Abstract:
Medical researchers use various optical devices for diagnosis, detection, treatment, and therapy. In some embodiments, they do not have the equipment necessary to determine how much light is emitted by the optical device or how far it penetrates tissue. The present invention provides for a method and apparatus for characterizing light from an optical device by using a tissue phantom. The method includes coupling light from an optical source into a device, transmitting the light through a tissue phantom, detecting a transmitted light, optionally electrically processing the detected output, and displaying the corresponding optical characterization. In some embodiments, the apparatus obtains input light from an optical source, and may include a tissue phantom, an optical detector, an electrical processing unit, and a display for displaying the corresponding optical characterization.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This invention claims benefit of U.S. Provisional Patent Application Ser. No. 60/872,930 filed Dec. 4, 2006 by James S. Webb et al. and entitled “APPARATUS AND METHOD FOR CHARACTERIZING OPTICAL SOURCES USED WITH HUMAN AND ANIMAL TISSUES,” which is hereby incorporated by reference in its entirety. This invention is also related to U.S. Provisional Patent Application Ser. No. 60/715,884 filed September 9, 2005 by James S. Webb et al. and entitled “APPARATUS AND METHOD FOR OPTICAL STIMULATION OF NERVES,” U.S. patent application Ser. No. 11/257,793 filed Oct. 24, 2005 by James S. Webb et al. and entitled “APPARATUS AND METHOD FOR OPTICAL STIMULATION OF NERVES AND OTHER ANIMAL TISSUE” (which issued as U.S. Pat. No. 7,736,382 on Jun. 15, 2010), U.S. patent application Ser. No. 11/536,639 filed Sep. 28, 2006 by James S. Webb et al. and entitled “MINIATURE APPARATUS AND METHOD FOR OPTICAL STIMULATION OF NERVES AND OTHER ANIMAL TISSUE” (which issued as U.S. Pat. No. 7,988,688 on Aug. 2, 2011), and U.S. patent application Ser. No. 11/536,642 filed Sep. 28, 2006 by Mark P. Bendett et al. and entitled “APPARATUS AND METHOD FOR STIMULATION OF NERVES AND AUTOMATED CONTROL OF SURGICAL INSTRUMENTS” (which published as U.S. Patent Application Publication 2008/0077200 on Mar. 27, 2008), which are all incorporated herein in their entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to tissue optics (interactions of light with human or animal tissue), and more particularly to methods and apparatus to characterize optical sources (sources of light energy at various wavelengths) used in medical treatments and research involving light such as infrared or optical nerve stimulation, laser-vision correction, cosmetic laser skin treatments like laser hair removal, photodynamic therapy, and microdisection and microablation. 
     BACKGROUND OF THE INVENTION 
     Medical professionals use various optical devices for research, diagnosis, detection, treatment, and therapy. Such optical devices generate, condition, and/or deliver light that may be used to optically stimulate nerves or correct eyesight, for example. Typically, medical researchers do not have the measurement devices necessary to determine how far the light penetrates into a tissue or what cross-sectional area is illuminated. To determine these quantities, the researcher needs to measure power, beam diameter and shape, divergence, and wavelength, as well as the optical properties of the tissue in question. 
     U.S. Pat. No. 6,475,800 issued to Hazen, et al. on Nov. 5, 2002 entitled “Intra-serum and intra-gel for modeling human skin tissue” and is hereby incorporated by reference. Hazen et al. describe a class of samples that model the human body and are based upon emulsions of oil in water with lecithin acting as the emulsifier. These solutions that have varying particle sizes may be spiked with components (albumin, urea and glucose) to simulate skin tissues, and used in the medical field where lasers and spectroscopy-based analyzers are used in treatment of the body. Hazen et al. say that the samples allow one to gather data on net analyte signal, photon depth of penetration, photon radial diffusion, photon interaction between tissue layers, photon density (all as a function of frequency) and on instrumentation requirements such as resolution and dynamic range. 
     U.S. Pat. No. 6,224,969 issued to Steenbergen, et al. on May 1, 2001 entitled “Optical phantom suitable for stimulating the optical properties of biological material and a method of producing said phantom” and is hereby incorporated by reference. Steenbergen, et al. describe an optical phantom for simulating optical properties of biological material and a method of making the phantom, which includes a matrix of poly(vinyl alcohol) (PVA) and spherical particles whose refractive index differs from that of the PVA. Preferably the PVA has a level of hydrolysis of &gt;98%, and the spherical particles are hollow polystyrene particles. In addition, light-absorbing and light-scattering substances may be added. 
     U.S. Pat. No. 6,353,226 issued Mar. 5, 2002 and U.S. Pat. No. 6,630,673 issued Oct. 7, 2003 to Khalil et al., both titled “Non-invasive sensor capable of determining optical parameters in a sample having multiple layers,” and are hereby incorporated by reference. The apparatus measures light that is substantially reflected, scattered, absorbed, or emitted from a shallower layer of the sample of tissue, measures light that is substantially reflected, scattered, absorbed, or emitted from a deeper layer of the sample of tissue, determines at least one optical parameter for each of these layers, and accounts for the effect of the shallower layer on the at least one optical parameter of the deeper layer. 
     U.S. Pat. No. 5,261,822 to Hall, et al. issued Nov. 16, 1993 entitled “Surgical refractive laser calibration device”, and U.S. Pat. No. 5,464,960 issued to Hall, et al. on Nov. 7, 1995 entitled “Laser Calibration Device” which are both hereby incorporated by reference, each describe a phantom cornea for calibrating surgical lasers is formed by superimposition of thin-films of alternating colors. After ablation by a laser beam, the resulting spherical cavity appears as a pattern of nested circles whose concentricity and spacing reflect the alignment and intensity of the laser beam. 
     U.S. Patent Publication US 2005/0142344 by Michael Toepel entitled “Laser Test Card” is hereby incorporated by reference. Toepel describes a card for testing and displaying a shape of a laser beam. 
