Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/41—Detecting, measuring or recording for evaluating the immune or lymphatic systems
  • A61B5/414—Evaluating particular organs or parts of the immune or lymphatic systems
  • A61B5/415—Evaluating particular organs or parts of the immune or lymphatic systems the glands, e.g. tonsils, adenoids or thymus
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B18/18—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves
  • A61B18/20—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves using laser
  • A61B18/203—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body by applying electromagnetic radiation, e.g. microwaves using laser applying laser energy to the outside of the body
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B18/00—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body
  • A61B2018/00315—Surgical instruments, devices or methods for transferring non-mechanical forms of energy to or from the body for treatment of particular body parts
  • A61B2018/00452—Skin
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
  • A61B5/14532—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue for measuring glucose, e.g. by tissue impedance measurement
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/145—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue
  • A61B5/1455—Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissue using optical sensors, e.g. spectral photometrical oximeters
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N5/00—Radiation therapy
  • A61N5/06—Radiation therapy using light
  • A61N5/0613—Apparatus adapted for a specific treatment
  • A61N5/062—Photodynamic therapy, i.e. excitation of an agent

Definitions

• the present invention relates to modifying the optical properties of tissue on a transient basis, and more particularly, it relates to a method and apparatus for delivery of a chemical agent to a target tissue, in order to increase the optical transmission through this tissue, on a transient basis.
• the administered chemical agent displaces the aqueous interstitial fluid of the tissue, thereby effectively altering the interstitial refractive index of the tissue. If the index of refraction of the administered chemical is closer to that of the other components of the tissue, the introduction of this chemical will result in a reduction in the heterogeneity of the refractive indices of the tissue, which in turn reduces the level of scattering within the tissue. Since optical attenuation through the tissue is primarily due to absorption and scattering, a substantial change in scattering dramatically affects the optical attenuation characteristics of most biological tissues.
• the present invention is distinct from the prior art in that it changes the scattering properties of biological tissues, underlying the surface permeability barrier of tissue covering the said biological tissue, by changing the refractive index of the interstitial fluid within the stroma and the entire volume of the covered biological tissue. While topical administration of immersion fluids affects the optical transmission through biological tissues by only 3-4%, the present invention can improve light transmission through biological tissues by up to five or six hundred percent.
• the underlying target tissue layers are impermeable, and the chemicals administered topically to the outermost tissue layer will not reach the interstitial space of the tissue, and therefore will have no impact on the optical properties of the tissue.
• the authors indicate that a "360° peritomy was performed on the conjunctiva", but peritomy alone, which is an incision on the conjunctiva at the corneoscleral limbus of the eye, is not sufficient to allow sufficient volume of the clarifying agent to reach the target tissue (in this case, the sclera).
• a full surgical separation of the conjunctiva from the sclera is necessary, to allow the topical chemical agent to permeate into the interstitial space of the sclera.
• One of the objects of this invention is to provide a method and apparatus for enhancing optical transmission through biological tissues. Other objects of this invention will become apparent from the specifications, drawings, and by reference to the appended claims.
• Figure 1 illustrates the optical transmission characteristics of diatrizoate meglumine acid.
• Figures 2(a), 2(b), and 2(c) illustrate the results of measurement of the diffuse transmission characteristics for porcine sclera, before and after submersion in glycerol, after 5, 10, and 15 minutes, respectively.
• Figures 3(a), 3(b), and 3(c) illustrate the result of measurement of the diffuse transmission characteristics for porcine sclera, before and after submersion in diatrizoate meglumine acid, after 5, 10, and 15 minutes, respectively.
• Figure 4 illustrates the absorbance of human skin, in-vivo, immediately before and approximately 8 minutes after topical administration of glycerol, over a 460 nm to 800 nm spectral range.
• Figure 5 illustrates the absorbance of human skin, in-vivo, immediately before and approximately 8 minutes after topical administration of diatrizoate sodium injection solution (25%), over a 460 nm to 800 nm spectral range.
• Figure 6 illustrates diagrammatically a generalized system for bypassing surface permeability barrier of tissue, administering a topical chemical, and delivery of light.
• Figure 7 illustrates diagrammatically a suggested pattern for removing the stratum corneum.
• Figure 8 is a flowchart of a diagnostic algorithm which can be carried out in accordance with the invention.
• FIG. 9 is a flowchart of a treatment algorithm which can be carried out in accordance with the invention.
