Patent Publication Number: US-9895063-B1

Title: Sensing and avoiding surgical equipment

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a division of application Ser. No. 14/506,335, filed Oct. 3, 2014, which application is incorporated herein by reference. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     A variety of methods exist to generate information about biological tissues. Such methods can include exposing the biological tissues to an energy or field (e.g., an electric field, a magnetic field, an electromagnetic field, a light, an acoustic energy) and detecting a response of the biological tissues (e.g., a modification of the energy, and/or the emission of a second energy) that is related to one or more properties of the biological tissues. Properties of the biological tissues could include a type and/or distribution of cells and/or tissues within the biological tissues, a health or disease state of the biological tissues, the presence of a fluorophore or other contrast agent in the biological tissues, or some other information about the biological tissues. Such measured properties could be related to a health or medical condition of a human or animal containing the biological tissues and/or from which the biological tissues are derived. 
     In some examples, information about biological tissues could be generated to guide a surgical intervention related to the biological tissues. For example, the presence, location, extent, or other information about cancerous cells in a biological tissue could be determined and a surgical intervention (e.g., a removal or destruction of the cancerous cells, a placement of a drug-eluting device or other artifact within a mass of the cancerous cells) could be performed based on the determined information. In some examples, such information is generated before a surgical intervention (e.g., by a pre-surgical MRI, CT, or other type of scan or imaging) and used to inform a surgeon&#39;s actions during the surgical intervention. 
     SUMMARY 
     Some embodiments of the present disclosure provide a method including: (i) illuminating, by a light source, a portion of a surgical environment, wherein the surgical environment comprises tissue subject to a surgical intervention involving one or more surgical instruments (ii) receiving light from the illuminated portion of the surgical environment; (iii) determining a spectrographic content of the received light; and (iv) identifying at least one of a portion of the tissue or a portion of a foreign body in the illuminated portion of the surgical environment based on the spectrographic content of the received light. 
     Some embodiments of the present disclosure provide a system including: (i) a light source configured to illuminate a portion of a surgical environment, wherein the surgical environment comprises a tissue subject to a surgical intervention involving one or more surgical instruments; (ii) a detector configured to detect a spectrographic content of light received from the illuminated portion of the surgical environment; and (iii) a controller operatively coupled to the light source, wherein the controller includes a computing device programmed to perform operations comprising: (a) controlling the light source to illuminate the portion of the surgical environment; (b) controlling the detector to obtain the spectrographic content of the light received from the illuminated portion of the surgical environment; and (c) identifying at least one of a portion of the tissue or a portion of a foreign body in the illuminated portion of the surgical environment based on the spectrographic content of the received light. 
     Some embodiments of the present disclosure provide a system including: (i) means for illuminating a portion of a surgical environment, wherein the surgical environment comprises a tissue subject to a surgical intervention involving one or more surgical instruments; (ii) means for detecting a spectrographic content of light received from the illuminated portion of the surgical environment; and (iii) means for controlling the light source and the detector and configured to perform operations comprising: (a) controlling the means for illuminating the portion of the surgical environment to illuminate the portion of the surgical environment; (b) controlling the means for detecting the spectrographic content of light received from the illuminated portion of the surgical environment to obtain the spectrographic content of the light received from the illuminated portion of the surgical environment; and (c) identifying at least one of a portion of the tissue or a portion of a foreign body in the illuminated portion of the surgical environment based on the spectrographic content of the received light. 
     These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example surgical environment. 
         FIG. 2A  illustrates example spectrographic content of light received from a portion of a surgical environment. 
         FIG. 2B  illustrates example spectrographic content of light received from a portion of a surgical environment. 
         FIG. 2C  illustrates example spectrographic content of light received from a portion of a surgical environment. 
         FIG. 2D  illustrates example spectrographic content of light received from a portion of a surgical environment. 
         FIG. 2E  illustrates example spectrographic content of light received from a portion of a surgical environment. 
         FIG. 3A  illustrates an example image of the surgical environment of  FIG. 1  determined based on spectrographic content of light received from the surgical environment. 
         FIG. 3B  illustrates an example image of the surgical environment of  FIG. 1  determined based on spectrographic content of light received from the surgical environment. 
         FIG. 3C  illustrates an example image of the surgical environment of  FIG. 1  determined based on spectrographic content of light received from the surgical environment. 
         FIG. 4A  illustrates an example surgical environment containing a fluorophore. 
         FIG. 4B  illustrates an example image of the surgical environment of  FIG. 4A  determined based on spectrographic content of light received from the surgical environment. 
         FIG. 5A  illustrates an example system imaging a surgical environment. 
         FIG. 5B  illustrates example spectrographic content of light received from a portion of the surgical environment of  FIG. 5A  by the system of  FIG. 5A . 
         FIG. 6A  illustrates an example system imaging a surgical environment. 
         FIG. 6B  illustrates an example image of the surgical environment of  FIG. 6A  obtained by the system of  FIG. 6A . 
         FIG. 7A  illustrates an example system imaging a surgical environment. 
         FIG. 8A  illustrates an example system imaging a surgical environment. 
         FIG. 8B  illustrates example spectrographic content of light received from portions of the surgical environment of  FIG. 8A  by the system of  FIG. 8A . 
         FIG. 9  is a functional block diagram of an example imaging system. 
         FIG. 10  is a flowchart of an example method. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying figures, which form a part hereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, figures, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     Further, while embodiments disclosed herein make reference to use on or in conjunction with a living human body and/or tissues thereof, it is contemplated that the disclosed methods, systems and devices may be used in any environment where spectrographic imaging and/or identification of tissues or other objects or elements of an environment is desired. The environment may be any living or non-living body or a portion thereof, a work piece, an implantable device, etc. Moreover, while the present disclosure describes embodiments for use in vivo, one of skill in the art will also recognize that in vitro applications are possible as well. Accordingly, the environment may also include a test tube or other vessel for holding a fluid, a transplant tissue, and/or a stereotaxically or otherwise immobilized tissue. 
     I. Overview 
     A variety of information about tissues or other contents of a surgical environment (i.e., of a region containing tissue(s) of a human or animal body subject to some surgical intervention) could be determined based on spectrographic or other optical information about the contents of the surgical field. That is, spectrographic information about a particular portion or region of tissue within the surgical environment could be used to determine a tissue type, a disease state (e.g., a presence of cancer cells), the presence of a marker or fluorophore, a health state (e.g., a degree of perfusion), or some other information about the portion or region of tissue. Additionally or alternatively, such spectrographic information could be used to determine that a particular portion or region of the surgical environment contains a surgical instrument, suture, drape, staple, stent, or other artificial device or foreign body. Such information could be used to guide and/or plan a surgical intervention, to image tissue(s) of a human or animal body, to determine the effect of a surgical intervention (e.g., to determine a degree of ablation, cautery, debridement, or other surgical processes), or to enable some other applications. 
     Spectrographic information (or content) could include any information about the dependence of the absorbance, reflectance, excitation, emission, or some other interaction of a particular portion of a surgical environment with light applied to the portion (e.g., visible, infrared, or ultraviolet light) on the wavelength of the applied and/or emitted light. That is, spectrographic information could include one or more of an absorbance spectrum, a reflectance spectrum, an excitation spectrum, an emission spectrum, or some other spectrum detected and/or determined for a plurality of wavelengths. For example, spectrographic information could include a spectrum of light (e.g., a plurality of detected amplitudes corresponding to the amplitudes of light received in a plurality of respective ranges of wavelengths) emitted from a portion of the surgical environment in response to illumination of the portion of the surgical environment by light having a single specified wavelength. In another example, spectrographic information could include the amplitude of light emitted from a portion of the surgical environment in response to illumination of the portion of the surgical environment by light having a plurality of different wavelengths (i.e., a reflectance and/or absorbance spectrum), or a plurality of different polarizations, intensities, or other properties. 
     In some embodiments, a system includes a laser (or similar source of substantially monochromatic light) configured to illuminate a portion of a surgical environment. The system further includes a spectrometer (or similar optical imaging equipment) configured to detect light emitted from the portion of the surgical environment in response to illumination such that spectrographic information (e.g., an emission spectrum) can be determined for the portion of the surgical environment. This determination could be performed by a controller of the system. Such a controller could be further configured to determine some information about the portion of the surgical environment based on the determined spectrographic information, e.g., to determine that the portion contains a portion of tissue of a particular type, that the portion contains a portion of a surgical instrument or other foreign body, that the portion contains a fluorescent or other type of marker chemical(s), or some other determination or classification based at least on the determined and/or detected spectrographic information. 
     In some embodiments, a system includes a tunable laser configured to illuminate a portion of a surgical environment with illumination having a controllable wavelength. The system further includes a light sensor (or similar optical imaging equipment) configured to detect light emitted from the portion of the surgical environment in response to illumination (e.g., a photodetector, photodiode, phototransistor, or other photosensitive element(s)). Thus, spectrographic information (e.g., a reflectance and/or absorbance spectrum) can be determined for the portion of the surgical environment by illuminating the portion of the surgical environment with light having a plurality of different respective wavelengths during a respectively plurality of periods of time and detecting the amplitude (or other property) of light responsively emitted (e.g., reflected, absorbed, scattered) from the portion of the surgical environment during the plurality of periods of time. This operation of the system could be performed by a controller of the system. Such a controller could be further configured to determine some information about the portion of the surgical environment based on the determined spectrographic information, e.g., to determine that the portion contains a portion of tissue of a particular type, that the portion contains a portion of a surgical instrument or other foreign body, that the portion contains a fluorescent or other type of marker chemical(s), or some other determination or classification based at least on the determined and/or detected spectrographic information. 
     Spectrographic information (and determinations or other processes performed based on such information) could be determined for a particular portion of a surgical environment or for a plurality of portions of the surgical environment. Determination of spectrographic information for an area of a surgical environment could be performed by illuminating and/or detecting light from a plurality of spots or other sub-regions of the area of the surgical field. For example, spots, lines, or other portions of the surgical environment could be illuminated by focusing a beam from a light source. Further, a light sensor could be configured to detect light from specified spots, lines, or other portions of the surgical environment. Additionally or alternatively, determination of spectrographic information for an area of a surgical environment could be performed by illuminating and/or detecting light from the entire area at once (e.g., by imaging the area using a CCD, an array of active pixel sensors, or some other imaging device). 
     Determined spectrographic information for a portion of a surgical environment could be used in a variety of ways to determine the identity of contents and/or one or more properties of the contents of the portion of the surgical environment. For example, a classifier could be used to determine that the portion of the surgical environment contains a portion of a surgical implement or other foreign body, that the portion of the surgical environment contains a portion of tissue of a particular type (e.g., connective tissue, blood vessels, blood, white matter brain tissue, grey matter brain tissue, cancerous tissue, muscle tissue), that the portion of the surgical environment contains a particular marker or contrast agent (e.g., a fluorophore, a chromophore, a Raman dye, a nanodiamond, a conductive nanostructure), or some other state or property of the portion of the surgical environment. Such classifiers could additionally be used to determine that the portion of the surgical environment contains a combination of tissues and/or objects. 
     Such classifiers could include a variety of algorithms and/or combinations of algorithms, including support vector machines, k-means clustering, neural nets, principal component or other dimensionality reductions, or other classification techniques or algorithms. Further, such classifiers could be created from supervised learning (e.g., trained using a number of samples having known contents or some other known property). Additionally or alternatively, such classifiers could be trained wholly or partially using unsupervised learning techniques. 
     Determined information about the identity or other properties of contents of a portion of a surgical environment could be used to enable a variety of applications. For example, such information could be used to determine the extent, location, or other information about tissues in a surgical field (e.g., the location and extent of an aggregation of cancerous cells in a tissue, of a nerve, of a blood vessel). Such information could be used to guide and/or plan a surgical intervention (e.g., to excite, ablate, debride, or otherwise remove a target tissue). For example, such information could be presented to a surgeon (e.g., on the display of a device and/or through an augmented reality head-mounted display) such that the surgeon could operate a scalpel, cautery tool, laser, RF, and/or contact thermal ablation tool, a surgical tele-robot, cryosurgical implement, a high-intensity focused ultrasound (HIFU) instrument, or some other surgical tool(s). Additionally or alternatively, a computer-guided surgical implement (e.g., a computer-controlled carbon-dioxide laser configured to ablate tissue through heating) could be operated according to such determined information (e.g., the computer-controlled laser could be operated to ablate tissues in regions of the surgical field determined, using spectrographic data, to contain cancer cells and not to contain surgical instruments or other foreign bodies). Other applications of and/or operations relative to determined spectrographic information are anticipated. 
