Magnetic resonance device and method
A device performs MR imaging of a body ( 7 ) placed in a stationary and substantially homogeneous main magnetic field, with an RF transmit antenna ( 6 ) for radiating RF pulses towards the body ( 7 ), which RF transmit antenna ( 6 ) has different resonance modes. In order to improve image uniformity in high field MR imaging, the device ( 1 ) is arranged to determine the size and/or the aspect ratio of the body ( 7 ), and to acquire an MR image of the body ( 7 ) by an imaging sequence including RF pulses. The phases and amplitudes of the different resonance modes of the RF transmit antenna ( 6 ) excited during irradiation of the RF pulses are controlled on the basis of the size and/or aspect ratio of the body ( 7 ).
1. A device for MR imaging of a body comprising:
a magnetic coil configured to generate a stationary and substantially homogeneous magnetic field;
an RF transmit antenna configured to radiate RF pulses towards the body, wherein RF transmit antenna has different resonance modes; and
a computer with a program control configured to determine an aspect ratio of the body, and acquire an MR image of the body by an imaging sequence comprising RF pulses, wherein phases and amplitudes of the different resonance modes of the RF transmit antenna excited during irradiation of the RF pulses are controlled on the basis of the aspect ratio of the body.
2. The device of claim 1 , wherein the computer with the program control is further configured to determine the aspect ratio of the body by a calibration procedure, wherein the calibration procedure involves the acquisition of either a low resolution MR image or at least two projection MR images of the body.
3. The device of claim 2 , wherein the computer with the program control is configured to compute the aspect ratio from the MR images acquired during the calibration procedure as the ratio of dimensions of the body in two orthogonal spatial directions.
4. The device of claim 1 , further comprising a transmit unit connected to two or more separate transmit channels, each transmit channel being associated with one of the resonance modes of the RF transmit antenna, wherein the phases and amplitudes of the RF signals supplied to the separate transmit channels are individually controllable by the transmit unit.
5. The device of claim 1 , further comprising a receiving unit connected to two or more separate receiving channels of the device, each receiving channel being associated with one of the resonance modes of the RF transmit antenna.
6. The device of claim 1 , wherein the computer with the program control is configured to select the phases and amplitudes of the different resonance modes on the basis of a lookup table or a functional relationship relating the aspect ratio of the body to corresponding phase and amplitude values.
7. A method for MR imaging at least a portion of a body placed in a stationary and substantially homogeneous main magnetic field, with an RF transmit antenna for radiating RF pulses towards the body, which RF transmit antenna has different resonance modes, the method comprising the following steps:
with a computer, determining an aspect ratio of the body; and
from an MR imaging device, acquiring an MR image of the body by an imaging sequence comprising RF pulses, wherein phases and amplitudes of different resonance modes of an RF transmit antenna excited during generation of the RF pulses are controlled independently on the basis of the aspect ratio of the body.
8. The method of claim 7 , wherein the aspect ratio of the body is determined by a calibration procedure involving the acquisition of either a low resolution MR image or at least two projection MR images of the body.
9. The method of claim 7 , wherein the phases and amplitudes of the different resonance modes are selected on the basis of a lookup table or a functional relationship relating the aspect ratio of the body to corresponding phase and amplitude values.
10. A tangible machine readable media comprising a computer program for an MR imaging device, with instructions for:
determining an aspect ratio of a body placed in a stationary and substantially homogeneous main magnetic field of the MR imaging device,
controlling the acquisition of MR image data of the body by an imaging sequence comprising RF pulses,
selecting phases and amplitudes of different resonance modes of an RF transmit antenna excited during generation of the RF pulses on the basis of the aspect ratio of the body.
11. The tangible machine readable media comprising a computer program of claim 10 , further comprising instructions for selecting the phases and amplitudes of the different resonance modes on the basis of a lookup table or a functional relationship relating the aspect ratio of the body to corresponding phase and amplitude values.