Abstract:
Method and apparatus can be provided according to an exemplary embodiment of the present disclosure. For example, with at least one first section of an optical enclosure, it is possible to provide at least one first electro-magnetic radiation. In addition, with at least one second section provided within the enclosure, it is possible to cause, upon impact by the first radiation, a redirection of the first radiation to become at least one second radiation. Further, with at least one third section of the optical enclosure, it is possible to cause at least one second radiation to be provided to a tissue. For example, the redirection of the first radiation causes, at least approximately, a uniform optical illumination on of a surface of the tissue.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application relates to and claims priority from U.S. Provisional Patent Application Ser. No. 61/933,669 filed Jan. 30, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    Various exemplary embodiments of the present disclosure relate generally to apparatus, systems and methods, which can characterize, image and/or or modify an object (e.g., tissue). In particular, various exemplary embodiments of the present disclosure can relate to apparatus, systems and methods for measuring photoacoustic signals. Further, various exemplary embodiments of the present disclosure relate to apparatus, systems and methods which can facilitate a low-risk assessment of cardiovascular function and diseases, such as, e.g., monitoring hemodynamic changes. 
       BACKGROUND INFORMATION 
       [0003]    Use of light for characterizing, imaging and altering tissue has seen dramatically expansion during the last decade. A challenge for designing an optical device can be how to make an efficient use of light to generate a maximal diagnostic signal or treatment outcome. Further, many optical diagnosis and therapy are performed using endoscopes. The permissible optical fluence density on tissue surface can be regulated by laser safety standards. Thus, it is likely preferable to enlarge and/or homogenize the illumination to admit more optical power. However, it can be difficult to achieve a sufficient large uniform illumination area from a compact endoscope following the current paradigm, which uses light guides, lenses and mirrors. 
         [0004]    Photoacoustic imaging is a radiological technology, which generates high-definition volumetric images of tissue by measuring light-induced sound waves—one or more photoacoustic signals—from its optically absorbing structures. Through exciting various biomolecules at their characteristic absorption wavelengths, photoacoustic signals can be used to analyze the molecular composition of a tissue at a clinically relevant depth. For example, through exploiting the differential absorption spectra of oxy- and deoxy-hemoglobin, photoacoustic signal, measured from blood at a plurality of selected optical wavelengths, can be used to evaluate local blood oxygenation of each individual blood vessel, and provide information regarding cancer biology and cardiovascular diseases. When optimizing a photoacoustic system, a major challenge can be how to maximize photoacoustic generation using finite optical exposure allowed by established safety standards. 
         [0005]    Hemodynamic monitoring plays an important role in managing critically ill patients in emergency departments, surgical rooms and intensive care units. Adequate blood oxygen supply to tissue can be essential to sustain human life. A lasting deficiency of tissue oxygen could lead to the failure of vital organs, and is likely ultimately responsible for many deaths from a variety of diseases, such as, e.g., trauma, burn, heart attack and sepsis. Mixed venous oxygen saturation (SvO 2 ) is a preferred target of hemodynamic monitoring. SvO 2 , the oxygen saturation measured from the mixed venous blood in a pulmonary artery, can reflect a dynamic balance between body&#39;s global oxygen supply and demand. Normally, SvO 2  is closely maintained between 60-80%. In patients, there are various challenges to the balance of oxygen metabolism. For example, the oxygen demand can increase in case of fever, shivering and/or seizure, while the oxygen supply can decrease when bleeding. When challenged, stable patients can restore the oxygen equilibrium by increasing the cardiac output, and do not require hemodynamic intervention. 
         [0006]    However, in high-risk patients, especially those with a poor cardiopulmonary reserve, a compensatory increase in cardiac output can be limited. As a result, such patients have to call on bodies&#39; last line defense by extracting more oxygen from blood, i.e., when SvO 2  starts to decrease. For example, an immediate intervention can be indicated if &gt;10% deviation of SvO 2  from baseline is seen to last beyond, e.g., 3 minutes. In current practice, SvO 2  can be measured with an indwelling pulmonary artery catheter (PAC), introduced invasively from a peripheral vein. The use of the PAC was found to be associated with about 10% incidence of complications, including hematoma, vessel puncture and cardiac arrest. As a result, the use of the PAC has been significantly decreased, e.g., by 65% between 1993˜2004. 
         [0007]    Accordingly, there may be a need to address and/or overcome at least some of the issues of deficiencies described herein above. 