     Other configurations, modes and methods of operation, and other embodiments are anticipated. System and/or methods described herein could include additional imaging modalities to improve the identification of the contents of portions of a surgical environment according to an application. A system as described herein could include multiple light emitters, multiple light sensors, and/or additional components according to an application. The system could be applied toward implementing, planning, and/or assessing a surgical intervention (e.g., ablation of a tissue), imaging a tissue, or some other application. Further, systems as described herein could be applied to the identification of the contents of portions of environments other than surgical environments (e.g., food processing environments, industrial fabrication environments, environments under study in scientific research) by determining spectrographic information about the portions of the other environments. Other applications and configurations of systems as described herein are anticipated. 
     It should be understood that the above embodiments, and other embodiments described herein, are provided for explanatory purposes, and are not intended to be limiting. 
     Further, the term “surgical intervention” as used herein should be understood broadly to include any activities applied toward the modification of the anatomy and/or tissue(s) of a human or animal body by the application of external forces and/or energies to the human or animal body; e.g., incision, ablation and/or cauterization by RF or other directed energies, excision, resection, suturing, application of surgical adhesives, stapling, transplanting, cauterizing, sawing, abrading, applying a surgical fluid to (e.g., sterile, isotonic saline), cooling, heating, or any other surgical operation or procedure. 
     II. Example Surgical Environment and Spectrographic Content 
       FIG. 1  illustrates an example surgical environment  100 . The surgical environment  100  includes biological tissues (e.g.,  130 ,  140 ,  150 ,  160 ,  170 ) that are subject to a surgical intervention using surgical instruments (e.g.,  110 ,  120   a ,  120   b ) and other foreign bodies (e.g.,  180 ). The biological tissues include skin  130  that has been cut a retracted away and muscles  140 ,  160  exposed by the retraction of the skin  130 . The first muscle  140  has a tendon  150 , and a blood vessel  170  is present on the surface of the muscles  140 ,  160 . Further, a fluorophore (e.g., a fluorescent dye, a fluorescent marker configured to selectively interact with an analyte in the muscle  145 ) is present in a fluorescent portion  145  of the first muscle  140 . The surgical instruments and other foreign bodies include a retractor having blades  120   a ,  120   b  being operated to retract the skin  130  to expose the underlying biological tissues (e.g.,  140 ,  150 ,  160 ,  170 ,  145 ). A hemostat  110  that is clamping the blood vessel  170 , and sutures  180  that have been sewn into the second muscle  160  (e.g., to close a wound or other cut or incision). The hemostat  110  has a fluorescent portion  115  (e.g., that is contaminated with a fluorophore, e.g., is coated with a fluorescent dye) that has similar fluorescent properties (e.g., emission wavelength(s), excitation wavelength(s)) as the fluorescent portion  145  of the first muscle  140 . Note that the illustration of muscle tissue and other tissues, surgical instruments, and/or foreign bodies in  FIG. 1  and elsewhere herein are intended as non-limiting illustrative examples. Systems and methods described herein could additionally or alternatively be applied to other organs, tissues, and tissue types, e.g., liver tissue, kidney tissue, connective tissue, pancreatic tissue, bowel tissue, prostate tissue, cortical tissue, nerve tissue, lung tissue, or some other type or types of tissue at some other location(s) of a body. 
     The biological tissues (e.g.,  130 ,  140 ,  145 ,  150 ,  160 ,  170 ), surgical instruments (e.g.,  110 ,  120   a ,  120   b ), and other foreign bodies (e.g.,  180 ) in the surgical environment  100  could, respectively, have a number of properties relating to receiving, emitting, modifying, or otherwise interacting with electromagnetic energy (e.g., visible light, ultraviolet light, infrared light). A particular element (e.g., the hemostat  110 ) or portion of an element (e.g., the fluorescent portion  145  of the first muscle  140 ) in the surgical environment could have a wavelength-dependent interaction with electromagnetic radiation, i.e., the particular element could have an absorption, reflection, scattering, excitation, emission, or other type of spectrum related to the wavelength dependence of the absorption, reflection, scattering, emission, or other type of interaction between the particular element and electromagnetic radiation. 
     For example, an absorption or other spectrum of a biological tissue could be related to the presence of water, melanin, hemoglobin, or other substances in the tissue. In another example, an excitation and/or emission spectrum of a biological tissue, surgical instrument, or other foreign body could be related to the presence of one or more fluorophores or other fluorescent elements on or within in the biological tissue, surgical instrument (e.g., a contamination of fluorescent dye on the surface of the surgical instrument), or other foreign body. In some examples, an absorbance and/or reflectance spectrum of a metallic surgical instrument or foreign body, or a metallic portion thereof, could be related to a composition, geometry, surface texture, electron band structure, or other property of the metallic surgical instrument, foreign body, or portion thereof. Properties of a biological tissue (e.g., absorption spectrum, excitation spectrum, emission spectrum) could be related to a medical state of the biological tissue. For example, a cancerous tissue could have an absorbance spectrum (e.g., could be a different color) different from the absorbance spectrum of a non-cancerous tissue. Additionally or alternatively, a fluorophore, chromophore, or other marking agent could be introduced (e.g., by direct application, by injection into the bloodstream of a person) to a particular tissue (e.g., a cancerous tissue) and one or more spectrographic properties of the marking agent and/or of the combination of the marking agent and the particular tissue could be detected to determine the location, shape, or other properties of the particular tissue. Such a marking agent could be configured to selectively interact with a particular tissue (e.g., by binding to a protein or other element specific to the particular tissue) such that systemic application of the marking agent (e.g., by injection into the bloodstream of a person) could allow the marking agent to be concentrated in the particular tissue. In another example, the absorption spectrum of a tissue could be related to the amount of oxygenation of hemoglobin in the tissue, such that the oxygen content, perfusion rate, or other information about the tissue could be determined based on a determined and/or detected absorption spectrum or features thereof. 
     Spectrographic information about a biological tissue, surgical instrument, foreign body, or other portion of a surgical environment could be detected and/or determined by illuminating the portion of the surgical environment, detecting light that is emitted from the portion in response to the illumination, and determining some spectrographic content of the received light. Determining spectrographic content could include generating a spectrum (e.g., a reflectance spectrum, an emission spectrum, an absorbance spectrum) from the received light by detecting the a plurality of amplitudes of the received light within a respective plurality of ranges of wavelengths. That is, the spectrographic content could include a plurality of detected and/or determined amplitudes corresponding to wavelengths of the received light, e.g., at specified wavelengths linearly spaced within a range of wavelengths. Such a determined spectrographic content could be generated related to the illumination of the contents by light of a single wavelength. Alternatively, such spectrographic content could be determined a plurality of times corresponding to illumination of the contents during a respective plurality of different periods of time by light of a respective plurality of different single wavelengths. 
     Spectrographic contents could include a description of one or more features of a spectrum or other wavelength-dependent optical properties of the contents; for example, spectrographic content could include an absolute or relative amplitude, mean wavelength, width at half maximum, or other descriptive information about a peak or other feature of a spectrum of a portion of a surgical environment. Such spectrographic contents could be determined based on a determined and/or detected spectrum (e.g., by extracting an amplitude, width, or wavelength location of a peak within a determined and/or detected plurality of detected amplitudes corresponding to wavelengths of light received from the surgical environment). Alternatively, such spectrographic contents could be determined in other ways, e.g., through an iterative process that includes controlling a wavelength of light illuminating a portion of the surgical environment to minimize an amplitude of light received from the portion in response to the illumination, e.g., to determine a wavelength of a peak within the absorbance spectrum of the portion. Other types of spectrographic contents and methods of detecting and/or determining such spectrographic contents are anticipated. 
     In some examples, one or more spectra of a biological tissue, surgical instrument, foreign body, or other object in the surgical environment could be altered by the addition of a fluorophore, chromophore, pigment, dye, coating, or other substance according to an application. For example, a fluorophore configured to selectively interact with an analyte (e.g., with an enzyme, protein, marker, or other element expressed by cancer cells) could be introduced into a body containing tissues subject to a surgical intervention (e.g., a body of a person to be surgically treated for cancer) such that the analyte could be detected, localized, and/or identified in the tissue using methods as described herein. Such identification could be performed to guide the ablation, resection, removal, or other surgical modification or interaction with a tissue containing the analyte. This could include presenting imaging information related to the identification of the analyte throughout an imaged surgical environment, operating a surgical laser or other automated or semi-automated surgical instrument relative to the identified tissues containing the analyte, or according to some other method. Additionally or alternatively, an introduced fluorophore, chromophore, pigment, dye, coating, or other substance could have one or more spectrographic properties (e.g., an amplitude, center wavelength, width, or other property of a peak within an absorption or other spectrum of the introduced substance) that are related to properties (e.g., a temperature, a pH, an osmolality, a strain, a stress, a pressure) of one or more portions of a surgical environment. In some examples, such an introduced substance could be introduced to mark the location of one or more biological tissues (e.g., to mark the location of a tumor detected using CT, MRI, palpation by a surgeon, or some other method). 
       FIG. 2A  illustrates a first example spectrum  210   a  of light received from a first portion of a surgical environment in response to illumination of the first portion by light having a specified wavelength. The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The first example spectrum  210   a  illustrates the amplitude of light received from the first portion of tissue as a function of wavelength. Further, the wavelength of the illumination is illustrated by the first tick  220   a . The first example spectrum  210   a  includes a first peak  215   a  having a center wavelength substantially equal to the wavelength of the illumination ( 220   a ) and a second peak  217   a  that is at a greater wavelength. The first peak  215   a  could correspond to illumination received by the first portion that is scattered, refracted, diffracted, reflected, or otherwise directed back toward a light sensor configured to detect light from the first portion. The second peak  217   a  could correspond to light emitted by fluorophores (e.g., elements of the first portion that can receive illumination at the wavelength of the illumination  220   a  and responsively emit light at a different, greater wavelength) of the first portion of the surgical environment in response to the illumination. 
       FIG. 2B  illustrates a second example spectrum  210   b  of light received from a second portion of the surgical environment in response to illumination of the second portion by light having a specified wavelength equal to the specified wavelength of the light used to illuminate the first portion to generate the first example spectrum  210   a . The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The second example spectrum  210   b  illustrates the amplitude of light received from the second portion of tissue as a function of wavelength. Further, the wavelength of the illumination is illustrated by the first tick  220   b . The second example spectrum  210   b  includes a first peak  215   b  having a center wavelength substantially equal to the wavelength of the illumination ( 220   b ) and a second peak  217   b  that is at a greater wavelength. The first peak  215   b  could correspond to illumination received by the second portion that is scattered, refracted, diffracted, reflected, or otherwise directed back toward a light sensor configured to detect light from the second portion. The second peak  217   b  could correspond to light emitted by fluorophores (e.g., elements of the second portion that can receive illumination at the wavelength of the illumination  220   b  and responsively emit light at a different, greater wavelength) of the second portion of the surgical environment in response to the illumination. 
