System and Method For Phase-Contrast MRI with Hybrid One-and Two-sided Flow Encoding and Velocity Spectrum Separation (HOTSPA)

A method for acquiring flow encoded data from a subject using a magnetic resonance imaging (MRI) system to reconstruct an image of the subject illustrating flow within the subject, the method includes steps comprising:

• (i) using the MRI system, acquiring flow encoded (FE) data with alternating encoding polarities and along at least two of three orthogonal directions through the subject over at least two cycles of the flow within the subject;
• (ii) separating the FE data into directional FE datasets using a temporal filter that separates the FE data based on temporal modulation of FE directions caused by the alternating encoding polarities extending over the at least two cycles of the flow within the subject that shift the Fourier spectrum of velocity waveforms corresponding to the FE data;
• and
• (iii) using the directional FE datasets, generating an image of the subject showing flow within the subject caused by the at least two cycles of flow within the subject.

A magnetic resonance imaging (MRI) system comprising:

• a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject arranged in the MRI system;
• a plurality of gradient coils configured to apply a gradient field to the polarizing magnetic field;
• a radio frequency (RF) system configured to apply an excitation field to the subject and acquire MR image data therefrom;
• a computer system programmed to:
• control the plurality of gradient coils and the RF system to perform a phase-contrast pulse sequence to acquire imaging data by:
• acquiring a first set of MR data that is flow encoded along a first direction (FE1) using a two-sided flow-encoding strategy that is free of flow compensation;
• acquiring a second set of MR data that is flow encoded along a second direction (FE2) and flow encoded along a third direction (FE3) using a hybrid one- and two-sided flow encoding strategy;
• separate the first set of MR data into a background phase signal ϕ0(t) and a first directional phase signal ϕv,1(t);
• separate the second set of MR data into a second directional phase signal ϕv,2(t) and a third directional phase signal ϕv,3(t);
• and
• reconstruct MRA images of the subject using the background phase signal ϕ0(t), the first directional phase signal ϕv,1(t), the second directional phase signal ϕv,2(t), the third directional phase signal ϕv,3(t).

A magnetic resonance imaging (MRI) system comprising:

• a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject arranged in the MRI system;
• a plurality of gradient coils configured to apply a gradient field to the polarizing magnetic field;
• a radio frequency (RF) system configured to apply an excitation field to the subject and acquire MR image data therefrom;
• a computer system programmed to:
• control the plurality of gradient coils and RF system to acquire flow encoded (FE) data with alternating encoding polarities and along two of three orthogonal directions through the subject over at least two cycles of physiological flow within the subject;
• separate the FE data into directional FE datasets using a temporal filter that separates the FE data based on temporal modulation of the FE directions caused by the alternating encoding polarities extending over the at least two cycles of the flow within the subject that shift the Fourier spectrum of velocity waveforms corresponding to the FE data;
• and
• using the directional FE datasets, generate an image of the subject showing flow within the subject caused by the at least two cycles of flow within the subject.

A method for acquiring flow encoded data from a subject using a magnetic resonance imaging (MRI) system to reconstruct an image of the subject illustrating flow within the subject, the method includes steps comprising:

• (i) using the MRI system, acquiring flow encoded (FE) data with alternating encoding polarities and along at least one direction through the subject;
• (ii) determining a velocity of the flow within the subject in the at least one direction by analyzing a Fourier spectrum of the FE data to determine temporal modulation caused by the alternating encoding polarities that shift the Fourier spectrum;
• and
• (iii) using the FE data and the velocity of flow determined in step (ii), generating an image of the subject showing the velocity of flow within the subject.