Non-invasive sensing of a physical parameter

Details Non-invasive sensing of a physical parameter Non-invasive sensing of a physical parameter

2000-02-16

2001-09-18

Lacyk, John P. (Department: 3736)

Surgery

Diagnostic testing

Detecting nuclear, electromagnetic, or ultrasonic radiation

C600S409000, C600S481000, C600S529000, C600S549000, C600S587000

Reexamination Certificate

active

06292680

ABSTRACT:

TECHNICAL FIELD
This invention is generally directed to a device and method for non-invasively sensing a physical parameter and, more specifically to the monitoring of a magnetically-based sensing device to sense a change in a physical parameter.
BACKGROUND OF THE INVENTION
There are numerous medical devices which are implanted into the body of animals, including humans (hereinafter collectively referred to as “patients”). These devices are resident for periods of time ranging from several days to the lifetime of the patient. Such implanted devices encompass a wide range of applications, including (but not limited to) artificial joints, artificial ligaments, artificial tendons, bone implants, orthotic devices, orthopedic correctional and supporting devices (e.g., screws and braces), shunts, stents, pumps, collection reservoirs, drug delivery depots, temperature sensors, pressure sensors, temporary surgical staples, and the like.
Such implanted devices may be related to one or more changing physical parameters. These changes may be associated with, for example, a feature of the device, a result of a physiological impact on the implanted device, or may be indicative of the success or failure of the implanted device. In this context, representative changing physical parameters include temperature, strain, oscillation, pressure, volume, flow, acceleration, angular momentum, angular velocity, chemical composition, pH, ionic content, changing material characteristics of an anatomical structure or of the implantable, and the like.
There is clinical value in being able to measure certain physical parameters associated with physiological processes and anatomical conditions. This measurement process involves four parts: (1) the sensing of a condition or a changing condition; (2) the transduction of the sensor input to an appropriate energy or signal format; (3) signal conditioning to make the transduced signal suitable for transmission; and (4) the reporting or transmission of the information. There exist systems to address all four parts, though these are usually made of discrete components dedicated to each of the four parts. For example, an implanted thermistor would measure temperature, convert the temperature change into an impedance change, registering a voltage drop, the numerical value of which is transmitted in coded format via dynamic electromagnetic signal. Similarly, an implanted blood pressure monitoring device may consist of an air-filled dome over a silicon-based pressure sensor which converts strain to a change of an electrical parameter. This change is measured, coded, transmitted via high frequency electromagnetic emission. For both examples, a receiver external to the body would register the emitted coded signal, providing decoding, interpretation, and data display.
Certain physiological and anatomical parameters can also be detected by entirely non-invasive means, such as magnetic resonance imaging (MRI), ultrasound, and X-ray techniques. However, these methods have come to rely more and more on the infusion of certain contrast agents in the subject area. Such infusion is an invasive process.
While such sensing and transmission techniques have shown to be effective, there is still a need in the art for improved devices and methods for non-invasively sensing changing physical parameters. The present invention fulfills these needs, and provides further related advantages.
SUMMARY OF THE INVENTION
In brief, this invention discloses a method and device for non-invasive sensing of a physical parameter (or parameters) within the body of a patient by employing a magnetically-based sensing device and a monitoring device. As used herein, the term “non-invasive” means that sensing of the physical parameter is performed without requiring access to or removal of the sensing device, and without physical contact between the sensing device and the monitoring device. (It should be noted, however, that location of the sensing device within the body of the patient typically constitutes an invasive procedure.) Also as used herein, the term “physical parameter” includes (but is not limited to) temperature, strain, oscillation, pressure, volume, flow, acceleration, angular momentum, angular velocity, chemical composition, pH, ionic content, and/or changing material characteristics of an anatomical structure or of an implanted device.
The magnetically-based sensing device of this invention comprises a first magnet and a second magnet in close proximity thereto. The first magnet generates a first magnetic field, the second magnet generates a second magnetic field, and the sum of the first and second magnetic fields generate a combined magnetic field. The first magnet is associated with the implanted device itself, or with tissue (including bone) associated therewith while the second magnet is positioned such that a change in a physical parameter results in displacement of the first and/or second magnet, thus changing the combined magnetic field. Such magnetically-based sensing devices may take a variety of forms, as disclosed in greater detail in the following detailed description.
The monitoring device is any suitable apparatus capable of detecting the combined magnetic field of the magnetically-based sensing device. As mentioned above, changes in the combined magnetic field strength indicate a changed or changing physical parameter. As with the sensing device, the monitoring device may also take a variety of forms as disclosed in greater detail in the following detailed description.
In another embodiment of this invention, a method is disclosed for sensing a physical parameter by associating a first magnet with, for example, an implanted device, and positioning a second magnet in close proximity to the first magnet such that the sum of the first and second magnetic fields yields a combined magnetic field. This combined magnetic field is then monitored, typically over a period of time, to detect changes in the physical parameter of interest.
These and other aspects of the present invention will be better understood upon reference to the following detailed description and accompanying drawings.


REFERENCES:
patent: 5176618 (1993-01-01), Freedman
patent: 5425382 (1995-06-01), Golden et al.
patent: 5622169 (1997-04-01), Golden et al.
patent: 5879297 (1999-03-01), Haynor et al.

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