• Optical transmission through biological tissue is one of the major challenges of all optical diagnostic and therapeutic modalities which are intended to access structures underlying the tissue surface.
• diagnostics e.g., imaging tissue structures with microscopes
• signature optical information e.g., spectroscopic information
• Such images or optical information are distorted due to the attenuation of light, which is transmitted through, or reflected from, the tissue specimens.
• the goal is to selectively cause thermal necrosis in the target structures, without compromising the viability of surrounding tissues.
• the highly scattering medium of biological tissues serves to diffuse the incident light, and causes thermal damage to tissues surrounding the target structures, impacting the selectivity of the procedure in destroying the target structures. It is therefore important to adopt a strategy which could minimize the optical attenuation of the overlying and surrounding tissues to treatment target structures, in order to minimize collateral tissue damage, and maximize the therapeutic effects at the target tissue.
• Attenuation mechanisms of tissue can be characterized by determining the optical properties of tissue.
• the optical properties of tissue provide a practical basis for characterizing light propagation in this medium.
• the fundamental parameters which describe tissue optics are the absorption coefficient, ⁇ a (cm "1 )' the scattering coefficient, ⁇ s (cm -1 ), and the average cosine of the scattering angle associated with single scattering phase function, g.
• the probability that a photon is absorbed or conservatively scattered as it propagates in tissue is given by the product of the path length of the photon, ⁇ s, and the absorption and scattering coefficients, respectively.
• the phase function describes the probability, per unit solid angle, that a photon will be scattered into an angle ⁇ .
• the average cosine of the phase function, g (also known as the anisotropy factor) provides a measure of the direction of scattering. Scattering is purely in the forward direction when g is 1 or ⁇ is 0°; the light is purely backscattered when g is -1, or ⁇ equals 180°. An isotropic scattering is specified by g equaling 0.
• the radiative transport theory provides a heuristic model that deals directly with the transport of power through turbid media.
• the distribution of light propagating through a turbid medium is given by the radiative transfer equation (Chandrasekar, 1960):
• ⁇ (s,s') represents the probability density function for scattering from direction s' to s.
• ⁇ (s,s') represents the probability density function for scattering from direction s' to s.
• isotropic media the phase function is simply l/(4 ⁇ ).
• anisotropic media such as most biological tissues
• anisotropic media such as most biological tissues
• Scattering in a turbid medium is due to the heterogeneity of the refractive index of the constituent elements in the medium.
• the main constituent of tissue water (by approximately 80%), has a refractive index of 1.33, whereas the refractive index of collagen is 1.45, and the refractive index of other constituents of tissue are also different from water, by a magnitude sufficient to result in a high level of optical scattering within the tissue. Any approach which serves to minimize this heterogeneity, will have a substantial impact on reducing the scattering within the tissue, leading to a higher optical transmission through the tissue.
• glycerol topically, to enhance visualization through edematous corneas to allow adequate gonioscopic and ophthalmoscopic examinations. It has been long since known that glycerol applied topically in concentrations from 50% to 100% is effective in clearing edematous corneas, within two minutes following administration (Flood et al, 1989). It should be noted, however, that this method of applying hyperosmotic topical agents has been limited only to the cornea, and the prior art does not suggest such application for any other tissue type. Moreover, the method of topical administration of such chemical agents is ineffective in altering the optical properties of tissues other than the cornea, so long as the surface permeability barrier of tissue of the tissue (e.g., stratum corneum for the skin) is in place.
• tissue of the tissue e.g., stratum corneum for the skin
• the present invention involves the application of a clarifying chemical agent to biological tissues, which are covered by a surface permeability barrier of tissue, in- vivo, ex -vivo, or in- vitro, for the purpose of augmenting the optical transmission through these tissues. While the basis of this effect has not been established definitively, in a number of experiments described below, it has been shown that optical transmission through tissues can be substantially enhanced, on a transient basis, using the topical administration of chemicals such as diatrizoate meglumine acid (commercially known as Hypaque®), glycerol, or glucose (hereinafter referred to as "clarifying agents").
• diatrizoate meglumine acid commercially known as Hypaque®
• glycerol glycerol
• glucose hereinafter referred to as "clarifying agents”
• the tissue transport phenomena replace a portion of the tissue's water content with the above chemical agents, and the optical properties of these chemicals alter the bulk optical properties of the tissue such that the optical transmission through the tissue is increased.
• the same transport phenomena replace these agents with water, restoring the tissue's original optical properties.
