Variable Length Antenna for Microwave Tissue Ablation
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Solution Overview
Problem
Microwave ablation probes face inefficiencies due to fixed resonant frequencies, leading to energy reflection and self-heating, as the resonant frequency of the antenna does not match the changing tissue properties during ablation, especially with temperature changes.
Innovation Solution
A microwave ablation probe with variable antenna parameters, including adjustable lengths of the radiating portion, arm, cap, and choke, allowing the antenna to operate at multiple resonant frequencies, ensuring efficient energy transmission across a range of tissue types and temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the antenna operates at a fixed resonant frequency, then the probe structure is simple, but energy reflection and self-heating occur when tissue properties change with temperature
Solution Approach 1:
The antenna structure is made dynamically adjustable through a mechanism that allows the radiating element length to be changed during operation. This enables the resonant frequency to be tuned in real-time to match changing tissue properties, resolving the contradiction between maintaining reliable energy transmission and avoiding the complexity of multiple fixed-frequency antennas.
Solution Approach 2:
The physical parameter of the antenna (radiating element length) is made variable to change the resonant frequency. By adjusting the length parameter, the antenna can adapt to different tissue types and temperature conditions, maintaining energy transmission efficiency without requiring a complex multi-antenna system.
2Adaptability or versatility
If the antenna length is fixed, then the manufacturing is simple, but the resonant frequency does not match changing tissue properties during ablation
Solution Approach 1:
The antenna is divided into adjustable segments or sections that can be reconfigured to change the effective radiating length. This segmentation allows the same basic structure to be manufactured simply while providing post-manufacturing adjustability to match different tissue properties, resolving the contradiction between adaptability and manufacturing ease.
Solution Approach 2:
The antenna incorporates a dynamic adjustment mechanism that allows the radiating element length to be modified after manufacturing. This maintains simple manufacturing processes while enabling adaptability to different tissue types and ablation conditions through real-time parameter adjustment.
3Temperature
If the antenna operates at high temperature, then faster heating and larger lesions are achieved, but the resonant frequency shifts away from the working frequency
Solution Approach 1:
A feedback mechanism is implemented that monitors the temperature or frequency deviation of the antenna during operation. Based on this feedback, the system automatically adjusts the radiating element length to maintain resonant frequency alignment with the working frequency, even as temperature changes. This resolves the contradiction between achieving high ablation temperatures and maintaining frequency matching.
Solution Approach 2:
The antenna length is made dynamically adjustable in response to temperature changes. As the ablation progresses and temperature increases, the system adjusts the radiating element length to compensate for frequency shifts, maintaining reliable energy transmission at high temperatures without frequency mismatch.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The variable parameter antenna maintains effective microwave energy transmission into tissue across varying temperatures and tissue types, reducing self-heating and improving ablation performance by aligning resonant frequencies with the working frequency over a wider temperature range.
Implementation Method 1
Microwave ablation energy causes water molecules to rotate due to the polarity of the molecules and generates heat due to hysteresis
Implementation Method 2
the resonant frequency of the antenna does not match the changing tissue properties during ablation, especially with temperature changes
Data Source
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AI summary
The present invention relates to a microwave ablation probe comprising: a probe body comprising a shielded portion and a radiation window that is at least partially transparent to microwave energy, wherein the shielded portion of the probe body comprises a metal cannula; a coaxial cable within the probe body comprising: a center conductor, a dielectric material surrounding the center conductor of the cable, and an outer conductor having an outer conductor distal boundary, wherein the center conductor comprises a radiating portion that extends beyond a distal boundary of the outer conductor, wherein the radiating portion is configured for emission of microwave energy, wherein the radiating portion is aligned with the radiation window; a cap located at a probe distal end, the cap comprising a cap proximal boundary; wherein the outer conductor distal boundary or the cap proximal boundary varies in its distance from the probe distal end; and a choke comprising: a choke contact between the metal cannula and the outer conductor, and a choke length extending between the choke contact and a distal end of the metal cannula, wherein the choke contact varies in its distance from the probe distal end.