Background of the Invention

The present invention relates generally to an apparatus and method for laser doppler flowmetry. More particularly, the present invention provides an apparatus and method for computer control of laser firing employing laser doppler flowmetry as the information feedback source for information relating to the tissue to be irradiated.

The development of the laser Doppler flowmetry technique has facilitated clinical monitoring of tissue microcirculation. The procedure is typically carried out endoscopically using a special probe. Quantitative measurements of the microculatory blood flow are typically difficult to perform in humans with available methods for blood flow evaluation. The laser Doppler flowmetry is a se iguantitative method and is well suited for measuring variations in the flux values of, for example, healthy versus pathological, comparisons within an organ or other tissue.

Laser Doppler flowmetry measures the difference in blood cell flux in the tissue. The use of laser Doppler for blood flow measurements was first employed in studying blood flow in retinal vessels in rabbits. Riva, et al , Laser Doppler measurements of blood flow in capillary tubes and retinal vessels , Invest. Opthalmol. (1972) 11:936. Laser Doppler flowmetry has been widely used for microcirculatory studies. See, e. g. , Kvernebo, K. , e. g. , Experiences with laser Doppler blood flow measurements in healthy human gastric mucosa, Int. J. Microcirc. Clin. Exp. (1984) 3:450; al-Khaja, N. , et al , Cutaneous microcirculation and blood rheology following cardiopulmonary bypass. Laser Doppler flowmetric and blood cell rheologic studies , Scand. J. Thorac. Cardiovasc. Surg. (1988) 22(2) :149-53.

The principle underlying the laser Doppler flowmetry technique is based upon the fact that the frequency of light

changes when scattered from a moving object, e. g. , an erythrocyte. The change in the reflected light spectrum depends upon the product of the number of moving erythrocytes in the illuminated tissue volume and their mean velocity. It will be understood, by those skilled in the art, that laser Doppler flowmetry is well suited for measuring variations in the flux values of, for example, healthy versus pathological comparisons within designated tissue.

Theoretically, it was expected that the output signal should decrease to zero level in coagulated areas. However, a reproducible flux activity in coagulated areas has been found to persist. This activity is defined as the baseline level. It has been found that electrocoagulation with diathermy did not decrease the flux to the same degree and in the same constant manner as did laser irradiation. It is believed, therefore, that laser irradiation seems to be more reliable technique for destruction of bladder tumors. Beisland, H.O., et al , The Microcirculation in Neodymion-YAG Laser Irradiated and in Electro Coagulated Urinary Bladder Tumors Evaluated with Laser Doppler _7V_.OTt_i.etry, Urol. Res. (1986) 12:149-152.

There is substantial activity in studying and utilizing the application of laser energy to internal tissue through optical fibers. There is presently no reliable method for quantitatively determining the extent and depth of laser penetration into the tissue. Currently qualitative estimates are made based upon previous dosimetry and comparing to histological readings. The surface area is typically judged by visual inspection in color or by spectral analysis. These methods grossly approximate quantitative analysis and do not accurately differentiate, in real time, the tissue area-volume which has been adequately exposed to laser irradiation to abolish tissue microcirculation.

Summary of the Invention

According to a broad aspect of the present invention, there is provided an apparatus and method employing laser Doppler flowmetry to identify the presence of microcirculation in tissue and transmit that information to a laser firing computer control. In this manner, the firing of the laser is controlled by the tissue information garnered from laser Doppler flowmetry to delineate which tissue areas-volumes have been sufficiently exposed to laser irradiation. The apparatus comprises a catheter having laser fibers which transmit the laser energy to the end of the catheter. A flexible probe, which may be constructed as part of the catheter or as a separate probe, contains the laser Doppler apparatus, as is known in the art. A receiver is coupled to the laser Doppler probe to display the Doppler signals relating to tissue information. A laser source is connected to the laser fibers and to a computer which controls firing of the laser.. The laser Doppler receiver transmits the flux information to the computer. The computer is, in turn, programmed to activate the laser and regulate the laser firing, both in energy level and in duration of firing, to sufficiently irradiate the tissue until the base line Doppler reading is achieved. This level is indicative of the complete abolition of microcirculation in the tissue.

Those skilled in the art will understand and appreciate that the foregoing apparatus and method will provide real time information relating to the tissue microcirculation and permit the physician to accurately delimit the laser energy and dosage to ensure against hypoirradiation or hyperirradiation.

These and other features and advantages of the present invention will be better understood by those skilled in the art from the following more detailed description of the preferred embodiments of the invention taken with reference to the accompanying drawings in which like reference numerals identify like elements.

B-rief Description of the Drawings

Figure 1 is a diagrammatic view of the present invention. Figure 2 is a diagrammatic partial cross-sectional view of a catheter probe in accordance with the present invention.

