Abstract:
An imaging probe for a biological sample includes an OCT probe and an ultrasound probe combined with the OCT probe in an integral probe package capable of providing by a single scanning operation images from the OCT probe and ultrasound probe to simultaneously provide integrated optical coherence tomography (OCT) and ultrasound imaging of the same biological sample. A method to provide high resolution imaging of biomedical tissue includes the steps of finding an area of interest using the guidance of ultrasound imaging, and obtaining an OCT image and once the area of interest is identified where the combination of the two imaging modalities yields high resolution OCT and deep penetration depth ultrasound imaging.

Description:
RELATED APPLICATIONS 
     The present application is related to U.S. Provisional patent application Ser. No. 61/109,146, filed on Oct. 28, 2008, which is incorporated herein by reference and to which priority is claimed pursuant to 35 USC 119. 
    
    
     GOVERNMENT SUPPORT 
     This invention was made with government support under Contract Nos. EB000293 and P41 EB002182 awarded by the National Institutes of Health. The government has certain rights in the invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of intravascular imaging, in particular to an integrated ultrasound guided optical coherence tomography, photoacoustic probe used in intravascular or biomedical imaging and a method of using the same. 
     2. Description of the Prior Art 
     Intravascular ultrasound (IVUS) is a medical imaging methodology that has been used to show the anatomy of the wall of blood vessels in living animals and humans by using a miniaturized ultrasound probe. IVUS can help physicians determine the amount of plaque from the cross-sectional image of blood vessels. In other words, IVUS can visualize not only the lumen of the coronary arteries but also the objects hidden within the wall, such as atheroma. However, because the reflection coefficient of the ultrasound of blood vessel is quite small, high sensitivity and larger bandwidth ultrasound probe are key factors of high-quality intravascular ultrasound images. High sensitivity and large bandwidth probes can be fabricated by using high electromechanical coupling coefficient (K t ) piezoelectric materials. Research shows Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3  (PMN-PT) is the one of the most promising high K t  commercial piezoelectric materials. It has been reported that a PMN-PT may be used as a single crystal transducer with a −6 dB fractional bandwidth of 114%. 
     On the other hand, the outer diameter of the ultrasound probe should be less than 3 mm to fulfill the requirement of IVUS biomedical imaging applications. Therefore, the fabrication of a miniaturized ultrasound probe is another important issue for IVUS imaging. High frequency (40 MHz) PMN-PT needle ultrasound transducers for biomedical applications have been made known in the art. 
     Optical coherence tomography (OCT) is a recently developed imaging modality using coherent gating to obtain high-resolution surface images of tissue microstructure. OCT endoscope design uses a fixed gradient-index (GRIN) lens and prism as the optical tip. Rotational torque is transferred from the endoscope&#39;s proximal end to the distal tip. OCT can provide imaging resolutions that approach those of conventional histopathology and can be performed in situ and in vivo. In vivo images of living animals have been demonstrated by using motor-based scanning endoscopic probes known in the art. 
     Nevertheless, one of drawbacks of OCT is that it needs to use saline water to flush blood away from the probe in order to remove the interference received from the blood. Therefore, how to minimize the times of saline water flushing is becoming a major topic in the OCT research filed nowadays. This problem is currently solved by inserting a balloon catheter at the imaging region to achieve blood occlusion, or by injecting relative large amounts of saline or other agents to flush away blood. However, both solutions have medical safety concerns. In the case of IVUS imaging, blood serves as the natural transmission media of the sound wave. 
     Additionally, the imaging resolution of IVUS is much less than that of OCT. In particular, IVUS is able to visualize the coronary artery from the inside-out owing to its larger penetration depth than OCT. In direct contrast, OCT can provide high-quality, micrometer-resolution, and three-dimensional images which are superior to IVUS. 
     Therefore, what is needed is a novel imaging probe combining a high frequency IVUS transducer with a 3-D scanning OCT probe to obtain the high-resolution cross-sectional intravascular images. 
     Optical coherent tomography (OCT) and ultrasound imaging are two of the most widely used image modalities. These image modalities share with common advantages, including: low-cost, high spatial resolution, portable, real-time, noninvasive, and non-radioactive. OCT and ultrasound imaging both measure cross-sectional tissue image. OCT measures tissue surface profile and cross-sectional image within a few millimeter depth range under the skin with a superior image resolution of 10 micrometers; high frequency ultrasound imaging also measures cross-sectional tissue image with a much deeper depth but with lower image resolution, on the order of 100 micrometers. OCT and ultrasound imaging modalities can be combined to provide a deeper cross-sectional imaging (tomography). 
     However, conventional ultrasound imaging performs relatively poor in blood vessel imaging, with lower imaging contrast, due to weak echo-genicity of blood. With recent developments in photoacoustics imaging, this limitation can be resolved. Photoacoustics imaging exploits the selective absorption property of hemoglobin to visible and near infrared (500-1200 nm) radiation, while tissues are relatively transparent in this optical spectrum. Through the optical absorption and thermoelastic expansion of blood vessels to short laser pulses, broadband ultrasound echo signals, up to 40 MHz, are generated from nanosecond laser radiated blood vessels. Since photoacoustic signals share the same acoustic spectra with ultrasound, photoacoustics imaging can be acquired and reconstructed by conventional ultrasound system. 
     A paper, entitled “Photoacoustic imaging of blood vessels with a double-ring sensor featuring a narrow angular aperture” by Kolkman et al. (Journal of Biomedical Optics, 9(6), 1327-1335, 2004) has proposed the development of a photoacoustic imaging probe, consisting of a double-ring polyvinylidene fluoride (PVDF) piezoelectric polymer sensor and an optical fiber located at its center. A 600 micrometer diameter optical fiber is used to transmit near infrared light to excite blood vessels; the double-ring piezoelectric polymer sensors acquire acoustic signal to generate ultrasound image. 