     U.S. Pat. No. 5,480,482 that issued to Novinson on Jan. 2, 1996 entitled “Reversible thermochromic pigments”, is incorporated herein by reference, and describes a color changing pigment composition which changes color reversibly when ted comprising (a) a cyclic aryl lactone dye, (b) a diaminoalkane activator and (c) an ester. The pigment composition can also include a white pigment such as titanium dioxide as an opacifier or a yellow dye such Hansa yellow G. The pigment composition changes from a dark color, e.g., blue, to white when the composition is heated to a specified temperature, e.g., to a temperature of 52 degrees C., and reversibly changes from white back to the blue color when the pigment composition is cooled, e.g., to a temperature below about 25 degrees C. 
     U.S. Pat. No. 6,669,765 that issued to Senga, et al. on Dec. 30, 2003 entitled “Thermochromic dry offset ink, and printed article produced using the same”, is incorporated herein by reference, and describes a thermochromic dry offset ink comprising a dry offset ink medium and a thermochromic pigment material dispersed therein, wherein the thermochromic pigment material is a pigment material which has a microcapsular form having non-round particle cross section and has a thermochromic material enclosed in the microcapsules. Also disclosed is a printed article produced using the ink. The thermochromic dry offset ink can more improve pressure resistance and heat resistance and also can more satisfy uniform printability and high-speed continuous printability in offset printing especially on articles such as containers. 
     U.S. Pat. No. 4,681,791 that issued to Shibahashi, et al. on Jul. 21, 1987 titled “Thermochromic textile material”, is incorporated herein by reference, and describes a textile material in the form of fiber, raw stock, yarn or fabric, which comprises fibers each of which is coated with a thermochromic layer containing a thermochromic pigment having a particle size satisfying [a particular formula] of a fiber. The textile material can undergo reversible color change in a wide variety of colors and can be applied to any kind of textile products. 
     U.S. Pat. No. 6,444,313 that issued to Ono, et al. on Sep. 3, 2002 entitled “Thermochromic acrylic synthetic fiber, its processed article, and process for producing thermochromic acrylic synthetic fiber”, is incorporated herein by reference, and describes a thermochromic acrylic synthetic fiber comprising an acrylonitrile polymer in which a thermochromic pigment composition with an average particle diameter of from 0.5 micron to 30 microns is dispersedly contained in an amount of from 0.5% by weight to 40% by weight based on the weight of the polymer, and being made into fibers; the pigment composition containing (a) an electron-donating color-developing organic compound, (b) an electron-accepting compound and (c) a reaction medium that determines the temperature at which the color-developing reaction of the both compounds takes place. Also disclosed are a processed article of the above thermochromic acrylic synthetic fiber, and a process for producing the thermochromic acrylic synthetic fiber. 
     U.S. Pat. No. 7,040,805 that issued to Ou, et al. on May 9, 2006 titled “Method of infrared thermography”, is incorporated herein by reference, and describes “A method of infrared thermography is described. The invention utilizes a high resolution infrared thermography system with an infrared camera and associated computer in conjunction with a test chamber to determine heat-transfer coefficients and film effectiveness values from a single test. 
     U.S. Pat. No. 6,585,411 that issued to Hammarth, et al. on Jul. 1, 2003 titled “Aerosol dispenser temperature indicator”, is incorporated herein by reference, and describes a liquid crystal temperature indicator, and aerosol dispensers equipped with a properly placed indicator, to facilitate using aerosols within preferred temperature ranges or at optimum temperatures. The temperature indicator uses different colors to graphically illustrate temperatures and/or temperature ranges, as well as temperatures above and below optimal temperatures or preferred temperature ranges. Temperature indicators are reusable; they may be self-adhesive and may optionally be transferred from a liquid crystal temperature indicator is either permanently or reversibly adhered to the outer surface of an aerosol dispenser in a location that will allow estimation of the temperature of the liquid inside the dispenser. Liquid crystals are composed of elongated organic molecules that can exhibit different physical properties (e.g., optical and electrical properties) at different temperatures. Using, for example, changes in the color of a plurality of liquid crystals at different temperatures arranged in numerical (i.e., ascending or descending) order, temperature indicators of the present invention can be coupled to aerosol dispensers to indicate desired temperature adjustments to a dispenser within a range of temperatures. The temperature indicators thus act as guides for the use of appropriate heat flow control methods for achieving preferred temperature conditions for making and using aerosol. United States Patents related to temperature measurement using liquid crystals include U.S. Pat. No. 4,064,872 (Caplan), issued Dec. 27, 1977; U.S. Pat. No. 6,257,759 (Witonsky, et al.), issued Jul. 10, 2001; U.S. Pat. No. 6,294,109 (Ratna, et al.); and U.S. Pat. No. 6,284,078 (Witonsky, et al.), issued Sep. 4, 2001, each of which is incorporated herein by reference. 
     In an article by Passos D. et al., “Tissue phantom for optical diagnostics based on a suspension of microspheres with a fractal size distribution,” J Biomed Opt. 2005 November-December; 10(6):064036 (which is hereby incorporated by reference) there is a description of a phantom for reproducing the phase function, absorption, and scattering coefficients of a real biological tissue (adult brain white matter and liver) using a suspension of polystyrene microspheres with a fractal size distribution. The design of a light scattering goniometer with a cylindrical cell in air is discussed, and phase function measurements using the device are described. 
     The paper by Viator J A, et al., “Spectra from 2.5-15 microns (i.e., micrometers) of tissue phantom materials, optical clearing agents and ex vivo human skin: implications for depth profiling of human skin,” Phys Med Biol. 2003 Jan. 21; 48(2):N15-24 (which is hereby incorporated by reference) describes tissue phantoms for human skin in the IR wavelengths; it also details the constituents used for the phantom and their relation to the optical properties. They used Fourier-transform infrared spectroscopy in attenuated total reflection mode to measure the infrared absorption spectra, in the range of 2-15 microns, of water, polyacrylamide, Intralipid, collagen gels, four hyperosmotic clearing agents (glycerol, 1,3-butylene glycol, trimethylolpropane, Topicare), and ex vivo human stratum corneum and dermis. 
