Magnetic resonance imaging using driven equilibrium fourier transform
AssigneeThe Board of Trustees of the Leland Stanford Junior University
InventorsBrian A. Hargreaves, Dwight G. Nishimura
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Abstract
A new technique for imaging a material with a high T2/T1 ratio such as articular cartilage uses driven equilibrium Fourier transform (DEFT), a method of enhancing signal strength without waiting for full T1 recovery. Compared to other methods, DEFT imaging provides a good combination of bright cartilage and high contrast between cartilage and surrounding tissue. Both theoretical predictions and images show that DEFT is a valuable method for imaging articular cartilage when compared to spoiled gradient recalled acquisition in the steady-state (SPGR) or fast spin echo (FSE). T2-decay, T1 recovery, echo time, magnetization density, proton density, and equilibrium density per proton are related by a derived equation.
Claims16
A method of imaging a material with improved contrast in a region of an objectxsing magnetic resonance, said material having relaxation times T1 and T2, said method comprising the steps of:
- a) placing the object in a static magnetic field along a longitudinal axis (z),
- b) applying a first slice selective excitation pulse to tip nuclear spins through an angle α about a second axis (x) in a rotating frame (x,y),
- c) applying a first refocusing pulse along a third axis in the rotating frame (y),
- d) detecting a first spin echo at a time TE after application of the slice selective pulse,
- e) applying a second refocusing pulse along the third axis in the rotating frame (y),
- f) applying a second slice selective excitation pulse through an angle -α about the second axis (x) in the rotating frame at a time TE after detecting the first spin echo for driving any remaining transverse magnetization back to the longitudinal axis, and
- g) repeating steps b) through f) with step b) repeated at a time τ1 after applying the second slice selective excitation pulse, time τ1 being equal to the process repetition rate, TR, minus twice the echo time, TE.
A method of imaging with improved contrast a material in a region of an object sing magnetic resonance, said material having relaxation times T1 and T2, said method comprising the steps of:
- a) placing the object in a static magnetic field along a longitudinal axis (z),
- b) detecting a magnetic resonance signal using a pulse echo sequence including a first transverse excitation pulse and a first refocusing pulse to form a pulse echo at an echo time, TE, after applying the first transverse excitation pulse,
- c) applying a second refocusing pulse,
- d) applying a second transverse excitation pulse at a time, TE, after detecting the magnetic resonance signal for driving any remaining transverse magnetization back to the longitudinal axis,
- e) repeating steps b) through d) with the pulse echo sequence beginning at a time τ1, after applying the second transverse excitation pulse, τ1 being equal to the process repetition rate, TR, minus twice the echo time, TE.
Dependencies are inferred from the claim text.