Spatial encoding MR data of a moving subject using a higher-order gradient field

1. A method of acquiring spatially encoded magnetic resonance (MR) data comprising the steps of:

applying a gradient field having an exponential relation higher than a single order along an object direction;

moving an object to be scanned in the object direction through the gradient field; and

acquiring MR data as the object moves with contiguous continuity in the object direction.

2. The method of claim 1 wherein the gradient field is applied in a Z-direction and is a pulsed phase encoding gradient having a constant value such that at any given Z-location, a value of the gradient field is a linear function of the given Z-location.

3. The method of claim 2 wherein the object is moved in the Z-direction on successive TRs to acquire a full range of k z data.

4. The method of claim 1 wherein the gradient field is a pulsed Z 2 gradient field.

5. The method of claim 1 further comprising:

phase correcting acquired MR data along the object direction;

Fourier transforming the phase corrected MR data; and

reconstructing an image with spatial encoding in the object direction.

6. An magnetic resonance (MR) apparatus to acquire continuous imaging of a moving object over an extended field-of-view (FOV) comprising:

a magnetic resonance imaging (MRI) system having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images, wherein at least one of the gradient coils is constructed to impart

a higher-order gradient field;

a table moveable along a longitudinal axis into and out of the bore of the magnet; and

a computer programmed to:

transmit a series of RF pulses;

apply a higher-order gradient field between each RF pulse in the series of RF pulses; and

move the table and acquire data.

7. The MR apparatus of claim 6 wherein the computer is further programmed to reconstruct a continuous image from the data acquired after each periodic table movement.

8. The MR apparatus of claim 6 wherein the computer is further programmed to step-wise move the table a given increment based on desired K z encoding resolution.

9. The MR apparatus of claim 6 wherein the computer is further programmed to apply a higher-order gradient of consistent value in each TR.

10. The MR apparatus of claim 6 wherein the computer is further programmed to reconstruct a seamless image of length greater than that of a default FOV for the MRI system without piecing together raw data or multiple out-images.

11. A method of acquiring magnetic resonance (MR) images with expanded FOV in a longitudinal direction of an object comprising the steps of:

defining a direction of motion of an object to be scanned;

arranging the object such that a longitudinal axis is positioned along the direction of motion;

applying a non-linear gradient field in the direction of motion;

moving the object through the applied non-linear gradient field; and

acquiring k-space data with spatial encoding in the direction of motion.

12. The method of claim 11 wherein the higher-order gradient is a spatial Z 2 gradient and wherein the step of moving the object is further defined as moving the object a given distance ΔZ.

13. The method of claim 12 further comprising the step of calculating ΔZ based on the higher-order spatial gradient field to provide sufficient K z encoding.

14. The method of claim 11 wherein the higher-order spatial gradient is a gradient other than a first order spatial gradient.

15. The method of claim 11 further comprising the steps of applying the higher-order spatial gradient at a same value for each TR period.

16. The method of claim 11 further comprising the steps of applying a rewinder gradient to rephase spins during each TR period, wherein the rewinder gradient is applied with a same value for each period.

17. A computer readable storage medium having a computer program stored thereon and representing a set of instructions which, when executed by a computer, cause the computer to:

A) initiate transmission of an RF signal toward an imaging object;

B) energize a higher-order gradient coil;

C) enquire MR data;

D) move the imaging object;

E) repeat steps A–D until sufficient magnetic resonance (MR) data is acquired along a desired length of the imaging object coincident with a direction of motion; and

F) reconstruct a contiguous image of the desired length of the object.

18. The computer readable storage medium of claim 17 wherein the higher-order gradient coil emits a Z 2 gradient field and the imaging object is moved continuously from a +Z maximum position to a −Z maximum position to achieve contiguous Z-direction coverage.

19. The computer readable storage medium of claim 17 wherein the higher-order gradient coil is energized to provide a field having consistent value over an entire imaging space.

20. The computer readable storage medium of claim 17 wherein the set of instructions further causes the computer to:

phase correct acquired MR data in a direction of imaging object movement;

Fourier transform the phase corrected MR data; and

reconstruct a single contiguous image with MR data acquired over the desired length of the imaging object.

21. A method of acquiring magnetic resonance (MR) images with expanded field-of-view (FOV) comprising the steps of;

defining a default FOV based on characteristics of an MR scanner;

defining a desired FOV larger than the default FOV;

defining a motion axis to move an object through the MR scanner;

applying a non-linear gradient field;

moving the object along the motion axis and through the non-linear gradient field; and

acquiring k-space data over the desired FOV to reconstruct a contiguous image over the desired FOV.

22. The method of claim 21 wherein the non-linear gradient field has a quadratic dependence on a location along the motion axis.

23. The method of claim 22 where the quadratic dependence provides a local gradient field with a slope equal to that of the quadratic dependence.