Magnetic resonance imaging receive chain with dynamic gain and wireless receiver coil

• US 20060244452A1
• Filed: 09/01/2004
• Published: 11/02/2006
• Est. Priority Date: 09/10/2003
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Den Boef, Johannes H.
• Granted Patent: US 7,323,876 B2
• Time in Patent Office: Days
• US Class Current: 324/322
• CPC Class Codes: G01R 33/3621 NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation
• CPC Class Codes: G01R 33/3692 involving signal transmission without using electrically conductive connections, e.g. wireless communication or optical communication of the MR signal or an auxiliary signal other than the MR signal
• CPC Class Codes: G01R 33/54 Signal processing systems, e.g. using pulse sequences ; Generation or control of pulse sequences; Operator console
• CPC Class Codes: G01R 33/543 Control of the operation of the MR system, e.g. setting of acquisition parameters prior to or during MR data acquisition, dynamic shimming, use of one or more scout images for scan plane prescription G01R33/546 takes precedence

Abstract

Dynamic adjustment of the receiver gain during an MRI scan. To account for magnitude and/or phase distortions introduced by the receiver that are not necessarily identical at various receiver gains, a reference rf signal is applied to the receive chain by an additional antenna. Preferably the reference signal is adjusted such that its frequency lies at the border of the frequency band detected by the MR scan. Comparing the a priori known amplitude and phase of the reference signal with the amplitude and phase of the received reference signal allows to determine the distortions introduced at the respective receiver gain which are subsequently corrected. In a further embodiment, the reference signal is used to synchronize the modulation and demodulation units of a wireless transceiver system.

Claims

1. A magnetic resonance imaging system including:

a magnetic resonance scanner for exciting and spatially encoding a magnetic resonance signal;

a reference radio frequency signal generating means for generating a reference radio frequency signal;

a receiving means for receiving radio frequency signals including the excited and spatially encoded magnetic resonance signal and the reference radio frequency signal; and

a correcting means for correcting the spatially encoded magnetic resonance signal in accordance with the received reference radio frequency signal.

2. The magnetic resonance imaging system as set forth in claim 1, further including:

a signal processing means for performing signal processing on the received radio frequency signals, the signal processing means including;

a signal conditioning means for conditioning the received radio frequency signals to produce conditioned radio frequency signals,

a digitizing means for a converting the conditioned radio frequency signals into digitized radio frequency signals, and

a reconstruction means for reconstructing at least a magnetic resonance signal component of the digitized radio frequency signals into a reconstructed image; and

wherein the correcting means includes;

a reference signal recovery means for recovering a reference radio frequency signal component of the digitized radio frequency signals, and

a control means for controlling the signal processing means based on comparison of the reference radio frequency signal component of the digitized radio frequency signals and the reference radio frequency signal.

3. The magnetic resonance imaging system as set forth in claim 2, wherein the signal conditioning means includes:

an amplifying means for amplifying the received radio frequency signals with a selectable amplification gain.

4. The magnetic resonance imaging system as set forth in claim 3, wherein the control means includes:

an amplitude comparing means for producing an amplitude control parameter based on comparison of an amplitude of the reference radio frequency signal component of the digitized radio frequency signals and an amplitude of the reference radio frequency signal; and

an automatic gain control means for adjusting the selectable amplification gain of the amplifying means based on the amplitude control parameters.

5. The magnetic resonance imaging system as set forth in claim 4, wherein the amplifying means includes:

a plurality of constant-gain amplifiers the automatic gain control means selecting one or more of the constant-gain amplifiers for amplifying the received radio frequency signals.

6. The magnetic resonance imaging system as set forth in claim 5, wherein the automatic gain control means includes:

a plurality of analog-to-digital converters corresponding to the plurality of constant-gain amplifiers, each analog-to-digital converter outputting a digitized signal; and

a selection means that selects the highest output digitized signal for which the corresponding analog-to-digital converter is not overloaded.

7. The magnetic resonance imaging system as set forth in claim 4, wherein the amplifying means includes:

an amplifier; and

an attenuator;

wherein the automatic gain control means adjusts an attenuation of the attenuator to effect the selectable amplification gain based on the amplitude control parameters.

