Method and system for improving image contrast in fast driven equilibrium inversion recovery imaging
View Patent ↗A method and a magnetic resonance imaging (MRI) system improve an MRI signal from a magnetization of interest. The method includes performing an MRI pulse sequence containing three consecutive radio frequency (RF) elements, namely, a first element that is an inversion-recovery pulse sequence characterized by a time of inversion, a second element that is an image-encoding pulse sequence starting at the time of inversion with an excitation RF pulse followed by an image-encoding gradient and a data sampling. The second element is followed by a third element. An MRI signal generated by the object and sampled by image readout blocks applied to the object by the MRI system during each repetition time, is acquired. From the MRI signal, an image of the object is reconstructed. The third element is a modified driven-equilibrium (mDE) pulse sequence configured for achieving a conversion of a transverse magnetization component.
1 . A magnetic resonance imaging (MRI) method for improving an MRI signal generated by a magnetization of interest when imaging an object placed in an examination volume of an MRI system, the method comprises the steps of:
performing, by the MRI system, an MRI pulse sequence containing three consecutive radio frequency (RF) elements, namely, a first element being an inversion-recovery pulse sequence characterized by a time of inversion), a second element being an image-encoding pulse sequence starting at the time of inversion with an excitation RF pulse followed by at least one image-encoding gradient and at least one data sampling, the second element being followed by a third element, the third element being a modified driven-equilibrium (hereafter “mDE”) pulse sequence configured for achieving a conversion of a transverse magnetization component of the magnetization of interest into positive longitudinal magnetization, aligned with positive z-axis and B0-field direction;
acquiring, by the MRI system, an MRI signal generated by the object and sampled by image readout blocks applied to the object by the MRI system during each repetition time; and
reconstructing, from the MRI signal, an image of the object.
2 . The MRI method according to claim 1 , wherein the mDE pulse sequence ends by a phase shifted flip-back pulse characterized by a +90 degree flip angle.
3 . The MRI method according to claim 1 , wherein the first element is a STIR pulse sequence.
4 . The MRI method according to claim 1 , wherein the second element contains a single or multiple data samplings.
5 . The MRI method according to claim 1 , wherein the second element is a sequence configured for generating at least one multiple gradient or spin echo.
6 . The MRI method according to claim 1 , wherein the second element is a sequence configured for generating a combination of gradient and spin echoes.
7 . The MRI method according to claim 1 , wherein the second element is a turbo-spin-echo-based pulse sequence.
8 . A magnetic resonance imaging (MRI) system, comprising:
a processor configured for carrying out the MRI method according to claim 1 .
9 . The MRI method according to claim 2 , wherein the phase shifted flip-back pulse is characterized by a 90° phase shift relative to a refocusing RF pulse, or non phase shifted relative to the excitation RF pulse, or 180° phase shift relative to a flip-back pulse of a driven-equilibrium pulse sequence.
10 . The MRI method according to claim 2 , wherein the mDE pulse sequence contains a first RF pulse temporally located in a middle of a time period separating a time at which the +90° phase shifted flip-back pulse is applied and a last time at which a magnetization was refocused.
11 . The MRI method according to claim 2 , wherein the mDE pulse sequence contains a first RF pulse that is a 180-degree RF pulse applied at a time equal to half an echo spacing after a last echo signal of an echo train, and the +90° flip-back pulse is applied at a time equal to half the echo spacing after the first 180-degree RF pulse.