     U.S. Pat. No. 5,718,231, entitled “Laser ultrasound probe and ablator” describes a laser ultrasound probe, consisting of a ultrasound receiving sensor, made of PVDF piezoelectric polymer material for receiving photoacoustic signals and an optical fiber for transmitting laser radiation and generating photoacoustic signals by radiating the laser onto blood vessels. 
     Both of the above related prior art documents fail to present the concept of integrating OCT/ultrasound imaging/photoacoustics imaging modalities into a single image probe. 
     BRIEF SUMMARY OF THE INVENTION 
     The illustrated embodiment of the disclosure covers an imaging probe which integrates optical coherence tomography (OCT) and ultrasound imaging. Ultrasound guided optical coherence tomography (ultra-OCT) is a new imaging modality that integrates optical coherence tomography with ultra sound imaging. 
     A hollow-core ultrasound transducer is provided with the optical tip of an OCT probe inserted into its core. The optical tip of the OCT probe includes an 8 degree cut single mode fiber and a GRIN lens. The OCT probe is combined with an ultrasound transducer. A focused light beam together with ultrasound wave are reflected by a prism, and the focal point of the light is in tissue. 
     The purpose of this system is to provide a means for high resolution imaging of biomedical tissue. The guidance of ultrasound imaging allows the area of interest to be found and thus a relatively smaller amount of flush agent will be needed, which provides a safer way to obtain intravascular OCT images. The combination of the two imaging modalities yields high resolution thanks to OCT and deep penetration depth due to ultrasound imaging. 
     The Ultra-OCT probe uses its ultrasound modality to acquire images and search along inside of the vessel first. When finding area of interest, a small amount of flushing agent is applied to create an imaging window for OCT. No blood occlusion is needed, and a smaller amount of flushing is required, thus ultrasound guided OCT is potentially safer than conventional intravascular OCT, and it provides much higher resolution than intravascular ultrasound (IVUS). 
     The invention will be used to develop a clinically useful endoscopic Ultra-OCT system that can provide high resolution optical imaging of internal organs and tissues such as vessels. OCT can provide high resolution cross sectional imaging that conventional endoscopy cannot. At the same time, a reduced dose of flush agent will be needed using this invention compared with conventional OCT imaging system. The current invention allows OCT to be used potentially anywhere that can be accessed by endoscopy. Examples of use include but are not limited to intravascular catheter vessel imaging, bladder cancer detection and other aspects in the field of urology, lung cancer detection and inflammation and other aspects in pulmonary medicine, arterial anastomosis other minimally invasive surgeries, cardiac cancer detection, gynecological diagnosis of endometriosis and cancer, and cancer and inflammation detection in the gastrointestinal tract. 
     Other functions can also be added to this invention to give arise to multiple applications; polarization sensitive OCT can offer the information on light polarization changing properties of tissue; Doppler OCT can yield quantification of blood flow velocity; imaging guided therapy can also be achieved by adding an therapeutic channel to the probe, etc. Any OCT modality now known or later devised can be employed in the combination. 
     Further, an integrated biomedical multimodality image probe is disclosed which combines OCT, ultrasound imaging, and photoacoustics imaging to provide morphological as well as function imaging of tissues and blood vessels with a high spatial resolution and imaging contrast. The image probe acquires image on its front or on its side. The image probe is moved in a linear scan mode or a helical scan mode by linear translation stage and microelectromechanical system (MEMS) motor to acquire and construct 2D or 3D cross-sectional tissue images. 
     This embodiment of the illustrated invention includes an integrated biomedical multimodality image probe that combines three different image modalities: OCT, high frequency ultrasound imaging, and photoacoustics imaging, all together into a portable image probe. Cross-sectional images of tissue on the front or on the side of the probe can be obtained by these three image modalities. The multimodality imaging probe combines OCT, ultrasound imaging, and photoacoustics imaging components into an integrated system that measures cross-sectional images of tissue on the front or on the side of the probe. OCT measures tissue surface profile and cross-sectional tissue and blood vessel image within 1 mm range with superior image resolution, high frequency ultrasound imaging also measures tissue cross-sectional image with superior image depth but with inferior image resolution. 
     In addition, photoacoustics imaging and ultrasound imaging share with the same imaging system on the receiving side, photoacoustics imaging measures blood vessel image with superior image contrast than conventional ultrasound imaging. Therefore, these image modalities are ready to be integrated, and the new image can be shown in one image format. By combining these image modalities into an integrated image probe, it can image high resolution tissue image by OCT and ultrasound imaging and high contrast blood vessel image and functional imaging by photoacoustics imaging. In addition, it provides an integration of OCT and ultrasound imaging that covers from tissue surface profiles to 1 cm below the skin. It can be used for clinical imaging applications, including tissue physiological (oxi-hemoglobin/deoxi-hemoglobin) parameter monitoring, blood vessel measurements, or early tumor and dysplasia monitoring. 
     The purpose of this embodiment is to provide a noninvasive and portable image probe that provides superior images resolution, contrast, and depth of image on real-time basis. This multimodality image probe can provide 10-100 micrometers image resolution for tissue and blood vessel cross-sectional image within 1 cm depth range. 