8. The magnetic resonance imaging system as set forth in claim 2, wherein the control means includes:

a phase comparing means for producing a phase shift parameter based on comparison of a phase of the reference radio frequency signal component of the digitized radio frequency signals and a phase of the reference radio frequency signal.

9. The magnetic resonance imaging system as set forth in claim 8, wherein the control means further includes:

a phase correction means communicating with the signal conditioning means for correcting a phase shift introduced by the signal conditioning means based on the phase shift parameter.

10. The magnetic resonance imaging system as set forth in claim 8, wherein the receiving means is electrically isolated from the signal processing means, the system further including:

a wireless transmitting means communicating with the receiving means for wireless transmitting a heterodyned signal formed by mixing the received radio frequency signals and a transmitter reference signal;

a wireless receiving means communicating with the signal processing means for wireless receiving the heterodyned signal and for recovering the received radio frequency signals; and

a correcting means for correcting a synchronization difference between the receiver reference signal and the transmitter reference signal based on the phase shift parameter.

11. The magnetic resonance imaging system as set forth in claim 2, wherein:

the reconstruction means includes a Fourier transform means for converting the digitized radio frequency signals to produce a frequency spectrum; and

the reference signal recovery means includes a means for reading a selected frequency component of the frequency spectrum corresponding to a frequency of the reference radio frequency signal.

12. The magnetic resonance imaging system as set forth in claim 11, wherein the control means includes one of:

an amplitude correction means for amplitude scaling a magnetic resonance signal component of the frequency spectrum based on comparison of an amplitude of a reference radio frequency signal component of the frequency spectrum with an amplitude of the reference radio frequency signal, and

a phase comparing means for phase shifting a magnetic resonance signal component of the frequency spectrum based on comparison of a phase of a reference radio frequency signal component of the frequency spectrum with a phase of the reference radio frequency signal.

13. The magnetic resonance imaging system as set forth in claim 1, wherein the reference radio frequency signal generating means includes an antenna selected from a group consisting of a flux probe coil and a tuning coil.

14. A magnetic resonance imaging method including:

exciting and spatially encoding a magnetic resonance signal;

generating a reference radio frequency signal;

receiving radio frequency signals including the excited and spatially encoded magnetic resonance signal and the reference radio frequency signal; and

correcting the magnetic resonance signal in accordance with the received reference radio frequency signal.

15. The magnetic resonance imaging method as set forth in claim 14, further including:

conditioning the received radio frequency signals to produce conditioned radio frequency signals;

converting the conditioned radio frequency signals into digitized radio frequency signals; and

reconstructing at least a magnetic resonance signal component of the digitized radio frequency signals into a reconstructed image; and

wherein the correcting of the magnetic resonance signal includes;

recovering a reference radio frequency signal component of the digitized radio frequency signals, and

controlling at least one of the conditioning, the converting, and the reconstructing based on comparison of the reference radio frequency signal component of the digitized radio frequency signals and the reference radio frequency signal.

16. The magnetic resonance imaging method as set forth in claim 15, wherein:

the reconstructing includes gridding and Fourier transforming the digitized radio frequency signals to produce binned frequency components stored in frequency bins; and

the generating of a reference radio frequency signal includes generating a modulated reference radio frequency signal;

wherein the reference radio frequency signal component of the digitized radio frequency signals includes a single or multi-tone reference frequency signal each corresponding to one of the frequency bins.

17. The magnetic resonance imaging method as set forth in claim 15, wherein:

the conditioning of the received radio frequency signals includes amplifying the received radio frequency signals prior to the converting using a bi-linear amplifier; and

the controlling of at least one of the conditioning, the converting, and the reconstructing includes controlling the bi-linear amplifier based on comparison of an amplitude of the reference radio frequency signal component of the digitized radio frequency signals and an amplitude of the reference radio frequency signal.

18. The magnetic resonance imaging method as set forth in claim 14, further including:

wireless transmitting the received radio frequency signals; and

synchronizing a wireless receiving of the wireless transmitted radio frequency signals with the wireless transmitting based on a phase shift between the reference radio frequency signal component of the digitized radio frequency signals and the reference radio frequency signal.