     The first  210   a  and second  210   b  example spectra could be emission spectra of respective first and second portions of a surgical environment. A difference between the first and second portions of the surgical environment and/or an identity of the first and/or second portions could be determined based on features of the first  210   a  and second  210   b  example spectra. For example, a difference in the amount of a fluorophore could be determined based on a difference in amplitude of the second peak  217   a ,  217   b  between the first  210   a  and second  210   b  spectra. A tissue type of tissue in the first or second portions could be determined based on features or other information about the spectra. A tissue type could include one or more classifications applied to a portion of biological tissue (e.g., “muscle,” “skeletal muscle,” “pennate muscle,” “fast-fatigue muscle,” “tendon,” “epithelium,” “cartilage,” “bone,” “cortical bone,” “blood,” “vasculature,” “artery,” “vein,” “lymph,” “nerve,” “fat,” “smooth muscle,” “necrotic tissue,” “ischemic tissue,” “neoplastic tissue,” “cancerous tissue,” “melanoma,” “cyst” or some other class or classes of biological tissue). Further, the presence of a surgical instrument, suture, or other foreign body in the first or second portions could be determined. For example, the amplitude or other information about the first peak  217   b  in the second example spectrum  210   b  could indicate a high reflectivity or other optical property indicative of a metallic foreign body or surgical instrument. In a particular example, the first example spectrum  210   a  could correspond to a first portion of the surgical environment containing a portion of biological tissue that includes a fluorophore, and the second example spectrum  210   b  could correspond to a second portion of the surgical environment containing a portion of a metallic surgical instrument that is coated in an amount of a fluorophore dye. Other distinctions and/or identifications of portions of a surgical environment, based on additional or alternative features of a spectrum of the portions, are anticipated. 
     Contents of the first  210   a  and second  210   b  example spectra could be determined based on light received from the first and second portions using the same detector in response to illumination of the first and second portions by the same light source. For example, the first and second portions could be illuminated by a laser configured to control a direction of illumination emitted by the light source (e.g., by including galvanometers or other actuators configured to actuate mirrors or other optical elements of the light source) to illuminate different portions of the surgical environment. Further, amplitudes of light within specified wavelength ranges or other properties of light emitted by the first and second portions could be detected by a spectrometer configured to receive light from different portions of the surgical environment. Spectrographic contents determined from light received in such a way could include a set of the detected amplitudes, a description (e.g., amplitude, width, mean wavelength) of peaks or other features of the spectrum, or some other information. 
       FIG. 2C  illustrates a third example spectrum  210   c  of light received from a third portion of a surgical environment in response to illumination of the third portion by a plurality of lights having a variety of wavelengths. The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The third example spectrum  210   c  illustrates the amplitude of light received from the third portion of tissue as a function of the wavelength of light illuminating the third portion of tissue. The third example spectrum  210   c  includes a first peak  215   c  and a second peak  217   c . The first  215   c  and second  215   c  peaks could correspond to ranges of light that are less scattered, absorbed, or otherwise not directed back toward a light sensor configured to detect light from the third portion. 
       FIG. 2D  illustrates a fourth example spectrum  210   d  of light received from a fourth portion of a surgical environment in response to illumination of the fourth portion by a plurality of lights having a variety of wavelengths. The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The fourth example spectrum  210   d  illustrates the amplitude of light received from the fourth portion of tissue as a function of the wavelength of light illuminating the fourth portion of tissue. 
       FIG. 2E  illustrates a fifth example spectrum  210   e  of light received from a fifth portion of a surgical environment in response to illumination of the fifth portion by a plurality of lights having a variety of wavelengths. The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The fifth example spectrum  210   e  illustrates the amplitude of light received from the fifth portion of tissue as a function of the wavelength of light illuminating the fifth portion of tissue. The fifth example spectrum  210   e  includes a first peak  215   e  and a second peak  217   e . The first  215   e  and second  215   e  peaks could correspond to ranges of light that are less scattered, absorbed, or otherwise not directed back toward a light sensor configured to detect light from the fifth portion. 
     The third  210   c , fourth  210   d , and fifth  210   e  example spectra could be absorption spectra of respective third, fourth, and fifth portions of a surgical environment. A difference between the third, fourth, and/or fifth portions of the surgical environment and/or an identity of the third, fourth, and/or fifth portions could be determined based on features of the third  210   c , fourth  210   d , and fifth  210   e  example spectra. For example, the third and fifth portions of the surgical environment could be portions of biological tissue containing a chromophore (e.g., hemoglobin) having one or more optical properties related to a state of the chromophore and/or of a biological tissue containing the chromophore (e.g., an absorbance at one or more wavelengths related to an oxygenation state of the tissue and/or of the chromophore). Thus, a relative state (e.g., a relative level of oxygenation) of the third and fifth portions could be determined based on a difference between the third  210   c  and fifth  210   e  example spectra (e.g., a relative amplitude of the first  215   c ,  215   e  and/or second  217   c ,  217   e  peaks). A tissue type of tissue in the third, fourth, and/or fifth portions could be determined based on features or other information about the spectra. Further, the presence of a surgical instrument, suture, or other foreign body in the third, fourth, and/or fifth portions could be determined. For example, a shape, smoothness, or other information about the fourth example spectrum  210   d  through a range characterized by less smooth spectra in biological tissue could indicate that the fourth portion of the surgical environment contains a portion of a metallic foreign body or surgical instrument. Other distinctions and/or identifications of portions of a surgical environment, based on additional or alternative features of spectra of the portions, are anticipated. 
     Contents of the third  210   c , fourth  210   d , and fifth  210   e  example spectra could be determined based on light received from the third, fourth, and fifth portions using the same detector in response to illumination of the third, fourth, and fifth portions by the same light source. For example, the third, fourth, and fifth portions could be illuminated by a tunable laser (e.g., a laser configured to emit a beam having a controllable wavelength and/or a set of lasers configured to emit beams having different wavelengths) configured illumination an area of the surgical environment containing the third, fourth, and fifth portions (e.g., by including a beam spreader or other optical element(s) to widen a beam emitted by the tunable laser). Further, amplitudes or other properties of light emitted by the third, fourth, and fifth portions could be detected by a camera or other photodetector configured to receive light from different portions of the surgical environment. Spectrographic contents determined from light received in such a way could include a set of amplitudes of light detected from one or more portions of the surgical environment (e.g., detected using more or more pixels of a camera) corresponding to a set of lights (having respective different wavelengths) used to illuminate the one or more portions, a description (e.g., amplitude, width, mean wavelength) of peaks or other features of the spectrum, or some other information. 
     Note that the example spectra (e.g.,  210   a ,  210   b ,  210   c ,  210   d ,  210   e ) and their relationships to properties of corresponding example portions of a surgical environment are meant to illustrate by example and are not intended to be limiting. Other methods of detecting and/or determining spectrographic information and/or content for one or more portions of a surgical environment are anticipated. Further, additional or alternative methods of identifying the contents and/or properties of a portion of a surgical environment based on determined spectrographic content corresponding to the portion are anticipated. 
     Such spectrographic content and/or information determined therefrom (e.g., determination that spectrographic content corresponds to a biological tissue, to a particular type of biological tissue, to a surgical instrument or other foreign body) could be determined for a plurality of portions of a surgical environment. This could be performed sequentially for a series of portions of the surgical environment (e.g., by scanning a laser configured to emit a beam of illumination to illuminate a spot, line, or other-shaped region containing portions of the surgical environment, by scanning a direction of focus and/or sensitivity of a light detector across a plurality of portions of the surgical environment). Additionally or alternatively, a camera or other sensor containing a plurality of light-sensitive components could be operated to receive light from a plurality of corresponding portions of the surgical environment in response to illumination of the plurality of portions of the surgical environment. Such information about a plurality of portions of a surgical environment could be used to determine spectrographic or other images of the surgical environment. 
     As an illustrative example,  FIG. 3A  illustrates a first example image  300   a  of the surgical environment  100 . The first example image  300   a  indicates portions  310   a  of the surgical environment  100  that contain surgical instruments, sutures, or other foreign bodies. The first example image  300   a  is determined based on determined spectrographic contents corresponding to a plurality of portions of the surgical environment  100  spanning the field of view of a surgical imaging system or other apparatus configured to illuminate portions of the surgical environment, to receive light from the illuminated portions, and to determine the spectrographic content of the received light. Such an image could be presented to a surgeon or other user to inform some action of the user (e.g., to determine that all sutures, drains, pads, catheters, sponges, gauze, staples, other medical supplies, and/or other foreign bodies have been removed from the surgical environment). Such an image could additionally or alternatively be used to inform the operation of an automated surgical instrument, e.g., to specify regions of the surgical environment that should not be exposed to the output of a surgical laser. 
       FIG. 3B  illustrates a second example image  300   b  of the surgical environment  100 . The second example image  300   b  indicates portions  310   b  of the surgical environment  100  that contain a fluorophore. The second example image  300   b  is determined based on determined spectrographic contents corresponding to a plurality of portions of the surgical environment  100  spanning the field of view of a surgical imaging system or other apparatus configured to illuminate portions of the surgical environment, to receive light from the illuminated portions, and to determine the spectrographic content of the received light. Such an image could be presented to a surgeon or other user to inform some action of the user (e.g., to determine the location and extent of a labeled tissue or surgical instrument, to determine the degree of ablation of such a tissue in response to the operation of a surgical laser). Such an image could additionally or alternatively be used to inform the operation of an automated surgical instrument, e.g., to specify regions of the surgical environment that should be ablated by application of the output of a surgical laser. 
       FIG. 3C  illustrates a third example image  300   c  of the surgical environment  100 . The third example image  300   c  indicates the type of tissue contained by portions of the surgical environment  100 . Tissue types include skin  310   c , a first muscle tissue  320   c , tendon  340   c , a second muscle tissue  330   c , and blood vessel tissue  350   c  The third example image  300   c  is determined based on determined spectrographic contents corresponding to a plurality of portions of the surgical environment  100  spanning the field of view of a surgical imaging system or other apparatus configured to illuminate portions of the surgical environment, to receive light from the illuminated portions, and to determine the spectrographic content of the received light. Such an image could be presented to a surgeon or other user to inform some action of the user (e.g., to determine the location and extent of a diseased tissue, to determine a health or other state of such a tissue). Such an image could additionally or alternatively be used to inform the operation of an automated surgical instrument, e.g., to specify regions of the surgical environment that should or should not be ablated by exposure to the output of a surgical laser. 
     Such images of a surgical environment (e.g.,  300   a ,  300   b ,  300   c ) and/or information about a portion of a surgical environment could be determined based on determined spectrographic contents of light received from the surgical environment and/or portion thereof in a variety of ways. Generally, spectrographic contents for a particular portion of a surgical environment could be used by a processor, controller, or other computational system to identify a portion of tissue, a portion of a surgical instrument, a portion of a foreign body, or some other contents of the portion of the surgical environment. This could include the controller applying a classifier to the determined spectrographic contents to generate an identifier (e.g., ‘surgical instrument,’ ‘retractor,’ ‘foreign body,’ ‘biological tissue,’ ‘tumor,’ ‘blood vessel,’ ‘nerve,’ ‘muscle’) or other information for the portion of the surgical environment. The spectrographic contents could include vectors of amplitude or other detected properties of the received light (e.g., vectors of amplitudes corresponding to received light within corresponding ranges of wavelengths), information (e.g., amplitudes, center wavelengths, peak widths, fall-off rates) about features (e.g., peaks, troughs, slopes, inflections) of a spectrum of received light, or some other information about received light. In some examples, spectrographic information corresponding to light received from a surgical instrument contaminated with a fluorophore or other marking agent could be intermediate between spectrographic information corresponding to the marking agent alone and spectrographic information corresponding to an uncontaminated surgical instrument. 
     A controller could implement a variety of classifiers and/or combinations of classifiers to identify or otherwise assign a classification to a portion of a surgical environment based on a spectrographic contents of light received from the portion. Classifiers could generate a binary output (e.g., “biological tissue” vs. “not biological tissue”) or an output having a plurality of possible states (e.g., “artery,” “vein,” “nerve,” “tendon,” “skin,” “muscle,” “fat,” “necrosis,” “tumor”). A plurality of possible outputs states could be nominal (i.e., categorical and non-ordered) or ordinal (e.g., “very unlikely to contain cancer cells,” “slightly unlikely to contain cancer cells,” “slightly likely to contain cancer cells,” “very likely to contain cancer cells”). Output of a classifier corresponding to a particular portion of a surgical environment could be based only on spectrographic content from the particular portion or could be based additionally on spectrographic content from other portions of the surgical environment (e.g., neighboring portions of the surgical environment to enable a spatially smooth output of the classifier across portions; a portion of the surgical environment containing a calibration object having known spectrographic properties to act as a baseline for comparison). A classifier could generate multiple outputs for a single portion (e.g., could output one of “biological tissue” and “surgical instrument” and one of “contains fluorophore” and “does not contain fluorophore”). Such multiple outputs of a classifier could be used to make a further determination about the single portion, e.g., that the single portion contains a surgical instrument or other foreign body contaminated with a fluorophore. 