     An OCT image is obtained by transmitting/receiving visible or near-infrared laser light to acquire tissue surface profile and cross-sectional tissue and blood vessel images. Ultrasound imaging and OCT are very similar in imaging principle; ultrasound imaging is formed by sending and receiving ultrasound waves. Although, photoacoustics imaging requires sending nano-second visible/near infrared laser pulses to excite blood vessels and generate photoacoustic pressure waves. However, photoacoustics imaging measures the thermoelastic pressure waves generated from the blood vessels, and these pressure waves can be received and constructed by ultrasound imaging using the same ultrasound imaging system. Therefore, the ultrasound transducer can be used for acquiring a traditional Ultrasound tissue image and a photoacoustic image. These images are ready to be superimposed and integrated to form a new type of data image. Traditional OCT image is limited to a shallow imaging depth, near 1 mm. In addition, ultrasound imaging also has limitation in achieving high image contrast for blood vessels. By combining OCT, ultrasound imaging and photoacoustics imaging image modalities into an integrated image probe, it provides tissue and blood vessel cross-sectional image with a deeper depth of image. 
     In addition, it is worth noting that the integration of the OCT, ultrasound imaging and photoacoustics imaging does not further complicate the structure of the image probe head. Ultrasound imaging and photoacoustics imaging shares the same ultrasound transducer. 
     There is no exact prior device known for direct comparison to the integrated probe of the illustrated embodiment. The combined OCT, ultrasound imaging and photoacoustics imaging probe has superior imaging capability over each of the individual image modalities. It has superior image resolution to ultrasound imaging with a resolution within 1 mm by using OCT; it covers a deeper imaging depth than OCT by using ultrasound imaging; it has higher blood vessel contrast than ultrasound imaging by using photoacoustics imaging. 
     Thus, in summary the illustrated embodiment of the invention is an imaging probe for a biological sample which includes an OCT probe and an ultrasound probe combined with the OCT probe in an integral probe package capable of providing by a single scanning operation images from the OCT probe and ultrasound probe to simultaneously provide integrated optical coherence tomography (OCT) and ultrasound imaging of the same biological sample. 
     In one embodiment the OCT probe may include an optical fiber coupled to a GRIN lens adapted for forward scanning and the ultrasound probe may include a needle intravascular ultrasound (IVUS) transducer with a flat distal end adapted for forward scanning. 
     In another embodiment the OCT probe includes an optical fiber coupled to a GRIN lens and a prism reflector adapted for side scanning and the ultrasound probe includes an angled distal end adapted for side scanning. 
     In still another embodiment the OCT probe includes an optical fiber coupled to a GRIN lens and a mirror/reflector optically coupled thereto adapted in combination for side scanning and where the ultrasound probe includes a needle intravascular ultrasound (IVUS) transducer sonically coupled to the mirror/reflector adapted in combination for side scanning. 
     In yet another embodiment the OCT probe includes an optical fiber coupled to a GRIN lens and a mirror/reflector optically coupled thereto adapted in combination for side scanning and the ultrasound probe includes a ring-type intravascular ultrasound (IVUS) transducer sonically coupled to the mirror/reflector adapted in combination for side scanning, wherein the OCT probe is disposed longitudinally through the ring-type intravascular ultrasound (IVUS) transducer. 
     The imaging probe may further include a motor coupled to the mirror reflector for selectively rotating the mirror/reflector relative to the OCT probe and ultrasound probe. 
     In one illustrated embodiment the OCT probe includes an optical fiber coupled to a GRIN lens and a prism reflector adapted for side scanning and where the ultrasound probe includes an annular linear array ultrasound transducer adapted for side scanning with dynamic depth focusing. 
     In still another illustrated embodiment the OCT probe includes an optical fiber coupled to a GRIN lens adapted for forward scanning and where the ultrasound probe includes a ring-type intravascular ultrasound (IVUS) transducer adapted for forward scanning, wherein the OCT probe is disposed longitudinally through the ring-type intravascular ultrasound (IVUS) transducer. 
     The optical fiber in some of the illustrated embodiments includes an 8 degree cut single mode fiber. 
     The illustrated embodiment of the imaging probe further includes a device for linearly moving the OCT probe and ultrasound probe together and/or a device for rotating the OCT probe and ultrasound probe together. 
     The illustrated embodiment of the invention also includes within its scope a method to provide high resolution imaging of biomedical tissue comprising the steps of finding an area of interest using the guidance of ultrasound imaging and applying a reduced amount of flush agent to obtain an OCT image and once the area of interest is identified as compared to the amount of flush that would used if the area of interest was not first identified, where the combination of the two imaging modalities yields high resolution OCT and deep penetration depth ultrasound imaging. 
     More generally, the illustrated embodiment includes a method to provide high resolution imaging of biomedical tissue including the steps of finding an area of interest using the guidance of ultrasound imaging, and obtaining an OCT image and once the area of interest is identified where the combination of the two imaging modalities yields high resolution OCT and deep penetration depth ultrasound imaging. 
     The method further includes the step of using an ultra-OCT probe in its ultrasound modality to acquire images and search along inside of the vessel first, and when finding area of interest, applying a reduced amount of flushing agent to create an imaging window for OCT without occluding blood flow, and whereby a smaller amount of flushing is required than in conventionally used in OCT endovascular imaging, so that ultrasound guided OCT is safer than conventional intravascular OCT, while providing higher resolution than intravascular ultrasound (IVUS). 
     The steps of finding an area of interest using the guidance of ultrasound imaging and applying a reduced amount of flush agent to obtain intravascular OCT images is employed in a procedure related to intravascular catheter vessel imaging, urology-bladder cancer detection, pulmonary medicine, lung cancer detection and inflammation, surgery/minimally invasive surgery, arterial anastomosis, cancer detection, gynecological diagnosis including endometriosis or cancer, or gastrointestinal cancer and inflammation detection. 