• the higher refractive index of these fluids (more than that of water, and closer to the refractive index of collagen and other constituents of tissue), leads to a reduction in the heterogeneity of refractive indices of the constituents of tissue, and therefore reduces the overall scattering of light as it is transmitted through the tissue.
• This method can be termed "interstitial refractive index matching", or IRIM.
• Glycerol is a trihydric alcohol, a naturally occurring component of body fat. It is absorbed from the gastrointestinal tract rapidly, but at a variable rate. As such, topical administration of glycerol is not expected to cause any adverse effects, and should be a completely safe approach for altering the optical properties of tissues, prior to light irradiation.
• Diatrizoate meglumine acid which is commercially known as Hypaque®, is a radiographic injection solution.
• Hypaque® the increased transmission through the tissue may be due to IRIM, or optical transmission characteristics which are superior to that of water, or a combination of both effects.
• a cuvette was filled with diatrizoate meglumine acid and its optical transmission characteristics were evaluated using a Varian CARY 5ETM UV-Vis-NIR spectrophotometer. The transmission characteristics were similar to that of a "high- pass filter", and the chemical exhibited very low transmission for wavelengths below approximately 400 nm, and very high transmission for wavelengths above 400 nm (see Figure 1).
• Porcine eyes were enucleated immediately post-mortem, and were transported to the laboratory in a wet gauze pad, held at 4°C during transport in a well-insulated cooler. Each eye was inflated with saline. Limbal conjunctiva and Tenon's capsule were dissected and excised using a pair of blunt Wescott scissors. A No. 64 Beaver blade was then used to outline 20 mm X 20 mm sections of the sclera from the limbus to the equator of the globe. Incisions were deepened to the supra-choroidal space. Sections of sclera were then lifted off the intact choroid and ciliary body. Scleral thickness was measured and was determined to be 1.65 mm on average.
• the conjunctiva was stretched over the sclera, again, and stay sutures were used to re-attach the conjunctiva to the limbal region.
• Ocumycin® was administered topically to both eyes which had undergone surgery, to prevent infection. After approximately 5-10 minutes, the sclera in both eyes became opaque, again.
• follow up examination on days 1, 3, and 5 showed no signs of inflammation on either eye.
• Two skin surfaces on the forearm were shaved and cleaned prior to measurements.
• a tape-strip method was used to remove the stratum corneum.
• Droplets of glycerol were then topically administered on one site, and droplets of the diatrizoate sodium injection fluid were administered on the second site, which was separated from the first site by 5 cm (a sufficient distance to ensure that the topical drug administered on one site does not interfere with the drug administered on the other site, through diffusion).
• the topical drugs administered formed an approximate circle of 1 cm in diameter. The drugs were left to diffuse into the tissue for approximately 8 minutes.
• FIGS. 4 and 5 illustrate the results from the above measurements.
• the data displayed in these graphs have been limited to a range of 480 nm to 800 nm to remove the portions of the spectra which were fraught with noise.
• the tape stripping of the skin causes a mild irritation of the skin, leading to a transient erythema. This erythema was noticed in both sites immediately after tape stripping, and subsided by the time the measurement after topical administration of the drug was made.
• the spectra measured prior to topical administration of the drugs clearly demonstrate the higher concentration of blood immediately below the surface, as evidenced by the strong oxyhemoglobin peaks at approximately 530 nm and 560 nm.
• Figure 4 and 5 demonstrate that the topical administration of glycerol and diatrizoate sodium injection solution, respectively, lead to an increase in absorbance of tissue, in-vivo, of up to 60.5% and 107% respectively.
• This increase in tissue-absorbance is believed to be caused by IRIM, leading to a reduction of the scattering of the superficial layers of the skin, thereby allowing a larger percentage of light to reach (and get absorbed by) the native chromophores of the skin (melanin and blood), thereby increasing the measured absorbance of the tissue.
• the apparatus of the present invention comprises the following components: a) apparatus for bypassing the surface permeability barrier of tissue, such as the stratum corneum for the skin, or the conjunctiva for the eye; b) apparatus for topically or interstitially applying a chemical agent; and c) apparatus for delivery or collection of light for diagnostic or therapeutic purposes. Since each of these components consists of devices which are individually known to those skilled in the art, they are shown diagrammatically in Figure 6. The preferred embodiment of this invention may be a combination of all three components, or different combinations of the above in twos.
