Magnetic resonance imaging apparatus

Patent metadata

Field	Value
Publication number	US-9746532-B2
Application number	US-201314043225-A
Country	US
Kind code	B2
Filing date	Oct 1, 2013
Priority date	Nov 26, 2009
Publication date	Aug 29, 2017
Grant date	Aug 29, 2017

Abstract

A magnetic resonance imaging apparatus includes an imaging unit configured to carry out magnetic resonance imaging of a patient using a transmitting QD coil that allows at least one of phase and amplitude of a radio-frequency transmit pulse on at least one input channel of the transmitting QD coil to be adjusted independently of each other, and an adjustment unit arranged to adjust at least one of the phase and the amplitude of the radio-frequency transmit pulse according to imaging conditions.

First claim

What is claimed is:

1. A magnetic resonance imaging apparatus comprising:
radio frequency (RF) transmitter circuitry having an RF output split into phase quadrature first and second RF output channels, a controllable RF phase adjustment circuit being included in at least one of said channels and a controllable RF gain adjustment circuit being included in at least one of said channels thereby providing controllable adjustments of relative phase and relative amplitude gain between the channels;
a transmitting QD coil including a first RF input port connected to said first RF output channel and a second RF input port connected to said second RF output channel; and
processing circuitry connected to control said controllable RF phase adjustment circuit and said controllable RF gain adjustment circuit, said processing circuitry being configured to adjust the relative phase and amplitude of an RF transmit pulse between the first and second RF output channels according to selected imaging conditions based on previously collected MRI signals for those conditions so as to enhance uniformity of RF B1 fields within the QD coil during imaging scans for the selected imaging conditions;
the magnetic resonance imaging apparatus further comprises a storage device configured to store (A) selectable imaging conditions and (B) at least one of phase and amplitude parameters of the RF transmit pulse associated with the imaging conditions; and
the processing circuitry is configured to acquire at least one of the phase and amplitude parameters of the RF transmit pulse associated with selected imaging conditions from the storage device as an initial value, and to adjust the at least one of the phase and amplitude parameters using the acquired initial value.

2. The magnetic resonance imaging apparatus according to claim 1 , wherein
the imaging conditions include at least one of (i) an imaging region of a patient and (ii) a type of QD coil.

3. The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to collect elicited magnetic resonance RE signal data while changing at least one of the phase and amplitude parameters from the acquired initial value and to adjust the at least one of the phase and the amplitude based on the collected data.

4. The magnetic resonance imaging apparatus according to claim 3 , wherein the processing circuitry is further configured to obtain an index which represents non-uniformity of a radio-frequency magnetic field formed by the QD coil, from the collected data and to adjust the at least one of the phase and amplitude parameters so as to minimize the index.

5. The magnetic resonance imaging apparatus according to claim 4 , wherein the collected RF magnetic resonance signal data is adjustment data collected using a spin echo pulse sequence with a flip angle set to be smaller than a typical flip angle for a spin echo pulse sequence.

6. The magnetic resonance imaging apparatus according to claim 4 , wherein the collected data is a RF magnetic field map.

7. The magnetic resonance imaging apparatus according to claim 5 , wherein the processing circuitry is further configured to enhance a strength variation to the adjustment data.

8. The magnetic resonance imaging apparatus according to claim 6 , wherein the processing circuitry is further configured to enhance a strength variation to the RF magnetic field map.

9. The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to acquire an axial section image of the patient, to determine an angle difference between a specific axis in the axial section image and an actual axis of the patient corresponding to the specific axis as a correction value, and to correct the initial value of the phase stored in the storage device by the correction value.

10. The magnetic resonance imaging apparatus according to claim 3 , wherein the processing circuitry is further configured to adjust the at least one of the phase and amplitude parameters so as to minimize forward power of a refocusing RF pulse measured while changing at least one of the phase and amplitude parameters.

11. The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to adjust at least one of the phase and amplitude parameters based on a first RF magnetic field map collected by RF transmission via the first output channel alone and a second RF magnetic field map collected by RF transmission via the second channel alone.

12. The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is further configured to adjust phase based on an angle formed by maximum uniformity lines extracted from the first RF magnetic field map and the second RF magnetic field map.

13. The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is further configured to adjust amplitude based on a contribution to uniformity of a RF magnetic field of the QD coil, the uniformity having been calculated from the first and second RF magnetic field maps.

14. The magnetic resonance imaging apparatus according to claim 3 , wherein the processing circuitry is further configured to adjust an output level of the RF transmit pulse based on at least one of the phase and amplitude being subjected to adjustment.

15. The magnetic resonance imaging apparatus according to claim 14 , wherein the processing circuitry is further configured to adjust the output level so as to minimize an index which represents non-uniformity of a RF magnetic field collected by changing the output level.

16. The magnetic resonance imaging apparatus according to claim 14 , wherein the processing circuitry is further configured to adjust the output level so as to maximize strength of a magnetic resonance RF signal collected by changing the output level.

17. The magnetic resonance imaging apparatus according to claim 11 , wherein the processing circuitry is further configured to adjust an output level of the RF transmit pulse based on at least one of the phase and amplitude being subjected to adjustment.

18. The magnetic resonance imaging apparatus according to claim 17 , wherein the processing circuitry is further configured to adjust the output level so as to minimize an index which represents non-uniformity of a RF magnetic field collected while changing the output level.

19. The magnetic resonance imaging apparatus according to claim 17 , wherein the processing circuitry is further configured to adjust the output level so as to maximize strength of a magnetic resonance RF signal collected while changing the output level.

20. The magnetic resonance imaging apparatus according to claim 2 , wherein the processing circuitry is further configured to acquire at least one of the phase and amplitude parameters of the RF transmit pulse which corresponds to the imaging conditions retrieved from the storage device, and to multiply the acquired parameter(s) by −1 when body position of the patient indicates a lateral recumbent position.

21. The magnetic resonance imaging apparatus according to claim 1 , wherein the processing circuitry is further configured to adjust the amplitude after adjusting the phase.

22. The magnetic resonance imaging apparatus according to claim 1 , wherein:
the imaging conditions include at least one of (a) an imaging region of the patient and (b) the type of QD coil;
the magnetic resonanc

Assignees

• Toshiba Medical Sys Corp

Inventors

• Umeda Masaaki
• Ishihara Takahiro

Classifications

• G01R33/5612

  Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels · CPC title

• G01R33/246

  Spatial mapping of the RF magnetic field B1 · CPC title

• G01R33/3628 Primary

  Tuning/matching of the transmit/receive coil · CPC title

• G01R33/3678 Primary

  involving quadrature drive or detection, e.g. a circularly polarized RF magnetic field · CPC title

• G01R33/5659

  caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title