     Papers by Nakagawa A., et al., “Pulsed holmium:yttrium-aluminum-garnet laser-induced liquid jet as a novel dissection device in neuroendoscopic surgery.” J. Neurosurg. 2004 July; 101(1):145-50 and Nakagawa A., et al., “Holmium: YAG laser-induced liquid jet knife: possible novel method for dissection.” Lasers Surg Med. 2002; 31(2):129-35 (which are hereby incorporated by reference) describe use of the Ho:YAG in neuroendoscopic ablative surgery applications for small-vessel ablation. This would be useful for muscle tissue phantoms, since blood vessels are made up of smooth muscle. The authors of the first paper describe experiments aimed at solving problems associated with pressure-driven continuous jet of water for neuroendoscopic dissection by using a pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser-induced liquid jet (LILJ). They examined its mechanical characteristics and controllability in an artificial tissue phantom (10% gelatin of 1-mm thickness). The authors of the first paper describe the effect on artificial organs made of 10 and 30% (w/v) gelatin, each of which represent features of soft tissue and blood vessels. 
     The paper by Ovelmen-Levitt J., et al., “Brain ablation in the rat cerebral cortex using a tunable-free electron laser,” Lasers Surg Med. 2003; 33(2):81-92 (which is hereby incorporated by reference) describes research done at Vanderbilt using their MARK III free electron laser (FEL) tuned to molecular vibrational absorbance maxima in the infrared (IR) wavelength range of 3.0-6.45 microns to study the effect of these various wavelengths and a power level of 5 mJ/2 microseconds macropulse on photoablation of CNS (central-nervous-system) tissue. 
     There are relatively high costs and various difficulties encountered using the above methods and apparatus. Accordingly, there is a need for an apparatus and method that, in a standardized manner, can cheaply, easily, and directly characterize the optical sources used in optical devices and their interactions with different types of tissue. 
     BRIEF SUMMARY OF THE INVENTION 
     In some embodiments of the present invention, a method is described that includes providing light from an optical source, shining the output beam onto a “tissue phantom,” allowing the light to be transmitted, scattered, absorbed, and potentially reemitted, detecting the transmitted light on the far side of the tissue phantom, optionally processing the detector response, and displaying the result, either visibly as an image or with a numeric readout that corresponds to an optical characterization associated with the light. 
     In some embodiments of the present invention, an apparatus is described that includes light from an optical source, a tissue phantom, a detector, an optional electrical or non-electrical processing unit, and a display for displaying a numeric result and/or graphical image that corresponds to an optical characterization associated with the light. 
     In some embodiments, the present invention includes an apparatus comprising means for inputting light from an optical source, means for simulating an organic tissue, means for transmitting, scattering, absorbing, and potentially reemitting the light in a simulated organic tissue, means for detecting the transmitted light, optional means for electrically processing the light on the output side of the “tissue phantom,” and means for displaying a numeric result and/or graphical image that corresponds to an optical characterization associated with the light. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic of a tissue-penetration-depth monitor (TPDM)  100 . 
         FIG. 1B  is a schematic of a rectangular-shaped tissue phantom  149 . 
         FIG. 1C  is a schematic of a wedge-shaped tissue phantom  150 . 
         FIG. 1D  is a schematic of a tissue phantom  151  that has steps of different thicknesses. 
         FIG. 1E  is a schematic of a tissue phantom  152  that has steps of different thicknesses. 
         FIG. 2  is a schematic of a TPDM  200  used to characterize the optics of a laser handpiece  201 . 
         FIG. 3  is a schematic of a TPDM  300  that can display the IR output from a laser handpiece  201  as visible light. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following preferred embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon the claimed invention. 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
     The leading digit(s) of reference numbers appearing in the Figures generally corresponds to the Figure number in which that component is first introduced, such that the same reference number is used throughout to refer to an identical component that appears in multiple Figures. Signals and connections may be referred to by the same reference number or label, and the actual meaning will be clear from its use in the context of the description. 
       FIG. 1A  is a schematic of a tissue-penetration-depth monitor (TPDM)  100 . The TPDM  100  is used to characterize the optical source (e.g., optical power, beam diameter, and divergence) and its interaction with a specified tissue (e.g., transmitted power, dispersion, scatter, and absorption) of a medical light source (MLS)  122 . (The TPDM  100  can be used with any medical light source  122  (e.g., photo-dynamic-therapy lasers, dental lasers and light sources, eye-surgery lasers, low-light-level-therapy optical sources, cosmetic laser treatment sources such as hair or tattoo removal lasers, nerve-stimulation optical sources (such as lasers, light-emitting diodes (LEDs) or other optical sources capable of optically stimulating nerves in an animal), and the like). In some embodiments, for example, the TPDM  100  can determine tissue-penetration depth, provide a calibrated measurement of transmitted power, provide spot size and beam-profile measurements, or provide absorbed power measurements. In some embodiments, the TPDM has an overall enclosure  110  that includes an input fiber connector  120  (e.g. an SMA-type fiber connector, an FC-type fiber connector, or a v-groove to place a fiber probe against.) In some embodiments, the output of the MLS  122  (e.g., infrared light (IR light), visible light, pulsed laser light, ultraviolet (UV) laser light, broadband LED output, superluminescent or other narrowband LED output, continuous wave (CW) laser light, or tunable laser light) is coupled into the TPDM  100  via a fiber or fiber probe  121  which inserts into aperture  105  of TPDM  100  at input fiber connector  120 . 
     Upon entering the TPDM  100 , the light from the MLS  122  passes through a tissue phantom  141  that has substantially the same optical properties as a particular tissue type (e.g. skin, neurons, fat, muscle), an optional lens  147  that forms an image, and an optional neutral density filter (NDF)  148  that reduces the intensity of the light before it is detected. Light from MLS  122  travels into the closer side of the tissue phantom, is acted upon (e.g. transmitted, absorbed, scattered, and refracted) by the tissue phantom and a transmitted beam  146  is formed on the far surface of tissue phantom  141  (the right-hand surface in  FIG. 1A ), and this transmitted beam  146  can then be processed by the optional lens  147  and the optional NDF  148 . The transmitted beam  146  approximates the beam that would be generated (e.g., by transmission, scattering, absorption, fluorescence, and/or other interactions) if the light from the MLS  122  was passed through actual human and/or animal tissue of a given depth and tissue composition. In some embodiments, the tissue phantom  141 , which is formed of materials that have substantially the same optical properties at the relevant wavelengths as one or more types of human tissue, is connected to a handle  142  so that it can be inserted and removed from the TPDM  100 . In some embodiments, tissue phantom  141  is inserted in the TPDM  100  at a phantom insertion port  106 . In some embodiments, the phantom insertion port  106  includes a seal also made of flexible opaque rubber, forms a light-tight seal around the issue phantom  141 , and, when the tissue phantom  141  is removed, automatically closes to prevent laser light from fiber  121  from exiting through phantom insertion port  106  and to prevent outside light from entering the TPDM  100  (this is useful when using TPDM  100  to image the end of LNSS  122  without a tissue phantom, e.g., to verify that its tip is clean and unobstructed). In some embodiments, the phantom can be inserted a measured distance (e.g. as measured by rulings on the tissue phantom). For tissue phantoms with variable thicknesses, inserting the phantom further would simulate a thicker tissue sample (in some embodiments). 
