Ultrasonic thermal ablation probe
Inventors
Canney, Michael • BOUCHOUX, Guillaume • Vignot, Alexandre • Lacoste, Francois
Assignees
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Publication Number
US-11135455-B2
Publication Date
2021-10-05
Expiration Date
Abstract
The present invention relates to an ultrasonic probe for heating, internally, an ultrasonically absorbent target medium, the probe comprising: at least one piezoelectric transducer (21) having a front face (212) intended to be positioned facing the target medium and a back face (211) opposite the front face (212), the transducer being able to emit at least one primary wave emanating from its front face and at least one secondary wave emanating from its back face, the probe being noteworthy in that it furthermore comprises: a reflector (24) facing the back face (211) of the transducer (21), the reflector (24) being suitable for reflecting the secondary wave emitted by the transducer (21); and a cooling-fluid layer (25) between the transducer (21) and the reflector (24).
Core Innovation
The invention relates to an interstitial ultrasonic hyperthermia/thermal ablation probe for heating, internally, an ultrasonically absorbent target medium. At least one piezoelectric transducer has a front face designed to face the target medium and a rear face opposite the front face. The transducer emits at least one primary wave from the front face and at least one secondary wave from the rear face.
A reflector faces the rear face of the transducer and is designed to reflect the secondary wave emitted by the transducer. A layer of cooling fluid is disposed between the transducer and the reflector. The thickness of the cooling-fluid layer is designed based on the material constituting the cooling fluid, the thickness and the material constituting the reflector, and the nominal frequency of the transducer.
The cooling-fluid layer thickness is selected so that a secondary ultrasonic wave reflected by the reflector and propagating toward the front face interferes constructively with a primary ultrasonic wave emanating from the front face of the transducer. The disclosed design considers constructive interference constraints using wavelength-related relations for the cooling-fluid layer thickness, including quarter-wavelength and half-wavelength relations, and includes prohibited thickness ranges for avoiding near-resonant conditions.
Claims Coverage
The document includes one independent claim, supported by dependent claims that refine the constructive interference and cooling-fluid design using additional parameters and geometric constraints. The main inventive features revolve around emitting primary and secondary ultrasonic waves from a piezoelectric transducer with a rear-facing reflector and selecting a cooling-fluid layer thickness to ensure constructive interference at a nominal transducer frequency.
Ultrasonic probe with primary/secondary wave transducer and rear reflector
An ultrasonic probe for heating, internally, an ultrasonically absorbent target medium, comprising at least one piezoelectric transducer including a front face designed to be positioned facing the target medium and a rear face opposite to the front face, the transducer being capable of emitting at least one primary wave emanating from its front face and at least one secondary wave emanating from its rear face, and a reflector facing the rear face of the transducer, the reflector being designed to reflect the secondary wave emitted by the transducer.
Cooling-fluid layer thickness selected for constructive interference
An ultrasonic probe further comprising a layer of cooling fluid between the transducer and the reflector, wherein the thickness of the layer of cooling fluid is designed based on the material constituting the cooling fluid, the thickness and the material constituting the reflector, and the nominal frequency of the transducer, so that a secondary ultrasonic wave reflected by the reflector and propagating toward the front face interferes constructively with a primary ultrasonic wave emanating from the front face of the transducer.
Acoustic thresholds for cooling and reflection performance
The probe uses electrical excitation to emit ultrasonic waves at a nominal frequency between 3 and 10 MHz, a reflector that reflects at least 80% of the acoustic energy of the secondary wave at the nominal frequency, and a cooling fluid with an acoustic attenuation coefficient below 1 dB/cm (preferably below 0.1 dB/cm) at the nominal frequency.
Quarter-wavelength cooling-fluid thickness with odd multiple
The probe has a reflector material with acoustic impedance greater than 10^7 kg/(m^2 s) and a cooling-fluid layer thickness equal to an odd multiple of one-quarter of the wavelength of a secondary ultrasonic wave in the cooling-fluid material.
Exclusion zone for thickness avoiding odd quarter-wavelength conditions
The probe defines an internal-wall acoustic impedance between 1×10^6 and 10×10^6 kg/(m^2 s), and requires that the internal-wall thickness and cooling-fluid layer thickness are not within ±25% of odd multiples of one-quarter of the wavelength of the secondary ultrasonic wave in the internal-wall material.
Remote pressure control to vary cooling-fluid thickness
The probe further includes a junction box mounted to a remote unit that varies the pressure of cooling fluid within the internal wall in order to vary the thickness of the layer of cooling fluid.
Segmentation of a tubular transducer into piezoelectric elements with longitudinal grooves
The transducer is composed of piezoelectric elements obtained by segmentation of a one-piece tubular transducer by means of a high-power laser or mechanical milling allowing for the formation of longitudinal grooves, the width of the grooves being less than the wavelength of the primary wave, and the sum of the width of the grooves being less than one-eighth of the perimeter of the exterior of the probe.
Overall, the claim set protects an ultrasonic probe that emits a primary wave from a transducer front face and a secondary wave from a rear face, uses a rear-facing reflector to create a reflected secondary wave, and selects a cooling-fluid layer thickness based on cooling-fluid material, reflector material/thickness, and nominal frequency to obtain constructive interference with the primary wave. Dependent claims further specify numerical acoustic thresholds and impedance-related quarter-/half-wavelength thickness rules, including thickness prohibited ranges, plus optional structures for varying cooling-fluid thickness and segmenting a tubular transducer with longitudinal grooves.
Stated Advantages
High electro-acoustic efficiency comparable to an air-backed design while cooling to prevent overheating/vaporization.
Documented Applications
Internally heating an ultrasonically absorbent target medium using an interstitial ultrasonic hyperthermia/thermal ablation probe.
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