Microwave Ablation Applicator Shaft Cooling via Return Apertures
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Solution Overview
Problem
Microwave ablation applicators face challenges in achieving a narrow and lightweight shaft with high stiffness while ensuring non-conductive materials are used to prevent interference with microwave energy radiation, as carbon fibre reinforced plastics (CFRP) are electrically conductive and unsuitable for attachment to the antenna assembly.
Innovation Solution
A shaft assembly with a coolant delivery tube that includes return apertures along its side wall, allowing controlled fluid flow to manage temperature distribution and prevent overheating or undercooling, ensuring the applicator tip and shaft are cooled appropriately without interfering with microwave energy transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If carbon fibre reinforced plastics (CFRP) are used for the shaft to achieve narrow diameter and high stiffness, then the shaft becomes narrower and stiffer, but the carbon fibres become electrically conductive and interfere with microwave energy radiation
Solution Approach 1:
The patent extracts the problematic carbon fibres from the shaft structure by replacing the CFRP material with a non-conductive composite material in the shaft region adjacent to the applicator tip. This allows the shaft to maintain structural integrity while eliminating electrical conductivity that would interfere with microwave energy radiation from the antenna assembly.
Solution Approach 2:
The patent applies different material properties to different regions of the shaft. The shaft has a first region further from the applicator tip that can use CFRP for high stiffness, and a second region adjacent to the applicator tip that uses a non-conductive composite material to prevent electrical interference with the antenna assembly, thus achieving local optimization of material properties.
2Length of moving object
If the shaft is made narrow and lightweight to improve patient comfort and minimally-invasive characteristics, then the overall diameter is reduced, but the shaft stiffness decreases
Solution Approach 1:
The patent uses composite fibre-resin materials (FRP) for the shaft construction, combining materials with different properties to achieve both narrow diameter and adequate stiffness. The shaft is constructed as a composite structure that provides the necessary mechanical strength while maintaining a compact, minimally-invasive profile for patient comfort.
3Temperature
If coolant flow is increased to improve cooling of the applicator tip and shaft, then temperature control improves, but the complexity of the coolant delivery system increases
Solution Approach 1:
The patent employs a porous structure in the coolant delivery tube that allows coolant to flow through it and cool the applicator tip and shaft. The porous material provides distributed cooling pathways, enabling effective temperature control through passive flow distribution without requiring complex active flow control mechanisms, thus reducing system complexity while maintaining effective cooling.
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
This design achieves improved temperature control, reducing unwanted tissue ablation and damage by maintaining optimal cooling of the applicator tip and shaft, while maintaining the necessary stiffness and narrow diameter for effective microwave energy delivery.
Implementation Method 1
a coolant delivery tube having a side wall which defines an elongate hollow interior, the coolant delivery tube extending along the inner volume of the shaft, coaxial therewith, the coolant delivery tube having a first end towards the first end of the shaft for reception of coolant fluid therein, and a second end towards, and spaced from, the second end of the shaft
Data Source
AI summary
A shaft assembly for a microwave ablation applicator which includes a shaft assembly and an antenna assembly located within the shaft assembly is disclosed. The shaft assembly comprises an elongate shaft which extends from a first end to a second end thereof, and which defines therein a hollow inner volume and a longitudinal axis of the antenna assembly, and an applicator tip mounted on the second end of the elongate shaft. The shaft assembly further includes a coolant delivery tube having a side wall which defines an elongate hollow interior.