Multi-channel real-time phase modulation for EMI reduction in an ultrasound device
Inventors
Kurtz, Ron • Leonard, Patrick • Zhang, Xiaoyu
Assignees
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Publication Number
US-12128256-B2
Publication Date
2024-10-29
Expiration Date
Abstract
Methods for reducing electromagnetic interference arising from use of multiple ultrasound transducers in an array, particularly inside a human body that is inside a magnetic resonance imaging device. Electrical signals driving the transducers are offset in phase with respect to one another so as to achieve maximum offset of electrical and magnetic fields arising from such signals and transducers. Phase offsets are dynamically adjusted to respond to changes in driving amplitudes and frequencies so as to maintain optimal reduction of electromagnetic interference.
Core Innovation
The invention relates to MRI-guided ultrasound thermal therapy apparatus in which electromagnetic interference is reduced by driving an array of ultrasound transducers with phase modulation. The set of ultrasound transducers are active channels that are electrically driven with driving signals that have a common frequency and individually determined phase angles. Phase modulation is used to reduce harmonic and intermodulation electromagnetic interference that arises from piezoelectric nonlinearity in the transducers.
The core approach determines and sets phase angles θ1…θN for each driving signal based on the driving signal amplitudes A1…AN. The method checks whether one amplitude Am is greater than or equal to the sum of the other amplitudes, and in that case sets the phase of the dominant transducer to 180° while setting all other phases to 0°.
When no amplitude dominates in that way, the method determines a vector P whose elements are either 1 or −1 to select phase relationships that yield a nonnegative scalar product with the amplitude vector [A1…AN], bounded in magnitude relative to other sign-vector possibilities. Using the selected sign vector P, the method defines a vector O whose elements Oi equal the product Pi·Ai, selects two positive elements of O, and defines γ as the absolute value of the sum of the remaining elements of O save those two elements.
The method then determines two phase angles using cosine-based relationships involving the selected elements and γ, and sets all other phase angles according to a cosine relationship based on −1·Oi. The document context further describes multi-channel real-time phase modulation to maximize cancellation of net electric/magnetic fields and to reduce harmonic peaks when out-of-phase behavior is introduced.
Claims Coverage
Independent claim clm-00001 provides the core coverage for reducing electromagnetic interference using determination and setting of phase angles for N ultrasound transducers with equal driving frequencies, with a dominant-amplitude special case and vector-based phase selection using amplitudes. Six additional inventive features are stated in the partial content.
Reducing electromagnetic interference via phase-angle determination for equal-frequency ultrasound transducers
A method of reducing electromagnetic interference arising from a set of ultrasound transducers in a thermal therapy apparatus, the set comprising N transducers, each transducer corresponding to an active channel and being electrically driven with a driving signal at an amplitude, a frequency, and a phase angle, the frequencies of the driving signals being the same for all transducers in the set; determining and setting phase angles θ1…θN; determining the amplitudes A1…AN; determining whether one amplitude Am is greater than or equal to the sum of all amplitudes other than Am and, if so, setting θm=180° and all other θi=0°; and if not, determining a vector P of N elements each either 1 or −1 such that a scalar product of P and the amplitude vector [A1…AN] is nonnegative and is not greater in magnitude than that of any other possible sign vector, defining a vector O with elements Oi=Pi·Ai; selecting two positive elements Oa and Ob; defining γ as the absolute value of the sum of remaining elements of O save Oa and Ob; setting θa and θb using cosine-based expressions in terms of Oa, Ob, and γ; and setting each remaining θi using a cosine relationship based on −1·Oi.
Deploying ultrasound transducers inside a magnetic resonance imaging apparatus
The method further specifies that the array of ultrasound transducers is deployed in a magnetic resonance imaging apparatus.
Applying conformal thermal therapy to a human patient
The method further specifies deploying the array of ultrasound transducers to apply conformal thermal therapy to a human patient.
Updating amplitudes and frequencies by changing the transducer set
The method further specifies updating the amplitudes and frequencies by adding and/or removing one or more ultrasound transducers from the array set.
Using sinusoidal driving signals
The method further specifies that the driving signals are sinusoidal signals.
Determining the sign vector P using an optimization algorithm
The method further specifies that the vector P is determined by applying an optimization algorithm.
Overall, the independent claim centers on reducing electromagnetic interference in an ultrasound transducer array by determining and setting phase angles for equal-frequency driving signals based on relative amplitudes, including a dominant-amplitude special case and otherwise selecting sign-vector-based phase relationships using a vector O, two selected positive components, and γ to compute two phase angles and set remaining phases.
Stated Advantages
Reduces electromagnetic interference arising from the ultrasound transducers, including harmonic and intermodulation electromagnetic interference associated with piezoelectric nonlinearity.
Documented Applications
MRI-guided ultrasound thermal therapy, including reduction of electromagnetic interference in an MRI apparatus using phase modulation of a multi-channel ultrasound transducer array.
Conformal thermal therapy applied to a human patient using the ultrasound transducer array in the thermal therapy apparatus.
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