     Classifiers implemented by a controller could include linear classifiers, nonlinear classifiers, support vector machines, decision trees, k-nearest-neighbors, neural networks, thresholds, or other classifiers and/or combinations thereof. Further, a controller could perform some preprocessing on input spectrographic content before the application of a classifier. For example, input content could be subject to some transformation (e.g., conversion by application to a logarithmic, hyperbolic, power series, or other nonlinear function), dimensionality reduction (e.g., principal components analysis, factor analysis, independent components analysis, isomap, linear discriminant analysis, non-negative matrix factorization), filtering (e.g., spatial filtering across spectrographic contents for neighboring portions, wavelength filtering to smooth a determined spectrum) or some other preprocessing step. 
     Parameters, structures, weights, or other properties of such classifiers could be determined in a variety of ways. In some examples, classifiers could be specified by supervised learning, wherein determined spectrographic contents for a set of known portions of a surgical environment (e.g., a set of portions whose identity is determined by a human being) along with the known classifier outputs corresponding to such spectrographic contents are used to train a classifier (e.g., to set weights, parameters, or the overall structure of a classifier). This could include performing a scan of a surgical environment containing a variety of contents (e.g., containing both biological tissues and non-biological elements, containing a variety of different types of biological tissues) and receiving a set of classifications corresponding to portions of the surgical environment (e.g., by receiving such classifier information from a surgeon). This could include performing a scan to determine spectrographic contents of light received from isolated biological tissues, surgical instruments, or other objects and receiving a set of classifications corresponding to the isolated objects. In some examples, spectrographic contents corresponding to a variety of biological tissues, surgical instruments, or other objects could be determined in simulation (e.g., by simulating the interaction of light with a model of a biological tissue or other object). 
     Additionally or alternatively, parameters, structures, weights, or other properties of such classifiers could be determined by unsupervised learning. For example, a controller could determine spectrographic contents for a plurality of portions of a surgical environment and could then specify a classifier to categorize the portions using an unsupervised learning algorithm. Determined regions of the surgical environment having similar classifications could then be identified by a surgeon or could be used according to some other application. 
     Information about a portion of a surgical environment (e.g., the identification of a portion of the surgical environment as containing a portion of biological tissue, the determination of a tissue type of or other information about such a portion of biological tissue, the identification of a portion of the surgical environment as containing a portion of a surgical instrument, suture, or other foreign body) could be determined based on determined spectrographic contents of light received from the portion in response to illumination of the portion could be used for a variety of applications. For example, such determined information could be displayed to a surgeon, pathologist, or other person to inform some course of action; e.g., to inform a surgical intervention (e.g., to indicate the location and extent of a diseased tissue to be incised, resected, ablated, or otherwise modified), to inform a course of treatment. Additionally or alternatively, such information could be used to implement a surgical intervention by a robotic surgical system. 
     Automated surgical interventions (e.g., surgical interventions performed wholly or partially by the operation of an artificial system) could include implementing some interaction with a target tissue (e.g., ablating a tissue containing cancer cells) while avoiding interaction with other biological tissues and/or non-biological contents of a surgical environment. In some examples, a surgical environment could contain a variety of surgical instruments (e.g., retractors, hemostats) and other foreign bodies (e.g., fiducials, screws, staples, sutures). For example, operation of an automated surgical laser configured to ablate tissue could include avoiding application of the output of the surgical laser to such surgical instruments or other foreign bodies. Application of the output to such contents of the surgical environment could cause unwanted effects, including but not limited to destruction of the surgical instruments or other foreign bodies (e.g., the destruction of a suture allowing tissues secured, ligated, or otherwise influenced by the suture to become loose), release of toxic or otherwise counter-indicated chemicals from heating and/or ablation of the surgical instruments or other foreign bodies, and uncontrolled optical effects on the light emitted by the surgical laser (e.g., reflection of a laser beam toward other portions of the surgical environment, potentially damaging biological tissues of a patient receiving the surgical intervention and/or nearby medical personnel). In some examples, the surgical environment could include blood vessels, nerves, tendons, or other sensitive tissues and performance of a surgical intervention (e.g., ablation) on such tissues could cause a negative outcome (e.g., blood loss, tissue necrosis, muscle paralysis, loss of sensation). 
     Information about the identity of portions of a surgical environment determined using spectrographic methods as described herein could be used to inform the performance of such wholly or partially automated surgical interventions. In some examples, this could include determining regions of the surgical environment to avoid interaction with. For example, a portion of the surgical environment could be determined to contain among other things (e.g., a portion of biological tissue) a portion of a surgical instrument, suture, or other foreign body, and this determination could be used by an automated surgical system to avoid ablating, heating, or otherwise directing energy toward or interacting with the portion of the surgical environment. In another example, a portion of the surgical environment could be determined to contain a portion of biological tissue of a certain type (e.g., a nerve, a blood vessel, a tissue that does not contain cancer cells), and this determination could be used by an automated surgical system to avoid ablating, heating, or otherwise directing energy toward or interacting with the portion of the surgical environment. In some examples, such information about the identity of portions of a surgical environment could be used to determine the efficacy and/or effects of an automated or other surgical intervention, e.g., to determine whether a cancerous tissue has been fully ablated by the operation of a surgical laser or other surgical instrument. 
     To illustrate the use of methods as described herein to inform automated and/or manual surgical interventions,  FIG. 4A  illustrates an example surgical environment  400 . The surgical environment  400  includes biological tissues (e.g., skin, muscle, a blood vessel  420 ) that are subject to a surgical intervention using surgical instruments (e.g., a retractor  440 ) and other foreign bodies (e.g., sutures  430 ). Further, a fluorophore configured to selectively interact with an analyte in the biological tissue is present in fluorescent portions  410  of the surgical environment in the biological tissue and on the surface of the retractor  440 . An automated surgical laser could be configured to emit a beam to ablate biological tissue and could be operably coupled to a surgical imaging system configured to illuminate portions of the surgical environment  400  and to receive light emitted by the portions of the surgical environment  400  in response to the illumination. Operation of a controller of the surgical imaging system to generate the example image  405  from determined spectroscopic contents corresponding to portions of the surgical environment  400  could include implementing a single classifier and/or multiple classifiers combined together. For example, the controller could determine a first output of a first classifier specified to determine that a portion of the surgical environment contains the fluorophore and a second output of a second classifier specified to determine whether a portion of the surgical environment contains a portion of biological tissue that is not a blood vessel. The example image  405  could be determined by the controller by combining the first and second outputs to generate an overall output of the combined classifier that comprises the first and second classifiers. 
     A controller of the surgical imaging system could be configured to operate elements of the surgical imaging system (e.g., light sources, light detectors) to determine spectrographic content of light received from portions of the surgical environment and to identify portions of the surgical environment based on the determined spectrographic content. This could include determining portions of the surgical environment that contain biological tissue that contains the analyte by determining portions of the surgical environment that contain biological tissue and that contain the fluorophore. For example,  FIG. 4B  illustrates an example image  405  of the surgical environment  400 . The example image  405  indicates portions  407  of the surgical environment  400  that contain biological tissue marked by the fluorophore and that do not contain elements that should not be exposed to energy emitted by the surgical laser (e.g., the blood vessel  420 , the retractor  440 , the sutures  430 ). 
     The example image  405  is determined based on determined spectrographic contents corresponding to a plurality of portions of the surgical environment  400  spanning the field of view of the surgical imaging system. Such an image could be presented to a surgeon or other user to inform some action of the user. For example, such an image could be presented to guide the surgeon in operating a surgical laser or other surgical instrument to ablate tissue containing the fluorophore without damaging or otherwise interacting with structures that could be damaged by the laser or whose exposure to the surgical laser could otherwise have a negative effect (e.g., the blood vessel  420 , the retractor  440 , the sutures  430 ). Such an image could additionally or alternatively be used by the controller to operate the surgical laser, e.g., to ablate regions of the surgical environment containing the fluorophore but without damaging or otherwise interacting with the blood vessel  420 , sutures  430 , and retractor  440 . 
     The identifying a portion of the surgical environment as containing a portion of a biological tissue, a portion of a particular type of biological tissue, a portion of a surgical instrument, or some other identification could be based on information other than determined spectrographic content of light received from the portion of the surgical environment. For example, information from other imaging modalities or systems could be combined with determined spectrographic content to identify to portion of the surgical environment. For example, a CT scanner, ultrasound scanner, MR imager, or other device or combination of devices could be used to determine information about the portion of the surgical environment and the determined information could be used alone or in combination with the determined spectrographic content to identify the portion of the surgical environment. 
     III. Example Surgical Spectrographic Imaging Systems 
     Generally, a surgical imaging system as described herein include at least one light source configured to illuminate one or more portions of a surgical environment with light having one or more specified properties and a detector configured to detect a spectrographic content of light received from the one or more illuminated portions of the surgical environment. The light source could be configured and/or operated to illuminate a plurality of portions simultaneously (e.g., by illuminating a large area of the surgical environment) or one portion at a time (e.g., by emitting a beam to illuminate a single portion (i.e., a spot), a line, or some other shape) and scanning across the surgical environment to illuminate a plurality of portions over time. The light source could emit light at a single wavelength (or light having some other properties that are substantially the same over time) or could emit light at a plurality of wavelengths during a plurality of different periods of time. The detector could detect light within a single narrow range of wavelengths, within a wide range of wavelengths, and/or within a plurality of ranges of wavelengths. Further, the detector could be configured to receive light from a particular portion of the surgical environment (e.g., could include optics to focus the detector on a particular portion), a wide area of the surgical environment, or a plurality of portions of the surgical environment simultaneously (e.g., the detector could include a camera or other device including a plurality of light sensors configured to receive light from a respective plurality of portions of the surgical environment). A variety of combinations and configurations of light sources and detectors are anticipated. 
     The one or more light sources, detectors, controllers configured to operate such, and/or other components of a surgical imaging system as described herein could be disposed in a single housing or other apparatus or could be separate and put in communication with each other by one or more means known to one of skill in the art (e.g., cabling, wireless communication). Such a system could be handheld, attached to an armature, or maintained at a location proximate to a target surgical environment by some other means. A controller configured to determine spectrographic content of light received by a detector of the surgical imaging system, to identify a portion of the surgical environment based on such content, and/or perform some other operations could be located proximate to the light source and/or detector (e.g., could be disposed in a housing that also contains the light source and/or detector) or could be remote from those elements and could be in communication with those elements (e.g., via cabling, a wireless link, the internet, or some other network). 
       FIG. 5A  illustrates elements of a first example surgical imaging system  500   a  including a light source  510   a  and a detector  520   a . The light source  510   a  is configured to emit a beam of illumination  515   a  containing light at a specified wavelength and to illuminate a spot on the biological tissue  530   a . The biological tissue includes a first muscle  531   a  and a second muscle  533   a . The detector  520   a  is configured to receive light from an area of the biological tissue  530   a  and to generate information about the spectrographic contents of the received light. The second muscle  533   a  includes a tagged region  537   a  containing a fluorophore configured to selectively interact with an analyte that is present in the tagged region  537   a . Further, the tagged region  537   a  includes a portion of tissue  535   a  that is being illuminated by the light source  510   a  during a period of time illustrated in  FIG. 5A   
     The light source  510   a  could include a variety of light-emitting elements configured to produce light at substantially one wavelength (i.e., containing light of wavelengths within a specified narrow range of wavelengths). This could include lasers, light-emitting diodes (LEDs), or other substantially monochromatic light sources. Additionally or alternatively, the light source  510   a  could include a light emitting element that emits light across a wider range of wavelengths, and this non-monochromatic light could be emitted through one or more filters (e.g., filters including one or more Bragg reflectors, prisms, diffraction gratings, slit apertures, monochromators) configured to only allow the transmission of light within a narrow range of wavelengths. The light source  510   a  could include mirrors, lenses, diffraction gratings, or other optics controlled by galvanometers, motors, or other actuators to control the direction of the beam of illumination  515   a  such that the location of a portion of the surgical environment  530   a  could be controlled (e.g., by a controller operably coupled to the light source  510   a ). 