     In some embodiments, the light that transmits through the tissue phantom  141  must be processed for presentation to a human user. Many different detectors are possible.  FIG. 1A  and  FIG. 2  show embodiments that use electronic processing of the light that passes through the tissue phantom, while  FIG. 3  shows and embodiment that uses non-electronic processing of the infrared (IR) signal to a form visible to a human. 
     In  FIG. 1A , the transmitted light next undergoes electrical processing  130  for presentation of an analysis or representation of the light to a human user. The transmitted light is detected by electrical detector  132 , which is connected to a motherboard  131 . In some embodiments, the detector  132  is a thermopile power meter used to measure actual transmitted power. In some embodiments, the detector  132  is an infrared photocell. In some embodiments, the detector  132  is a linear or two-dimensional charge-coupled device (CCD) camera array. 
     In some embodiments, one or more processing units  133 , which are also connected to the motherboard  131 , convert the input from the detector  132  into a signal that is sent to a display  134 . In some embodiments, display  134  is on the outside of the TPDM  100 . In some embodiments display  134  displays a numeric readout of the optical power or optical power density at a given tissue-penetration depth that corresponds to the current thickness of the tissue phantom (or other optical characterization) that is associated with the MLS  122 . In other embodiments, display  134  also or alternatively displays one or more dimensions of the transmitted light (e.g., the full-width half-maximum (FWHM) measurement of the transmitted beam diameter in one or more directions (e.g., either in the X direction, the Y direction, or both, or using one or more other suitable measurements such as angle or area). In some embodiments, display  134  also or alternatively displays a pulse frequency, pulse duration, pulse repetition rate, pulse period, duty cycle and/or other data characterizing the light&#39;s temporal operation if the light is pulsed. In some embodiments, the display  134  shows a profile of the optical power density as a function of position on the detector, producing a beam profile. 
     In some embodiments, the incident side of the TPDM  100  has various methods for positioning the optical input to the TPDM  100 . In some embodiments, for example, the TPDM  100  has a V-groove in the surface that allows the user to set the optical input against the TPDM without damaging the tip. In some embodiments, the distance to the actual tissue phantom is calculated based on the diameter of the probe and the angle of the V-groove. In another embodiment, for example, the TPDM  100  has a surface along which a user can slide their optical input, to traverse along the tissue phantom  141 . 
       FIGS. 1B through 1D  are schematics of various designs for the tissue phantom  141 .  FIG. 1B  is a tissue phantom  149  that is rectangular in shape with one uniform depth. In some embodiments, tissue phantom  149  is of a single homogeneous material, while in other embodiments, a plurality of layers of different materials are used to simulate multiple layers of organic tissue (e.g., skin, muscle, fat and/or bone). In some embodiments, as described for  FIG. 1E , phantom  149  uses one thickness, but has a plurality of different materials are placed side-by-side in a single tissue-phantom device such that different tissues can be quickly analyzed by moving one or another of the different areas of one or more layers of different materials (e.g., side-by-side areas having skin only in one area, skin and muscle in another area, skin and fat in another area, skin muscle and bone in another area, muscle and bone in another area, and/or other combinations).  FIG. 1C  is a tissue phantom  150  that is wedge-shaped with the depth varying from a thicker thickness at the handle end to a thinner thickness at the end opposite the handle end.  FIG. 1D  shows a tissue phantom  151  that has steps of varying thicknesses. In  FIG. 1E  (see drawing sheet with  FIG. 3 ), a plurality of different materials are placed side-by-side in a single tissue-phantom device, but including a plurality of different thicknesses for at least some of the tissue types as well, such that different tissues can be quickly analyzed by moving one or another of the different areas of one or more layers of different materials (e.g., side-by-side areas having skin only in one area, skin and muscle in another area, skin and fat in another area, skin muscle and bone in another area, muscle and bone in another area, and/or other combinations). In some embodiments, the tissue phantom  141  is made of a gel or liquid sandwiched between two glass or plastic plates. The glass or plastic material (e.g. fused silica, sapphire crystal, or polycarbonate) is selected to transmit highly over a large range of wavelengths. Several different tissue types might be mimicked by the tissue phantom  141  using different materials. The tissue phantom  141  may simulate multiple layers of different kinds of tissues by including different layers of materials. In addition or alternatively, in some embodiments, different tissues are mimicked in the same tissue phantom. In addition or alternatively, in some embodiments, different tissues are mimicked in different versions of the tissue phantom. In some embodiments, a plurality of tissue phantoms  141  can be inserted simultaneously into TPDM  100  ( FIG. 1A ), TPDM  200  ( FIG. 2 ) or TPDM  300  ( FIG. 3 ) to simulate multiple layers of different kinds of tissue. 