• the stratum corneum is a sheet of essentially dead cells which migrate to the surface of the skin. It is well known that dry stratum corneum is relatively impermeable to water soluble substances, and it serves to maintain the hydration of the skin, by providing a barrier for evaporation of the water content of the skin, and also by serving as a barrier for fluids exterior to the body to diffuse into the skin.
• this surface tissue layer will be referred to as the "surface permeability barrier of tissue", or SPBT, and the underlying tissue layer, as “covered biological tissue” or CBT.
• a driving force can be applied to move molecules across the SPBT; this driving force can be electrical (e.g., iontophoresis, electroporation) or it may be physical, or chemical force, such as that provided by a temperature gradient, or a concentration gradient of a clarifying agent, or of a carrier agent (carrying clarifying agent) for increasing the permeability of the surface permeability barrier of tissue; alternatively, the driving force may be due to acoustic or optical pressures, as described by Weaver, et al. (Weaver, Powell, & Langer, 1991).
• one configuration for component 1 of Figure 6 can be an electric pulse generator for inducing electroporation of the stratum corneum.
• This system for instance, can be similar to the apparatus described by Prausnitz, et al.(Prausnitz et al., 1997).
• component 1 may consist of a mechanical device with adhesive tape on the distal end, which may be brought in contact with the skin for tape stripping the stratum corneum. With each adhesion and detachment of the tape from the skin surface, a layer of the stratum corneum can be removed.
• the component may include means of advancing the tape with each application, so that a fresh tape surface can be used in each application.
• component 1 may consist of a device which physically breaches the surface permeability barrier of tissue by abrasion, to expose the underlying tissue (CBT) which has a greater permeability. In the case of skin, this method is commonly known as dermabrasion.
• component 1 may be an ablative solid state laser, such as any one of the following lasers: E ⁇ YAG, Nd:YAG, Ho:YAG, Tm:YAG, Er:YSGG, E ⁇ Glass, or an ablative semiconductor diode laser, such as a high-powered GaAs laser, or an ablative excimer laser, such as an ArFl or a XeCl laser.
• ablative semiconductor diode laser such as a high-powered GaAs laser
• an ablative excimer laser such as an ArFl or a XeCl laser.
• These lasers can be used to ablate the stratum corneum in its entirety with each pulse, over the surface area covered by the laser spot size.
• the short ablation depth of such lasers in human tissue allows for a rapid removal of the stratum corneum with each laser pulse.
• component 1 may be an ultrasonic generator, causing poration of the stratum corneum, for instance as described by Kost (Kost et al., 1998). This approach is sometimes referred to as sonophoresis, or phonophoresis.
• component 1 may be a radiofrequency generator, selectively ablating a finite volume of the stratum corneum with each application, in a similar manner, for instance, as described by Manolis et al. (Manolis, Wang, & Estes, 1994) for ablation of arrhythmogenic cardiac tissues.
• component 1 may be an iontophoresis system for drug delivery through the stratum corneum, for instance as described by Prausnitz, et al. (Prausnitz et al., 1997).
• component 1 may be a microfabricated microneedle array, long enough to cross the SPBT , but not long enough to reach the nerve endings of the tissue, as that conceived, for instance, by the needle a ⁇ ay developed by Henry et al. (Henry, McAllister, Allen, Prausnitz et al., 1998).
• the clarifying agent can be topically administered onto the SPBT and the microneedle array can then be inserted through the same surface permeability barrier of tissue. The insertion of the needle array will produce an array of apertures through the SPBT, which will then cause an increase in the permeation of the clarifying agent to the covered tissue (CBT).
• electrical arcing may be used to ablatethe SPBT. This may be done by an electrical generator that delivers electrical arcs at its delivery probe tip. Since stripping a large surface area of the stratum corneum, for instance, may be detrimental for the viability of the skin, the openings may be formed in an array of channels, or apertures, as shown in Figure 7.
• component 1 may be a dispenser for a chemical enhancer or carrier agent for transdermal drug delivery.
• a chemical enhancer for transdermal drug delivery.
• DMSO dimethyl sulfoxide
• Other examples include different alcohols such as ethanol.
• Component 1 can consist of a device to create a surgical flap of the conjunctiva, which can subsequently be sutured back onto the intact ocular tissues.
• Component 1 can consist of a device to create a surgical flap of the conjunctiva, which can subsequently be sutured back onto the intact ocular tissues.
• the epithelium of mucosa it is possible to use the same device to create openings in the underlying tissue.