     The detector  520   a  could include one or more light-sensitive elements configured to detect the amplitude or other properties of light received by the detector  520   a  within one or more respective ranges of wavelengths. That is, the detector  520   a  could be configured to act as a spectrometer, receiving light from the biological tissue  530   a  and outputting information related to the spectrum of the received light (i.e., outputting information relating to the spectrographic content of the received light). This could include the detector  520   a  containing a prism and a linear (or otherwise arranged) array of light sensitive elements (e.g., photodiodes, phototransistors, pixels of a charge-coupled device (CCD), active pixel sensors) configured such that the output of an individual light sensitive element is related to the amplitude of the received light within a specified range of wavelengths. Other configurations of the detector  520   a  to enable the detection and/or determination of the spectrographic content of light received by the detector  520   a  are anticipated. The detector  520   a  is configured to receive light from a plurality of portions of the biological tissue  530   a  within an area of view of the surgical imaging system  500   a.    
     Spectrographic content of light received by the surgical imaging system  500   a  from a portion of a surgical environment (e.g., from the portion of tissue  535   a ) could take the form of an emission or other spectrum of the received light (e.g., a vector or other arrangement of detected amplitudes of the received light within corresponding specified ranges of wavelengths). An example of such spectrographic content is illustrated in  FIG. 5B .  FIG. 5B  includes an example spectrum  510   b  of light received from the portion of tissue  535   a  in response to illumination of the portion of tissue  535   a  by the beam of illumination  515   a . The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. The example spectrum  520   b  illustrates the amplitude of light received from the portion of tissue  535   a  as a function of wavelength. Further, the wavelength of the beam of illumination  515   a  is illustrated by the first tick  520   b . The example spectrum  510   b  includes a first peak  515   b  having a center wavelength substantially equal to the wavelength of the beam of illumination  515   a  and a second peak  517   b  that is at a greater wavelength. The first peak  515   b  could correspond to illumination received by the portion of tissue  535   a  that is scattered, refracted, diffracted, reflected, or otherwise directed back toward detector  520   a . The second peak  517   b  could correspond to light emitted by the fluorophore in the portion of tissue  535   a  in response to being illuminated by the beam of illumination  515   a.    
     To improve the signal-to-noise ratio, or according to some other application, the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could be operated in a dim environment, could be configured to detect light within a range of wavelengths that is substantially dark in an operating environment of the surgical imaging system  500   a , or could be operated and/or configured in some other way. In an example, the output of the light source  510   a  (i.e., the beam of illumination  515   a ) could be pulsed, and the detector  520   a  could be operated to generate a first output during a first period of time when the light source  510   a  is emitting a first amount of illumination and a second output during a second period of time when the light source  510   a  is emitting a second amount of illumination that is less than the first amount of illumination (e.g., the light source  510   a  could be emitting substantially no illumination during the second period of time). Spectrographic content of the light received from the portion of tissue  535   a  could be determined based on a difference, a ratio, or some other relationship between the first and second outputs of the detector  520   a . Additionally or alternatively, the light source  510  could be operated to emit illumination at a sufficiently high amplitude that the effects of background illumination (e.g., from ambient light sources in an operating environment of the surgical imaging system  500   a ) on the operation of the surgical imaging system  500   a  are minimized. 
     The surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could be operated to determine and/or detect spectrographic content of light received from a plurality of portions of biological tissue. For example, the light source  510   a  could be operated to illuminate a plurality of portions of tissue (e.g., a set of portions of tissue that are regularly spaced) during a respective plurality of time periods. Correspondingly, the detector  520   a  could be operated during the plurality of time periods to receive light from respective portions of tissue illuminated by the light source  510   a  and to determine and/or detect a plurality of spectrographic contents of the received light corresponding to the plurality of portions of tissue. 
     The wavelength of the illumination emitted by the light source  510   a , the specified ranges of wavelengths of light detected by the detector  520   a , and other parameters of the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could be chosen relative to an application. For example, the wavelength of illumination emitted by the light source  510   a  could correspond to an excitation wavelength of a fluorophore in a biological tissue imaged by the surgical imaging system  500   a  (e.g., a fluorophore introduced into the biological tissue, e.g., to mark a target analyte, e.g., cancer cells). The wavelength of illumination emitted by the light source  510   a  could be selected to minimize autofluorescence, scattering, or some other optical process(es) in a target tissue. 
     Information generated by the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could include determined and/or detected spectrographic content for a plurality of portions of a biological tissue, identification information corresponding to the plurality of portions of the biological tissue based on such determined spectrographic content, an image generated based on determined and/or detected spectrographic content and/or identification information. Such information could be used to generate one or more images of the biological tissue, e.g., an image of tissue types of the biological tissue, an image of diseased regions (e.g., cancer-cell-containing regions) of the biological tissue. Such images could be presented to a surgeon (e.g., via a display, a head-mounted display, an augmented reality device, a display of a console used to operate a tele-surgical system) to inform a surgical intervention or other actions of the surgeon. Additionally or alternatively, such images could be used to perform a surgical intervention using an automated surgical system (e.g., to automatically ablate diseased and/or cancerous tissue using a surgical laser). 
     As shown in  FIG. 5A , the detector  520   a  is not co-axial with the light source  510   a . That is, the light source  510   a  is not located on or substantially proximate to an optical axis of the detector  520   a  (e.g., an axis passing through the detector  520   a  and directed toward the center of a field of view of the detector  520   a ); conversely, the detector  520   a  is not located on or substantial proximate to an emitted beam axis of the light source  510   a  (i.e., an axis substantially coincident with the beam of illumination  515   a ). In some embodiments (e.g., embodiments wherein the detector  520   a  includes a camera or other light sensitive elements configured to detect the angle or other location information of received light), the detector  520   a  and light source  510   a  could be co-axial; that is, the detector  520   a  and light source  510   a  could be disposed proximate to each other and/or could share one or more optical elements such that an emitted beam of illumination  515   a  originates from a point substantially the same as an optical feature (e.g., an aperture) of the detector  520   a . In some examples, the surgical imaging system  500   a  could include a surgical laser configured to emit a beam of light to heat, ablate, or otherwise modify a target portion of biological tissue. Such a surgical laser could be located proximate to and/or share optical elements with (e.g., emit light via actuated mirrors or other light-orientation-controlling elements in common with) the light source  510   a  such that such that operation of the light source  510   a  to orient the beam of illumination  515   a  additionally orients a beam of light emitted by the surgical laser. In some examples, the detector  520   a  could be located away from an optical axis of the light source  510   a  and could include a camera or other light sensitive elements configured to detect the angle or other location information of received light; further, such a detector  520   a  could be operated to determine the location in space of an illumination portion of tissue (relative to the surgical imaging system  500   a ) in addition to determined spectrographic content of light received from the portion of tissue. 
     The surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) or components thereof could be configured to rotate, translate, or otherwise move such that the region imaged by surgical imaging system  500   a  (i.e., the biological tissue  530   a ) could be controlled and/or changed. For example, the surgical imaging system  500   a  could be mounted on a gimbal. Movement of the surgical imaging system  500   a  could be effected by servos, galvanometers, motors, or some other mechanical actuator(s). In some examples, motions of the surgical imaging system  500   a  could be controlled to automatically track the biological tissue  530   a . In some examples, the surgical imaging system  500   a  could be manually moved such that a field of view of the surgical imaging system  500   a  includes a target region (e.g., the biological tissue  530   a ). For example, the surgical imaging system  500   a  could be positioned at the beginning of a surgical intervention to image the biological tissue  530   a.    
     A variety of mechanical apparatus could be employed to secure the light source  510   a , detector  520   a , and other components of the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) in place relative to a target region or object (e.g., the biological tissue  530   a ). For example, the light source  510   a , detector  520   a , and/or other components could be mounted on a surgical table, a wall, a ceiling, a cart, a wearable device worn by a surgeon or other person, a surgical device or implement (e.g., to the end of a laparoscopic and/or endoscopic instrument), or to some other support. The light source  510   a , detector  520   a , and/or other components could be part of some other surgical or other apparatus (e.g., an imaging system, a stereotactic surgical system, a robotic surgical system) and could be mounted to a mount, support, or other component(s) of the other surgical or other apparatus. Further, the surgical imaging system  500   a  could include additional components, e.g., surgical lasers, robotic surgical systems, CT and/or X-ray imagers, MR imagers, ultrasonic imagers, laparoscopic and/or endoscopic systems, and/or other components according to an application. For example, the surgical imaging system  500   a  could include multiple light sources  510   a  and/or detectors  520   a.    
     A surgical laser (not shown) included as part of the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) or as part of some other surgical instrument or system (e.g., a wholly or partially automated surgical system) could include any device configured to emit a directed beam of light sufficient to cause localized heating of a target region of a biological environment (or some other environment of interest) proximate to where the emitted beam intersects with the biological environment (or other environment of interest). The surgical laser could include a CO 2  laser, a semiconductor diode laser, a dye laser, an excimer laser, a fiber laser, a gas laser, a free electron laser, or some other type or types of laser. The surgical laser could include optical elements configured to affect one or more properties of the beam of light emitted by the surgical laser, e.g., lenses, mirrors, diffraction gratings, volume holographic gratings, collimators, nonlinear optical elements (e.g., frequency doubling or tripling media), or other elements. For example, the surgical laser could include a collimator configured to cause the beam of light to have a specified width. 
     The surgical laser could be configured such that one or more properties of the beam of light have a specified value. For example, the surgical laser could be configured such that a wavelength of the beam of light is a specified wavelength. The specified wavelength could be specified according to an application. For example, the specified wavelength could be an absorption wavelength of hemoglobin such that the beam of light preferentially heats blood. In another example, the specified wavelength could be an absorption wavelength of a contrast agent that is configured to bind to cancer cells such that the beam of light preferentially heats cancer cells and/or tumors. Additionally or alternatively, the specified wavelength could be a wavelength that is not substantially absorbed by a tissue to be spared during a surgical intervention. Other specified wavelengths and/or specified other properties of the beam of light emitted by a surgical laser are anticipated. 
     In embodiments of the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) wherein a surgical laser is included and the surgical laser and light source  510   a  are co-axial, control of the location of a beam of light emitted by the surgical laser relative to the location of portions of the biological tissue  530   a  illuminated by the light source  510   a  could be simplified, taking into account the surgical laser and light source  510   a  being co-axial. For example, a simple mapping between points in an image generated using the light source  510   a  and detector  520   a  and angles of the beam of light emitted by the surgical laser could be determined and used to control the surgical laser such that beam of light is emitted in a direction such that the beam of light interests with the biological tissue  530   a  at a controlled location that is based on a location of a target determined based on information generated by the detector  520   a . Other methods of controlling a surgical laser based on information (e.g., images of the identity of portions of a biological tissue  530   a ) generated by the surgical imaging system  500   a  and/or other information are anticipated. 
     The surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could include additional elements or components (not shown). The surgical imaging system  500   a  could include one or more controllers configured to operate the light source  510   a , detector  520   a , and/or other elements of the surgical imaging system  500   a . The surgical imaging system  500   a  could include communications devices (wireless radios, wired interfaces) configured to transmit/receive information to/from other systems (e.g., servers, medical imaging devices, surgical implements, surgical robots) to enable functions and applications of the surgical imaging system  500   a . For example, the surgical imaging system  500   a  could include an interface configured to receive imaging information about a target environment of the surgical imaging system  500   a  (e.g., the biological tissue  530   a ). The surgical imaging system  500   a  could include an interface configured to present information about the surgical imaging system  500   a  to a user and/or to allow the user to operate the surgical imaging system  500   a.    
     Additionally or alternatively, the surgical imaging system  500   a  (or other example surgical imaging systems described herein, e.g.,  600   a ,  700   a ,  800   a ,  900   a ) could be configured to communicate with another system (e.g., a cellphone, a tablet, a computer, a remote server) and to present a user interface using the remote system. In some examples, the surgical imaging system  500   a  could be part of another system. For example, the surgical imaging system  500   a  could be implemented as part of a robotic surgical system (e.g., the light source  510   a , detector  520   a , and other components (e.g., surgical laser(s)) configured as described herein could be disposed as part of a robotic surgical system and could be operated as described herein). In some examples, the surgical imaging system  500   a  could include multiple light sources  510   a , multiple detectors  520   a , or other additional components. The surgical imaging system  500   a  could include sensors and/or be in communication with sensors configured to image other properties of a target environment (e.g., the biological tissue  530   a ). Other configurations, operations, and applications of surgical imaging systems as described herein are anticipated. 
