Claims
- 1. A method of acquiring signal for motion in a slice through an object using magnetic resonance imaging, such method comprising the steps of:
a) acquiring first signals from a slice using a first slice selection gradient and a first phase encoding gradient, b) acquiring second signals from the slice using a second slice selection gradient which is an inversion of the first slice selection gradient whereby the two slice selection gradients have different first moments and c) obtaining signals of motion through the slice from the first signals and a second signals.
- 2. The method as defined by claim 1 wherein the signal of motion in step c) depends on the difference in phase between the first signals and the second signals.
- 3. The method as defined by claim 1 wherein the motion signals are proportional to differences in the first moments of the slice selection gradient and proportional to motion velocity through the slice (along the slice encoding direction).
- 4. The method as defined by claim 3 wherein the phase difference in these signals Δφ(r) is related to the velocity component vz(r) through the slice and first moments M1+ and M1− as follows:
- 5. The invention as defined by claim 4 wherein flow sensitivity (venc) is the velocity that produces a phase shift Δφ of π radians and is given by
- 6. The invention as defined by claim 1 wherein said motion signals are obtained at multiple points in a cardiac cycle.
- 7. A method for obtaining motion signals in an object comprising the steps of:
a) placing the object in a static magnetic field, b) applying an rf magnetic excitation to the object, c) concurrently with and after step b) applying to the object a slice selection gradient having positive and negative values, d) after step b) applying to the object a phase encoding gradient, e) after step d) reading magnetic resonance signals for the selected slice, f) after step e) applying an inverted phase encoding gradient and an inverted readout and slice selection gradient for zeroth and first order moment nulling, g) repeating steps a) through f) with the positive and negative values of the slice selection gradient in step c) being inverted, and h) processing the magnetic resonance signals read in step c) and read in step g) to obtain motion signals.
- 8. The method as defined by claim 7 wherein the motion signals are proportional to difference in first moments of the slice selection gradients before and after inversion of the positive and negative values and is proportional to motion velocity through the slice (along the slice encoding direction).
- 9. The method as defined by claim 7 wherein the motion signals are phase difference images Δφ(r), related to velocity vz(r) and first moments M1+ and M1− as follows:
- 10. The method as defined by claim 9 wherein flow sensitivity (venc) is the velocity that produces a phase shift Δφ of π radians and is given by
- 11. The method as defined by claim 10 wherein the application of rf magnetic excitation pulses is timed to a cardiac cycle.
- 12. The method as defined in claim 9 wherein the first moments M1+ and M1− are proportional to the width of a slice gradient.
- 13. A method of acquiring signal for motion in an object using magnetic resonance imaging, such method comprising the steps of:
a) acquiring first signals from using a first readout gradient and a first phase encoding gradient, b) acquiring second signals using a second readout gradient which is an inversion of the first readout gradient whereby the two readout gradients have different first moments and c) obtaining signals of motion through from the first signals and second signals.
- 14. The method as defined by claim 1 wherein the signal of motion in step c) depends on the difference in phase between the first signals and the second signals.
- 15. The method as defined by claim 1 wherein the motion signals are proportional to differences in the first moments of the readout gradient and proportional to motion velocity in the readout direction.
- 16. The method as defined by claim 15 wherein the phase difference in these signals Δφ(r) is related to the velocity component vz(r) in the readout direction and first moments M1+ and M1− as follows:
- 17. The invention as defined by claim 16 wherein flow sensitivity (venc) is the velocity that produces a phase shift Δφ of π radians and is given by
- 18. The invention as defined by claim 13 wherein said motion signals are obtained at multiple points in a cardiac cycle.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] The U.S. Government has rights in the claimed invention pursuant to NIH grants No. P41 RR09784 and R01 HL46347 to Stanford University.