       OBJECT AND SUMMARY OF EXEMPLARY EMBODIMENTS 
       [0008]    To that end, apparatus, systems and methods according to certain exemplary embodiments of the present disclosure can be provided to overcome both aforementioned challenges by, e.g., increasing light-tissue interaction, thereby be utilized in broad applications in optical spectroscopy (e.g., scattering, fluorescence and Raman spectroscopy, etc.), imaging (e.g., photoacoustic imaging, diffuse optical tomography), or intervention (e.g., photodynamic, photothermal or low-level light therapy, etc.). 
         [0009]    According to another exemplary embodiment of the present disclosure, apparatus, systems and methods for measuring a photoacoustic signal can be provided. Such exemplary apparatus, systems and methods can be utilized for measuring the photoacoustic signals using a light-integrating enclosure, which can safely increase light absorption in a targeted tissue, and generate a stronger photoacoustic signal for the detection. In still another exemplary embodiment of the present disclosure, apparatus, low-risk systems and methods can be provided so as to facilitate monitoring of the oxygen metabolism, e.g., in critical care. In addition, exemplary transesophageal photoacoustic endoscope, system and method according to a further exemplary embodiment of the present disclosure can be provided, which can be used to measure the photoacoustic signal from a pulmonary artery through a esophageal wall, and evaluate SvO 2  in, e.g., a less risky manner. 
         [0010]    According to another exemplary embodiment of the present disclosure, apparatus, systems and methods can be provided to characterize, image and/or modify tissue with light (or other electro-magnetic radiation), which can include a source generating light, an optical integrating enclosure that performs (a) redirecting the light or other radiation to illuminate a tissue and (b) increasing of an optical fluence on a tissue surface. Such exemplary apparatus, systems and methods can be further configured to perform optical spectroscopy (e.g., scattering, fluorescence, Raman spectroscopy, etc.), imaging (e.g., photoacoustic imaging, diffuse optical tomography, etc.), and/or a treatment (e.g. photodynamic, photothermal or low-level light therapy, etc.). 
         [0011]    In yet a further exemplary embodiment of the present disclosure, apparatus, systems and methods can be provided to measure the photoacoustic signal. For example, with a source, it is possible to generate light or other electro-magnetic radiation with a time-varying intensity. In addition, using an optical integrating enclosure, it is possible to perform (a) redirecting of the light or other radiation to illuminate the tissue, and (b) increasing the optical fluence on the tissue surface. Further, with at least one acoustic transducer, it is possible to detect acoustic signals generated from the illuminated tissue volume. 
         [0012]    According to yet another exemplary embodiment of the present disclosure, endoscopic apparatus, systems and methods can be provided for assessing cardiovascular functions or diseases, such as, e.g., monitoring a mixed venous oxygen saturation. For example, using the source, it is possible to generate light or other electro-magnetic radiation with a time-varying intensity. In addition, using an optical integrating enclosure, it is possible to redirect the light or the electro-magnetic radiation to illuminate a pulmonary artery or other cardiac tissue through a wall of an esophagus. Further, with at least one acoustic transducer, it is possible to detect acoustic signals generated from the pulmonary artery, and with a computer processing arrangement or unit, it is possible to determine at least one property of the pulmonary artery or other cardiac tissue. 
         [0013]    Thus, method and apparatus can be provided according to an exemplary embodiment of the present disclosure. For example, with at least one first section of an optical enclosure, it is possible to provide at least one first electro-magnetic radiation. In addition, with at least one second section provided within the enclosure, it is possible to cause, upon impact by the first radiation, a redirection of the first radiation to become at least one second radiation. Further, with at least one third section of the optical enclosure, it is possible to cause at least one second radiation to be provided to a tissue. For example, the redirection of the first radiation causes, at least approximately, a uniform optical illumination on of a surface of the tissue. 
         [0014]    According to another exemplary embodiment of the present disclosure, the first section can have a cross-section that extends for a first extension, and the second section can have a cross-section that extends for a second extension. The first extension can be smaller than the second extension. The enclosure can be structured such that when at least one third radiation enters the enclosure from the tissue via the third section, the third radiation is deflected at at least one fourth section or at the second section within the enclosure, and forwarded back onto the surface of the tissue. The third radiation can be a return radiation from the tissue associated with the second radiation. 