     The method further includes within its scope using polarization sensitive OCT, Doppler OCT, or imaging guided therapy using a therapeutic channel to the probe. 
     While the apparatus and method has or will be described for the sake of grammatical fluidity with functional explanations, it is to be expressly understood that the claims, unless expressly formulated under 35 USC 112, are not to be construed as necessarily limited in any way by the construction of “means” or “steps” limitations, but are to be accorded the full scope of the meaning and equivalents of the definition provided by the claims under the judicial doctrine of equivalents, and in the case where the claims are expressly formulated under 35 USC 112 are to be accorded full statutory equivalents under 35 USC 112. The invention can be better visualized by turning now to the following drawings wherein like elements are referenced by like numerals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side plan view of an OCT probe according to the invention. 
         FIG. 1   a  is a side cross-sectional view of one embodiment of the OCT probe of  FIG. 1  in enlarged scale showing the distal tip portion. 
         FIG. 1   b  is a side cross-sectional view of another embodiment of the OCT probe of  FIG. 1  in enlarged scale showing the distal tip portion. 
         FIG. 2  is a side cross-sectional view of a first embodiment of the ultra-OCT imaging probe of the illustrated embodiments using a needle IVUS ultrasound probe and the OCT probe of  FIG. 1 . 
         FIG. 3   a  is a side cross-sectional view of a first embodiment of the needle ultrasound transducer. 
         FIG. 3   b  is an end plan view of the needle ultrasound transducer of  FIG. 3   a.    
         FIG. 4  is a side cross-sectional view of a second embodiment of the ultra-OCT imaging probe of the illustrated embodiments using a needle IVUS ultrasound probe using a mirror/reflector and the OCT probe of  FIG. 1 . 
         FIG. 5  is a side cross-sectional view of a second embodiment of the ultra-OCT imaging probe of the illustrated embodiments using an angled needle IVUS ultrasound probe and the OCT probe of  FIG. 1 . 
         FIG. 6   a  is a side cross-sectional view of a ring-type IVUS ultrasound probe. 
         FIG. 6   b  is an end plan view of the ring-type IVUS ultrasound probe of  FIG. 6   a.    
         FIG. 7  is a side cross-sectional view of a third embodiment of the ultra-OCT imaging probe of the illustrated embodiments using a ring-type IVUS ultrasound probe of  FIGS. 6   a  and  6   b  and the OCT probe of  FIG. 1 . 
         FIG. 8  is a side cross-sectional view of a fourth embodiment of the ultra-OCT imaging probe of the illustrated embodiments using a ring-type IVUS ultrasound probe of  FIGS. 6   a  and  6   b  and the OCT probe of  FIG. 1  using a MEMS motor. 
         FIG. 9  is a side cross-sectional view of the embodiment of  FIG. 8  showing more detail and the use of a linear transversal stage. 
         FIG. 10   a  is a side cross-sectional view of a fifth embodiment of the ultra-OCT imaging probe of the illustrated embodiments using an annular linear array ultrasound probe and the OCT probe of  FIG. 1 . 
         FIG. 10   b  is a plan end view of the ultra-OCT imaging probe of  FIG. 10   a.    
         FIG. 11  is a side cross-sectional view of a sixth embodiment of the ultra-OCT imaging probe of the illustrated embodiments using ring-type ultrasound probe and the OCT probe of  FIG. 1  adapted for forward scanning. 
         FIG. 12  is a side cross-sectional view of a seventh embodiment of the ultra-OCT imaging probe of the illustrated embodiments using needle ultrasound probe and the OCT probe of  FIG. 1  adapted for forward scanning. 
         FIG. 13  is a schematic diagram of one embodiment of the imaging system used for data generation, collection, and analysis of the illustrated embodiments of ultra-OCT imaging probe of the illustrated embodiments. 
         FIG. 14  is a graph of the voltage output of pulse-echo signals of the needle ultrasound probe as a function of time and its frequency spectrum. 
         FIGS. 15   a  and  15   b  are ultrasound and OCT images respectively of a rabbit aorta taken with the ultra-OCT probe of the invention. 
         FIGS. 16   a  and  16   b  are ultrasound and OCT images respectively of a rabbit trachea taken with the ultra-OCT probe of the invention. 
         FIG. 17  is a block diagram of a presently preferred embodiment of a multimodality imaging system in accordance with the present invention. 
         FIG. 18  is general perspective view showing a probe according to this embodiment of the invention, together with a coupling element for connecting optical fibers to the OCT laser/receiving unit and photoacoustic laser unit, and electrical connection to ultrasound pulser/receiver unit. These units are shown in  FIG. 17 . 
         FIGS. 19   a  and  19   b  schematically depict the embodiment the probe head arrangement of the invention. It includes: (1) OCT optical head, located at the center of the probe, (2) a circle of photoacoustics imaging excitation optical fibers, and (3) ultrasound double-ring transducers for acquiring ultrasound images and photoacoustics images. 
         FIGS. 20   a  and  20   b  show an embodiment of a side-firing image probe with its side and top view, respectively; the ultrasound transducer is an annular array transducer. 
         FIG. 21  schematically illustrates another embodiment of a side-firing image probe with phased array transducer. 
         FIGS. 22   a  and  22   b  illustrate diagrammatic side cross-sectional view of the side and top view of a lensed optical fiber OCT probe with a ball lens. 
         FIGS. 23   a  and  23   b  illustrate diagrammatic side cross-sectional view of the side and end view of an OCT probe with a distal membrane ultrasound transducer. 
         FIGS. 24   a  and  24   b  illustrate diagrammatic side cross-sectional view of the side and end view of a lensed optical fiber OCT probe with a ball lens with a distal membrane ultrasound transducer. 