       FIG. 2  is a schematic of a TPDM  200  used to characterize the output from laser handpiece  201 . In some embodiments, the output from the laser handpiece  201  is controlled by an exposure controller  202  (e.g., optionally including a manual shutter  320 , or electrical shutter or foot control within controller  202  through control link  205 ), that, in some embodiments, is located remotely (e.g., on the floor or in a neighboring room). The light emitted from the handpiece  201  (e.g., IR light) can either pass through a tissue phantom  242 , connected to a handle  243 , or the tissue phantom  242  can be removed and the light can pass straight through to the optional imaging optics and detector. In some embodiments, if the light from the laser handpiece  201  passes straight through because there is not tissue phantom  241  in the beam path (e.g., the imaging optics  212  are focused to the tip of the handpiece  201  such that the system obtains an image of the endface of the handpiece  201 ), the TPDM  200  can be used to determine if the end face  201  of the output of the medical light source (MLS)  222  is clean or not. In other embodiments, the imaging optics  212  are focused to some intermediate focal plane (e.g., in some embodiments, optionally using a translucent object screen  211 ). For example, if the end face is dirty, the beam incident on the detector  232  will not be uniform or symmetric, so the image  251  generated by the TPDM  200  will not be uniform or symmetric. After the light from the laser handpiece  201  passes through optional tissue phantom  242 , the light goes through the optional imaging optics  212 . In some embodiments, for example, the imaging optics  212  includes a lens that reimages the light onto the detector  232  so that it can undergo electrical processing  230 . In some embodiments, housing  210  includes a light-tight box that encloses at least the end of laser handpiece  201 , the tissue phantom  242 , any screen  211  and/or focusing optics  212 , and detector  232 . 
     A detector  232  contains various grids of pixels and is connected to a motherboard  231 . Image processor  233 , which is also connected to the motherboard  231 , converts the input from the detector  232  into data that is sent to the exterior of the TPDM  200  via a data line  235 . On the exterior of the TPDM  200 , the data line  235  continues out until it ends at an optional Universal Serial Bus (USB) connector  236 . The optional USB connector  236  or the data line  235  is plugged into a processor (e.g., a personal computer)  250 . The processor  250  takes the data from the data line  235  and converts it into various images and numeric readouts that represent the input to the detector  232 . These images and readouts are displayed by a display  260  (e.g., a liquid-crystal-display (LCD) monitor). In some embodiments, the processor  250  creates a display image  251  of the transmitted light incident on the detector  232 . The display image  251  can show the intensity profile of the transmitted light incident on the detector  232 , the intensity profile of the light at the laser handpiece  201 , and/or, as mentioned above, it can be used to determine whether the end face of the laser handpiece  201  is dirty. In some embodiments, the processor  250  also creates a graph  252  representing the cross-sectional intensity of the light incident on the detector  232 . In some embodiments, the processor  250  creates a numeric readout  253  which represents the tissue penetration depth (or other optical characterization) that is associated with the output of the MLS  222 . 
       FIG. 3  shows a non-electronic processing system  300  wherein, in some embodiments, the detector  311  is a card made of material coated with fluorescing chromophores. Some embodiments of system  300  optionally include an automatic opening and closing aperture  105 , which opens when laser handpiece  201  is thrust into it, and which automatically closes when laser handpiece  201  is withdrawn. Similarly, in some embodiments, an automatic opening and closing aperture  106  is provided for insertion and position adjusting of tissue phantom  341 , as controlled by handle  342 , and/or an automatic opening and closing aperture  107  is provided for insertion and position adjusting of detector card  311  on handle  312 . In some embodiments, different chromophores would be used for different wavelengths of light or different intensities of light. The detectors  311  could be swapped for use with different medical light source (MLS)  322  or tissue phantoms  341 . In some embodiments, detector  311  is a ceramic wafer having a non-linear material that doubles or triples the frequency of the IR stimulation radiation from MLS  322  (e.g., 1060-nm IR radiation would be frequency doubled to 530-nm blue-green light, 1300-nm IR radiation would be frequency doubled to 650-nm red light, 1550-nm IR radiation is frequency tripled to 517-nm blue-green light and/or 1800-nm IR radiation is frequency tripled to 600-nm orange-red light). In some embodiments, the present invention uses (for detector  311 , which is permanently or removably installed) a standard color-change ceramic wafer having a non-linear up-conversion material, such as VIEW-IT® discs available from www.kentek.com (Kentek Corporation, 1 μm St., Pittsfield, N.H. 03263, United States). In some embodiments, a shutter  320  having a time-adjustment mechanism  322  and/or shutter trigger  321 , in order to limit the time that detector  311  is exposed to output of the MLS  322 , as modified by the tissue phantom  341 , and thus provide a more accurate indication of the power and/or energy of the stimulation laser beam. 
     In other embodiments, detector  311  is a permanent-change multilayer card wherein, when exposed to light of sufficient energy one or more successive layers are ablated away or change color in order to show the pattern and intensity of the laser beam. For example, in some embodiments, the outermost interacting layer is black and is removed or changes color when exposed to the lowest-energy interacting beam. Deeper layers would require higher intensity light to ablate or change color (e.g., for very low intensity beams that still have enough energy, the outermost layer(s) ablates or otherwise changes to expose one or more lower-level layers that have different colors and energy-absorption characteristics). In some embodiments, the present invention uses, for detector  311 , a card such as described in U.S. patent application Ser. No. 10/744,127 (Patent Publication US 2005/0142344) by Michael Toepel entitled “Laser Test Card” which is hereby incorporated by reference. In some embodiments, the present invention uses (for detector  311 ) a standard color-change test paper, such as ZAP-IT® available from www.zap-it.com or www.kentek.com (Kentek Corporation, 1 μm St., Pittsfield, N.H. 03263, United States), wherein a plurality of different color changes each correspond to a particular power or energy in the output of the MLS  122 . In some such embodiments, the tissue phantom is modified and calibrated such that a particular color on the test paper will correspond to a particular irradiance of transmitted light (e.g., level of nerve stimulation and/or a level of tissue damage from the optical source). For example, if a standard tissue phantom (i.e., one that accurately simulated the reduction in intensity and the dispersion that light would undergo traveling through a given tissue of a given thickness) would affect (e.g., ablate) too many layers of detector  311 , the modified tissue phantom  341  in system  300  would be darkened and/or thickened (thus reducing the transmitted power and energy) in order that the desired range of stimulation intensities would activate the available range of colors on the permanent-change detector card. As an alternative or additional measure, some embodiments use a shutter  320  that is kept closed until detector card  311  is in place and the MLS  122  is activated, such that shutter  320  limits the duration of exposure or the number of pulses that are recorded on detector  311 . Conversely, if light transmitted through a standard tissue phantom would affect too few layers of detector  311 , the modified tissue phantom  341  in system  300  would be lightened and/or thinned (thus increasing the transmitted power and energy) in order that the desired range of stimulation intensities would activate the available range of colors on the permanent-change detector card. As an alternative or additional measure, some embodiments use a shutter  320  that is kept closed until detector card  311  is in place and the MLS  122  is activated, and then shutter  320  is kept open for a longer time or MLS  122  is activated to emit enough pulses such that the duration or the number of pulses that are recorded are sufficient to affect the desired range of layers on detector  311 . In some embodiments, the tissue phantom  341  and the permanent-change detector paper  311  are attached to a single handle inserted and moved from a single side of enclosure  310  (e.g., the top side) such that one spot is exposed and recorded for each of a plurality of different tissue-phantom thicknesses  351 ,  352 ,  353 ,  354 , and/or  355 , and/or with no tissue phantom (i.e., with the laser beam shined directly onto the permanent-change detector paper  311 ), thus recording the light intensities for each of a plurality of different tissue depths, and/or conversely, the tissue depth reached by a particular light intensity. In some embodiments, the permanent-change detector card shows markings for the thickness of the tissue phantom  341  at that location and/or has grid lines to allow the user to measure the size or shape of the transmitted light beam. 