         [0015]    In addition, according to yet further exemplary embodiment of the present disclosure, an acoustic detector arrangement can be provided which is configured to receive an acoustic wave information from the tissue. The acoustic wave can be generated within the tissue in response to the second radiation provided on the tissue, the third radiation provided from the tissue, and/or at least one fourth radiation provided from the enclosure that is a redirected radiation of the third radiation within the enclosure. The enclosure can be composed of at least one material that allows most or entirety of the acoustic wave from the tissue to penetrate at least most of the enclosure. The enclosure can be provided in an approximate contact with the acoustic detector. Further, an acoustic matching layer can be provided between the acoustic detector and the enclosure. 
         [0016]    According to still another exemplary embodiment, the first portion and/or the third portion can have a curvature that facilitates (i) a uniform distribution or (ii) a large area of illumination of at least one of the second radiation provided on the tissue, the third radiation provided from the tissue, and/or at least one fourth radiation provided from the enclosure that is a redirected radiation of the third radiation within the enclosure. The enclosure can have a shape of an acoustic lens. The second section can be (i) composed of a scattering material and/or (ii) have a scattering coating thereon, to effectuate the redirection of the first radiation. The scattering material can include a combination of an optically-transparent silicon rubber with light scattering particles. The enclosure can also comprise at least one fourth section through which the first radiation travels to reach the second section, where the fourth section can be approximately transparent. The transparent fourth section can be composed at least in part of silicon rubber, which can be substantially optically transparent. 
         [0017]    In yet a further exemplary embodiment of the present disclosure, at least one fiber arrangement can be provided which can facilitate thereon or therethrough the first radiation. Further, an acoustical detector can be provided which is configured to receive an acoustic radiation from the tissue based on at least one of the second radiation provided on the tissue, the third radiation provided from the tissue, and/or at least one fourth radiation provided from the enclosure that is a redirected radiation of the third radiation within the enclosure. The enclosure, the fiber arrangement and the detector can be provided in a probe. The fiber arrangement can have a distal end in a proximity of the enclosure that has a curved shape to facilitate (i) a uniform distribution or (ii) a large area of illumination of the second radiation provided on the tissue, the third radiation provided from the tissue, and/or at least one fourth radiation provided from the enclosure that is a redirected radiation of the third radiation within the enclosure. 
         [0018]    These and other objects, features and advantages of the exemplary embodiments of the present disclosure will become apparent upon reading the following detailed description of the exemplary embodiments of the present disclosure, when taken in conjunction with the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Further objects, features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying figures showing illustrative embodiments of the present disclosure, in which: 
           [0020]      FIG. 1  is a cross-sectional side-view diagram of an optical apparatus according to an exemplary embodiment of the present disclosure; 
           [0021]      FIG. 2  is a cross-sectional side-view diagram of a photoacoustic measuring apparatus according to an exemplary embodiment of the present disclosure; 
           [0022]      FIG. 3  is a diagram of a transesophageal photoacoustic endoscopic system for monitoring a mixed venous oxygen saturation, according to an exemplary embodiment of the present disclosure; 
           [0023]      FIG. 4  is an exemplary wide-field optical illumination on tissue surface achieved by one exemplary embodiment of the apparatus, systems and methods according to the present invention illustrated in  FIG. 3 ; and 
           [0024]      FIG. 5  is a graph illustrating a mixed venous oxygenation changes over time in response to varying fraction of inspired oxygen, evaluated by the transesophageal photoacoustic endoscope, according to the exemplary embodiment of the present disclosure illustrated in  FIG. 3 . 
       
    
    
       [0025]    Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject disclosure will now be described in detail with reference to the figures, it is done so in connection with the illustrative embodiments. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure as defined by the appended claims. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0026]      FIG. 1  illustrates a cross-sectional view of an exemplary apparatus that includes an optical enclosure  110  according to one exemplary embodiment of the present disclosure. For example, light  102  (or other electro-magnetic radiation) can be delivered by the enclosure  110  to characterize, image and/or modify a targeted object  152  in a tissue  150 . The enclosure  110  can include a light-transporting medium  112 , a light-redirecting coating  114 , an input port  116 , and/or an output port  118 . The light  102  (or other electro-magnetic radiation) can be provided into said the enclosure  110  via the input port  116 , and exit to impact a surface of the tissue  150  through the output port  118 . The light-transporting medium  112  can be composed of a material with a low optical absorption, such as, e.g., air, water, saline, oil, clear rubber, plastic and/or gel. The light-transporting medium  112  can also contain a small amount of optical scatters (e.g., &lt;5% weight ratio), such as, e.g., titanium dioxide, hafnium oxide, zinc oxide, ytterbium oxide or hafnium oxide particles. 
