Safety tests for systems monitoring local SAR

Patent metadata

Field	Value
Publication number	US-9625541-B2
Application number	US-201313933083-A
Country	US
Kind code	B2
Filing date	Jul 1, 2013
Priority date	Jul 1, 2013
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

In order to provide online monitoring of local specific absorption rate (SAR) within a body subject to a magnetic resonance imaging (MRI) scan, directional couplers measure a phase and an amplitude of a transmission radio frequency (RF) pulse generated and transmitted by an MRI system. A measured local SAR value is calculated based on the measured phase and the measured amplitude of the transmission RF pulse using a voxel model of the body and an electromagnetic (EM) simulation. In order to verify proper operation of the local SAR monitoring, the measured local SAR value is compared to a predetermined local SAR value.

First claim

The invention claimed is:

1. A method for testing a system for monitoring local specific absorption rate (SAR) for a body within a magnetic resonance imaging (MRI) system, the method comprising:
receiving a measured phase and a measured amplitude of a transmission radio frequency (RF) pulse generated and transmitted by the MRI system;
calculating, by a processor, a measured local SAR value based on the measured phase and amplitude of the transmission RF pulse;
verifying accurate operation of the system for monitoring local SAR with respect to a predetermined local SAR value, the verifying comprising comparing the measured local SAR value to the predetermined local SAR value; and
resetting the MRI system to a predetermined safe state based on the comparison.

2. The method of claim 1 , wherein the predetermined local SAR value is a predetermined local SAR limit value, and
wherein the resetting comprises the MRI system to the predetermined safe state when the measured local SAR value exceeds the predetermined local SAR limit value.

3. The method of claim 1 , wherein calculating the measured local SAR value comprises calculating the measured local SAR value at one or more representative positions within a model of the body.

4. The method of claim 1 , wherein the receiving comprises receiving the measured phase and the measured amplitude of the transmission RF pulse from a directional coupler.

5. The method of claim 1 , wherein the calculating comprises inputting the received measured phase and measured amplitude of the transmission RF pulse into a mathematical model representing the body and a transmission coil of the MRI system.

6. The method of claim 5 , further comprising generating the mathematical model, the generating comprising compressing a model of the body to be scanned by the MRI system into a plurality of voxel clusters, each voxel cluster of the plurality of voxel clusters defining a virtual observation point with a peak sensitivity to local SAR for the voxel cluster.

7. The method of claim 6 , wherein generating the mathematical model further comprises:
assigning each voxel cluster of the plurality of voxel clusters to a hotspot; and
establishing a sensitivity matrix for each of the hotspots.

8. The method of claim 5 , further comprising:
identifying a measurement protocol, the identified measurement protocol comprising a defined phase and a defined amplitude for the transmission RF pulse, and a defined termination of a transmission line operable to transmit the transmission RF pulse; and
calculating a theoretical local SAR value based on the identified measurement protocol, the calculating of the theoretical local SAR value comprising inputting at least a portion of the identified measurement protocol into the mathematical model or another mathematical model,
wherein the predetermined local SAR value is the theoretical local SAR value, and
wherein the comparing comprises comparing the measured local SAR value to the theoretical local SAR value to determine whether the measured local SAR value matches the theoretical local SAR value within a predetermined threshold.

9. The method of claim 1 , wherein the calculating comprises calculating the measured local SAR value within 10 ms of the transmission RF pulse being transmitted.

10. The method of claim 1 , wherein comparing the measured local SAR value to the predetermined local SAR value comprises:
calculating a difference between the measured local SAR value and the predetermined local SAR value; and
comparing the calculated difference to a predetermined threshold,
wherein accurate operation of the system for monitoring local SAR is verified when the calculated difference is less than the predetermined threshold.

11. In a non-transitory computer-readable storage medium that stores instructions executable by one or more processors to test a system for monitoring local specific absorption rate (SAR), the instructions comprising:
identifying a theoretical local SAR value based on a measurement protocol, the measurement protocol comprising a defined phase and amplitude for a defined transmission radio frequency (RF) pulse;
receiving a measured phase and a measured amplitude of a transmission RF pulse generated based on the measurement protocol, and transmitted by a magnetic resonance imaging (MRI) system;
calculating a measured local SAR value based on the measured phase and amplitude of the transmission RF pulse;
verifying accurate operation of the system for monitoring local SAR with respect to a predetermined threshold, the verifying comprising comparing a difference of the measured local SAR value to the theoretical local SAR value with the predetermined threshold; and
resetting the MRI system to a predetermined safe operating state when the difference exceeds the predetermined threshold.

12. The non-transitory computer-readable storage medium of claim 11 , wherein the instructions further comprise identifying the measurement protocol,
wherein the identifying of the theoretical local SAR value comprises calculating the theoretical local SAR value based on the identified measurement protocol, the calculating of the theoretical local SAR value comprising inputting the defined phase and amplitude for the defined transmission RF pulse into a mathematical model representing the body and a transmission coil of the MRI system, and
wherein the calculating of the measured local SAR value comprises inputting the measured phase and amplitude of the transmission RF pulse into the mathematical model or another mathematical model representing the body and the transmission coil of the MRI system.

13. The non-transitory computer-readable storage medium of claim 12 , wherein the receiving comprises receiving measured phases and measured amplitudes of a plurality of parallel transmission RF pulses generated by the MRI system, the plurality of parallel transmission RF pulses comprising the transmission RF pulse, and
wherein the calculating of the measured local SAR value comprises inputting the measured phases and the measured amplitudes of the plurality of parallel transmission RF pulses into the mathematical model or the other mathematical model representing the body and a plurality of transmission coils of the MRI system, the plurality of transmission coils comprising the transmission coil.

14. The non-transitory computer-readable storage medium of claim 12 , wherein the calculating of the measured local SAR value comprises inputting the measured phase and amplitude of the transmission RF pulse into the other mathematical model, and
wherein the mathematical model requires more data processing than the other mathematical model.

15. The non-transitory computer-readable storage medium of claim 11 , wherein the instructions further comprise comparing the measured local SAR value to a predetermined local SAR limit value.

16. The non-transitory computer-readable storage medium of claim 11 , wherein the receiving comprises receiving the measured phase and the measured amplitude of the transmission RF pulse from a directional coupler.

17. A system for testing a specific absorption rate (SAR) monitor, the system comprising:
a processor configured to:
identify a theoretical local SAR value based on a measurement protocol, the measurement protocol comprising defined phases and amplitudes for a plurality of parallel defined transmission radio frequency (RF) pulses;
receive measured phases and amplitudes of a plurality of parallel transmission RF pulses generated based on the measurement protocol, and transmitted throu

Assignees

• Fontius Jörg Ulrich
• Adolf Holger
• Benner Thomas
• Fautz Hans-Peter
• Gebhardt Matthias
• Gumbrecht Rene
• Siemens Ag

Inventors

• Fontius Jörg Ulrich
• Adolf Holger
• Benner Thomas
• Fautz Hans-Peter
• Gebhardt Matthias
• Gumbrecht Rene

Classifications

• G01R33/288 Primary

  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 title

• G01R33/36

  Electrical details, e.g. matching or coupling of the coil to the receiver · CPC title