         FIGS. 25   a  and  25   b  illustrate diagrammatic side cross-sectional view of the side and end view of a lensed optical fiber OCT probe with a ball lens with a distal membrane ultrasound transducer array. 
     
    
    
     The invention and its various embodiments can now be better understood by turning to the following detailed description of the preferred embodiments which are presented as illustrated examples of the invention defined in the claims. It is expressly understood that the invention as defined by the claims may be broader than the illustrated embodiments described below. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An optical coherence tomography (OCT) probe is shown in the side plan view of  FIG. 1  and is generally represented by reference numeral  10 . A single mode optical fiber  12  is used to transmit light from a light source to biomedical sample or target (both not shown). Any type of light source used or usable in optical coherence tomography may be employed. The single mode fiber  12  is protected by a steel tube  14 , which helps increase the stiffness of the proximal portion of the fiber  12  that is near an adaptor  16  where mechanical rotation is introduced. A flexible coil wire  18  is disposed through and beyond the distal end of the steel tube  14  to give flexibility to the distal tip of the probe  10  contained within a polyimide tube  22 . Light from the distal tip of the single mode fiber  12 , which may be an angle polished fiber, is focused by a gradient-index (GRIN) lens  20  into a focusing point in or on the target tissue as seen in  FIGS. 1   a  and  1   b .  FIG. 1   a  is a side cross-sectional view of a first embodiment of the distal end of the polyimide tube  22  in enlarged scale showing a first embodiment employing GRIN lens  20  to provide a longitudinal beam, while  FIG. 1   b  is a side cross-sectional view of a second embodiment of the distal end of the polyimide tube  22  in enlarged scale showing a second embodiment employing GRIN lens  20  and optically coupled prism  24  to provide a side beam. The focal length of the beam can be adjusted from 0 to 5 mm by changing the distance between the fiber  12  and the GRIN lens  20  during assembly of the probe  10 . 
     As shown in  FIG. 1   b  the OCT probe  10  may be used to focus light into tissue to the side of the probe  10  by means of employing a prism  24  disposed after the GRIN lens  20 . The prism  20  is coupled to the GRIN lens  20  to reflect the light beam perpendicular to its incident or longitudinal direction. In cases where only forward scanning is needed, the prism  20  will not be necessary. 
       FIG. 2  shows in side cross-sectional view a first embodiment of the current invention as a combination of a needle intravascular ultrasound (IVUS) transducer  32  and the OCT probe  10  to form an ultra-OCT probe  30 . Both the ultrasound transducer  32  and OCT probe  10  are contained within an elongate housing  36  comprised of fluorinated ethylene propylene (Teflon-FEP, or FEP) tubing or other similar material known in the art. In this particular embodiment, the ultrasound transducer  32  is disposed above the OCT probe  10  within the housing  36 . The ultrasound waves produced by ultrasound transducer  32  and the light beam produced by the OCT probe  10  propagate perpendicular to the longitudinal axis of the ultra-OCT probe  30 . A conventional guide wire  34  is coupled to the distal tip of the ultra-OCT probe  30  in the intravascular imaging application. The outside diameter of the ultra-OCT probe  30  is less than 3 mm. The ultra-OCT probe  30  may be used for rotational scanning by mechanically rotating the ultra-OCT probe  30  around the longitudinal axis of housing  36  as shown in  FIG. 2 . In the case of linear scanning, only transverse motion of housing  36  is performed. 
     Another embodiment of ultrasound transducer  32  can be seen in  FIGS. 3   a , and  3   b  and combined with an OCT probe  10  in  FIG. 4 . The ultrasound transducer  32  of  FIGS. 3   a ,  3   b  comprises a stainless steel housing  38 . At the distal tip of the housing  38  is a gold conduction layer  40 . Proximally disposed to the gold conduction layer  40  is a first matching layer  42  and a piezoelectric layer  44 . Proximally adjacent to the piezoelectric layer  44  is a backing  46 . Coupled to the proximal end of the backing  46  is a wire  48  that extends to the proximal end of the ultra-OCT probe  30 . The wire  48 , backing  46 , PMN-PT  44 , and matching layer  42  are embedded or potted within the distal portion of housing  38  in an epoxy  39 . 
     The piezoelectric layer  44  preferably has a sufficiently high coupling coefficient K t . High K t , one the most important parameters in ultrasound transducer applications, allows for higher sensitivity and larger bandwidth for the small aperture ultrasound transducers, such as for a needle single element ultrasound transducer  32  seen in  FIG. 3   a . A Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3  (PMN-PT) (K t =0.58, HC Materials Corp., Urbana, Ill.) single crystal is preferably used as the piezoelectric transducing material  44  of the high frequency ultrasonic needle transducer  32 . The needle ultrasound transducer  32  was designed using a commercial transducer modeling software PiezoCAD (Woodinville, Wash.) to optimize its performance. The center frequency of the ultrasound needle transducer  32  was designed at 35 MHz as a trade-off between resolution and penetration depth. The aperture size of the ultrasound transducer  32 , which has a square cross-section as shown in the end plan view of  FIG. 3   b , is diced to 0.6 mm×0.6 mm in 2  to match electrical impedance (50 ohms). The outside diameter of the needle ultrasound transducer  32  is 1.5 mm as seen in the cross-sectional drawing of the needle ultrasound transducer  32  of  FIG. 3   b.    