         [0027]    The medium  112  can be surrounded by a light-redirecting coating  114 , except at the input port  116  and/or the output port  118 . The coating  114  can have a high optical reflectance, e.g., close to unity, and/or a near-Lambertian optical scattering phase function. The coating  114  can be composed of commercially available high diffusive reflectance material, such as, e.g., Spectralon, Spectraflect and/or Permaflect (Labsphere), and Avian-B or Avian-D white paint (Avian Technologies). Alternatively or in addition, the light-redirecting coating  114  can also be made by doping a medium with light scattering particles, such as, e.g., titanium dioxide, hafnium oxide, zinc oxide, ytterbium oxide and/or hafnium oxide, at a high concentration (e.g., &gt;20% weight ratio). The coating  114  can also have a partial and/or high specular reflectance. After entering the enclosure  110 , most of the light  102  or other electro-magnetic radiation can bounce around the enclosure  110 , impact one or more surfaces of the coating  114 , thereby become homogenized inside the medium  112 . Such light  102  or radiation can only exits through either the output port  118  or the input port  116 . In one exemplary embodiment, the output port  118  can have a larger area than the input port  116 . Therefore, the optical enclosure  110  can redirect and/or expand most of the light  102  or other radiation to create a uniform wide-area illumination on a surface of the tissue  150  through the output port  118 . Since a maximal permissible optical fluence density on the tissue surface is generally regulated by established safety standards, by enlarging and/or homogenizing the illumination, the enclosure  110  facilitates a delivery of a larger amount of optical energy onto the tissue  150 . As an exemplary result, the interaction between the light  102  (or other radiation) and the target  152  can be increased. The input port  116  and/or the output port  118  can further be configured, shaped or constructed to have a desired curvature, e.g., in order to shape the light  102  (or other radiation) at the entrance and/or the exit to further homogenize and/or expand the illumination. 
         [0028]    Furthermore, the enclosure  110  can be designed and/or modified to make a more efficient use of the same amount of the input light. Since the biological tissue is highly scattering to light, a significant portion of the light  102  (or other electro-magnetic radiation), which originally exits from the output port  118 , is backscattered out from the tissue  150 . The enclosure  110  can have a configuration to capture the re-emitted portion of the light  102  (through the input port  116  and/or the output port  118 ), send such light  102  (or other radiation) back through the output port  118  onto a surface of the tissue  150 , so as to further increase the chance or an actuality of the interaction between the light  102  and the target  152 . Therefore, the optical enclosure  110  can be used to further enhance a light-tissue interaction in various optical modalities, such as spectroscopies (e.g., scattering, fluorescence, Raman spectroscopy, etc.), imaging (e.g., photoacoustic imaging, diffuse optical tomography, etc.), or treatment (e.g., photodynamic, photothermal, low-level light therapy, etc.). Further, e.g., in order to obtain a uniform large-area optical illumination, the optical enclosure  110  can be shaped and or provided in a smaller size, e.g., when compared to other light-redirecting apparatus or systems that use only light guides, lenses or mirrors. Therefore, the exemplary enclosure  110  can be used in an optical endoscope system. 
         [0029]      FIG. 2  illustrates a cross-sectional side-view diagram of a photoacoustic apparatus or device  200  according to an exemplary embodiment of the present disclosure. The exemplary photoacoustic device  200  can illuminate the tissue with light  202  or other electro-magnetic radiation, induce emission of an acoustic wave  206  from an optically absorbing object  252 , such as, e.g., a blood vessel, within a tissue  250 , record the light-induced sound remotely by an acoustic detector  220 , and obtain information regarding the tissue by analyzing or reconstructing the recorded signals. The light  202  (or other radiation) can have a time-varying intensity. Examples of the acoustic detector  220  can include, but are not limited to, a microphone, a hydrophone, a piezoelectric transducer, a polyvinylidene fluoride film transducer, a capacitor micro-machined transducer, an optical acoustic sensor based on light interferometry, etc. The acoustic detector  220  can also be or include a combination of a plurality of aforementioned acoustic detectors, such as a phased array acoustic probe, etc. For example, a central frequency of the acoustic detector can preferably be in the range of about or exactly 0.5˜100 MHz. 