Detailed Description of the Preferred Embodiments

The present invention is illustrated with reference to Figures 1 and 2. The apparatus 10 of the present invention consists generally of a laser doppler device 12 and a laser doppler receiver 14 of conventional availability for use in laser Doppler flowmetry. The apparatus 10 further consists of a laser device 16 and laser power supply 18, also of conventional availability for use in laser surgery. The laser Doppler receiver 14 and the laser power supply 18 are coupled to a control computer 20. Control computer 20 is pre-programmed with a control program which receives tissue microcirculation information from the laser doppler 12 and calculates the required duration and energy of the laser irradiation necessary to abolish microcirculation in the tissue. Manual override of the control computer is permitted. Manual override will permit physician intervention in the determination of energy level and/or duration of irradiation of the tissue. Both the laser device 16 and the laser doppler 12 may be operably connected to a single catheter containing the laser fibers and the laser Doppler transmitter/receiver as illustrated with reference to Figure 2. It is possible, within the scope and contemplation of the present invention, to employ a separate laser probe and laser doppler probe (not shown) both of which are under control of the physician. In accordance with a preferred embodiment of the present invention, however, as illustrated with reference to Figure 2, there is shown a combined laser and laser Doppler catheter 22. The laser and laser Doppler catheter 22 consists of a laser device 16, an laser Doppler device 12 and a catheter 22.

Catheter 22 comprises an elongated flexible catheter tube constructed of any suitably biologically and chemically inert material as is well known in the art. The catheter tube has a generally circular, transverse cross section, which defines a lumen. The lumen may be use to accommodate a guide wire, introduce fluids, extract fluids or may be closed. The diameter of the catheter tube may vary according to the desired application, i. e. , the size of the body tubing system into which it will be introduced. According to one preferred embodiment of the invention, at least one of a plurality of optical fibers 15 are disposed about the inner circumference of the lumen. Those skilled in the art will understand and appreciate, however, that according to another preferred embodiment of the invention, the plurality of optical fibers 15 may be disposed about the outer circumference of the catheter tube 22 or within the wall of the catheter tube 22 itself. The optical fibers 15 may be adhered to the catheter tube by any suitable means, i. e. , gluing embedding in the material of the catheter tube wall. Each of the plurality of optical fibers 15 are made of a material such as is well known in the optical fiber art and are of sufficient size to transmit sufficient laser irradiation to destroy the internal unwanted tissue or structure without detrimentally increasing thermal conductivity of the optical fiber itself. Each of the plurality of optical fibers 15 may protrude from the distal end of the catheter tube 22 and, at the proximal end of the catheter tube 22, are individually connected to and controlled by the laser device 16 and computer system 20.

At least one laser Doppler transmitter/receiver or separate transmitter and receiver apparatus 16 is mounted at the distal end of the catheter tube 22 and electrically connected to the laser Doppler device 12 by suitable electrical conductors which are preferably affixed to or embedded in the catheter tube wall.

As described in U.S. Patent Application Serial No.

07/387,949 filed July 31, 1989, co-owned and co-pending herewith (hereinafter "the Barken Patent Application") , which is hereby incorporated by reference, the protruding distal end of each of the plurality of optical fibers 15 may be configured to direct the laser irradiation at an pre-determined angle from the longitudinal axis of the catheter tube 15. According to the preferred embodiment of the present invention, though not to be construed as limiting the scope of the invention, each of the plurality of optical fibers 15 are configured to fire the laser irradiation at an angle of approximately 90° relative to the longitudinal axis of the optical fiber carrying the laser. Those skilled in the art will understand and appreciate, however, that this configuration of laser fiber firing is not mandated nor required by the present invention, and that the laser firing may occur from a single laser fiber and be directed co-axial with the laser fiber.

The firing of each of the plurality of optical fibers 15 is under the control of the computer system 20 and responds to the feedback received from the laser Doppler 12 or to control from the physician 5. As the plurality of optical fibers 15 are provided about the entire inner or outer circumference of the catheter 22 and each of the plurality of optical fibers 15 direct the laser firing generally perpendicular to the longitudinal axis of each optical fiber, the laser and laser Doppler catheter apparatus 10, of the present invention, is able to selectively irradiate virtually any sector of the 360" cross-sectional area about the catheter tube 22. It will be understood by those skilled in the art, therefore, that each of the plurality of optical fibers 15 fires only to a predetermined sector of the surrounding tissue.

While the described laser and laser Doppler catheter apparatus 10 is primarily adapted for use with any natural tubing system, e. g. , transrectally, intravessically, intratracheally, intraesophageally, or intrathecally, it utility is not limited to

body system subserved by a natural passageway. In cases where no natural passage exists, such as breast tissue, liver, "brain or kidney, the laser and laser Doppler catheter 10 may be introduced through an introductory balloon catheter as more fully described in the Barken Patent Application, which is hereby incorporated by reference.

The foregoing description is included to illustrate the preferred embodiments of the invention and their operation and is not meant, nor intended, to limit its scope or content. Rather many variations within the spirit and scope of the invention will be apparent to those skilled in the art. For example, the substitution of a plurality of ultrasonic transducers for a single ultrasonic transducer may be made to provide radial imaging of the tissue imaging with respect to the catheter, changes in materials, or usage may be made and sti.ll fall within the scope of the described and claimed invention.