     The needle ultrasound transducer  32  of  FIG. 3   a  is combined with an OCT probe  10  of the type described above in connection with  FIG. 1 , both of which are similarly embedded or potted in an epoxy filled distal portion of polyimide tube  22  as shown in  FIG. 4 . The longitudinal light beam and ultrasound beam are directed to a corner optical mirror and sound reflector  50  mounted at the distal end of tube  22  to reflect the light beam and ultrasound beam through an open window  27  defined in tube  22  as side beams. In  FIG. 4 , an alternative embodiment of the ultra-OCT probe  30  is shown where the OCT probe  10  is disposed above or in combination with the ultrasound transducer  32  within the polyimide tube  22 . The OCT probe  10  uses a fixed gradient-index (GRIN) lens  20  as the optical tip. The 1310 nm single mode fiber  12  within the OCT probe  10  was cut to 8 degrees and glued to a focusing GRIN lens  20 . A 2 mm diameter prism with aluminum coating (Edmund Optics, Barrington, N.J.) was used as mirror  50  to reflect the ultrasound beams from the ultrasound transducer  32  and the light beams form the OCT probe  10  from the forward direction to a substantially side direction. Tube  22  is in turn disposed within FEP housing  36 , which may be capped at its distal end with an distal guidewire  34  attached by medical glue  41  to facilitate endovascular applications. The entire ultra-OCT probe  30  diameter of  FIG. 4  is approximately 3 mm or less. Like the previous embodiment, mechanical rotation in the direction indicated in  FIG. 4  is required in order to achieve rotational scanning. 
     In a further embodiment depicted in  FIGS. 6   a ,  6   b  and  7 , a ring type ultrasound transducer  52  is employed within the ultra-OCT probe  30 . A side cross-sectional view of the ring ultrasound transducer  52  is seen in  FIG. 6   a . Like the ultrasound transducer  32  disclosed above, the ring ultrasound transducer  52  comprises a gold conduction layer  56  at its most distal tip, followed proximally by a first matching layer  58 , a piezoelectric layer  60 , and a backing layer  62  in that order and all embedded or potted in an epoxy fill  39  contained within an elongate stainless steel housing  64 . Wire  48  extends from the backing layer  62  to the proximal end of the ultra-OCT probe  30 . However defined through the entire longitudinal length of the ring ultrasound transducer  52  is an inner axial longitudinal cavity  54 . The inner cavity  54  is substantially cylindrical in shape and is defined through the center of the ring ultrasound transducer  52  as seen in the end plan view of  FIG. 6   b . The OCT probe  10  is then disposed through cavity  54 . 
     The combination of the ring ultrasound transducer  52  with OCT probe  10  into the ultra-OCT probe  30  is seen in the side cross-sectional view of  FIG. 7 . The OCT probe  10 , including the GRIN lens  20 , is disposed within the inner cavity  54  of the ring ultrasound transducer  52 . The combined ring ultrasound transducer  52  with OCT probe  10  are disposed, embedded or potted within FEP tube  22  and combined with mirror/reflector  50  mounted at the distal end of tube  22 . Light from the OCT probe  10  that is surrounded by ultrasound from the ring ultrasound transducer  52  is then sent forward to the mirror/reflector  50  to reflect the incoming light and sound beams perpendicularly to the incident longitudinal direction through FEP tubing  22 . In this configuration, the ultrasound and light beams can be focused on a small region of target tissue at the same time. Again probe  30  may be capped at its distal end with medical glue  41  and provided with a guidewire  34 . 
     Another embodiment of probe  30  is made with a ring type ultrasound transducer  52 , an OCT probe  10  as described above in connection with  FIGS. 6   a ,  6   b  and  7  and a MEMS motor  66  as schematically depicted in cross-sectional side view in  FIG. 8 . The OCT probe  10  is inserted into the center hole  54  of ring type ultrasound transducer  52 . A mirror/prism  50  is mounted at a shaft of the MEMS motor  66  at an angular position of 45° relative to the longitudinal axis of rotation to allow selective change the propagation direction of the ultrasound beam and the laser or light beam by selective rotation of the motor shaft. The features of this embodiment include the fact that the ultrasound beam and the light beam can focus on the small region of the target tissue at the same time while the MEMS motor  66  is rotating to reflect the two beams. 
       FIG. 9  is a side cross-sectional view of a schematic diagram of the embodiment with more details. The proximal portion  68 , which is hollow and which contains flexible optical fiber  12 , is arranged and configured to be substantially flexible to adapt the probe to practical endovascular use, while distal portion  70  is the only rigid portion and typically is 2.5 cm or less in length. Motor  66  and transducer  52  are provided with power and control signals by means of wire  72  disposed along or in the longitudinal wall of transparent FEP tube  22 , which wire  72  is coupled to source of power (not shown) at the proximal end of probe  30 . A linear transversal stage  74  is coupled to proximal portion  68  to provide controlled selective longitudinal movement of probe  30 . Motor  66  independently provides selectively controlled rotational movement or scanning of probe  30 . The overall diameter of probe  10  is approximately 0.5 mm while the overall diameter of transducer  52  is 2.0 mm. A guide wire  34  can be attached to the probe tip for intravascular imaging application. 
       FIG. 10A  illustrates another embodiment of the probe  30  made by a conventional annular linear array ultrasound transducer  76  well known to the art such as shown in U.S. Pat. No. 5,520,188 and elsewhere and OCT probe  10 . The structure of annular linear array transducer  76  is comprised of an annular or ring array of a plurality of ultrasound transducers, which are arranged into a hollow ring and driven to provide a dynamically focused side beam. OCT probe  10  is disposed through the center, axial opening defined in array  76  as shown in  FIG. 10B  and reflected by prism  24  into a side beam through transparent FEP tube  22 . In this embodiment the overall diameter of probe  10  is approximately 0.6 mm and the overall diameter of transducer  76  is approximately 2.0 mm with the overall diameter of tube  22  within which transducer  76  and probe  10  are embedded or potted is approximately 2.2 mm. Annular linear array ultrasound transducer  76  provides a dynamic focusing depth according to conventional control principles used with annular ultrasound arrays. Mechanical rotation of the probe  30  is required for rotational scanning. A guide wire  34  can be attached to the distal probe tip for the application of intravascular imaging. 
