Method and apparatus for magnetic resonance guided high intensity focused ultrasound focusing under simultaneous temperature monitoring

An apparatus for localizing a high intensity focused ultrasound (HIFU) focal point in magnetic resonance guided HIFU, comprising the steps of:

• a magnetic resonance data acquisition unit adapted to receive an examination subject therein;
• a control unit being configured to operate said data acquisition unit to scan the examination subject with a first GRE magnetic resonance pulse sequence that comprises a positive monopolar gradient pulse followed by sonification of the examination subject with HIFU overlapping with activation of a motion encoding gradient, said HIFU causing an acoustic radiation force phase shift of magnetic resonance signals arising in the examination subject, to produce a first imaging data set;
• said control unit being configured to operate said data acquisition unit to scan the examination subject with a second GRE magnetic resonance pulse sequence in parallel with irradiation of the examination subject with said first GRE sequence said second GRE sequence comprising a negative monopolar gradient pulse followed by said sonification of the examination subject with HIFU overlapping with activation of a motion encoding gradient in said second GRE sequence, said HIFU causing an acoustic radiation force-induced phase shift and a PRFS temperature-induced phase shift of magnetic resonance signals arising in the examination subject in said second GRE sequence, to produce a second imaging data set;
• a processor configured to use Fourier reconstruction or partial Fourier reconstruction to reconstruct a first GRE phase image from said first image data set and to reconstruct a second GRE phase image from said second image data set;
• said processor being configured to form a subtraction image as a difference between said first GRE phase image and said second GRE phase image and, from said subtraction image, identify a location and/or an acoustic intensity and/or a shape of said HIFU focal point;
• said processor being configured to form an average image of said first GRE phase image and said second GRE phase image;
• and
• a display at which said processor is configured to display said average image in a form indicating temperature at the location of said HIFU focal point.