In cryosurgical probes of a type now undergoing development, the flow of coolant (typically, liquid nitrogen) would be regulated by magnetostrictively actuated needle valves controlled by use of superconductive electromagnet coils. In comparison with cryosurgical probes now in use, the developmental probes would be smaller and lighter, and would afford better regulation of temperature. This concept is made feasible by two recent advances:
- Research at NASA's Jet Propulsion Laboratory has shown that reliable magnetostrictive cryogenic actuators can be manufactured relatively inexpensively by making actuator elements from commercial-grade magnetostrictive polycrystallike materials through a simple deformation process.
- Solenoids made from high-temperature superconductors, in the size and actuating-current ranges needed for cryosurgical probes, have recently become available in research quantities and are becoming commercially available.
Cryosurgical probes are used in some abdominal surgery and in prostate surgery to remove tumors. The basic concept in cryosurgery of the prostate is to place a probe in contact with the tumor, then use the probe to kill the tumor by freezing it. To freeze the affected prostate tissue to a fatal temperature without excessively damaging adjacent tissues, it is necessary to have a high cooling rate and to turn the cooling on and off at the proper times. Such thermal control is difficult to achieve in current cryosurgical probes and, as a result, adjacent tissues are damaged.
The main reason for the difficulty of thermal control in a current cryosurgical probe is that the valve that controls the flow of coolant is located near the coolant supply, and not in the probe. The approach taken in the present development effort is to exploit the inherent capability for miniaturization of a magnetostrictively actuated needle valve, placing the valve inside a cryosurgical probe within 1 or 2 cm of the tip. Thus, a small, rapidly controllable valve would be placed close to the location to which the cryogen is required to be delivered, making it possible to achieve better control over the timing and the rate of cooling. Moreover, the placement of the valve near the probe tip would make it possible to use narrower coolant-supply tubes with thinner insulation, so that the probe could be made smaller and lighter.
This work was done by Jennifer Dooley, Christian Lindensmith, and Robert Chave of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Physical Sciences category.
NPO-20575
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Magnetostrictively Actuated Valves for Cryosurgical Probes
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Overview
The document discusses advancements in cryosurgical probes, particularly focusing on the development of magnetostrictively actuated valves that enhance the precision and effectiveness of cryosurgery, especially for prostate and abdominal surgeries. Traditional cryosurgical probes face challenges in thermal control, which can lead to damage of adjacent tissues during procedures aimed at freezing and killing tumors. The primary issue arises from the location of the coolant flow control valve, which is typically situated far from the probe tip, making it difficult to regulate the cooling rate effectively.
Recent research at NASA’s Jet Propulsion Laboratory (JPL) has led to the creation of a new type of cryosurgical probe that incorporates a magnetostrictively actuated needle valve positioned close to the probe tip. This innovative design allows for better control over the flow of coolant, typically liquid nitrogen, enabling rapid adjustments to the cooling rate. The proximity of the valve to the point of cryogen delivery significantly improves thermal regulation, reducing the risk of damage to surrounding healthy tissue.
The document highlights two key advancements that make this development feasible: the availability of low-cost, reliable cryogenic actuators made from commercial-grade magnetostrictive materials, and the recent progress in high-temperature superconducting solenoids. These technologies allow for the creation of smaller, lighter probes that are easier for surgeons to handle, thereby improving the overall surgical experience.
The authors, Jennifer Dooley, Christian Lindensmith, and Robert Chave, emphasize that the new design not only enhances the precision of cryosurgery but also addresses the limitations of existing technology, which often results in complications for patients. By integrating the valve directly into the probe, the system becomes more manageable, allowing for narrower coolant supply tubes and thinner insulation, further contributing to the reduction in size and weight of the probes.
In summary, the document presents a significant technological advancement in cryosurgical probes, promising improved outcomes for patients undergoing tumor removal procedures. The innovative use of magnetostrictively actuated valves represents a leap forward in the field of cryosurgery, with the potential to enhance surgical precision and patient safety.
