Method and circuit arrangement for operating multi-channel transmit/recieve antenna devices

• US 8,099,059 B2
• Filed: 04/27/2006
• Issued: 01/17/2012
• Est. Priority Date: 04/29/2005
• 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: Graesslin, Ingmar, Vernickel, Peter, Leussler, Christoph
• Primary Examiner(s): Ghebretinsae, Temesgh
• Assistant Examiner(s): Tsvey, Gennadiy
• Application Number:
  US11/912,684
• Publication Number:
  US 20080182524A1
• Time in Patent Office: 2,091 Days
• Field of Search: None
• US Class Current: 455/73
• CPC Class Codes: G01R 33/288 Provisions within MR facilities for enhancing safety during MR, e.g. reduction of the specific absorption rate [SAR], detection of ferromagnetic objects in the scanner room
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/3607 RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal
• CPC Class Codes: G01R 33/5612 Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels
• CPC Class Codes: H04B 17/23 Indication means, e.g. displays, alarms, audible means
• CPC Class Codes: H04W 52/34 TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range

Abstract

A multi-channel transmit/receive antenna device or arrangement for use in a magnetic resonance imaging (MRI) system includes a power monitoring unit. To ensure that a specific absorption rate of a patient is not exceeded, transmitted power levels and reflected power levels on channels for a plurality of coils and/or coil segments are monitored. Each coil/coil segment is supplied with RF transmit signals with different amplitudes and/or phases and/or waveforms and/or power levels.

Claims

1. A circuit arrangement for operating a multi-channel transmit receive antenna device or arrangement, comprising a power monitoring unit for:

monitoring;

a weighted sum of transmit power levels which are supplied in a plurality of transmit channels to the antenna device or arrangement, and

a weighted sum of reflected power levels which are reflected in the plurality of transmit channels; and

switching off at least one of the transmit channels if the monitored weighted sum of the transmit and/or reflected power levels exceeds a set maximum weighted sum transmit or reflected power level.

2. The circuit arrangement according to claim 1, wherein the power monitor unit further monitors for:

a transmit power level which is supplied on each transmit channel to the antenna device or arrangement, and

a reflected power level which is reflected on each transmit channel; and

switches off at least one of the transmit channels if the monitored transmit or reflected power level on one or more of the transmit channels exceeds a set maximum transmit or reflected power level.

3. A magnetic resonance imaging system comprising the circuit arrangement according to claim 1.

4. A method of monitoring transmit power levels which are transmitted to each of a plurality of channels of a multi-channel antenna device or arrangement and reflected power levels which are reflected on each of the channels, the method comprising:

(a) setting a limit or maximum transmit power level for each of the channels,

(b) setting a sum transmit limit or maximum power level for the plurality of channels,

(c) setting a limit or maximum reflected power level for each of the channels,

(d) setting a sum reflected limit or maximum power level for the plurality of channels,

(e) detecting and comparing the transmit power level which is supplied by each channel to the antenna device or arrangement with the limit or maximum transmit power level which is set for the channel,

(f) detecting and comparing a sum of the transmit power levels which are supplied in the channels to the antenna device or arrangement with the sum transmit limit or maximum power level, and

(g) detecting and comparing the reflected power level on each of the plurality of channels to the antenna device or arrangement with the reflected limit or maximum power level which is set for the channel,

(h) detecting and comparing a sum of the reflected power levels on the plurality of channels with the sum reflected limit or maximum power level, the sum reflected power level including weighted summing the reflected power levels on each of the plurality of channels, wherein the weighting factors are constant preset factors or adapted during an examination, and

(i) activating an alarm state if

the monitored transmitted power level on one of the channels exceeds the set limit or maximum transmit power level for the transmit channel, or

the monitored reflected power level on one of the channels exceeds the set limit or maximum reflected power level for that h channel, or

the supplied transmit power level exceeds the sum transmit limit or maximum power level, or

the sum reflected power level on channels exceeds the set sum reflected limit or maximum power level.

5. The method according to claim 4, wherein activating the alarm state includes:

generating a warning or error signal and/or by a turning off or separating at least one of the transmit channels from the antenna device or arrangement.

6. The method according to claim 4, further including:

supplying transmit RF signals with different amplitudes and/or phases and/or waveforms and/or power levels on at least some of the channels, wherein the limit or maximum transmit and/or reflected power levels are set with different values for different channels.

7. The method according to claim 4, wherein the monitored transmit power level and the monitored reflected power level are subtractively combined to determine an RF power level supplied to an examined object.

8. A non-transitory computer-readable medium carrying software which controls one or more processors to perform the method according to claim 4.

9. A power monitor which monitors power levels in a multi-channel magnetic resonance coil system, the monitor comprising:

one or more comparators which;

compare current transmit power levels of transmit signals on each of a plurality of channels with a preselected maximum transmit power level for each channel, the transmit signals having independently controlled phase and amplitude on each channel, and

compare current reflective power levels on each of the plurality of channels with a preselected maximum reflected power level for each channel;

a control unit which generates a warning signal in response to;

the transmit power level on any one of the channels approaching the preselected maximum transmit power level for the one channel, and

the reflected power level on any one of the channels approaching the preselected maximum reflected power level for the one channel;

a summing unit which generates a weighted sum of the reflected power levels on the plurality of reflected channels; and

wherein the one or more comparators compare the weighted sum of the reflected power levels with a preselected maximum reflected power level sum.

10. The power monitor according to claim 9, further including:

a summing unit which generates a weighted sum of the transmit power levels on the plurality of transmit channels; and

wherein the one or more comparators compare the weighted sum of the transmit power levels with a preselected maximum transmit power level sum.

11. The power monitor according to claim 9, wherein the control unit further determines an amount of power applied by the coil array by determining a difference between the transmitted and reflected power levels.

12. The power monitor according to claim 9, wherein the control unit further generates an error signal in response to the transmit power level on any one of the channels meeting or exceeding the preselected maximum transmit power level or the reflected power level on any one of the channels meeting or exceeding the preselected maximum reflected power level for the one channel.