     Note that the configuration and/or operation of the light source  510   a  to illuminate a portion of a surgical environment with a spot of monochromatic illumination is intended as a non-limiting example. Alternatively, a larger and/or differently-shaped region of the surgical environment (e.g., a line within the surgical environment; substantially the entire surgical environment and/or the entire surgical environment within a field of view of the surgical imaging system) could be illuminated by a light source of a surgical imaging system. Further, a light source could emit illumination at a controllable wavelength (e.g., illumination that is substantially monochromatic, but having a wavelength that can be altered by operation of the light source) and/or at a range of wavelengths (e.g., a broadband source that emits light across some specified range of wavelengths). 
     Similarly, the detector of a surgical imaging system could include individual light-sensitive elements configured to detect light within a particular specified narrow range of wavelengths (e.g., by including a filter, a prism and other optics, and/or having an intrinsic sensitivity to the light across the range of wavelengths) or configured to be sensitive to a broad range of wavelengths of light (e.g., broadband light-sensitive elements). Further, such a detector could include a camera or other elements configured to receive and detect properties of light from a plurality of separate regions of a surgical environment simultaneously, or could include light sensitive elements configured to receive light from an entire field of view of the surgical environment and to provide a single output related to the received light (similar to the detector  520   a  of the first example surgical imaging system  500   a ). 
     In some examples, a surgical imaging system could include a light source configured to illuminate an area of a surgical environment with light at a plurality of respective different wavelengths.  FIG. 6A  illustrates elements of a second example surgical imaging system  600   a  including a light source  610   a  and a detector  620   a . The light source  610   a  is configured to emit illumination  615   a  containing light at a plurality of specified wavelengths during a respective plurality of periods of time to illuminate a field of view of a surgical environment containing a biological tissue  630   a . The biological tissue  630   a  includes a first muscle  631   a  and a second muscle  633   a . The detector  620   a  is configured to receive light from the field of view containing the biological tissue  630   a  and to generate a plurality of images of the field of view corresponding to the illumination of the biological tissue  630   a  by the light of the respective plurality of different wavelengths during the respective plurality of periods of time. From the plurality of images, information about the spectrographic contents of the received light can be determined. The second muscle  633   a  includes a tagged region  637   a  containing marker (e.g., a dye or chromophore) configured to selectively interact with an analyte that is present in the tagged region  637   a.    
     The light source  610   a  could include a tunable laser controllable to emit light at any of a plurality of different wavelengths (e.g., wavelengths ranging between approximately 400 nanometers and approximately 2.5 micrometers). Such a tunable laser could include an excimer laser, a dye laser, a CO 2  laser, a free-electron laser, or some other laser element configured to emit light at a plurality of different, controllable wavelengths. In some examples, the wavelength of the light emitted by such a tunable laser could be controlled by controlling a geometry or size of one or more elements (e.g., a reflector, a resonating cavity) of the tunable laser. In some examples, a Bragg reflector or other element of the tunable laser could be rotated or otherwise actuated to control the wavelength of light emitted by the tunable laser. In some embodiments, the light source  610   a  could include a plurality of lasers configured to emit light at wavelengths corresponding to respective different wavelengths, and operation of the light source  610   a  to emit light of a particular wavelength could include operating the corresponding laser of the light source  620   a  to emit light at the controlled wavelength. Other configurations and operations of a tunable laser are anticipated. 
     The detector  620   a  could include a camera configured to detect the amplitude or other properties of light received by the detector  620   a  across a broad range of wavelengths (e.g., across the range of wavelengths of light that can be emitted by the tunable laser). That is, the detector  620   a  could be configured to act as broadband monochrome camera, receiving light from the biological tissue  630   a  during a plurality of periods of time and outputting a respective plurality of images related to the absorption or other interactions of the biological tissue  630   a  with light of a corresponding plurality of wavelengths emitted by the light source  610   a  during a the respective plurality of periods of time. This could include the detector  620   a  containing a regular two-dimensional (or otherwise arranged) array of light sensitive elements (e.g., photodiodes, phototransistors, pixels of a charge-coupled device (CCD), active pixel sensors) configured such that the output of an individual light sensitive element is related to the amplitude of the light received by the detector  620   a  from a particular direction (corresponding to a particular portion of the biological tissue  630   a ). Spectrographic content of light received from a particular portion of the biological tissue  630   a  could be determined based on a plurality of detected amplitudes (or other properties of light) detected by a particular pixel (or other light sensitive element) of the detector  620   a  corresponding to the particular portion of the biological environment  630   a  during the respective plurality of periods of time and corresponding to receptive wavelengths of illumination emitted by the light source  610   a . Other configurations of the detector  620   a  to enable the detection and/or determination of the spectrographic content of light received by the detector  620   a  are anticipated. 
     Spectrographic content of light received by the surgical imaging system  600   a  from a portion of a surgical environment (e.g., from the biological tissue  630   a ) could take the form of a plurality of images of the light received from the biological tissue  630   a . An example of such an image is illustrated in  FIG. 6B . The example image  600   b  illustrates the amplitude of light received from regions of the biological tissue  630   a  in response to illumination of the biological tissue  630   a  by light at a particular wavelength as emitted by the light source  610   a  during a period of time corresponding to the period of time during which the image  600   b  is taken. So, the image  600   b  includes first  601   b , second  602   b , and third  603   b  image regions corresponding to light received from the first muscle  631   a , and tagged region  637   a  of the second muscle  602   b , respectively. Spectrographic content (or other information) about light received from a particular portion of the biological tissue  630   a  could be determined based on an amplitude or other image data from a particular pixel of the image  600   b , and of a plurality of additional image (not shown) taken when the biological tissue is illuminated by a respective plurality of different wavelengths of light by the light source  610   a , where the particular pixel is positioned to receive light from the particular portion of the biological tissue  630   a . Such spectrographic content could be determined for a plurality of pixels and/or corresponding portions of the biological tissue based on the plurality of taken images. 
     A light source of a surgical imaging system could include optics or other elements configured to emit a beam of light configured to illuminate a line-shaped region of a target surgical environment, and to scan such a surgical environment by scanning the emitted beam of light across the target surgical environment.  FIG. 7A  illustrates elements of a third example surgical imaging system  700   a  including a light source  710   a  and a detector  720   a . The light source  710   a  is configured to emit a beam of illumination  715   a  containing light at a specified wavelength and to illuminate a line  735   a  on the biological tissue  730   a . The biological tissue includes a first muscle  731   a  and a second muscle  733   a . The detector  720   a  is configured to receive light from an area of the biological tissue  730   a  and to generate information about the spectrographic contents of the received light. The second muscle  733   a  includes a tagged region  737   a  containing an optical marker (e.g., a chromophore, a fluorophore) configured to selectively interact with an analyte that is present in the tagged region  737   a.    
     The light source  710   a  could include a variety of light-emitting elements configured to produce light at substantially one wavelength (i.e., containing light of wavelengths within a specified narrow range of wavelengths). This could include lasers, light-emitting diodes (LEDs), or other substantially monochromatic light sources. Additionally or alternatively, the light source  710   a  could include a light emitting element that emits light across a wider range of wavelengths, and this non-monochromatic light could be emitted through one or more filters (e.g., filters including one or more Bragg reflectors, prisms, diffraction gratings, slit apertures, monochromators) configured to only allow the transmission of light within a narrow range of wavelengths. The light source  710   a  could include mirrors, lenses, diffraction gratings, or other optics controlled by galvanometers, motors, or other actuators to control the direction of the beam of illumination  715   a  such that the location of an illuminated line of the surgical environment  730   a  could be controlled (e.g., by a controller operably coupled to the light source  710   a ). 
     The detector  720   a  could include a plurality of light-sensitive elements configured to detect the amplitude or other properties of light received by the detector  720   a  within one or more respective ranges of wavelengths from respective particular portions of the illuminated line  735   a  of the biological tissue  730   a . That is, the detector  720   a  could be configured to act as a hyperspectral imager, receiving light from the line  735   a  of the biological tissue  730   a  in sync with the illumination of the line  735   a  of the biological tissue  730   a  by the light source  710   a  and outputting information related to a plurality of spectra of the received light (i.e., outputting information relating to a plurality of spectrographic contents of the received light) corresponding to the plurality of portions within the line  735   a  of the biological tissue  730   a . This could include the detector  720   a  containing a prism, aperture, actuated optics (e.g., mirrors, lenses) and a two-dimensional array of light sensitive elements (e.g., photodiodes, phototransistors, pixels of a charge-coupled device (CCD), active pixel sensors) configured such that the output of an individual light sensitive element is related to the amplitude of the light received from a particular portion of the line  735   a  and within a specified range of wavelengths. Other configurations of the detector  720   a  to enable the detection and/or determination of spectrographic content of light received by the detector  720   a  from a plurality of portions of a surgical environment are anticipated. 
     Spectrographic content or other optical information generated by a surgical imaging system could be relative (i.e., having an amplitude or other property defined in terms of some other amplitude or variable generated and/or detected by the surgical system) or absolute (i.e., having an amplitude or other property defined in terms of some calibrated physical baseline). In some embodiments, the surgical imaging system could be operated to calibrate one or more elements of the surgical imaging system. For example, the surgical imaging system could be operated to generate spectrographic content or other information related to a calibration object having one or more known optical and/or spectrographic properties (e.g., a uniform reflectivity as a function of wavelength across a specified range of wavelengths) and a difference and/or correspondence between the spectrographic content or other information and the known optical and/or spectrographic properties could be used to correct subsequent spectrographic content or other information generated by the surgical imaging system. 
     Such a calibration object could be flat (e.g., could take the form a sheet or plate configured to be placed on tissue or other elements of a surgical environment) or could have some other shape (e.g., a sphere, a cube, a rod). A calibration object could be attached to an armature or to a surgical object (e.g., a retractor) within the surgical environment. Additionally or alternatively, a calibration object could be attached and/or mounted to a light source and/or detector of the surgical imaging system. In some examples, the calibration object could be internal to the surgical imaging system; for example, light emitted by the light source could be directed within the surgical imaging system (e.g., along a calibration light path) to illuminate the calibration object, and light emitted from the calibration object in response to such illumination could be directed to one or more light-sensitive elements of the detector of the surgical imaging system. The calibration object could be a black object (e.g., absorbing substantially all illumination across a range of wavelengths), a white object (e.g., absorbing substantially no illumination across a range of wavelengths), a colored object (e.g., absorbing substantially all illumination outside of a specified narrow range of wavelengths), or could have some other specified and/or determined wavelength-dependent optical property. 
     As an example,  FIG. 8A  illustrates elements of a fourth example surgical imaging system  800   a  including a light source  810   a  and a detector  820   a . The light source  810   a  is configured to emit a beam of illumination  815   a  containing light at one or more specified wavelengths during one or more periods of time and to illuminate a surgical environment  830   a . The surgical environment  830   a  includes a calibration object  840   a . The detector  820   a  is configured to receive light from the surgical environment  830   a  and to generate information about the spectrographic contents of the received light. 
     Example baseline spectrographic content  820   b  corresponding to the spectrographic content of light received from the calibration object  840   a  is illustrated in  FIG. 8B .  FIG. 8B  additionally includes uncorrected spectrographic content  810   b  corresponding to the spectrographic content of light received from another, non-calibration portion of the surgical environment  830   a . The horizontal axis indicates wavelength (increasing to the right) and the vertical axis indicates amplitude. Corrected spectrographic content  830   b  corresponding to the non-calibration portion of the surgical environment  830   a  could be determined by determining a difference between the baseline spectrographic content  820   b  and the uncorrected spectrographic content  810   b . Additionally or alternatively, corrected spectrographic content for a particular portion of the surgical environment could be determined based on a ratio, logarithmic function, nonlinear function power function, product, exponential, or some other operation or combination of operations of uncorrected spectrographic content for the particular portion and baseline spectrographic content corresponding to a calibration object. 
