Method for temporally resolved, three-dimensional MR volume acquisitions

• US 6,185,447 B1
• Filed: 03/26/1998
• Issued: 02/06/2001
• Est. Priority Date: 03/26/1998
• Status: Expired due to Term

• Current Assignee: Leland Stanford Junior University (Stanford University)
• Original Assignee: Leland Stanford Junior University (Stanford University)
• Inventors: Alley, Marcus T., Pelc, Norbert J.
• Primary Examiner(s): Oda, Christine K.
• Assistant Examiner(s): Fetzner, Tiffany A.
• Application Number:
  US09/049,281
• Time in Patent Office: 1,048 Days
• Field of Search: 324/307, 324/309, 600/420, 424/9
• US Class Current: 600/420
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: G01R 33/4822 in three dimensions
• CPC Class Codes: G01R 33/4824 using a non-Cartesian trajectory
• CPC Class Codes: G01R 33/561 by reduction of the scanning time, i.e. fast acquiring systems, e.g. using echo-planar pulse sequences
• CPC Class Codes: G01R 33/56308 Characterization of motion or flow; Dynamic imaging

Abstract

Disclosed is an apparatus and a method for three dimensional magnetic resonance data acquisitions using a fast 3D sequence to acquire volumetric data in a cine mode. The entire heart can be imaged in the same amount of time that a conventional cine scan requires for a single section. The true temporal resolution is similar to that of the segmented k-space acquisition. The sequence uses very short repetition times (TR), and hence the inherent contrast is poor. This problem is overcome with the use of a T₁ shortening agent. Since contrast between blood and the myocardium is no longer flow dependent, it is more stable throughout the heart cycle.

Claims

1. A method of temporally resolved three dimensional dynamic magnetic resonance data acquisitions for an object with substantially cyclical motion comprising the steps of:

a) placing the object in a static magnetic field;

b) applying an RF excitation pulse followed by in-plane phase encode and slice direction phase encode gradients;

c) detecting magnetic resonance signals in the presence of read-out gradients;

d) repeating steps b) and c) for different values of slice direction phase encode gradients during a first cycle of motion of the object, while employing at least one amplitude of the in-plane phase encode gradient;

e) repeating step d) for a time period greater than one minute over a plurality of motion cycles with other amplitudes of in-phase encode gradients;

f) applying a phase encode rewinder gradient after each step of detecting magnetic resonance signals to reduce artifacts;

g) applying crusher gradients before applying an RF excitation pulse to improve suppression of static tissue signals; and

h) applying a contrast agent which alters the relaxation time of blood during the acquisition time to improve contrast in detected signals.

2. The method as defined by claim 1 wherein first-order moment nulling is avoided to reduce the echo time.

3. The method as defined by claim 1 wherein the RF pulse is on the order of 600 μ

s in duration with a flip angle on the order of 20°

.

4. A method for temporally resolved three dimensional magnetic resonance data acquisitions for an object with cyclical motion comprising the steps of:

a) placing the object in a static magnetic field;

b) applying an RF excitation pulse followed by in-plane phase encode and slice direction phase encode gradients;

c) detecting magnetic resonance signals in the presence of read-out gradients;

d) repeating steps b) and c) for different values of in-plane phase encode gradients during a first cycle of motion of the object, while employing at least one amplitude of the slice direction phase encode gradient;

e) repeating step d) for a time period greater than 72 seconds over a plurality of motion cycles with other amplitudes of in-phase encode gradients;

f) applying a phase encode rewinder gradient after each step of detecting magnetic resonance signals to reduce artifacts;

g) applying crusher gradients before applying an RF excitation pulse to improve suppression of static tissue signals; and

h) applying a contrast agent which alters the relaxation time of blood during the acquisition time to improve contrast in the detected signals.

5. The method as defined by claim 4 wherein first-order moment nulling is avoided to reduce the echo time.

6. The method as defined by claim 4 wherein the RF pulse is on the order of 600 μ

s in duration with a flip angle on the order of 20°

.

7. Magnetic resonance imaging apparatus for obtaining temporally resolved three dimensional magnetic resonance data for an object with cyclical motion comprising:

a) means for applying a static magnetic field through the object along one axis;

b) means for applying slice direction phase encode gradients and in-plane phase encode gradients to the object;

c) means for applying an RF excitation pulse to the object followed by said gradients;

d) means for detecting magnetic resonance signals in the presence of read-out gradients;

said apparatus repeating the application of RF excitation pulses and the detecting of magnetic resonance signals for different values of slice direction phase encode gradients during each cycle of motion of the object while employing at least one amplitude of the in-plane phase encode gradient constant during each cycle of motion of the object;

e) means for applying an in-plane phase encode rewinder gradient after each step of detecting nuclei relaxation signals to reduce artifacts;

f) means for applying crusher gradients before applying an RF excitation pulse to improve suppression of static tissue relaxation time;

wherein the RF pulse is on the order of 600 μ

s in duration with a flip angle on the order of 20°

.

8. The apparatus as defined by claim 7 wherein the time between repetitions of RF excitation pulses is no more than 10 ms.

9. Magnetic resonance imaging apparatus for obtaining temporally resolved three dimensional magnetic resonance data for an object with cyclical motion comprising:

a) means for applying a static magnetic field through the object along one axis;

b) means for applying slice direction phase encode gradients and in-plane phase encode gradients to the object;

c) means for applying an RF excitation pulse to the object followed by said gradients, wherein the RF pulse is on the order of 600 μ

s in duration with a flip angle on the order of 20°

;

d) means for detecting magnetic resonance signals;

e) means for applying an in-plane phase encode rewinder gradient after each step of detecting magnetic resonance signals to reduce artifacts;

f) means for applying crusher gradients before applying an RF excitation pulse to improve suppression of static tissue relaxation time;

and said apparatus repeating the application of RF excitation pulses and the detecting of magnetic resonance signals for different values of in-plane phase encode gradient constant during each cycle of motion of the object while employing at least one amplitude of slice direction phase encode gradients.

10. A method of temporally resolving three dimensional magnetic resonance data acquisitions for an object with substantially cyclical motion comprising the steps of:

a) placing the object in a static magnetic field;

b) administering a contrast agent which alters the relaxation time during the acquisition time of at least some components of the object;

c) applying an RF excitation pulse followed by in-plane phase encode and slice direction phase encode gradients;

d) detecting magnetic resonance signals in the presence of a read-out gradient; and

e) repeating steps c) and d) for different values of slice direction phase encode gradients during a first cycle of motion of the object, while employing at least one amplitude of the in-plane phase encode gradient; and

f) repeating step d) for a time period greater than one minute over a plurality of motion cycles with other amplitudes of in-phase encode gradients.

11. The method as defined by claim 10 and further including the steps of:

g) applying a phase encode rewinder gradient after each step of detecting magnetic resonance signals to reduce artifacts; and

h) applying crusher gradients before applying an RF excitation pulse to improve suppression of static tissue signals.