     In some embodiments, a plurality of different detectors  311  are mounted on handles  312  and inserted into aperture  105 , such that either a real-time-viewable up-conversion disc, such as a VIEW-IT® disc, or a permanent-change card (such as ZAP-IT® paper) may be interchangeably installed into system  300  with one or more different tissue phantoms  341 , in order to interactively view and/or permanently record the shape, size and intensity of the nerve-stimulation laser beam (i.e., wherein a particular brightness of the up-conversion spot or the ZAP-IT spot, correlated with a given tissue-phantom thickness, indicates the tissue depth to which the stimulation-effective portion of the laser beam reaches). 
     In some embodiments, the detector  311  includes a strip of material that permanently discolors or changes to expose lower layers of material having contrasting color or brightness when exposed to a high enough irradiance (e.g., a burn strip). 
     In some embodiments, the detector  311  includes a laser-sensitive ceramic material such as VIEW-IT®. (such as are available from Kentek Corporation, 1 Elm St., Pittsfield, N.H. 03263, United States), which is a high-efficiency, laser-sensitive ceramic disc that provides a convenient method of viewing beam shape, mode structure and beam alignment when held in the path of a laser beam, and provides continuous viewing of the laser beam in action. VIEW-IT® provides an unlimited period of viewing for both pulsed and continuous wave lasers. Beam quality and mode structures can be observed in real time using their white ceramic disc with strong nonlinear (up-conversion) on a base of unique ion combination. This nonlinear optical process doubles the initial laser beam frequency. For example, if an initiated wavelength of 1064 nm (1.06 g) strikes the VIEW-IT® disc, it will be observed as green light. 
     In some embodiments, the detector  311  includes a laser-sensitive cards (such as Model F-IRC1, F-IRC2, and F-IRC-4 cards, which are available from Newport Corporation, 1791 Deere Avenue, Irvine, Calif. 92606. These allow the present invention to locate and analyze light beams in the 0.7-1.7 mm wavelength range with these pocket sized, low-cost IR detectors. These cards contain a special sensor area that emits clearly visible light when illuminated by near infra-red (NIR) and infra-red (IR) sources. Model F-IRC1, F-IRC2, and F-IRC-4 are credit card-size cards containing a 2 in. (50 mm) square sensor area. Model F-IRC2-F is also a smaller card containing a 0.5 in. (12.5 mm) square sensor area, and is used primarily with optical fiber outputs. The F-UVC1 is an Ultraviolet sensor card with 2 in. (50 mm) square sensor area for locating and analyzing light beams in the 0.24-0.60 mm wavelength range. The IR sensor cards are encapsulated between durable clear plastic layers. The UV sensor card has the protective polyester coating removed from the front of the sensor.) 
     In some embodiments, detector  311  is made of one or more strips that reversibly change color at different irradiances. In some embodiments, detector  311  includes a liquid-crystal detector (such as are available from B&amp;H Liquid Crystal Resources Ltd, Riverside Buildings, Dock Road, Connahs Buildings, Dock Road, Connahs Quay, Deeside, Flintshire, CH5 4DS, Great Britain, which shows both the beam diameter and irradiance gradients within the beam). In other embodiments, the detector  311  performs temperature measurement using liquid crystals such as described in U.S. Pat. No. 6,585,411 that issued to Hammarth, et al. on Jul. 1, 2003, U.S. Pat. No. 4,064,872 (Caplan), issued Dec. 27, 1977; U.S. Pat. No. 6,257,759 (Witonsky, et al.), issued Jul. 10, 2001; U.S. Pat. No. 6,294,109 (Ratna, et al.); and U.S. Pat. No. 6,284,078 (Witonsky, et al.), issued Sep. 4, 2001, each of which is incorporated herein by reference. 
     In some embodiments, detector  311  includes a material or surface having a reversible thermochromic pigment (such as described in U.S. Pat. No. 5,480,482 that issued to Novinson on Jan. 2, 1996 entitled “Reversible thermochromic pigments”, which is incorporated herein by reference), used to provide a reusable indicator of beam intensity and extent. 
     In some embodiments, the detector  311  includes one or more strips that irreversibly change color at different irradiances (such as Tempilabel and Thermax, available from Tempie, Inc., 2901 Hamilton Blvd, South Plainfield, N.J. 07080). These allow the present invention to monitor and verify temperature specific operations such as spot size and intensity. In some embodiments, they feature adhesive backing allowing them to be affixed to any surface quickly and easily. When desired temperature is reached the dot in the middle changes to black and remains that way indicating that the desired temperature has been reached. Accurate to +/−2% of the Fahrenheit rating, Tempilabel and Thermax brands are both available in either the multiple temperature range configuration or single temperature design. 