     The calibration object  840   a  could be an object having a known and/or stable emission, reflection, absorption, excitation, or other spectrum. The known spectrographic properties of the calibration object could be specified (i.e., selected by the composition and/or manufacture of the object) and/or could be measured (e.g., by a laboratory spectrometer or other optical measurement device). The composition and/or manufacture of the calibration object could be specified to have a particular uniform reflectivity or other optical property across a wide range of wavelengths. The composition and/or manufacture of the calibration object could be specified to have a particular reflectivity or other spectrum having one or more peaks to enable calibration of the wavelength of light emitted by a tunable laser of other optical device. 
     Other methods of configuring and/or operating a light source, detector, and/or other elements of a surgical imaging system (e.g., to identify one or more portions of a surgical environment, to ablate or otherwise interact with the portion of the surgical environment based on such identification) are anticipated. 
     IV. Example Surgical Imaging System 
       FIG. 9  is a simplified block diagram illustrating the components of a surgical imaging system  900 , according to an example embodiment. Surgical imaging system  900  may take the form of or be similar to one of the example surgical imaging systems  500   a ,  600   a ,  700   a ,  800   a  shown in  FIGS. 5A, 6A, 7A, and 8A . Surgical imaging system  900  may take a variety of forms, such as a wall, surgical table, ceiling, or floor-mounted device. Surgical imaging system  900  could also take the form of a system, device, or combination of devices that is configured to part of another device, apparatus, or system. For example, surgical imaging system  900  could take the form of a light source, detector, and other components configured to be mounted to or otherwise disposed as part of a surgical apparatus, tool, implement, or system (e.g., a robotic surgical system, a stereotactic surgical apparatus, an imaging-guided surgical system). Surgical imaging system  900  could also take the form of a system configured to illuminate and to receive light from some other industrial environment, medical environment, scientific environment, or some other environment. Surgical imaging system  900  also could take other forms. 
     In particular,  FIG. 9  shows an example of a surgical imaging system  900  having a light source  902 , a detector  904 , a surgical laser  906 , a user interface  920 , communication system(s)  930  for transmitting data to a remote system, and controller  910 . The components of the surgical imaging system  900  may be disposed on or within a mount or housing or on some other structure for mounting the system to enable stable imaging or other functions relative to elements in a surgical environment of interest, for example, to a surgical frame secured relative to a biological tissue subject to a surgical intervention. The surgical imaging system  900  could include additional components, for example, an actuated retractor, an actuated scalpel or electo-surgical instrument, or some other surgical instrument or other component(s) according to an application. 
     Controller  910  may be provided as a computing device that includes one or more processors  911 . The one or more processors  911  can be configured to execute computer-readable program instructions  914  that are stored in a computer readable data storage  912  and that are executable to provide the functionality of a surgical imaging system  900  as described herein. 
     The computer readable data storage  912  may include or take the form of one or more non-transitory, computer-readable storage media that can be read or accessed by at least one processor  911 . The one or more computer-readable storage media can include volatile and/or non-volatile storage components, such as optical, magnetic, organic or other memory or disc storage, which can be integrated in whole or in part with at least one of the one or more processors  911 . In some embodiments, the computer readable data storage  912  can be implemented using a single physical device (e.g., one optical, magnetic, organic or other memory or disc storage unit), while in other embodiments, the computer readable data storage  912  can be implemented using two or more physical devices. 
     The light source  902  is configured to illuminate one or more portions of a surgical environment with illumination at one or more specified wavelengths. The one or more portions of the surgical environment could comprise a spot, line, and/or some otherwise-shaped region of the surgical environment (e.g., substantially the entire surgical environment and/or the entire surgical environment within a field of view of the surgical imaging system  900 ). Further, the light source  902  could emit illumination at a fixed wavelength, a controllable wavelength (e.g., illumination that is substantially monochromatic, but having a wavelength that can be altered by operation of the light source) and/or at a range of wavelengths (e.g., a broadband or white illumination source across some specified range of wavelengths). The direction of illumination emitted by the light source  902  (and thus the location of any portion(s) of the surgical environment illuminated by the light source  902 ) could be controlled by one or more actuator(s)  908  configured to actuate one or more mirrors, lenses, diffraction gratings, or other optical elements optically coupled to the light source  902 . 
     The detector  904  includes a plurality of individual light-sensitive elements configured to detect light within a particular specified narrow range of wavelengths (e.g., by including a filter, a prism and other optics, and/or having an intrinsic sensitivity to the light across the range of wavelengths) and/or configured to be sensitive to broad range of wavelengths of light (e.g., broadband light-sensitive elements). Further, individual light-sensitive elements of the detector  904  could be configured to receive and detect properties of light from respective portions of a surgical environment, or could be configured to receive light from an entire field of view of the surgical environment and to provide a single output related to the received light (similar to the detector  520   a  of the first example surgical imaging system  500   a ). In some examples, the location of a portion of a surgical environment from which the detector  904  is configured to received light could be controlled by one or more mirrors, prisms, or other actuated optical elements (e.g., the detector  904  could be configured and operated as a line-scanning hyperspectral imager). 
     The surgical laser  906  could is configured to emit a directed beam of light sufficient to cause localized heating of a target portion of an environment of interest (e.g., a biological tissue subject to a surgical intervention) proximate to where the emitted beam intersects with the environment of interest. The surgical laser  906  could include a 2 micron laser, a CO 2  laser, a semiconductor diode laser, a dye laser, an excimer laser, a fiber laser, a gas laser, a free electron laser, or some other type or types of laser. The surgical laser  906  could include optical elements configured to affect one or more properties of the beam of light emitted by the surgical laser, e.g., lenses, mirrors, diffraction gratings, volume holographic gratings, collimators, nonlinear optical elements (e.g., frequency doubling or tripling media), or other elements. 
     The program instructions  914  stored on the computer readable data storage  912  may include instructions to perform any of the methods described herein. For instance, in the illustrated embodiment, program instructions  914  include an illumination and detection module  915 , an identification module  916 , and a surgical intervention module  917 . 
     The illumination and detection module  915  can include instructions for operating the light source  902 , detector  904 , and/or actuator(s)  908  to enable any of the functions or applications of a surgical imaging system to determine and/or detect spectrographic information and/or content corresponding to more or more portions of a surgical environment as described herein. Generally, instructions in the illumination and detection module  915  describe methods of operating the light source  902  and/or actuator(s)  908  to illuminate one or more portions of a surgical environment with light at one or more specified wavelengths during one or more respective periods of time. Instructions in the illumination and detection module  915  further describe methods of operating the detector  904  to receive light from illumination portions of the surgical environment and to determine spectrographic content for a particular portion of the surgical environment based on the light received from the particular portion of the surgical environment. Other operations, functions, and applications of the light source  902 , detector  904 , actuator(s)  908 , and/or of other components of the surgical imaging system  900  as described herein could be implemented as program instructions in the illumination and detection module  915 . 
     The identification module  916  can include instructions for identifying a particular portion of the surgical environment based on spectrographic content determined from light received from the portion of the surgical environment. The instructions could include instructions to implement a variety of classifiers and/or combinations of classifiers to identify or otherwise assign a classification to the portion of a surgical environment based on the spectrographic contents of light received from the portion. Implemented classifiers could generate a binary output (e.g., “biological tissue” vs. “not biological tissue”) or an output having a plurality of possible states (e.g., “artery,” “vein,” “nerve,” “tendon,” “skin,” “muscle,” “liver,” “kidney,” “pancreas,” “fat,” “necrosis,” “tumor”). A plurality of possible outputs states could be nominal (i.e., categorical and non-ordered) or ordinal (e.g., “very unlikely to contain cancer cells,” “slightly unlikely to contain cancer cells,” “slightly likely to contain cancer cells,” “very likely to contain cancer cells”). Output of a classifier corresponding to a particular portion of a surgical environment could be based only on spectrographic content from the particular portion or could be based additionally on spectrographic content from other portions of the surgical environment (e.g., neighboring portions of the surgical environment to enable a spatially smooth output of the classifier across portions; a portion of the surgical environment containing a calibration object having known spectrographic properties to act as a baseline for comparison). A classifier could generate multiple outputs for a single portion (e.g., could output one of “biological tissue” and “surgical instrument” and one of “contains fluorophore” and “does not contain fluorophore”). 
     Classifiers implemented by a controller could include linear classifiers, nonlinear classifiers, support vector machines, decision trees, k-nearest-neighbors, neural networks, thresholds, or other classifiers and/or combinations thereof. Further, a controller could perform some preprocessing on input spectrographic content before the application of a classifier. For example, input content could be subject to some transformation (e.g., conversion by application to a logarithmic, hyperbolic, power series, or other nonlinear function), dimensionality reduction (e.g., principal components analysis, factor analysis, independent components analysis, isomap, linear discriminant analysis, non-negative matrix factorization), filtering (e.g., spatial filtering across spectrographic contents for neighboring portions, wavelength filtering to smooth a determined spectrum) or some other preprocessing step. 
     The surgical intervention module  917  can include instructions for planning and/or executing one or more surgical interventions on a biological tissue based on information identifying particular portions of a surgical environment containing the biological tissue. The instructions could include instructions to determine a location, extent, or other properties of an identified target tissue (e.g., an extent of a tumor containing a cancerous target tissue). Instructions of the surgical intervention module  917  can further include instructions for controlling one or more surgical instruments (e.g., the surgical laser  906 , an actuated scalpel, an actuated retractor) to effect one or more surgical interventions on the biological tissue. For example, the surgical intervention module  917  can include instructions for operating the surgical laser  906  (e.g., controlling a wavelength, energy level, direction or other properties of the light emitted by the surgical light  906 ) according to a determined location, extent, or other properties of an identified target tissue such that the identified target tissue is ablated (e.g., such that a tumor containing cancerous target tissue is ablated). 
     Some of the program instructions of the illumination and detection module  915 , identification module  916 , and/or surgical intervention module  917  may, in some examples, be stored in a computer-readable medium and executed by a processor located external to the surgical imaging system  900 . For example, the surgical imaging system  900  could be configured to illuminate and to received light from a portion of a biological environment and then transmit related data to a remote server, which may include a mobile device, a personal computer, the cloud, or any other remote system, for further processing (e.g., for the determination of spectrographic content of the received light, for identifying the portion of the surgical environment based on the determined spectrographic content). 
     User interface  920  could include indicators, displays, buttons, touchscreens, head-mounted displays, displays of a console of a tele-surgical system, and/or other elements configured to present information about the surgical imaging system  900  to a user and/or to allow the user to operate the surgical imaging system  900 . Additionally or alternatively, the surgical imaging system  900  could be configured to communicate with another system (e.g., a cellphone, a tablet, a computer, a remote server) and to present elements of a user interface using the remote system. The user interface  920  could be disposed proximate to the light source  902 , detector  904 , surgical laser  906 , controller  910 , or other elements of the surgical imaging system  900  or could be disposed away from other elements of the surgical imaging system  900  and could further be in wired or wireless communication with the other elements of the surgical imaging system  900 . The user interface  920  could be configured to allow a user to specify some operation, function, or property of operation of the surgical imaging system  900 . The user interface  920  could be configured to present information about a biological tissue or other contents of the surgical environment (e.g., a tissue type, a presence of fluorophore) to the user using a display, to present a degree of progress of an ongoing function of the surgical imaging system (e.g., a degree of progress in ablating biological tissue along a specified trajectory using a surgical laser of the surgical imaging system  900 ), to present an image of a biological tissue or other contents of the surgical environment generated using the light source  902  and detector  904 , or using some other imaging component or sensor, or to present some other information to a user. Other configurations and methods of operation of a user interface  920  are anticipated. 
     Communication system(s)  930  may also be operated by instructions within the program instructions  914 , such as instructions for sending and/or receiving information via a wireless antenna, which may be disposed on or in the surgical imaging system  900 . The communication system(s)  930  can optionally include one or more oscillators, mixers, frequency injectors, etc. to modulate and/or demodulate information on a carrier frequency to be transmitted and/or received by the antenna. In some examples, the surgical imaging system  900  is configured to indicate an output from the controller  910  by transmitting an electromagnetic or other wireless signal according to one or more wireless communications standards (e.g., Bluetooth, WiFi, IRdA, ZigBee, WiMAX, LTE). In some examples, the communication system(s)  930  could include one or more wired communications interfaces and the surgical imaging system  900  could be configured to indicate an output from the controller  910  by operating the one or more wired communications interfaces according to one or more wired communications standards (e.g., USB, FireWire, Ethernet, RS-232). 