• porative approaches e.g., electroporation, ultrasonic poration, RF poration, microneedle array, chemical enhancement of trans-membrane delivery, or iontophoresis
• component 1 e.g., electroporation, ultrasonic poration, RF poration, microneedle array, chemical enhancement of trans-membrane delivery, or iontophoresis
• the chemical may be injected interstitially, using an apparatus similar to a syringe with a hypodermic needle, in order to bypass the surface tissue layer.
• This approach is more invasive, but the apparatus may be simpler.
• Component 2, in Figure 6, is an applicator for administering the chemical topically.
• One possible configuration is a syringe, which dispenses the desired chemical over the tissue.
• Component 3 of the overall system is the optical delivery or collection apparatus, which may be a fiberoptic probe (single or multi-fiber probe) , or an articulated arm with specialized optics, depending on the optical delivery system, or optical imaging systems for image acquisition, such as a microscope.
• the optical delivery or collection apparatus may be a fiberoptic probe (single or multi-fiber probe) , or an articulated arm with specialized optics, depending on the optical delivery system, or optical imaging systems for image acquisition, such as a microscope.
• the invention described here has broad applications across a wide range of optical procedures.
• the method described here essentially serves to augment optical penetration of biological tissues, whether for diagnostic or therapeutic purposes.
• the present method enhances any optical method that attempts to investigate objects or structures imbedded, or fluids within tissues, or analytes that exist within the blood or other biological fluids. Since this method serves to enhance transmission across a broad spectral range, it can be used in routine white-light microscopy to probe at focus planes underneath the surface. Alternatively, it could be used for spectroscopic (e.g., reflectance, fluorescence, or raman) information gathering.
• spectroscopic e.g., reflectance, fluorescence, or raman
• this invention can be used for confocal microscopy to penetrate deep into the covered tissue, CBT, (e.g., on the order of millimeters) to examine a variety of cellular information, including cellular structures, imbedded tissue appendages, and various pigmented and non-pigmented lesions.
• Optical coherence tomography is a diagnostic method which relies on the reconstruction of scanned interferometric information from backscattered light from the tissue. This method is also limited in its resolution by the extent of optical penetration through the superficial layers, to probe imbedded objects. The present method could again serve to substantially augment the utility of OCT in investigating objects/structures imbedded in tissue.
• Another application is the collection of fluorescence from fluorophores imbedded in tissue, as a diagnostic means of assessing presence or absence of biological parameters.
• the present method could enhance the signal to noise ratio of such a detection scheme.
• Another application is in sensing of analytes within biological fluids in the tissue.
• the present invention may be used to non-invasively measure spectroscopic information from fluids such as the blood or interstitial fluid, in order to determine glucose concentration, or cholesterol level.
• Another application for this method is in the use of other optical imaging methods for tumor detection, such as photon migration and optical tomography techniques.
• Another application is in the use of photodynamic means of diagnosis of diseased/abnormal tissues.
• the depth of penetration of the activating light generally limits photodynamic methods.
• the present invention will allow deeper penetration of visible-wavelength radiation for photodynamic activation.
• Figure 8 illustrates a typical algorithm for applying the present invention for a diagnostic procedure.
• the present method is applicable to a wide array of therapeutic means involving imbedded objects in the tissue. In the field of ophthalmology, it encompasses all transscleral procedures, including transscleral cyclophotocoagulation, and transscleral retinopexy.
• applications include (but are not limited to) optical (or laser) targeting of all skin appendages, including the hair follicle (for permanent laser hair removal), pigmented and vascular lesions, tattoo removal, sebaceous glands (for acne treatment), subcutaneous fat (for optical liposuction), and eccrine glands (for permanent treatment of body odor).
• optical or laser
• the present method is applicable for photodynamic therapy of various cancerous tissues, augmenting the delivery of light to the photosensitizers bound to diseased tissues.
• the present invention significantly enhances the depth of penetration of light across a broad wavelength range.
• Figure 9 illustrates a typical algorithm for applying the present invention to a therapeutic procedure.
• the present invention also improves the efficacy of the diagnostic and therapeutic procedures, when energy sources from other segments of the electromagnetic spectrum are used (e.g., radiofrequency, and microwaves). Since IRIM also affects the overall elastic properties of tissues, acoustic signals travelling through tissue could also be affected, leading to a deeper penetration for ultrasonic waves for diagnostic and therapeutic purposes.
• energy sources from other segments of the electromagnetic spectrum e.g., radiofrequency, and microwaves.

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