         [0030]    According to one exemplary embodiment of the present disclosure, the light  202  (or other radiation) can be delivered to the tissue  250  through a light-integrating enclosure  210 . The light-integrating enclosure  210  can include a light-transporting medium  212 , a light-redirecting coating  214 , an input port  216 , and an output port  218 , etc. The medium  212  can be made of a material with a low light absorption, such as, e.g., air, water, oil, clear rubber, plastic and/or gel, etc. The medium  212  can be surrounded by the light-redirecting coating  214 , e.g., except at the input port  216  and/or the output port  218 . The coating  214  can have a high optical reflectance close to, e.g., unity and/or a near-Lambertian optical scattering phase distribution. The coating  214  can be composed of a commercially available high optical diffusive reflectance material, such as, e.g., Spectralon, Spectraflect or Permaflect (Labsphere), and Avian-B or Avian-D white paint (Avian Technologies). Alternatively or in addition, the light-redirecting coating  214  can also be made by doping a optically clear medium with light scattering particles, such as, e.g., titanium dioxide, hafnium oxide, zinc oxide, ytterbium oxide or hafnium oxide, at a high concentration (e.g. &gt;20% weight ratio). As elaborated above, compared to a conventional photoacoustic device that utilizes a side illumination, the photoacoustic device  200  using a light-integrating enclosure  210  can produce a uniform illumination over a large surface of the tissue  250 , thereby facilitate a use of more total optical energy, a re-use of the back-scattered light from tissue and an increase of the optical energy absorbed by the object  252 , thereby boost the photoacoustic signal reaching the acoustic detector  220 . 
         [0031]    According to another exemplary embodiment of the present disclosure, the medium  212  and/or the light-redirecting coating  214  can further be made of a material having a low acoustic attenuation. Thus, the light-integrating enclosure  210  can act as an acoustic lens, and can be attached to the acoustic detector  220 . Most of the acoustic wave  206  can be propagated through the light-integrating acoustic lens  210  to reach the acoustic detector  220 . The low-acoustic-attenuation light-transporting medium  212  can be made of water, oil, poly(methyl methacrylate) (e.g., Arylic), polystyrene (e.g., Rexolite1422, C-lec Plastics), polymethylpentene (e.g., DX845, Mitsui Chemical), polyurethane, silicone rubber (e.g., RTV615, Momentive). The low-acoustic-attenuation light-redirecting coating can be made or otherwise generated by doping a medium, similar to that used to make the medium  212 , with light scattering particles, such as, e.g., titanium dioxide, hafnium oxide, zinc oxide, ytterbium oxide or hafnium oxide, at a high concentration (e.g., &gt;20% weight ratio). Furthermore, an acoustic matching layer  222  can be placed between the acoustic lens  210  and the acoustic detector  220 , e.g., to reduce an acoustic loss due to the reflection. In addition or as an alternative, the lens  210  can be made of a material with a different acoustic speed than that of the tissue  250 . To that end, the lens  210  can be shaped to diverge or converge the incoming acoustic wave  206 , thereby facilitating a zoom-in or wide-angle view inside the tissue  250 . 
         [0032]      FIG. 3  illustrates a transesophageal photoacoustic endoscope system  300  according to another exemplary embodiment of the present disclosure. The exemplary system  300  can comprise an optical light source  330 , a transesophageal probe (e.g., including a flexible shaft  340  and an inflexible in-esophagus head  342 ), an acoustic puller/receiver  332 , a processor  336  and a graphic user interface  338 . The flexible shaft  340  can contain a segment of a light guide  322  and an electric cable  324 . The inflexible head  342  can include a distal end of the light guide  322 , a light-integrating acoustic lens  310  described herein, and an acoustic transducer  320 . Either or both of the probe head  342  and the shaft  340  can have a diameter smaller than 15 mm, thereby facilitating an introduction thereof into the esophagus  308  through a mouth or a nose. Such exemplary system can be used to safely assess cardiovascular diseases and/or functions. For example, such exemplary system can be utilized to monitor mixed venous oxygen saturation (SvO 2 ) from a pulmonary artery  352  through a wall of an esophagus  350 . Other examples of using such exemplary system include diagnosing atherosclerosis, assessing myocardial diseases, evaluating cardiac defects, guiding atrial ablation, etc. 
