Electric lamp and discharge devices: systems – Pulsating or a.c. supply
Reexamination Certificate
2001-10-02
2003-07-15
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
C315S056000, C313S570000, C607S088000
Reexamination Certificate
active
06593706
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to arc lamps. More specifically, the invention relates to a high pressure neon arc lamp configured to efficiently produce incoherent light having wavelengths between about 625 nanometers and about 645 nanometers.
2. Relevant Technology
Light is a form of electromagnetic energy. Electromagnetic energy is divided into different spectrums based on the wavelength of the electromagnetic energy. Visible light is one of these spectrums. Within the visible light spectrum, light wavelengths may be identified by color. For example, light having wavelengths between about 625 nanometers and 645 nanometers appear to an observer as red. Electromagnetic energy with shorter wavelengths than visible light comprise the ultra-violet (UV) band of the spectrum. Electromagnetic energy with longer wavelengths than visible light comprise the infrared band of the spectrum.
Producing and using visible light is well understood. For example, it is conventional to produce light of different wavelengths using a variety of techniques such as incandescent, fluorescent, and arc lamps. It is also conventional to split or separate the different colors in light using a prism. Light can also be focused and intensified using conventional laser technology.
Visible light serves some important uses. Light is useful for interior and exterior lighting, traffic signals, tanning of skin, as well as a variety of other uses. Additionally, light is useful in medicine. Concentrated coherent light in the form of lasers provides very precise cutting tools for surgeons.
One field of medicine involves the use of light in a way other than as a high precision cutting tool. Photodynarnic therapy (PDT) is a medical treatment that uses visible light to activate a drug designed to destroy particular cells within a patient's body. PDT is becoming very popular. Generally, PDT involves a two part procedure for treating infectious diseases as well as cancer.
PDT begins by administering to a patient a drug known as a photosensitizer. Photosensitizers are drugs that are specifically engineered to target a particular kind of cell and tissue within the patient. Several photosensitizers are known including proprietary drugs such as Photofrin®. Generally, the photosensitizer is administered by injection. The photosensitizer may enter into, attach to, or surround the targeted cells and/or tissues. By way of example, PDT used to treat cancer involves photosensitizers that enter into the cancerous cells. The administration of the photosensitizer is completely harmless to the patient.
Next, PDT involves illuminating the target tissue, such as cancer cells, with a non-thermal, low powered light. Generally, this light should be red having wavelengths between 625 nanometers and 645 nanometers. Illumination of the target tissue with red light activates the photosensitizer to destroy the target tissue. Conventionally, the light source used is a low power laser.
Light of the red wavelength activates the photosensitizer concentrated in and around the target cells. In cancerous cells, the photosensitizer cooperates with oxygen to create an oxygen free-radical that destroys the cancerous cell. Because the photosensitizer exists primarily in the cancerous cells, the healthy cells remain unharmed. Unlike radiation therapy, PDT may be repeated with little recuperation time required for the patient. PDT may also be used to treat acne, remove unwanted hair, and in other applications. Generally, the effectiveness of PDT treatment depends on the amount of photosensitizer administered and the ability to illuminate enough of the photosensitizer at an appropriate intensity.
Generally, low powered, non-thermal lasers are used to activate the photosensitizer. There are several limitations to using lasers in PDT. Chief among the limitations of low powered, non-thermal lasers is the small area of illumination. Due to the nature of lasers and the manner in which they are generated, a very concentrated and small laser beam is generally created. Consequently, the laser beam has a small illumination area. Techniques exist to diffuse the laser light. However, such diffusion decreases the tissue penetration capability of the laser beam. The laser beam loses intensity. A small illumination area requires that the laser beam make several sweeps of an infected or cancerous area to illuminate the target cells. This increases the time required for treatment and may result in areas of tissue not being illuminated due to human error.
The limitation due to small illumination area is compounded when PDT is used to treat anti-biotic resistant infectious diseases of the skin. These diseases may cover large areas of a patient's skin. Thus, it is difficult to adequately treat these diseased areas using a laser with a small beam area. Effective treatment of the disease using PDT with lasers may require repeated illumination treatments.
Additionally, lasers are relatively expensive because by definition they produce coherent light. Coherent light is light in which all the photons are in phase. The cost is also high due to high power requirements for lasers. The expense used to produce coherent laser light is largely wasted when used for PDT.
PDT requires only a particular wavelength of photons to function. Coherency of the light is not a requirement. The photosensitizer is activated by the wavelength of the light. Generally, photosensitizers are activated regardless of the coherency of the light.
Additionally, lasers are generally very large and bulky in comparison to other medical equipment. Often, the portability of these devices is limited. Generally, the patient must be brought to the laser rather than the laser to the patient. Lasers may also require specialized training to operate.
PDT may also be used with incoherent light sources such as high pressure xenon or krypton arc lamps. A high pressure arc lamp is a lamp that creates light by passing an electrical arc between two electrodes through a specific gas. With high pressure xenon and krypton arc lamps the gas between the electrodes is pressurized to several hundred Torr. The gas is also substantially pure xenon or krypton. Generally, a xenon and krypton arc lamp provides a greater illumination area because the light is diffuse.
Xenon and krypton arc lamps however do not efficiently produce high intensity red light having wavelengths between 625 nanometers and 645 nanometers. The light generated by xenon and krypton arc lamps has wavelengths ranging from red to ultraviolet (UV). The majority of the light photons generated by xenon and krypton arc lamps are in the UV band of the electromagnetic spectrum. To provide the red light needed for PDT, the UV light is filtered out from the xenon and krypton arc lamp's output. UV light is also filtered to avoid burning the tissue of the patient. Because a majority of the light produced by a xenon or krypton arc lamp is filtered, the lamps are generally very inefficient.
Accordingly, what is needed is a high pressure arc lamp that efficiently produces photons in the red band of the electromagnetic spectrum, light having wavelengths between 625 nanometers and 645 nanometers, with minimal power requirements. Additionally, what is needed is a high pressure neon arc lamp that is less expensive to fabricate than conventional laser devices. Further, what is needed is a high pressure neon arc lamp that provides a comparably large illumination area at an operable intensity when compared to convention red light sources such as lasers. Such an invention is disclosed and claimed herein.
SUMMARY OF THE INVENTION
The invention is a high pressure neon arc lamp and method for using the lamp in photodynamic therapy. Conventionally, lasers, and xenon or krypton arc lamps are used in photodynamic therapy to provide a red light to activate photosensitive drugs within a patient to kill cells of cancer or other infectious diseases. However, xenon and krypton arc lamps produce mostly ultra-violet light rather than red
Bigio Irving J.
Sze Robert C.
Alemu Ephrem
Madson & Metcalf
The Regents of the University of California
Wong Don
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