Single-point dixon method for fat-water separation in chemical exchange saturation transfer magnetic resonance imaging

The invention provides for a method of operating a medical imaging system, wherein the method comprises:

• receiving magnetic resonance imaging data, wherein the magnetic resonance imaging data comprises a Z-spectrum acquisition for a set of saturation frequency offsets and at least one reference saturation frequency offset, wherein the Z-spectrum acquisition is according to a CEST magnetic resonance imaging protocol, wherein the Z-spectrum acquisition for the at least one reference saturation frequency offset comprises data for multiple echo shifts or multiple echo times, wherein the Z-spectrum acquisition for each of the set of frequency offsets and the at least one reference saturation frequency offset is descriptive of complex image data comprising a complex water signal and a complex fat signal;
• reconstructing saturation frequency offset complex image data for each of the set of saturation frequency offsets from the Z-spectrum acquisition, wherein the saturation frequency offset complex image data comprises voxels;
• reconstructing a B0 map, a water image, and a fat image using the data for multiple echo shifts or multiple echo times according to a Dixon-type magnetic resonance imaging protocol;
• calculating a water phase angle using the water image and/or the fat image;
• calculating rotated complex image data by rotating the phase of the saturation frequency complex offset image data for each of the voxels using the water phase angle such that the complex water signal is aligned with a real axis for each voxel;
• performing a B0 correction by calculating shifted complex image data using the rotated complex image data for each of the set of saturation frequency offsets and for each of the voxels using the B0 map;
• calculating a frequency dependent phase angle descriptive of a phase angle between the complex water signal and the complex fat signal for each of the set of saturation frequency offsets using a fat signal model comprising at least two fat species;
• calculating a residual fat component correction factor by projecting the complex fat signal onto the real axis for each of the set of saturation frequency offsets and for each of the voxels using the frequency dependent phase angle;
• and
• calculating corrected water Z-spectrum image data by subtracting the residual fat component correction factor for each of the set of saturation frequency offsets and for each of the voxels from the real component of the shifted complex image data.

A computer program product comprising machine executable instructions for execution by a processor controlling a medical imaging system, wherein execution of the machine executable instructions cause the processor to:

• receive magnetic resonance imaging data, wherein the magnetic resonance imaging data comprises a Z-spectrum acquisition for a set of saturation frequency offsets and at least one reference saturation frequency offset, wherein the Z-spectrum acquisition is according to a CEST magnetic resonance imaging protocol, wherein the Z-spectrum acquisition for the at least one reference saturation frequency offset comprises data for multiple echo shifts or echo times, wherein the Z-spectrum acquisition for each of the set of frequency offsets and the at least one reference saturation frequency offset is descriptive of complex image data comprising a complex water signal and a complex fat signal;
• reconstruct saturation frequency offset complex image data for each of the set of saturation frequency offsets from the Z-spectrum acquisition, wherein the saturation frequency offset complex image data comprises voxels;
• reconstruct a B0 map, a water image, and a fat image using the data for multiple echo shifts or echo times according to a Dixon-type magnetic resonance imaging protocol;
• calculate a water phase angle using the water image and/or the fat image;
• calculate rotated complex image data by rotating the phase of the saturation frequency complex offset image data for each of the voxels using the water phase angle such that the complex water signal is aligned with a real axis for each voxel;
• perform a B0 correction by calculating shifted complex image data using the rotated complex image data for each of the set of saturation frequency offsets and for each of the voxels using the B0 map;
• calculate a frequency dependent phase angle descriptive of a phase angle between the complex water and the complex fat signal for each of the set of saturation frequency offsets using a fat signal model comprising at least two fat species;
• calculate a residual fat component correction factor by projecting the complex fat signal onto the real axis for each of the set of saturation frequency offsets and for each of the voxels using the saturation frequency offset dependent phase angle;
• and
• calculate corrected water Z-spectrum image data by subtracting the residual fat component correction factor for each of the set of saturation frequency offsets and for each of the voxels from the real component of the shifted complex image data.