MAGNETIC RESONANCE MEASUREMENT OF ULTRASOUND PROPERTIES

• US 20130345547A1
• Filed: 03/12/2012
• Published: 12/26/2013
• Est. Priority Date: 03/17/2011
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Vahala, Erkki Tapani
• Granted Patent: US 9,993,196 B2
• Time in Patent Office: Days
• US Class Current: 600/411
• CPC Class Codes: A61B 2090/374 NMR or MRI
• CPC Class Codes: A61B 5/0036 including treatment, e.g., using an implantable medical device, ablating, ventilating
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61N 2007/0091 with moving parts, e.g. transducers, lenses, reflectors
• CPC Class Codes: A61N 2007/0095 by modifying an excitation signal
• CPC Class Codes: A61N 7/00 Ultrasound therapy lithotripsy A61B17/22, A61B17/225; massage using supersonic vibration A61H23/00 ; using ultrasound for introducing media into the body A61M37/0092
• CPC Class Codes: A61N 7/02 Localised ultrasound hyperthermia hyperthermia in general A61F7/00
• CPC Class Codes: G01R 33/4808 Multimodal MR, e.g. MR combined with positron emission tomography [PET], MR combined with ultrasound or MR combined with computed tomography [CT]
• CPC Class Codes: G01R 33/56358 Elastography

Abstract

An apparatus (500, 600) comprising an ultrasound transducer element (300) for generating an ultrasonic beam (302) through a target zone (308, 538). The ultrasonic beam has an ultrasound frequency. The apparatus comprises a magnetic resonance system (502) with a resonant frequency modulator (542, 544, 516) for modulating a magnetic resonance frequency relative to a magnetic resonance of molecules in the target zone at the ultrasound frequency. Instructions cause a processor to repeatedly generate (100, 204) first gradient commands (562) which cause a magnetic field gradient coil to generate a first gradient magnetic field (710, 810) through the target zone. The gradient magnetic field has field lines directed in a first direction (304). The processor repeatedly modulates (102, 206) the magnetic resonance frequency at the ultrasound frequency, generates (104, 208) ultrasound commands (566), acquires (106, 210) magnetic resonance data from the target zone, and generates (108, 212) second gradient commands (564).

Claims

1. An apparatus comprising:

an ultrasound transducer element for generating an ultrasonic beam through a target zone of a subject, wherein the ultrasonic beam has an ultrasound frequency, wherein the ultrasonic beam is directed in a first direction (304, 580) through the target zone;

a magnetic resonance system for acquiring magnetic resonance data from a data acquisition zone, wherein the target zone is within the data acquisition zone, wherein the magnetic resonance system comprises a resonant frequency modulator for modulating a magnetic resonance frequency relative to a magnetic resonance of molecules in the target zone, wherein the resonant frequency modulator is adapted for modulating the magnetic resonance frequency at the ultrasound frequency, wherein the magnetic resonance system further comprises a magnetic field gradient coil;

a processor for controlling the apparatus;

a memory containing machine executable instructions, wherein execution of the instructions causes the processor to repeatedly;

generate first gradient commands which cause the magnetic field gradient coil to generate a first gradient magnetic field through the target zone, wherein the gradient magnetic field has a gradient direction parallel to the first direction;

modulate the magnetic resonance frequency at the ultrasound frequency during the application of the first gradient magnetic field;

generate ultrasound commands which cause the ultrasound transducer to generate the ultrasound beam during the application of the first gradient magnetic field;

generate second gradient commands which cause the magnetic field gradient coil to generate a second gradient magnetic field through the target zone prior to the acquisition of the magnetic resonance data, wherein (i) the second gradient magnetic field has a polarity opposite to that of the first gradient magnetic field or (ii) the second gradient magnetic field has a polarity equal to that of the first gradient magnetic field and an inversion RF pulses is applied between the first and second gradient magnetic field and

acquire magnetic resonance data from the target zone.

2. The apparatus of claim 1, wherein the resonant frequency modulator is further adapted for controlling the phase of modulation relative to the ultrasonic beam, wherein execution of the instructions further cause the processor to:

generate a set of phases;

modulate the magnetic resonance frequency of molecules in the target zone at the ultrasound frequency using each of the set of phases during repeated application of the first gradient magnetic field;

determine the magnetic resonance signal from the target zone for each of the set of phases;

determine a phase using the set of phases which maximizes the magnetic resonance signal in the target zone; and

store the phase in the memory.

3. The apparatus of claim 1, wherein the resonant frequency modulator is further adapted for controlling the magnitude of the frequency modulation, wherein execution of the instructions further cause the processor to:

generate a set of frequency modulation magnitudes;

modulate the magnetic resonance frequency of molecules in the target zone at the ultrasound frequency using each of the set of frequency modulation magnitudes during repeated application of the first gradient magnetic field;

determine the magnetic resonance signal from the target zone for each of the set of frequency modulation magnitudes;

determine a maximizing magnitude using the set of frequency modulation magnitudes which caused the largest magnetic resonance signal in the target zone; and

store the maximizing magnitude in the memory.

4. The apparatus of claim 3, wherein execution of the instructions further cause the processor to calculate an ultrasound amplitude for the target zone using the maximizing magnitude.

5. The apparatus of claim 1, wherein execution of the instructions further cause the processor to:

generate a set of directions;

modulate the magnetic resonance frequency of molecules in the target zone at the ultrasound frequency using each of the set of directions during repeated application of the first gradient magnetic field;

determine the magnetic resonance signal from the target zone for each of the set of directions;

determine the first direction using the magnetic resonance signal from the target zone for each of the set of directions which maximizes the largest magnetic resonance signal in the target zone; and

store the first direction in the memory.