     The embodiments disclosed above are all configure siding-viewing designs. However, it must be expressly understood that forward scanning design can also be realized in for each of the embodiments.  FIG. 11  illustrates a schematic of one such forward-viewing ultra-OCT probe  30 , wherein a ring-type ultrasound transducer  52  with an axial OCT probe  10  of the type similar to that described in connection with  FIGS. 6   a ,  6   b  and  7  are disposed within a protective tube  78  capped with a clear or transparent glue covering  80  to provide longitudinal or forward scanning beams. The difference is that no prism is used in this embodiment, thus sound wave from the transducer  52  and focused light beam from the GRIN lens  20  transmit forwardly though the glue  80  and reach biomedical tissue. 
     Similarly,  FIG. 12  illustrates a schematic of another forward-viewing ultra-OCT probe  30 , wherein side-by-side ultrasound transducer  32  with an OCT probe  10  of the type similar to that described in connection with  FIG. 4  are disposed within a protective tube  78  capped with a clear or transparent glue covering  80  to provide longitudinal or forward scanning beams. In  FIG. 12 , a needle based transducer  32  and OCT probe  10  are combined together in parallel with the difference being that no prism is used in this embodiment either. Thus sound wave from a needle based transducer  32  and focused light beam from GRIN lens  20  transmit forwardly though the glue  80  and reach biomedical tissue. In all such forward scanning embodiments a PZT based motor or other mechanical method can be adopted to realize longitudinal movement or forward scanning of probe  30 . 
     Thus, it can be appreciated that what is disclosed is a biomedical imaging probe  30  combining intravascular ultrasound (IVUS) and optical coherence tomography (OCT). Pb(Mg 1/3 Nb 2/3 )O 3 —PbTiO 3  (PMN-PT) needle ultrasound transducers  32 , ring type transducer  52 , or an annular array transducer  76  with an aperture size of 0.6 mm were fabricated. The measured center frequency and −6 dB fractional bandwidth of the PMN-PT needle ultrasound transducer  32  were 35 MHz and 60% respectively. A mirror  24 ,  50  was mounted at the tip of the probe at position 45° to change the propagation direction of the ultrasound beam and the laser beam. In vitro images of rabbit trachea and aorta forming from this combined probe have been acquired. These results demonstrate that the complementary nature of these two modalities may yield beneficial results that could not be obtained otherwise. 
       FIG. 13  illustrates one example of a system wherein probe  30  may be utilized. An impedance analyzer (HP 4291B) was used to measure the electrical impedance of the needle ultrasound transducer  32 . A pulser/receiver  82  (Panametrics 5900) was used to characterize the needle ultrasound transducer  32 . The received echo waveform was displayed on an oscilloscope  84  (LeCroy LC534). The output light from a swept light source  86  (Santec Corporation, Komaki, Aichi, Japan) at 1310 nm with a FWHM bandwidth of 100 nm and output power of 5 mW was split into reference and sample arms by a 1×2 coupler  88  as part of the OCT optical interferometer. The light source  86  was operated at a sweeping rate of 20,000 Hz. Eighty percent of the incident power was coupled into the sample arm while 20% was fed into the reference arm. Mechanically rotating the UltraOCT probe  30  is required to get the intravascular ultrasound image and exciting the ultrasound transducer  32  and collecting the echo signals with 34 dB gain. The received A-mode echo signal was detected, sampled by an eight-bit analog-to-digital converter, converted by scan from a radial ultrasound data format to a rectangular format, and viewed as B-mode images in computer  90 . The step angles were chosen by two and four degrees. Therefore, 90 or 180 lines of echo data were used to make an ultrasound image respectively. Circulator  92  and coupler  94  formed optical components of the OCT interferometer coupling ultimately to optical detectors (not shown) and coupled to computer  90 . The data collection and analysis for both the ultrasound and OCT signals are conventional and are not further detailed here, but are well known. 
       FIG. 14  is a graph which shows the measured pulse-echo signals of PMN-PT needle ultrasound transducer  32  and its spectrum. It can be seen that the center frequency of the transducer was approximately 35 MHz. The fractional bandwidth at −6 dB was around 60%. Using the Pulser/Receiver  82  with 1 μJ energy setup, the maximum output voltage (Vpp) of pulse-echo signal was 2.1 V with no gain. These data show that PMN-PT needle ultrasound transducer  32  has a high sensitivity as a result of its excellent piezoelectric properties. It is quite suitable for intravascular ultrasound image applications due to the echo signals of ultrasound from soft tissues are extremely weak. 
       FIG. 15   a  shows the ultrasound image of rabbit aorta. It is clearly seen that the ultrasound penetrated through the blood vessel forming a cross-sectional image of rabbit aorta. From the cross-sectional image, the average thickness of blood vessel is 1.4 mm can be approximately calculated. The OCT image of the same rabbit aorta is shown for comparison in  FIG. 15   b . It reveals more detail in the microstructure of the vessel wall. The layered structure around 5 o′clock direction in  FIG. 15   b  is clearly visible. 
     The ultrasound image and OCT image of rabbit trachea are shown in  FIGS. 16   a  and  16   b , respectively.  FIG. 16   a  shows the cross-sectional image of trachea of a rabbit. The resolution of  FIG. 16   a  is not as good as  FIG. 15   a  due to fewer lines of echo data. Although, the average thickness of trachea 1.1 mm still can be estimated. From  FIG. 16   b , the surrounding trachea ring is clearly visible in the left side. 
