Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
1999-06-22
2002-07-16
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
C372S034000, C372S098000, C372S032000
Reexamination Certificate
active
06421361
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The field of this invention is diode laser systems for medical applications, in particular, tunable diode systems with interchangeable laser diode cartridges and recognition capabilities.
2. Invention Disclosure Statement
PhotoDynamic Therapy (PDT) is the activation of a pharmaceutical agent in the human body by a selected dose of a selected wavelength of radiation. PDT is gaining importance both for cancer and non-cancer applications. Typically, this therapy begins with the application of a photosensitizer (photoactive drug) that may be orally ingested, topically applied, injected, or intravenously introduced to a treatment site. After a suitable time interval depending on certain properties of the photosensitizer, radiation energy in a suitable wavelength band is selectively applied for a predetermined duration and intensity to the target site.
The basic concept of PDT is that certain molecules function as photosensitizers that absorb light of certain wavelengths. If light energy of the proper wavelength is delivered to the photosensitizer, it stores the energy from the photons by increasing its energy to a higher level called a triplet state. Inside the human body, some of the excited photosensitizer molecules transfer the stored energy to nearby oxygen molecules, exciting them to a higher energy level called a singlet state. Singlet oxygen is a highly reactive molecule that rapidly oxidizes essential cellular components that surround it, and in a living cell this oxidation causes necrosis.
PDT is a desirable form of treatment because it allows for treatment of very extensive tumors and growths without damaging healthy tissue to the extent of chemotherapy or radiation therapy. Most commonly, photosensitizers used in PDT consist of a hematoporphyrin derivative (HpD) such as porfimer sodium, or Photofrin. Although the mechanism of HpD's preferential location in malignant cells is uncertain, the total time that the derivatives are retained in the malignant tissue is much longer than in nonmalignant tissue, where it generally clears within 24-72 hours. As a result, there is a “window” of time in which the physician can exploit the differences in HpD concentrations to cause selective photodegradation of malignant tissue.
After photosensitizer administration, a delay of 24-72 hours allows for HpD to be expelled from healthy tissue, and the malignant tissue is irradiated with visible red light tuned to approximately 630 nm. Shortly after administering treatment, the tumor becomes necrotic and, when effectively treated, the tumor becomes a nonpalpable scab that is usually sloughed off within a few days. A high therapeutic ratio and relative lack of morbidity have made PDT a very attractive form of therapy.
Lasers have traditionally provided the preferred form of optical radiation to activate photosensitizers. To be used in medical applications, however, photosensitizers must be approved by the FDA in conjunction with a laser system and/or laser wavelength. This means that hospitals and other end users must purchase a new and different laser system for each photosensitizer that it wishes to activate, unless the laser system is tunable. This is the reason that inexpensive diode lasers have not been used in PDT applications, i.e. because their wavelength is fixed. Therefore, primarily because of tunability, costly dye laser systems have traditionally been used in this application.
Dye laser systems possess the desirable characteristic of being continuously tunable over a very broad range to emit radiation at different wavelengths. Dye laser systems, however, have several critical disadvantages. In addition to being expensive, dye laser systems are inefficient, large, complicated in operation, and difficult to maintain. Dye lasers use a dye solution as the active medium. The problem that ensues is that the dye solution is consumed in the lasing process. To solve this problem, ways of replenishing the dye solution were developed, such as reservoirs and fluid transport systems. Such replenishment systems, however, are also problematic. Firstly, a dye laser system, including fluid transport, can require a great deal of space. In fact, entire rooms in hospitals are often dedicated to the operation of such systems. The fluid transport system also may be awkward in terms of emptying old fluid and adding new chemicals. Another problem with dye laser systems is that they are inefficient. This is due to a two-step power conversion process. First, electricity must be coupled with a high intensity light source to be converted into optical energy. Second, optical energy emitted from the high intensity light source must activate the dye solution before laser light is generated for practical use. These steps are lossy. As a result, dye laser systems use significantly more energy per output watt than diode laser systems. Also, dye laser systems have a shorter life span than diode lasers.
Diode lasers possess many advantages when compared to dye lasers. They are efficient, inexpensive, easy to operate and maintain, and compact. However, the wavelength emitted by a diode laser is practically fixed due to its composition, with only minor tuning possible through adjustment of operating temperature. For example, temperature tuning can give up to 5 nm of tuning range. But, to activate a broad range of PDT compounds, a tuning range of roughly 200 nm, from 630 nm to 800 nm, is necessary.
Thus, the ideal laser for PDT applications, and similar multiple wavelength applications, would offer the equivalent tunability of a dye laser, but in a compact solid state electronic package, as in a diode laser system, possibly with radiative or air cooling.
U.S. Pat. No. 5,771,325 entitled “Modular Laser Systems”, invented by present inventor, Wolfgang Neuberger, and assigned to the Assignee of the present invention has some pertinent points in this area and is hereby expressly incorporated by reference as part of the present disclosure. This patent deals with diode laser systems and describes a system of interchangeable laser diode modules. In this system, laser diodes are contained in modules which can be easily interchanged. The goal of this invention was to create a more efficient, higher power laser, with reliable and stable output. Added efficiency came from having a low down time for repairs because of the ability to quickly replace nonfunctioning modules with working modules. Higher power resulted from having multiple diode modules of the same wavelength in operation simultaneously. Reliability and stability of output resulted from operating the laser system at lower than maximum current and the ability to operate the laser unit continuously despite the failure of one diode or diode array. Thus, this invention effectively treated power level and ease of serviceability of diode lasers, specifically relating to industrial applications. However, '325 does not address the real need of the present invention. The need addressed by the present invention is a tunable diode laser system for medical applications.
The '325 patent also describes a large system using a laser rod to combine laser power from multiple modules. Because of high power input levels, the invention in '325 also generates high temperature levels and therefore requires sizeable heat exchange apparatus.
The concept of modularity and easy replacement of diodes described by '325 may be useful for application to the problem addressed by the present invention. What is still lacking is how to create a diode laser system that is tunable. How to interchange diode modules of different wavelengths in a hospital or outpatient clinic setting must also still be addressed, as well as a desire to automate recognition of diode lasers available.
The process of interchanging diode modules or cartridges is inherently problematic. Coupling of laser diodes with optical fibers requires extreme precision. If the diode/fiber interface is slightly amiss, a malfunction will occur. Thus, to develop a syste
Neuberger Wolfgang
Spaniol Stefan
B J Associates
CeramOptec Industries Inc.
Jr. Leon Scott
Skutnik Bolesh J.
LandOfFree
Tunable diode laser system for photodynamic therapy does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tunable diode laser system for photodynamic therapy, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunable diode laser system for photodynamic therapy will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2849400