Surgery – Diagnostic testing – Measuring or detecting nonradioactive constituent of body...
Reexamination Certificate
2002-04-09
2004-03-23
Winakur, Eric F. (Department: 3736)
Surgery
Diagnostic testing
Measuring or detecting nonradioactive constituent of body...
C600S478000, C362S572000
Reexamination Certificate
active
06711426
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to illumination devices and systems for providing a high efficiency of broadband light delivery to thermally-sensitive or spatially-constrained environments, and more particularly relates to the embedding of a light source comprised of a white, conversion-efficient, narrow-angle, light emitting diode with integrated collimating and light collection optics into a medical catheter for indwelling gastrointestinal placement for the purpose of performing real-time in vivo tissue oxygenation measurements of mucosal surfaces via visible wavelength optical spectroscopy, thus avoiding some of the cost, risk, light level limitations inherent in conventional illuminator systems.
BACKGROUND OF THE INVENTION
The traditional broadband light sources for optical spectroscopy in the near UV, visible, and/or near-infrared wavelengths are the fluorescent, incandescent, and arc-lamp bulbs. Typically, spectroscopy bulb is optically coupled to the test sample via gratings, lenses, fibers, and/or free-space transfer. However, such traditional light sources have significant native disadvantages, including that: (a) they produce their light rather inefficiently, wasting a large proportion of the power supplied to them as heat and unusable wavelengths of light. This is a drawback in devices where significant local heating (such as medical devices in contact with tissue) or high power consumption (such as battery operated devices for field use) are undesirable or unacceptable, and (b) they emit light over a wide spherical angle from non-point sources, rendering inefficient any attempts to direct their light either onto spectroscopy samples (such as living tissue) or into optical delivery systems (such as fibers coupled to test samples), which in turn further raises heat production and power consumption for any desired level of sample illumination.
These limitations are best appreciated by example. First, with specific regard to the production of large amounts of heat, conventional bulbs are inefficient at best. The visible light output from a conventional incandescent light bulb represents only 4% of the total power consumed by the bulb. This conversion efficiency rises to only 14% for so-called high-output halogen lamps (though the improved efficiency results in accelerated drift and bulb aging). These efficiencies can easily drop farther, by a factor of 5 or more, if one considers only in-band light used in spectroscopic analysis (e.g., a 500-600 nm light band for hemoglobin analysis) in determination of the conversion efficiency.
The physical reason for this meager rate of energy conversion is that tungsten filaments, as well as heated arc lamp electrodes, operate as blackbody thermal radiators, and thus radiate mostly infrared radiation, plus a small component of UV radiation, at any temperature they can withstand. While in theory an ideal blackbody radiator produces visible light most efficiently at 6,600 K (11,500° F.), nothing known in the art remains solid for use as a filament at this temperature, which exceeds the temperature at the sun's surface. Even so-called “high-efficiency” projection-type halogen lamps must therefore operate far below this ideal temperature, often operating instead from 2,700 K to 3,500 K (just below Tungsten's melting point of 3,683 K). As a result, such bulbs typically require 6.9 W of power to produce 5.9 W of heat, in addition to 1.0 W of light.
Such poor conversion efficiencies result in a high degree of unwanted thermal output, making conventional bulbs run hot, and in turn preventing close illumination of the sample and often relegating bulb-based light sources into fiber-coupled hot, external, fan-cooled boxes.
Second, with regard to the broad spatial emission, conventional bulbs typically produce light in all directions in the absence of mirrors or lenses—that is, relatively uniformly over a full 4&pgr; spherical angle. Further, because a filament has a length and width, the light can no longer be focused to a point. This broad spatial emission typically makes a direct coupling of light from a conventional bulb onto a sample, or into an optical guide, inefficient. For illustration, consider a 1 cm diameter spherical bulb in which light from the bulb's filament radiates evenly in all directions. The glass surface resides approximately 5 mm from the filament in all directions, for a surface area of the glass sphere of 4/3*&pgr;*r
2
, or 105 mm
2
. The portion of this uniform field of radiated light reaching a 1 mm diameter sample, placed up against the bulb glass, measures only 0.79 mm
2
. Thus, this tiny sample intercepts (and is thus illuminated by) only 0.2% of the total light output from the bulb, as given by the ratio (0.79 mm
2
/105 mm
2
), with 99.8% of the bulbs output wasted. The less compact a lamp's source, the more difficult it becomes to focus and guide its light. This is especially true for UV fluorescent lamps, where focusing losses are far higher than for a halogen bulb.
Further, the surface temperature of a halogen bulb often exceeds 120° C. making a close approximation of a hot bulb and sample not wise or practical in many cases, especially if the sample is living or fragile. Moving the sample away from the bulb, in order to spare the sample from heating, only worsens the inefficiencies described above. Nor is the situation improved by separating the bulb and sample using optical fiber. Directly attaching an optical fiber to the glass or quartz surface of 1 cm diameter bulb discussed above (such as by using optical glue) allows the fiber to intercept and capture only those photons striking the face of the fiber. A fiber measuring only 100 microns in diameter has a tiny face area measuring just 0.0079 mm
2
. Thus, a 100 micron fiber, glued to the bulb 5 mm from the filament, collects only 0.002% of the bulb's emitted light, as given by the ratio (0.0079 mm
2
/105 mm
2
). Even if the diameter of the fiber in this example were to be enlarged 10 fold, this transfer ratio would rise to only 0.2% of the bulb's visible light output that is intercepted and transmitted to the sample, again with 99.8% of the bulbs output lost and wasted.
All told, when taking into consideration both of the above limitations, the poor conversion efficiency of energy to light and the poor transfer efficiency of light to the sample, only 0.0003% of the energy flowing into the 1 cm bulb discussed above ends up converted to visible light, captured, and successfully transmitted by a fiber to a tissue sample, for more than 99.9997% of the total light wasted. Here, we term the 0.0003% figure of merit the delivered efficiency. Another way of expressing how poor this net delivered efficiency is, in fact, is that for the preceding bare-fiber-to-bare-bulb example, 369,524 watts of energy would have been required by the bulb for each watt of light delivered to sample or tissue, with the remainder released and lost as heat. These limitations of conventional sources are apparent in the art.
Broadband lamp sources or lamp designs are known, and are used for spectroscopy. Most art regarding illumination sources for spectroscopy suggest devices or methods that describe conventional light sources, although some describe more exotic lamp sources (e.g., U.S. Pat. No. RE. 29,304). White LEDs are known (e.g., U.S. Pat. No. 6,252,254, WO 01/01070), however none are suggested as spectroscopic light sources, and their high conversion efficiency, narrow angle of emission, and optical stability have not been cited nor exploited for spectroscopy purposes, especially in medicine for in vivo uses, save merely that they have been mentioned in passing for the purpose of general non-spectroscopic endoscopic illumination (U.S. Pat. No. 6,251,068). Several schemes for reducing heat production or for transmitting light to a sample are known (e.g., such as light conducting rods in U.S. Pat. No. 5,974,210), but none with the purpose of improving the efficiency of delivery, nor are these sources specifically designed to operate
Benaron David A.
Parachikov Ilian H.
Spectros Corporation
Winakur Eric F.
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