     The computer readable data storage  912  may further contain other data or information, such as medical and health history of a patient whose biological tissue is being imaged or otherwise interacted with by the surgical imaging system  900 , that may be useful in tracking or otherwise interacting with a biological tissue or other environment of interest. Further, the computer readable data storage  912  may contain data corresponding to imaging information about a biological tissue or other environment of interest. The computer readable data storage  912  may contain calibration data corresponding to a configuration of the surgical imaging system  900 , a calibration object, or some other information. Calibration, model, imaging, and/or other data may also be generated by a remote server and transmitted to the surgical imaging system  900  via communication system(s)  930 . 
     In some examples, the collected calibration and/or model data, stored information about operation of the surgical imaging system  900  (e.g., information about identification of biological tissues or other contents of a surgical environment performed using the surgical imaging system  900 ), health state information (e.g., health state of biological tissues) detected by the surgical imaging system  900  and other usage or other information may additionally be input to a cloud network (e.g., using the communications system(s)  930 ) and be made available for download by users having sufficient permissions (e.g., a surgeon tasked with reviewing the outcome of a surgical intervention wholly or partially effected using the surgical imaging system  900 ). Other analyses may also be performed on the collected data, such as physiological parameter data and health state information, in the cloud computing network and be made available for download by physicians or clinicians. 
     Further, physiological parameter and health state data from individuals or populations of device users may be used by physicians or clinicians in monitoring outcomes of a surgical intervention or other treatment. For example, high-density, real-time data may be collected from a population of device users who have experienced a surgical intervention implemented using information generated by the surgical imaging system  900  to assess the safety and efficacy of the surgical intervention. Such data may also be used on an individual level to assess a particular patient&#39;s response to a surgical intervention or therapy. Based on this data, a physician or clinician may be able to tailor a future surgical intervention or other treatment to suit an individual&#39;s needs. 
     V. Example Methods 
       FIG. 10  is a flowchart of an example method  1000  for operating elements of a surgical imaging system to perform functions and/or applications of the surgical imaging system. The surgical imaging system includes a light source configured to illuminate one or more portions of a surgical environment, where the surgical environment contains a tissue subject to a surgical intervention involving one or more surgical instruments (e.g., a scalpel, a surgical laser, an RF or electrical cautery or ablation tool, a retractor, a hemostat). The surgical imaging system also includes a detector configured to receive light from the illuminated one or more portions of the surgical environment and to generate an output such that a spectrographic content of the received light can be determined. The surgical imaging system further includes a surgical laser configured to emit light sufficient to ablate, cauterize, or otherwise modify biological tissues. 
     The method  1000  includes operating the light source to illuminate a portion of the surgical environment ( 1002 ). This could include operating a light-emitting element (e.g., a laser) of the light source to illuminate the portion of the surgical environment with light at a particular fixed wavelength. This ( 1002 ) could include operating tunable laser of the light source to illuminate the portion of the surgical environment with light at a plurality of different wavelengths during a respective plurality of periods of time. This ( 1002 ) could include operating an actuator to control the configuration of a mirror, lens, or other optical element(s) to control the direction of a beam of light emitted by the light source to illuminate a spot, line, or other region of the surgical environment containing the portion of the surgical environment. 
     The method  1000  additionally includes receiving light from the illuminated portion of the surgical environment ( 1004 ). This could include operating a detector of the surgical imaging system to output a set of detected amplitudes or other properties of light received by the detector within one or more respective ranges of wavelengths. That is, the detector could be configured to act as a spectrometer, receiving light from the surgical environment and outputting information related to the spectrum of the received light (i.e., outputting information relating to the spectrographic content of the received light). Additionally or alternatively, this ( 1004 ) could include operating a detector of the surgical imaging system to output a set of detected amplitudes or other properties of light received by the detector during a plurality of periods of time in response to the illumination of the surgical environment by a light source with light at a respective plurality of different wavelengths. Further, receiving light from the illuminated portion of the surgical environment ( 1004 ) could include imaging the surgical environment. 
     The method  1000  additionally includes determining a spectrographic content of the received light ( 1006 ). This could include receiving from a detector (e.g., a spectrometer, a hyperspectral imager) a set of detected amplitudes or other properties of the received light within one or more respective ranges of wavelengths. This ( 1006 ) could include determining spectrographic content based on a plurality of detected amplitudes (or other properties of light) detected by a particular pixel (or other light sensitive element) of a detector during a respective plurality of periods of time and corresponding to a respective plurality of different wavelengths of light illuminating the portion of the surgical environment. Determining a spectrographic content of the received light ( 1006 ) could include spatially (i.e., across received lights and/or determined spectrographic content thereof corresponding to proximate portions of the surgical environment), temporally (i.e., across lights received at two or more points in time), by wavelength, or otherwise filtering and/or preprocessing determined spectrographic content. In some examples, determining a spectrographic content of the received light ( 1006 ) could include determining one or more properties (e.g., an amplitude, a center wavelength, a peak width) of one or more features (e.g., a peak, a trough, a pass band, a slope or other rate of change of amplitude according to wavelength within one or more ranges of wavelengths) of a detected and/or determined spectrum of the received light. 
     The method  1000  additionally includes identifying at least one of a portion of tissue or a portion of a foreign body in the portion of the surgical environment based on the determined spectrographic content ( 1008 ). This could include determining that the portion of the surgical environment contains biological tissue, that the portion contains biological tissue of a particular type (e.g., “muscle,” “skin,” “blood vessel,” “nerve,” “tumor,” “tendon”), and/or that the portion contains an amount of a particular chromophore fluorophore, or other marking agent. This ( 1008 ) could include determining that the portion of the surgical environment contains portion of a surgical instrument, a portion of a particular type of surgical instrument (e.g., “retractor,” “hemostat,” “stainless steel instrument,” “plastic retractor,” “titanium instrument,” “instrument contaminated or marked with a particular chromophore, fluorophore, or other marking agent”), a foreign body, and/or a particular type of foreign body (e.g., “suture,” “nylon suture,” “silk suture,” “surgical staple,” “implant device,” “electrode lead,” “drain catheter,” “surgical mesh”). Identifying at least one of a portion of tissue or a portion of a foreign body in the portion of the surgical environment ( 1008 ) could include implementing a classifier and/or combination of classifiers to identify or otherwise assign a classification to the portion of the surgical environment based on the determined spectrographic content. Implementing a classifier could include generating a binary output (e.g., “biological tissue” vs. “not biological tissue”) or an output having a plurality of possible states (e.g., “artery,” “vein,” “nerve,” “tendon,” “skin,” “muscle,” “fat,” “necrosis,” “tumor”). 
     The method  1000  additionally includes, responsive to identifying a target tissue in the illuminated portion of the surgical environment, emitting light from the surgical laser to the target tissue ( 1010 ). This could include emitting a beam of light to ablate, dissect, cauterize, or otherwise damage or destroy the target tissue. Emitting light from the surgical laser to the target tissue ( 1010 ) could include operating a 2 micron laser, CO 2  laser, an excimer laser, or some other variety of laser configured to apply energy to biological tissue sufficient to ablate or otherwise modify the biological tissue. Emitting light from the surgical laser to the target tissue ( 1010 ) could include operating optics of the surgical laser to control a direction and/or focus of the beam of light emitted by the surgical laser and/or operating an armature on which the surgical laser is disposed to control the location and/or orientation of the surgical laser. 
     The method  1000  could include additional steps. For example, the method could include illuminating, receiving light from, determining spectrographic content of the received light, and identifying a plurality of portions of the surgical environment. In some examples, the method  1000  could include implementing one or more surgical interventions in a wholly or partially automated manner based on identification or other information determined about a portion of the surgical environment. For example, identifying at least one of a portion of tissue or a portion of a foreign body in the portion of the surgical environment ( 1008 ) could include identifying a target tissue and, responsive that this identification, effecting one or more surgical interventions on the target tissue using a robotic surgical system (e.g., excision by an actuated scalpel, thermal, RF, and/or electrical ablation of a tissue, cauterization of a wound and/or target vascular tissue). 
     The method  1000  could further include calibrating one or more elements of the surgical imaging system. For example, a calibration object having one or more known optical and/or spectrographic properties could be present in the surgical environment (or some other environment accessible to the surgical imaging system). The surgical imaging system could illuminate, receive light from, and determine spectrographic content of the received light to determine calibration data (e.g., a baseline spectrum) for the surgical imaging system. Subsequently, the surgical imaging system could use the determined calibration data to offset, scale, or otherwise adjust spectrographic content determined based on received light from portions of the surgical environment. 
     The method  1000  could include other additional steps or elements. The method  1000  could include any additional steps, or could include details of implementation of the listed steps  1002 ,  1004 ,  1006 ,  1008  or of other additional steps, as described herein in relation to the operation of a surgical imaging system. Additional and alternative steps of the method  1000  are anticipated. 
     In some examples, the surgical environment described in relation to the method  1000  above could contain a biological tissue of a human body. For example, the environment could contain a tissue that has been determined to include a tumor that could be resected, ablated, or otherwise removed to change and/or affect a health state of the human body. Other examples of surgical environments, biological tissues, surgical interventions, surgical instruments, foreign bodies, methods of operating a surgical imaging system, configurations of surgical imaging systems, and other elements are anticipated. 
     VI. Conclusion 
     Where example embodiments involve information related to a person or a device of a person, the embodiments should be understood to include privacy controls. Such privacy controls include, at least, anonymization of device identifiers, transparency and user controls, including functionality that would enable users to modify or delete information relating to the user&#39;s use of a product. 
     Further, in situations in where embodiments discussed herein collect personal information about users, or may make use of personal information, the users may be provided with an opportunity to control whether programs or features collect user information (e.g., information about a user&#39;s medical history, information about a surgical intervention performed on the user, information about biological tissues of a user, a user&#39;s preferences, or a user&#39;s current location), or to control whether and/or how to receive content from a content server (e.g., a profile of power to ablate a tissue applied using a heating laser) that may be more relevant to the user. In addition, certain data may be treated in one or more ways before it is stored or used, so that personally identifiable information is removed. For example, a user&#39;s identity may be treated so that no personally identifiable information can be determined for the user, or a user&#39;s geographic location may be generalized where location information is obtained (such as to a hospital, city, ZIP code, or state level), so that a particular location of a user cannot be determined. Thus, the user may have control over how information is collected about the user and used by a content server. 
     The particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an exemplary embodiment may include elements that are not illustrated in the Figures. 
     Moreover, it is particularly noted that while devices, systems, methods, and other embodiments are described herein by way of example as being employed to image and/or manipulate biological environments (e.g., tissues) of a human body, it is noted that the disclosed devices, systems, and methods can be applied in other contexts as well. For example, imaging and/or ablation systems configured as disclosed herein may be included as part of other surgical and/or medical imaging apparatus. In some contexts, such an imaging system could be operated to detect one or more properties of a tissue or other element of a human body, possibly in concert with other medical imaging or other sensor apparatus. In another example, an imaging system could be configured to image and/or ablate specified elements and/or regions of a non-tissue element of a human body. For example, the imaging system could be configured and/or applied to image specified regions of an implantable device (e.g., a stent, an artificial joint, a pacemaker) to control the effecting of a desired change in the implantable device (e.g., to section the device, to weld an element of the device, to activate an element of the device, to trim an element (e.g., an electrode) of the device). 
     In other examples, devices, systems, and methods disclosed herein may be applied to image and/or ablate regions of environments that are not in or on a human body. For example, imaging systems disclosed herein may be included in systems used to image and/or ablate specified regions (e.g., tissues) of an animal. In another example, devices, systems, and methods disclosed herein may be applied to image and/or ablate regions of an industrial environment or a work element of an industrial process, such as a work element in a laser cutting process. 
     Additionally, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are included for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are contemplated herein.