METHOD AND MAGNETIC RESONANCE SYSTEM FOR IMAGING PARTICLES

• US 20110115487A1
• Filed: 11/09/2010
• Published: 05/19/2011
• Est. Priority Date: 11/13/2009
• Status: Abandoned Application

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Grodzki, David
• Application Number:
  US12/942,110
• Publication Number:
  US 20110115487A1
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: A61B 5/0515 Magnetic particle imaging
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: G01R 33/5601 involving use of a contrast agent for contrast manipulation, e.g. a paramagnetic, super-paramagnetic, ferromagnetic or hyperpolarised contrast agent
• CPC Class Codes: G01R 33/56316 involving phase contrast techniques
• CPC Class Codes: G01R 33/56509 due to motion, displacement or flow, e.g. gradient moment nulling G01R33/567 takes precedence

Abstract

A method and magnetic resonance system for imaging a particle that is located in an examination subject with an imaging magnetic resonance measurement execute a gradient echo sequence in which at least two gradient echoes are acquired following a single excitation pulse, wherein the particle in an applied basic magnetic field causes a magnetic interference field. An RF pulse is radiated to generate a transverse magnetization from a magnetization appearing in the basic magnetic field. A first dephasing gradient is shifted to adjust a first dephasing of the transverse magnetization, and the first gradient echo is acquired. A second dephasing gradient is shifted to adjust a second dephasing of the transverse magnetization that is different than the first dephasing, and the second gradient echo is acquired. The two dephasing gradients are shifted such that a dephasing of the transverse magnetization caused by the interference field of the particle is at least partially compensated in a region around the particle or within the particle given the acquisition of at least one of the echoes.

Claims

1. A method for imaging a particle located in an examination subject by implementing a magnetic resonance image data acquisition sequence in which at least a first gradient echo and a second gradient echo are acquired following a single excitation pulse while the examination subject is located in an applied basic magnetic field, said particle in said applied basic magnetic field causing a magnetic interference field, said magnetic resonance image data acquisition sequence comprising the steps of:

radiating a radio-frequency (RF) pulse into the subject to generate a transverse magnetization in the subject with respect to a magnetization in the subject produced by the basic magnetic field;

shifting a first dephasing gradient to adjust a first dephasing of said transverse magnetization;

acquiring said first gradient echo;

shifting a second dephasing gradient to adjust a second dephasing of the transverse magnetization that is different from said first dephasing;

acquiring said second gradient echo; and

shifting said first and second dephasing gradients to cause a dephasing of the transverse magnetization caused by the interference field produced by the particle to be at least partially compensated in a region around or within the particle during acquisition of at least one of said first and second gradient echoes.

2. A method as claimed in claim 1 comprising shifting said first and second dephasing gradients along a same gradient direction with the same polarity or opposite polarity.

3. A method as claimed in claim 1 wherein said magnetic resonance image data sequence has a slice selection direction, a frequency coding direction and a phase coding direction associated therewith, and comprising shifting said first and second dephasing gradients along one of said slice selection direction, said frequency coding direction, or said phase coding direction.

4. A method as claimed in claim 1 comprising shifting said first and second dephasing gradients to cause the second dephasing gradient to compensate said first dephasing and to generate said second dephasing.

5. A method as claimed in claim 1 comprising shifting said first and second dephasing gradients to cause a gradient of the phase position of the transverse magnetization to have a polarity sign after adjustment of said first dephasing that is inverted with respect to a polarity sign after adjustment of said second dephasing.

6. A method as claimed in claim 1 comprising setting said first or second dephasing to zero to cause the transverse magnetization to be rephased after the first dephasing gradient or the second dephasing gradient.

7. A method as claimed in claim 1 comprising configuring said first dephasing gradient to comprise a dephasing gradient and a rephasing gradient, each having a gradient moment, and adjusting the first dephasing of the transverse magnetization by adjusting a difference between the gradient moment of the rephasing gradient of the first dephasing gradient and the gradient moment of the dephasing gradient of the first dephasing gradient.

8. A method as claimed in claim 7 wherein said magnetic resonance image data acquisition sequence has a slice selection direction associated therewith, and comprising shifting the dephasing gradient of the first dephasing gradient in the slice selection direction during radiation of said RF pulse.

9. A method as claimed in claim 7 comprising shifting the rephasing gradient of the first dephasing gradient and the second dephasing gradient in the same direction or in opposite directions.

10. A method as claimed in claim 1 comprising, in said magnetic resonance image data acquisition sequence, following acquisition of said second gradient echo, implementing a plurality of additional readouts each comprising shifting of a dephasing gradient and acquisition of a subsequent gradient echo, to cause, in each readout, a different dephasing of the transverse magnetization, causing a different dephasing stage to be acquired with each gradient echo in the respective additional readouts.

11. A method as claimed in claim 1 comprising for each adjusted dephasing, reconstructing image data representing the particle or a region around the particle with different contrast, from the at least first and second gradient echoes.

12. A method as claimed in claim 11 comprising generating combined image data by addition or subtraction of the respective sets of image data for at least two different dephasings.

13. A method as claimed in claim 1 wherein said particle is a magnetically active particle comprising iron oxide.

14. A magnetic resonance system comprising:

a magnetic resonance data acquisition unit operable to image a particle located in an examination subject by implementing a magnetic resonance image data acquisition sequence in which at least a first gradient echo and a second gradient echo are acquired following a single excitation pulse while the examination subject is located in an applied basic magnetic field, said particle in said applied basic magnetic field causing a magnetic interference field; and

a computerized control unit configured to operate said data acquisition unit to radiate a radio-frequency (RF) pulse into the subject to generate a transverse magnetization in the subject with respect to a magnetization in the subject produced by the basic magnetic field, shift a first dephasing gradient to adjust a first dephasing of said transverse magnetization, acquire said first gradient echo, shift a second dephasing gradient to adjust a second dephasing of the transverse magnetization that is different from said first dephasing, acquire said second gradient echo, and shift said first and second dephasing gradients to cause a dephasing of the transverse magnetization caused by the interference field produced by the particle to be at least partially compensated in a region around or within the particle during acquisition of at least one of said first and second gradient echoes.

15. A non-transitory computer-readable data storage medium encoded with programming instructions, said medium being loaded into a computer system of a magnetic resonance system comprising a magnetic resonance data acquisition unit, and said programming instructions causing said computer system to operate said data acquisition system to:

radiate a radio-frequency (RF) pulse into the subject to generate a transverse magnetization in the subject with respect to a magnetization in the subject produced by the basic magnetic field;

shift a first dephasing gradient to adjust a first dephasing of said transverse magnetization;

acquire said first gradient echo;

shift a second dephasing gradient to adjust a second dephasing of the transverse magnetization that is different from said first dephasing;

acquire said second gradient echo; and

shift said first and second dephasing gradients to cause a dephasing of the transverse magnetization caused by the interference field produced by the particle to be at least partially compensated in a region around or within the particle during acquisition of at least one of said first and second gradient echoes.