         [0033]    The optical source  330  can generate a light  302  (or other electro-magnetic radiation) with a time-varying intensity. The light  302  (or other radiation) can have (but not limited to) a wavelength between, e.g., 600 and 1800 nm. The light source  330  can be or include a pulsed laser, such as a Q-switched Nd:YAG laser, a fiber laser, a dye laser, a Ti-sapphire laser, an OPO laser, or a pulsed diode laser. The pulse duration of the light  302  can be (but not limited to) at the order of nanoseconds. The source  330  can also be or include an intensity-modulated continuous-wave light source, such as a laser diode, a LED or a solid-state laser. The light guide  322  can be used to carry the light  302  from the source  330  into the head  342 . Examples of such light guide  322  include, but are not limited to a borosilicate or silica/silica fiber bundle, a photonic crystal fiber, an articulated arm with mirrors or prisms, etc. The middle segment of the light guide  322  can be included inside the shaft, can contain loose fibers and be flexible. The light guide  322  can have inflexible segments close to at least one of the proximal end and the distal end, by fusing, gluing or adding a rigid housing to optical fiber(s). The light  302 , generated by the optical source  330 , can be focused by optical lenses into the proximal end of the light guide  322 , exit from a distal end of said light guide  322 , and provide the light  302  to the light-integrating acoustic lens  310 . Then, the light  302  can be redirected to form a uniform wide-field illumination on a surface of the esophagus  350 . The distal end of the light guide  322  can further be polished into a shape, which can deflect, reflect or diverge the light  302  to so as to achieve a large uniform optical illumination on the tissue. 
         [0034]    According to an exemplary embodiment of the present, photoacoustic measurements can be made with the light at a plurality of wavelengths to evaluate a blood oxygen saturation, e.g., using one or more components described herein. For example, the source  330  can be tuned to generate the light with a plurality of wavelengths. In addition or alternatively, the source  330  can be or include a combination of a plurality of optical sources that can operate at distinct wavelengths. In addition, the shaft  340  and the head  342  can be configured, structured and/or sized to be navigated to characterize different tissue through the esophageal wall by advancing, rotating or flexing the drive shaft  340 . In addition, the acoustic detector  320  can be rotated inside the probe head  340  to view the tissue in a view plane of interest. For an exemplary evaluation of SvO 2 , as depicted in  FIG. 3 , a user can navigate the probe head  342  inside the esophagus  350  to obtain an appropriate good view of the pulmonary artery  352 . After absorbing part of the light  302 , the mixed venous blood inside a pulmonary artery  304  can emit an acoustic wave  306 , which can be converted by an acoustic detector  320  into electrical signal. The electric signal can be carried by an electrical cable  324  into the acoustic pulser/receiver  332 , where such electrical signal can be amplified, filtered and/or digitized. The digital samples of such signals can then be analyzed by a computer processor  334  to calculate or otherwise determine SvO 2  and analyze results, which can be provided thereby on a graphic interface  336 . In addition, the pulser/receiver  332  can also be configured to transmit, e.g., a high-voltage electrical signal through the cable  324  to energize the acoustic transducer  320  to emit an acoustic wave (not shown). By detecting the reflected acoustic waves from tissue, real-time sonographic images  338  depicting tissue anatomy can be obtained and/or provided to guide a rapid deployment of the probe head  342 . 
         [0035]      FIG. 4  shows a wide-field optical illumination on tissue surface achieved by the embodiment of the transesophageal photoacoustic endoscopic system according to the present disclosure illustrated in  FIG. 3 . For example, since the optical fluence density on tissue surface is regulated by laser safety standards, a wide-field illumination facilitates the use of more light to generate a higher photoacoustic signal. Simulation shows that, compared to a conventional photoacoustic endoscope where light is illuminated from a side of the acoustic detector, the exemplary transesophageal photoacoustic endoscopic system illustrated in  FIG. 3  can produce more than twice of a photoacoustic emission. As shown in  FIG. 4 , a homogenous 13 mm-diameter illumination is obtained by the light-integrating acoustic lens  310  of a thickness of only 3 mm, which demonstrates the exemplary embodiments of the present disclosure can be useful for making compact endoscopes. 
         [0036]      FIG. 5  shows a time profile of mixed venous oxygenation evaluated by the transesophageal photoacoustic endoscope according to the exemplary embodiment of the present disclosure. For example, blood can be circulated inside extracorporeal cardiopulmonary bypass circuit. Blood oxygen content can be modulated by varying the fraction of oxygen in the gas, which the blood breathes. The photoacoustic signals were measured from blood at two selected near-infrared wavelengths. The real-time oxygen saturation is estimated in the illustration of  FIG. 4  based on the ratio of the two photoacoustic signals. 
         [0037]    The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements and methods which, although not explicitly shown or described herein, embody the principles of the disclosure and are thus within the spirit and scope of the present disclosure. Further, the exemplary embodiments described herein can operate together with one another and interchangeably therewith. In addition, to the extent that the prior art knowledge has not been explicitly incorporated by reference herein above, it is explicitly being incorporated herein in its entirety. All publications referenced herein above are incorporated herein by reference in their entireties.