     In some embodiments, detector  311  includes a material or surface having a thermochromic ink (such as described in U.S. Pat. No. 6,669,765 that issued to Senga, et al. on Dec. 30, 2003 entitled “Thermochromic dry offset ink, and printed article produced using the same”, which is incorporated herein by reference). In some embodiments, detector  311  includes a material or surface having thermochromic fibers or fabric (such as described in U.S. Pat. No. 6,444,313 that issued to Ono, et al. on Sep. 3, 2002 entitled “Thermochromic acrylic synthetic fiber, its processed article, and process for producing thermochromic acrylic synthetic fiber”, or U.S. Pat. No. 4,681,791 that issued to Shibahashi, et al. on Jul. 21, 1987 titled “Thermochromic textile material”, which are incorporated herein by reference). 
     In some embodiments, detector  311  includes a high-resolution infrared thermography system with a near-infrared camera (such as described in U.S. Pat. No. 7,040,805 that issued to Ou, et al. on May 9, 2006 titled “Method of infrared thermography”, which is incorporated herein by reference). 
       FIG. 3  is also a schematic of a TPDM  300  that can also be used in a dynamic mode (rather than creating a permanent record on a one-time-use card as described above for  FIG. 3 ) to display the IR output from a MLS  322  as visible light. In contrast to the invention described above for TPDM  200 , which optically and electrically processes the light created by MLS  322 , TPDM  300  directly converts this light into a visible light source or a permanent color change via an IR-to-visible conversion screen (IRVCS)  311 . In some embodiments, the visible light pattern created by the IRVCS  311  can be observed from the exterior of the TPDM  300  because one side of the IRVCS  311  faces the interior of the TPDM  300  and receives the IR light and the other side of the IRVCS  311  faces the exterior of the TPDM  300  and emits the visible light. As with the TPDM  200  and TPDM  100 , the TPDM  300  also contains a tissue phantom  342 , which is connected to a handle  342  for easy changing of simulated tissue depths, or for removal. 
     In some embodiments, the TPDM of  FIG. 1 ,  FIG. 2 , or  FIG. 3  comes with wipes and solution for cleaning the windows and probe ends. In some embodiments, wipes and solution are not needed because the TPDM is disposable. 
     In some embodiments of the present invention, a method is described that includes providing a light from an optical source, optically processing (e.g. transmitting, reflecting, scattering, absorbing, and emitting) the light using a tissue phantom, detecting the transmitted light (which, in some embodiments, is a simulated stimulation pattern formed by the light), electrically processing the detector output, and displaying a numeric readout that corresponds to an optical characterization associated with the light. 
     In some embodiments of the present invention, an apparatus is described that includes a light from an optical source, a tissue phantom, an optical processing unit, an electrical processing unit, and a display for displaying a numeric readout that corresponds to an optical characterization associated with the light. 
     In some embodiments the present invention includes an apparatus comprising means for providing light from an optical source, means for simulating an organic tissue, means for optically processing the light using a simulated organic tissue, means for detecting the transmitted light, means for electrically processing the transmitted light, and means for displaying a numeric or graphical readout that corresponds to an optical characterization of the light. 
     In some embodiments, the present invention provides a method that includes receiving light from an optical source, providing a tissue phantom, transmitting at least a portion of the light through the tissue phantom, detecting the transmitted light and generating an electrical signal that characterizes the light transmitted through the tissue phantom, electrically processing the electrical signal, and displaying a representation of the electrically processed characterization associated with the light. 
     In some embodiments, the providing of the tissue phantom includes providing a plurality of areas on the tissue phantom including a first area and a second area, and wherein within the first area, the tissue phantom has a substantially constant first thickness, and within the second area, the tissue phantom has a substantially constant second thickness, and wherein the second thickness is different than the first thickness. 
     In some embodiments, the providing of the tissue phantom includes providing an area on the tissue phantom having a continuously varying thickness. 
     In some embodiments, the providing of the tissue phantom includes providing a plurality of areas on the tissue phantom including a first area and a second area, and wherein within the first area, the tissue phantom has a material representing a first tissue type, and within the second area, the tissue phantom has a material representing a second tissue type, and wherein the second tissue type is different than the first tissue type. 
     In some embodiments, the transmitted light corresponds to a pattern that simulates a pattern that would occur if the light were used to stimulate an animal tissue. 
     In some embodiments, the displaying includes displaying a plurality of different characteristics of the transmitted light. 
     In some embodiments, the displaying includes displaying a plurality of different characteristics of the transmitted light along each of a plurality of different transverse axes. 
     In some embodiments, the displaying includes displaying a numeric representation of an intensity of the transmitted light. 
     In some embodiments, the displaying includes displaying an iso-intensity map of the transmitted light. 
     In some embodiments, the displaying includes displaying a graph of light intensity along a cross-section of the transmitted light. 
     In some embodiments, the present invention provides an apparatus (e.g., system  100  of  FIG. 1A , or system  200  of  FIG. 2 ) that includes a first port configured to receive light from an optical source, a tissue phantom positioned such that at least a portion of the light passes through the tissue phantom, an optical detector operatively coupled to receive a portion of the light that passed through the tissue phantom and operable to generate a signal representing a characteristic of the received light, an electrical processing unit operatively coupled to receive the signal from the optical detector and operable to generate displayable information based on the signal, and a display operatively coupled to the electrical processing unit and configured to display the displayable information. 
     Some embodiments further include a second port configured to allow movement of the tissue phantom in order that different areas of the tissue phantom are successively placed between the received light and the detector. 
     Some embodiments further include a shutter configured to allow light to be detected only during a predetermined period of time. 
     Some embodiments further include a neutral density filter configured to reduce the intensity of light falling on the detector by a predetermined amount. 
     Some embodiments further include a lens or other focusing element (e.g., lens  147  of  FIG. 1  or imaging optics  212  of  FIG. 2 ) configured to form an image onto the detector of the transmitted light from the tissue phantom. 
     In some embodiments, the detector includes an infrared photocell (e.g., element  132  of  FIG. 1 ). 
     In some embodiments, the detector includes a two-dimensional array of pixels, each pixel detecting an amount of light falling on a predetermined area (e.g., element  232  of  FIG. 2 ). 
     In some embodiments, the tissue phantom (e.g., tissue phantom  151  of  FIG. 1D ) includes a first area and a second area, and wherein within the first area, the tissue phantom has a substantially constant first thickness, and within the second area, the tissue phantom has a substantially constant second thickness, and wherein the second thickness is different than the first thickness. 
