient axes that intersect at an origin, said gradient coil arrangement being operable to generate diffusion gradients defined by diffusion vectors in order to acquire diffusion-weighted MR raw data along anisotropic diffusion directions;
• a computer provided with an electronic designation of maximum gradient amplitudes of respective gradients to be generated by said gradient coil arrangement in respective directions of the physical gradient axes of said gradient coil arrangement;
• said computer being configured to define dependent on said maximum gradient amplitudes, a space of achievable diffusion gradient vectors as a cuboid with edges respectively oriented along said physical gradient axes, and with said edges of said cuboid respectively having an extent corresponding to the maximum gradient amplitude along the physical gradient axes of the respective edge;
• said computer being configured to select a value range for an effective gradient amplitude, said value range having a minimum value and a maximum value for the effective gradient amplitude;
• said computer being configured to determine a spherical shell around said origin, said spherical shell having an inside radius having said minimum value and an outside radius having said maximum value;
• said computer being configured to determine a plurality of sub-regions of said spherical shell that lie inside said cuboid and that represent end points of a plurality of candidate origin vectors that each originate at said origin and proceed to the respective end points;
• said computer being configured to select a set of at least six diffusion gradient vectors, which additionally satisfy directional constraints for tensors, from said set of candidate origin vectors;
• said computer being configured to make an electronic designation of said at least six diffusion gradient vectors available from said computer as an output;
• and
• said computer being configured to operate said MR data acquisition scanner to acquire said diffusion-weighted MR raw data with said gradient coil arrangement being operated to produce diffusion gradients in respective directions corresponding to the determined at least six diffusion gradient vectors;
• a reconstruction computer configured to reconstruct diffusion encoded image data from the acquired raw data;
• and
• said reconstruction computer being configured to present said diffusion-encoded image data in a visualization that shows diffusion behavior in said region.

A non-transitory, computer-readable data storage medium encoded with programming instructions, said data storage medium being loaded into a computer of a magnetic resonance (MR) apparatus comprising an MR data acquisition scanner having a gradient coil arrangement with physical gradient axes that intersect at an origin, said gradient coil arrangement being operable to generate diffusion gradients defined by diffusion vectors in order to acquire diffusion-weighted MR raw data along anisotropic diffusion directions, and said programming instructions causing said computer to:

• receive an electronic designation of maximum gradient amplitudes of respective gradients to be generated by said gradient coil arrangement in respective directions of physical gradient axes of said gradient coil arrangement, said physical gradient axes intersecting at an origin;
• dependent on said maximum gradient amplitudes, define a space of achievable diffusion gradient vectors as a cuboid with edges respectively oriented along said physical gradient axes, and with said edges of said cuboid respectively having an extent corresponding to the maximum gradient amplitude along the physical gradient axes of the respective edge;
• select a value range for an effective gradient amplitude, said value range having a minimum value and a maximum value for the effective gradient amplitude;
• determine a spherical shell around said origin, said spherical shell having an inside radius having said minimum value and an outside radius having said maximum value;
• determine a plurality of sub-regions of said spherical shell that lie inside said cuboid and that represent end points of a plurality of candidate origin vectors that each originate at said origin and proceed to the respective end points;
• select a set of at least six diffusion gradient vectors, which additionally satisfy directional constraints for tensors, from said set of candidate origin vectors;
• and
• make an electronic designation of said at least six diffusion gradient vectors available from said computer as an output.