Infrared endoscope with sensor array at the distal tip

Details Infrared endoscope with sensor array at the distal tip Infrared endoscope with sensor array at the distal tip

2000-10-25

2003-11-25

Robinson, Daniel (Department: 3742)

Surgery

Endoscope

Having flexible tube structure

Reexamination Certificate

active

06652452

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
Aspects of the invention relate to an infrared detection device including an endoscope with an array of infrared radiation detecting elements mounted at the distal end. The infrared array is sensitive at e.g. wavelengths from two to fourteen micrometers. An endoscope is a probing device used to gain access, for example visual access, to an interior cavity of a body through a relatively small hole or access channel. Examples of endoscopes used in medical applications include arthoscopes, laparoscopes, cystoscopes, bronchoscopes, etc. A preferred embodiment of the invention uses a two-dimensional array of microbolometer sensor elements packaged in an integrated vacuum package and co-located with readout electronics on the distal tip of an endoscope. An endoscope with an infrared sensing array can be used to accurately measure relative and absolute temperatures in e.g. medical, industrial, law enforcement, and other applications.
2. Description of Related Art
The electromagnetic spectrum includes ultraviolet (wavelengths from 0.1 to 0.4 micrometers), visible (from 0.4 to about 0.75 micrometers), near-infrared (From 0.75 to 1.2 micrometers), mid-infrared (from 2 to 5 micrometers) and far-infrared (from 8 to 14 micrometers). All materials at temperatures above zero degrees Kelvin emit infrared radiation. Most naturally occurring terrestrial objects have peak infrared emissions in the 8 to 14 micrometer range. Hot objects, such as jet engines, have peak infrared emissions in 3 to 5 micrometer range.
Early IR imaging systems developed in the 1970s and 1980s were unwieldy and did not lend themselves well to many applications. Physically large and technically complex, they required expensive liquid nitrogen or similar cryogenic cooling systems. IR imaging systems have been slow in delivering greater operational flexibility because of the cost, size, and weight of the cryogenic cooling components used in prior generations of high-performance IR sensors, and because of the size and power consumption of the supporting electronics.
In the early 1990s a revolutionary suite of imaging radiation sensors was developed (see U.S. Pat. Nos. RE036615, 6,114,697, 5,554,849, and 5,834,776, all of which are incorporated herein by reference). These sensors were revolutionary because they are mass-producible from materials such as low-cost silicon and they operate well at room temperatures (hence termed “uncooled”).
Uncooled IR sensors, such as of the microbolometer type that Honeywell has invented, typically consist of arrays of microscopic bridge-like structures micromachined from silicon. Given the extremely low mass of the microbridge structures (typically on the order of a nanogram), they respond to very low radiation levels. Accurate measurements of microbridge temperature changes are used to quantify incident IR radiation. Common methods for measuring microbridge temperatures include the use of thin-film thermocouples to generate a thermoelectric (TE) signal, or the use of thin-film resistors that undergo resistance changes according to temperature.
The basic operating principle of an uncooled silicon IR detector is as follows. Infrared energy emitted from the target object is focused onto an extremely low mass microstructure. The incident energy is absorbed by the microstructure and causes an increase in the temperature of the bulk of the material. This temperature rise can be exactly correlated to the temperature at the optically corresponding point on the target. Honeywell's uncooled IR imaging sensors consist of arrays of microscopic (typically 0.05 mm wide and 0.001 mm thick) bridge-like structures “micromachined” into silicon wafers by photolithographic processes similar to those used to make microprocessors. Calculation of the heating of microbolometers produced by focused IR radiation can be made using the well-known physical laws of radiation, and we find that such microbolometers can measure temperature changes in a remote object with sensitivity well below 0.1 C.
For best sensitivity, microbolometer arrays should operate in an air pressure of 50 mTorr or less in the vicinity of the pixels, to eliminate thermal loss from the pixel to the air. To minimize size and weight and production costs, Honeywell has developed and patented (U.S. Pat. No. 5,895,233, incorporated herein by reference) a process allowing the completed array to be have an infrared-transparent silicon top cap hermetically attached, to form an all-silicon integrated vacuum package (IVP). This technique allows a microbolometer imaging array to have small dimensions. Existing microbolometer packages require a vacuum-sealed package around the outside of the microbolometer, resulting in larger diameters. Arrays are typically close-packed across the wafer, with a very small spacing to allow wafer sawing to separate completed arrays.
Since the sensors are fabricated using silicon photolithography, it is cost effective to fabricate large one-dimensional (1D) and two-dimensional (2D) arrays complete with monolithic silicon readout electronics if required for a particular application. Two-dimensional arrays of IR sensors may be used with an IR-transmitting lens to produce a 2D temperature map of a target, analogous to the way a visible camera produces a two-dimensional image of a target.
Other methods have also been developed to construct arrays of infrared radiation detectors, including the use of pyroelectric detector elements, p-n junction devices, microcantilevers, or photoconductive or photovoltaic bandgap materials.
Recent advances in minimally invasive surgery, for example techniques that utilize heat treatment, have resulted in a need to monitor tissue temperatures with increased accuracy. Heat treatment procedures involve, but are not limited to, the use of lasers, radio frequency (RF) devices, and ultrasonic heating methods that are typically applied using an endoscope. An example of the use of heat treatment is in the destruction of internal cancerous tumors. The challenge is to monitor the temperature of the treatment area while the heat is being applied to avoid overheating surrounding tissue and causing irreparable damage. Current methods for monitoring heat treatments include looking for visible color changes in the tissue with a visible light endoscope and the use of thermocouples on the end of an endoscope. Tissue temperatures may be monitored using infrared detectors.
The use of a visible-light imaging array on the distal end of an endoscope is well established, for example using a silicon solid-state array called a charge coupled device (CCD). Methods and devices are taught for example in U.S. Pat. Nos. 4,971,035, 5,305,736, 5,827,190, 4,918,521, 4,868,644, 5,051,824 and 6,019,719, all of which are incorporated herein by reference. U.S. Pat. No. RE035076, incorporated herein by reference, discloses that an IR filter can be used with a CCD camera on an endoscope to sense in the near-IR range. However, such a system is limited to near IR (wavelengths from 0.75 to 1.2 micrometers). The near-IR image does not have the utility for monitoring temperatures as does mid-IR and far-IR.
The prior art also has taught the construction of endoscopes capable of making IR measurements in the mid-IR and far-IR ranges. One approach is to use a series of germanium lenses (germanium is transparent to IR radiation; glass is not) in a rigid endoscope to relay IR radiation from the distal end to an external IR camera (U.S. Pat. Nos. 5,833,596, 5,711,755, and 5,944,653, all incorporated herein by reference). A second approach is taught by U.S. Pat. No. 5,445,157, incorporated herein by reference, wherein an infrared transmitting fiber of chalcogenide or fluoride glass relays IR radiation from the distal end of a flexible endoscope to an external IR camera.
Conlan et al. (WO 98/32380), incorporated herein by reference, teach a single-point articulating thoracic endoscope where the imaging assembly is a thermal imaging assembly.
The construction of infrared sensitive arrays typ

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