DISPOSABLE CALIBRATION TARGET
This application is a continuation-in-part of U.S. patent application Ser. No. 08/904,766, filed Dec. 16, 1997, which in turn is a continuation-in-part of U.S. patent application Ser. No. 08/621,182, filed Mar. 21, 1996 now abandoned, which in turn is a continuation-in-part of U.S. patent application Ser. No. 08/587,949, filed Jan. 17,1996 now U.S. Pat. No. 5,860,421. The contents of all three parent applications are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an infection shield and a calibration or reference device for calibrating a measuring instrument or serving as a reference target. The invention also relates to methods of taking a reading or measurement of a patient or an object using the calibration or reference device.
2. Background of the Related Art
There are a variety of measuring instruments that utilize light to detect physical characteristics or conditions of a material. Some instruments are used by medical personnel to diagnose a condition of a patient.
In the case of medical instruments, the instrument will emit light at one or more wavelengths, and the emitted light is directed toward a target tissue on a patient. Reflected or scattered light that returns from the target tissue, or possibly fluorescent light generated by the target tissue in response to the emitted light, is then collected by the medical instrument and analyzed to determine characteristics of the target tissue, or a condition of the patient.
An example of such a medical instrument is shown in FIG. 1. The instrument 100 includes a trigger 102 for activating the device. When activated, the device emits light at one or more wavelengths from a nose portion 104. Light that is reflected or scattered from the patient is then collected by the nose portion 104 and analyzed to determine a condition of the patient.
Instruments like the one shown in FIG. 1 may require periodic calibration to maintain their accuracy. Over time, the amplitude and/or wavelength of light output by the light source within the instrument can vary due to environmental conditions, or simple aging of the light emitting elements. In addition, a detector of the instrument can have differing sensitivities depending upon environmental conditions or the age of the detector. For instance, a change in temperature of only a few degrees can significantly affect the sensitivity of a light detector.
For the above reasons, it is common to calibrate a medical instrument prior to taking a reading on a patient. Typically, the instrument is aimed at a calibration target having known optical properties. Light is then scattered or reflected by the calibration target and received back in the instrument. Because the calibration target has known optical properties, the instrument is able to perform a calibration operation to ensure that the instrument continues to deliver accurate results.
Also, some measuring instruments use a reference target as part of a measurement process. In such a device, the instrument is aimed at a reference target having known optical properties. Light from the instrument is scattered or reflected from the reference target, and a reading is taken. The results of the measurement operation conducted on the reference target can then be used as a standard or reference against which patient measurements are judged. For
instance, the result of a patient reading could be derived by determining a difference or ratio between a patient reading and a reading of the reference target. Because the optical properties of the reference target are known, variations in
5 light output or detector sensitivity can be accounted for by use of the reference target.
When such an instrument is used with human or animal patients, steps must be taken to ensure that use of the instrument does not contaminate or infect a patient. When
1° the instrument is successively used to examine two different patients, steps must be taken to ensure that there is no cross contamination between the patients.
SUMMARY OF THE INVENTION
15 The invention is a device and method that can be used to calibrate or reference a measuring instrument for purposes of taking a measurement. When the instrument is for medical diagnostic purposes, the device may include a shield to prevent patient contamination or infection. In some
20 embodiments, the device may comprise both an infection shield and a calibration or reference target with known optical properties integrated into a single unitary element. A device embodying the invention is configured to be
25 attached to the operative end of a measuring instrument. Once attached, the instrument may perform one or more measurement cycles using a calibration or reference target of the device having known optical properties. After a calibration/reference operation has been successfully
3Q performed, the target is removed while an infection shield of the device remains attached to the instrument to prevent contamination or infection. The device can then be used to carry out a measurement or examination of a patient or a material.
35 In a preferred embodiment, the device is configured such that removal of the target irrevocably destroys the portion of the target used to perform a calibration or reference operation. As explained more fully below, when such a device is used with a medical instrument which is configured to
40 perform only a single patient reading after each calibration/ reference operation, use of the device can help to ensure that patients are not contaminated or infected, and that no cross-contamination between patients is possible.
A method embodying the invention utilizes the calibration
45 or reference target to calibrate a measuring instrument or to provide a reference reading prior to taking an actual measurement on a patient or an object. Then, a measurement is taken on a patient or object. The results of the calibration/ reference measurement, and the results of the patient/object
50 measurement are used together to calculate a result.
In one method embodying the invention, a reference target is first attached to an output end of a measuring instrument. A first measurement is then taken with a light source of the measurement instrument turned off. This is
55 called a dark reference reading. Next, a measurement is taken on the reference target with the light source turned on. This is termed a reference reading. The reference target is then removed from the measurement instrument, and a first measurement is conducted on a patient or an object with the
60 light source of the instrument turned off. This is termed a dark object reading. Next, a patient or object measurement is conducted with the light source turned on. This is termed an object reading. A ratio is then created with a difference between the object reading and the dark object reading in the
65 numerator, and a difference between the reference reading and the dark reading being in the denominator. By creating a ratio of the differences, any variation in the light output of