     In some embodiments, the tissue phantom (e.g., tissue phantom  150  of  FIG. 1C ) includes an area having a continuously varying thickness. 
     In some embodiments, the tissue phantom (e.g., tissue phantom  151  of  FIG. 1D ) includes a first area and a second area, and wherein within the first area, the tissue phantom has a material representing a first tissue type, and within the second area, the tissue phantom has a material representing a second tissue type, and wherein the second tissue type is different than the first tissue type. 
     Some embodiments further include a handle (e.g., element  142  of  FIG. 1A , element  243  of  FIG. 2 , or element  342  of  FIG. 3 ) connected to the tissue phantom so that the tissue phantom can easily be inserted and removed from the path of the light being received from the optical source. 
     In some embodiments, the displayable information includes a numeric representation of an intensity of the transmitted light (e.g., element  134  of  FIG. 1A ). 
     In some embodiments, the displayable information includes an iso-intensity map of the transmitted light (e.g., element  251  of  FIG. 2 ). 
     In some embodiments, the displayable information includes a graph of light intensity along a cross-section of the transmitted light (e.g., element  252  of  FIG. 2 ). 
     In some embodiments, the present invention provides means for receiving light from an optical source, means for simulating the optical properties of organic tissue, means for transmitting at least a portion of the received light through the means for simulating the organic tissue, and means for displaying information about the light transmitted through the means for simulating organic tissue. 
     In some embodiments, the means for simulating the optical properties of organic tissue includes a means for representing organic tissue with a plurality of substantially constant and discrete thicknesses. 
     In some embodiments, the means for simulating the optical properties of organic tissue includes a means for representing organic tissue with a continuously varying thickness. 
     In some embodiments, the means for simulating the optical properties of organic tissue includes a means for representing a plurality of different organic tissue types on one device. 
     In some embodiments, the means for visibly displaying information about the transmitted light includes a means for numerically displaying a value of an intensity of the transmitted light. 
     In some embodiments, the means for visibly displaying information about the transmitted light includes a means for displaying an intensity of the transmitted light using iso-intensity lines. 
     In some embodiments, the means for visibly displaying information about the transmitted light includes a means for graphically displaying an intensity of the transmitted light along a cross-section of the transmitted light. 
     In some embodiments, the present invention provides an apparatus (e.g., tissue phantom  149  of  FIG. 1B , tissue phantom  150  of  FIG. 1C , tissue phantom  151  of  FIG. 1D , system  100  of  FIG. 1A , system  200  of  FIG. 2 , or system  300  of  FIG. 3 ) that includes a tissue phantom having a plurality of side-by-side areas each representing different tissue characteristics related to light transmission through organic tissue. 
     In some embodiments, the tissue phantom (e.g., tissue phantom  151  of  FIG. 1D ) includes a first area and a second area, and wherein the tissue phantom within the first area has a substantially constant first thickness, and the tissue phantom within the second area has a substantially constant second thickness, and wherein the second thickness is different than the first thickness. 
     In some embodiments, the tissue phantom (e.g., tissue phantom  150  of  FIG. 1C ) includes an area having a continuously varying thickness. 
     In some embodiments, the tissue phantom (e.g., tissue phantom  151  of  FIG. 1D ) includes a first area and a second area, and wherein within the first area, the tissue phantom has a material representing a first tissue type, and within the second area, the tissue phantom has a material representing a second tissue type, and wherein the second tissue type is different than the first tissue type. 
     In some embodiments, the tissue phantom includes a first area and a second area, and wherein the tissue phantom within the first area has a material representing a first tissue type stacked on a material representing a second tissue type, and wherein the second tissue type is different than the first tissue type, and wherein the tissue phantom within the first area has a material representing a third tissue type. 
     Some embodiments further include a handle (e.g., element  142  of  FIG. 1A , element  243  of  FIG. 2 , or element  342  of  FIG. 3 ) connected to the tissue phantom so that the tissue phantom can easily be inserted and removed from the path of the transmitted light. 
     Some embodiments further include an optical detector operatively coupled to receive a portion of light that passed through the tissue phantom and operable to display a representation of a characteristic of the received light. In some embodiments, the optical detector is configured to be separated from the tissue phantom after exposure to the light to provide a lasting representation of a characteristic of transmitted light. 
     Some embodiments further include an enclosure configured to hold the tissue phantom and a removable display card held in a fixed relationship to the tissue phantom by the enclosure, wherein the enclosure is configured to receive light from a medical light source at a predetermined distance from the tissue phantom and wherein the enclosure is configured to allow the removable display card to be removed after exposure to the light to provide a lasting representation of a characteristic of transmitted light. 
     In some embodiments, the present invention provides an apparatus that includes a first port configured to receive light from an optical source; a tissue phantom positioned such that at least a portion of the light passes through the tissue phantom; and an optical detector and display operatively coupled to receive a portion of the light that passed through the tissue phantom and operable to generate a visible representation of a characteristic of the received light. In some such embodiments, the detector and display are a unitary non-electronic laser-beam display unit, such as a frequency-doubling card (e.g., a cardboard substrate with a non-linear up-conversion material) that up-converts and displays infrared light (e.g., 1064 nm laser signal) as 532 nm visible green light, or such as a liquid-crystal thermographic display (irreversibly or reversibly changed by the laser beam, depending on the embodiment). 
     Some embodiments further include a tissue-phantom positioner configured to position one or more of a plurality of portions of the tissue-phantom between the first port and the optical detector, wherein the tissue phantom further comprises a first area and a second area, and wherein within the first area, the tissue phantom has a substantially constant first thickness, and within the second area, the tissue phantom has a substantially constant second thickness, and wherein the second thickness is different than the first thickness. 
     Some embodiments further include a tissue-phantom positioner configured to position one or more of a plurality of portions of the tissue-phantom between the first port and the optical detector, wherein the tissue phantom further comprises an area having a continuously varying thickness. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. Although numerous characteristics and advantages of various embodiments as described herein have been set forth in the foregoing description, together with details of the structure and function of various embodiments, many other embodiments and changes to details will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” and “third,” etc., are used merely as labels, and are not intended to impose numerical requirements on their objects.