Method and apparatus for spin-echo-train MR imaging using prescribed signal evolutions
AssigneeUniversity of Virginia Patent Foundation
InventorsJohn P. Mugler, III, James R. Brookeman
Life of this patent
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Abstract
A magnetic resonance imaging “MRI” method and apparatus for lengthening the usable echo-train duration and reducing the power deposition for imaging is provided. The method explicitly considers the t1 and t2 relaxation times for the tissues of interest, and permits the desired image contrast to be incorporated into the tissue signal evolutions corresponding to the long echo train. The method provides a means to shorten image acquisition times and/or increase spatial resolution for widely-used spin-echo train magnetic resonance techniques, and enables high-field imaging within the safety guidelines established by the Food and Drug Administration for power deposition in human MRI.
Claims46
A method for generating a spin echo pulse sequence for operating a magnetic resonance imaging apparatus for imaging an object that permits at least one of lengthening usable echo-train duration, reducing power deposition and incorporating desired image contrast into the tissue signal evolutions, said method comprising:
- a) providing contrast-preparation, said contrast-preparation comprising generating at least one of at least one radio-frequency pulse, at least one magnetic-field gradient pulse, and at least one time delay, whereby said contrast preparation encodes the magnetization with at least one desired image contrast;
- b) calculating flip angles and phases of refocusing radio-frequency pulses that are applied in a data-acquisition step, wherein said calculation provides desired prescribed signal evolution and desired overall signal level, said calculation comprises:
- i) selecting values of T1 and T2 relaxation times and selecting proton density;
- ii) selecting a prescribed time course of the amplitudes and phases of the radio-frequency magnetic resonance signals that are generated by said refocusing radio-frequency pulses;
- and
- iii) selecting characteristics of said contrast-preparation step, said data-acquisition step and a magnetization-recovery step, with the exception of the flip angles and phases of the refocusing radio-frequency pulses that are to be calculated;
- and
- c) providing said-data acquisition step based on a spin echo train acquisition, said data-acquisition step comprises:
- i) an excitation radio-frequency pulse having a flip angle and phase;
- ii) at least two refocusing radio-frequency pulses, each having a flip angle and phase as determined by said calculation step;
- and
- iii) magnetic-field gradient pulses that encode spatial information into at least one of said radio-frequency magnetic resonance signals that follow at least one of said refocusing radio-frequency pulses;
- d) providing magnetization-recovery, said magnetization-recovery comprises a time delay to allow magnetization to relax;
- and
- e) repeating steps (a) through (d) until a predetermined extent of spatial frequency space has been sampled.
A magnetic resonance imaging apparatus generating a spin echo pulse sequence in order to operate the apparatus in imaging an object that permits at least one of lengthening usable echo-train duration, reducing power deposition and incorporating desired image contrast into the tissue signal evolutions, the apparatus comprising:
- a main magnet system generating a steady magnetic field;
- a gradient magnet system generating temporary gradient magnetic fields;
- a radio-frequency transmitter system generating radio-frequency pulses;
- a radio-frequency receiver system receiving magnetic resonance signals;
- a reconstruction unit reconstructing an image of the object from the received magnetic resonance signals;
- and
- a control unit generating signals controlling the gradient magnet system, the radio-frequency transmitter system, the radio-frequency receiver system, and the reconstruction unit, wherein the control unit generates signals causing:
- a) providing contrast-preparation, said contrast-preparation comprising generating at least one of at least one radio-frequency pulse, at least one magnetic-field gradient pulse, and at least one time delay, whereby said contrast preparation encodes the magnetization with at least one desired image contrast;
- b) calculating flip angles and phases of refocusing radio-frequency pulses that are applied in a data-acquisition step, wherein said calculation provides desired prescribed signal evolution and desired overall signal level, said calculation comprises:
- i) selecting values of T1 and T2 relaxation times and selecting proton density;
- ii) selecting a prescribed time course of the amplitudes and phases of the radio-frequency magnetic resonance signals that are generated by said refocusing radio-frequency pulses;
- and
- iii) selecting characteristics of said contrast-preparation step, said data-acquisition step and a magnetization-recovery step, with the exception of the flip angles and phases of the refocusing radio-frequency pulses that are to be calculated;
- and
- c) providing said-data acquisition step based on a spin echo train acquisition, said data-acquisition step comprises:
- i) an excitation radio-frequency pulse having a flip angle and phase,
- ii) at least two refocusing radio-frequency pulses, each having a flip angle and phase as determined by said calculation step, and
- iii) magnetic-field gradient pulses that encode spatial information into at least one of said radio-frequency magnetic resonance signals that follow at least one of said refocusing radio-frequency pulses;
- d) providing magnetization-recovery, said magnetization-recovery comprises a time delay to allow magnetization to relax;
- and
- e) repeating steps (a) through (d) until a predetermined extent of spatial frequency space has been sampled.