6. The apparatus of claim 1, wherein the magnetic resonance system further comprises a transceiver system adapted for connecting a radio-frequency antenna for acquiring the magnetic resonance data, wherein the transceiver system is adapted for modulating the frequency and/or phase of radio frequency power generated by the transceiver relative to the proton resonance frequency of atomic spins within the target zone at the ultrasound frequency, and wherein the transceiver is the resonant frequency modulator.

7. The apparatus of claim 1, wherein the magnetic resonance system further comprises a B0 field modulation coil, wherein the magnetic resonance system further comprises a B0 field modulation power supply for supplying the B0 field modulation coil with current, wherein the B0 field modulation power supply is adapted for modulating the current supplied to the B0 field modulation coil at the ultrasound frequency, and wherein the resonant frequency modulator comprises the B0 field modulation coil and the B0 field modulation power supply.

8. The apparatus of claim 1, wherein the magnetic resonance system is a magnetic resonance imaging system.

9. The apparatus of claim 8, wherein the data acquisition zone is any one of the following:

a cell, a volume, or a slice.

10. The apparatus of claim 8, wherein the medical apparatus further comprises a high intensity focused ultrasound system, wherein the high intensity focused ultrasound system comprises an ultrasound transducer for sonicating the target zone, wherein the ultrasound transducer comprises the ultra sound transducer element.

11. The apparatus of claim 9, wherein the apparatus further comprises an ultrasound transducer power supply for supplying alternating current electrical power to the ultrasound transducer, wherein the ultrasound transducer comprises multiple ultrasound transducer elements, wherein execution of the instructions further causes the processor to:

calculate a set of control phases to sonicate the target zone, wherein the set of phases define the phase of alternating current supplied to each of the multiple ultrasound transducer elements;

generate sonication commands using the set of control phases, wherein the sonication commands cause the high intensity focused ultrasound system to sonicate the target zone, wherein the sonication commands are the ultrasound commands;

send the sonication commands to the high intensity focused ultrasound system,

calculate a set of corrected phases in accordance with the repeatedly acquired magnetic resonance data.

12. The medical apparatus of claim 1, wherein the medical apparatus is a nuclear magnetic resonance spectrometer.

13. A method of operating an apparatus, wherein the apparatus comprises an ultrasound transducer element for generating an ultrasonic beam through a target zone of a subject, wherein the ultrasonic beam has an ultrasound frequency, wherein the ultrasonic beam is directed in a first direction through the target zone, wherein the apparatus further comprises a magnetic resonance system for acquiring magnetic resonance data from a data acquisition zone, wherein the target zone is within the data acquisition zone, wherein the magnetic resonance system comprises a resonant frequency modulator for modulating a magnetic resonance frequency relative to a magnetic resonance of molecules in the target zone by the ultrasound frequency, wherein the magnetic resonance system further comprises a magnetic field gradient coil, wherein the method comprises repeatedly performing the steps of:

generating first gradient commands which cause the magnetic field gradient coil to generate a first gradient magnetic field through the target zone, wherein the gradient magnetic field has a gradient direction parallel to the first direction;

modulating the magnetic resonance frequency at the ultrasound frequency during the application of the first gradient magnetic field;

generating ultrasound commands which cause the ultrasound transducer to generate the ultrasound beam during the application of the first gradient magnetic field;

generating second gradient commands which cause the magnetic field gradient coil to generate a second gradient magnetic field through the target zone prior to the acquisition of the magnetic resonance data, wherein the second gradient magnetic field has (i) a polarity opposite to that of the first gradient magnetic field or (ii) the second gradient magnetic field has a polarity equal to that of the first gradient magnetic field and an inversion RF^, pulses is applied between the first and second gradient magnetic field and

acquiring magnetic resonance data from the target zone.

14. A computer program product comprising machine executable instructions for execution by a processor of an apparatus, wherein the apparatus comprises an ultrasound transducer element for generating an ultrasonic beam through a target zone of a subject, wherein the ultrasonic beam has an ultrasound frequency, wherein the ultrasonic beam is directed in a first direction through the target zone, wherein the apparatus further comprises a magnetic resonance system for acquiring magnetic resonance data from a data acquisition zone, wherein the target zone is within the data acquisition zone, wherein the magnetic resonance system comprises a resonant frequency modulator for modulating a magnetic resonance frequency relative to a magnetic resonance of molecules in the target zone by the ultrasound frequency, wherein the magnetic resonance system further comprises a magnetic field gradient coil, wherein execution of the instructions causes the processor to repeatedly:

generate first gradient commands which cause the magnetic field gradient coil to generate a first gradient magnetic field through the target zone, wherein the gradient magnetic field has a gradient direction parallel to the first direction;

modulate the magnetic resonance frequency at the ultrasound frequency during the application of the first gradient magnetic field;

generate ultrasound commands which cause the ultrasound transducer to generate the ultrasound beam during the application of the first gradient magnetic field;

generate second gradient commands which cause the magnetic field gradient coil to generate a second gradient magnetic field through the target zone prior to the acquisition of the magnetic resonance data, wherein (i) the second gradient magnetic field has magnetic field has a polarity opposite to the first gradient magnetic field or (ii) the second gradient magnetic field has a polarity equal to that of the first gradient magnetic field and an inversion RF pulses is applied between the first and second gradient magnetic field and

acquire magnetic resonance data from the target zone.