Phase contrast, line-scanned method for NMR angiography

Claim 2

In an NMR system a method for measuring the velocity of blood in a patient, the steps comprising: (a) generating a cardiac phase signal which indicates the phase of the patient's cardiac cycle; (b) producing a polarizing magnetic field around the region in which blood velocity is to be measured; (c) generating an RF excitation field in said region to produce transverse magnetization; (d) calculating the first moment M of a bi-polar magnetic field gradient as a function of the phase of the patient's cardiac cycle as determined by said cardiac phase signal; (e) generating a bi-polar magnetic field gradient in said region which has the first moment M and which velocity sensitizes the transverse magnetization; (f) acquiring an NMR signal produced by the velocity sensitized transverse magnetization; (g) repeating steps (b), (c), (e) and (f) with the sign of the bi-polar magnetic field gradient moment M reversed; and (h) producing output data which is indicative of the velocity of moving spins in the region by subtracting the two acquired NMR signals to generate difference data.

Claim 3

The method as recited in claim 1 which further includes: (i) applying a magnetic field gradient to the region to position encode the acquired NMR signal and to thereby indicate the position of moving spins in the region.

Claim 4

The method as recited in claim 1 in which step (h) includes: adjusting the value of the output data as a function of the calculated first moment M.

Claim 5

The method as recited in claim 1 which includes estimating the velocity of blood in the region at different phases of the patient's cardiac cycle, and the first moment M is calculated in step (d) as a function of the estimated velocity at the cardiac phase indicated by said signal.

Claim 6

The method as recited in claim 1 in which the RF excitation field is altered as a function of the patient's cardiac cycle as determined by said cardiac phase signal to change the amount of transverse magnetization which is produced as a function of the cardiac cycle phase.

Claim 7

In an NMR system a method for producing an angiogram of a patient, the steps comprising: (a) generating a cardiac phase signal which indicates the phase of the patient's cardiac cycle; (b) producing a polarizing magnetic field around the region in which an angiogram is to be produced; (c) generating an RF excitation field in said region to produce transverse magnetization; (d) calculating the first moment M of a bi-polar magnetic field gradient as a function of the phase of the patient's cardiac cycle as determined by said cardiac phase signal; (e) generating a bi-polar magnetic field gradient in said region which has the first moment M and which velocity sensitizes the transverse magnetization; (f) acquiring a first NMR signal produced by the velocity sensitized transverse magnetization while applying a readout magnetic field gradient in said region; (g) repeating steps (b) and (c); (h) generating a bi-polar magnetic field gradient in said region which has a negative first moment -M and which velocity sensitizes the transverse magnetization; (i) acquiring a second NMR signal produced by the velocity sensitized transverse magnetization while applying a readout magnetic field gradient in said region; (j) producing a difference signal by finding the difference between the first and second NMR signals; (k) Fourier transforming the difference signal to produce an output signal; and (l) using the output signal to produce an angiogram display.

Claim 8

In an NMR system a method for producing an angiogram of a patient, the steps comprising: (a) generating a cardiac phase signal which indicates the phase of the patient's cardiac cycle; (b) producing a polarizing magnetic field around the region in which an angiogram is to be produced; (c) generating an RF excitation field in said region to produce transverse magnetization; (d) calculating the first moment M of a bi-polar magnetic field gradient as a function of the phase of the patient's cardiac cycle as determined by said cardiac phase signal; (e) generating a bi-polar magnetic field gradient in said region which has the first moment M and which velocity sensitizes the transverse magnetization; (f) acquiring a first NMR signal produced by the velocity sensitized transverse magnetization while applying a readout magnetic field gradient in said region; (g) repeating steps (b) and (c); (h) generating a bi-polar magnetic field gradient in said region which has a negative first moment -M and which velocity sensitizes the transverse magnetization; (i) acquiring a second NMR signal produced by the velocity sensitized transverse magnetization while applying a readout magnetic field gradient in said region; (j) producing a difference signal by finding the difference between the first and second NMR signals; (k) Fourier transforming the difference signal to produce an output signal; and (l) using the output signal to produce an angiogram display.

Claim 9

The method as recited in claim 6 in which the RF excitation field is generated while a slice select magnetic field gradient is produced in the region such that the transverse magnetization is produced in a slice through the region; and in which steps (a) through (l) are repeated to acquire first and second NMR signals from a different slice and to produce a corresponding display of both slices.