A magnetic resonance imaging apparatus generating a spin echo pulse sequence in order to operate the apparatus in imaging an object that permits at least one of lengthening usable echo-train duration, reducing power deposition and incorporating desired image contrast into the tissue signal evolutions, the apparatus comprising:
- main magnet means generating a steady magnetic field;
- gradient magnet means generating temporary gradient magnetic fields;
- radio-frequency transmitter means generating radio-frequency pulses;
- radio-frequency receiver means receiving magnetic resonance signals;.
- reconstruction means reconstructing an image of the object from the received magnetic resonance signals;
- and
- control means generating signals controlling the gradient magnet means, the radio-frequency transmitter means, the radio-frequency receiver means, and the reconstruction means, wherein the control means generates signals causing:
- a) providing contrast-preparation, said contrast-preparation comprising generating at least one of at least one radio-frequency pulse, at least one magnetic-field gradient pulse, and at least one time delay, whereby said contrast preparation encodes the magnetization with at least one desired image contrast;
- b) calculating flip angles and phases of refocusing radio-frequency pulses that are applied in a data-acquisition step, wherein said calculation provides desired prescribed signal evolution and desired overall signal level, said calculation comprises:
- i) selecting values of T1 and T2 relaxation times and selecting proton density;
- ii) selecting a prescribed time course of the amplitudes and phases of the radio-frequency magnetic resonance signals that are generated by said refocusing radio-frequency pulses;
- and
- iii) selecting characteristics of said contrast-preparation step, said data-acquisition step and a magnetization-recovery step, with the exception of the flip angles and phases of the refocusing radio-frequency pulses that are to be calculated;
- c) providing said-data acquisition step based on a spin echo train acquisition, said data-acquisition step comprises:
- i) an excitation radio-frequency pulse having a flip angle and phase,
- ii) at least two refocusing radio-frequency pulses, each having a flip angle and phase as determined by said calculation step, and
- iii) magnetic-field gradient pulses that encode spatial information into at least one of said radio-frequency magnetic resonance signals that follow at least one of said refocusing radio-frequency pulses;
- d) providing magnetization-recovery, said magnetization-recovery comprises a time delay to allow magnetization to relax;
- and
- e) repeating steps (a) through (d) until a predetermined extent of spatial frequency space has been sampled.
A computer program provided on a computer useable readable medium having computer program logic enabling at least one processor in a magnetic resonance imaging apparatus to generate a spin echo pulse sequence that permits at least one of lengthening usable echo-train duration, reducing power deposition and incorporating desired image contrast into the tissue signal evolutions, said computer program logic comprising:
- a) providing contrast-preparation, said contrast-preparation comprising generating at least one of at least one radio-frequency pulse, at least one magnetic-field gradient pulse, and at least one time delay, whereby said contrast preparation encodes the magnetization with at least one desired image contrast;
- b) calculating flip angles and phases of refocusing radio-frequency pulses that are applied in a data-acquisition step, wherein said calculation provides desired prescribed signal evolution and desired overall signal level, said calculation comprises:
- i) selecting values of T1 and T2 relaxation times and selecting proton density;
- ii) selecting a prescribed time course of the amplitudes and phases of the radio-frequency magnetic resonance signals that are generated by said refocusing radio-frequency pulses;
- and
- iii) selecting characteristics of said contrast-preparation step, said data-acquisition step and a magnetization-recovery step, with the exception of the flip angles and phases of the refocusing radio-frequency pulses that are to be calculated;
- and
- c) providing said-data acquisition step based on a spin echo train acquisition, said data-acquisition step comprises:
- i) an excitation radio-frequency pulse having a flip angle and phase;
- ii) at least two refocusing radio-frequency pulses, each having a flip angle and phase as determined by said calculation step;
- and
- iii) magnetic-field gradient pulses that encode spatial information into at least one of said radio-frequency magnetic resonance signals that follow at least one of said refocusing radio-frequency pulses;
- d) providing magnetization-recovery, said magnetization-recovery comprises a time delay to allow magnetization to relax;
- and
- e) repeating steps (a) through (d) until a predetermined extent of spatial frequency space has been sampled.
Dependencies are inferred from the claim text.