     The quality of the images of rabbit aorta and trachea from a 35 MHz PMN-PT needle ultrasound transducer  32  and an OCT probe  10  can be improved by optimizing the design of the UltraOCT probe  30 . The disclosed data show that the complementary nature of these two modalities yield beneficial results that could not be obtained otherwise. 
     The block diagram, shown in  FIG. 17 , has a central controller  96  that controls the operation of: OCT unit  98 , photoacoustic excitation laser unit  100 , and ultrasound pulser/receiver unit  102 . An OCT image is acquired through the OCT Tx/Rx port  104 ; photoacoustic laser  100  excites through the photoacoustics imaging Tx port  106 ; ultrasound imaging and photoacoustics imaging are both acquired through the ultrasound imaging Tx/Rx port  110 . All these ports  104 ,  106 ,  108  are integrated into a multimodality image probe, generally denoted by reference numeral  112 . Probe  112  is moved in a linear scan mode or a helix scan mode by linear translation stage and microelectromechanical system (MEMS) motor  110  to acquire and construct 2D or 3D tissue cross-sectional imaging. 
     The OCT, ultrasound imaging, and photoacoustics imaging are further processed at the image processor  114 , including noise reduction, filtering, moving average, background reduction, normalization, and image fusion. The processed image contents are remapped through the scan converter  116  to match the image contents to the display coordinates and the data image displayed by display unit  118 . 
       FIG. 18  is a perspective diagram of a first embodiment of the image probe  112 . Probe  112  has two main ends, one is the image probe head  120 , the other is the connector end  122 . The image probe head  120  includes: one OCT optical fiber head  124 , located at the center of the probe  112 , a ring of six multimode optical fibers  126  which deliver photoacoustic excitation laser light, which may suitably be 300-500 micrometers diameter optical fibers, and a double-ring ultrasound transducer  128 . The connector end  122  provides connecting ports for a photoacoustic optical fiber connection  130 , OCT laser optical fiber connection  132 , and ultrasound coaxial cable connection  134 . The probe  112  can be held by hand for single point imaging or scanned by a motorized stage (not shown) for 2D or 3D cross-sectional tissue image. 
     Photoacoustic laser optical fiber connector  130 , OCT laser optical fiber connector  132 , ultrasound coaxial cable connector  134  and image probe head  120 , as shown in  FIG. 18 , is shown on a larger and detailed scale in  FIGS. 19   a  and  19   b .  FIG. 19   a  is a plan end view of the image probe head  120  and  FIG. 19   b  is a cross-sectional view of the structure of the image probe head  120 . At the center of the image probe head  120  is a GRIN lens  136  attached to the end of a single mode optical fiber  138  to focus the OCT laser beam from the OCT optical fiber  138 . In the illustrated embodiment there are six photoacoustic optical fibers  126  surrounding the OCT optical fiber  138 . The number of fibers  126  can be varied according to design choice. These optical fibers  126  transmit photoacoustic excitation laser light into tissues and heat the superficial blood vessels. On the outside of the probe  112 , there is a photoacoustic double-ring transducers  128 , which is designed for conducting traditional ultrasound imaging of tissues as well as photoacoustics imaging of blood vessels. The cross section of the double-ring transducers  128  show the structure of the active region of the double-ring transducers, including a protective layer made by parylene coating  152 , Au electrode  150  for grounding connection, silver-particle front-matching layer  148 , piezo-material with Cr/Au electrode  146 , silver-particle-back-matching layer  144 , conductive epoxy backing  142 , electrode conduct wire  140  for each ring  128 . There exists an insulation gap  154  between the rings of the double-ring transducer  128 . 
       FIG. 20   a  is a side cross-sectional view of the photoacoustic optical fiber GRIN Lens OCT optical fiber  124 , while  FIG. 20   b  is a top cross-sectional view of the same. The integrated image probe  112  in this embodiment is arranged for imaging on its side.  FIGS. 20   a  and  20   b  show the image probe  112  including a linear/rotation stage  110 , a photonic crystal fiber  156  and protection coil sheath  160 , GRIN lens  162 , reflector  164 , annular array ultrasound transducer  166 , and glass ferrule  168  filled with acoustic impedance matching oil. GRIN lens  162  is attached to the end of the photonic crystal fiber  156  to collimate and focus continuous NIR laser beam for OCT imaging and nano-second pulsed laser  100  for photoacoustic excitation. Both the continuous and pulsed laser beams are reflected by the reflector  164 , and then go through the hole  170  at the center of the annular array ultrasound transducer  166  to acquire OCT image and also to excite blood vessel for acquiring photoacoustics imaging. The image probe  112  is rotated and scanned by the linear/rotation stage  110  to construct 2D and 3D cross-sectional image. Note that photonic crystal fiber  156  is designed to support both single mode and low optical power transmission for OCT applications, and also support multi-mode and higher optical power transmission for photoacoustics imaging applications. 
       FIG. 21  shows another embodiment of the side-firing image probe  112  including linear/rotation stage  110 , photonic crystal fiber  156  and protection coil sheath  160 , GRIN lens  162 , dichroic reflector  172 , annular array ultrasound transducer  174 , and glass ferrule  168  filled with acoustic impedance matching oil. GRIN lens  162  is attached to the end of a photonic crystal fiber  156  to collimate and focus continuous NIR laser beams for OCT imaging. The NIR laser beam for OCT image is reflected by the dichroic reflector  172 , while the nano-second pulsed laser for photoacoustic excitation goes through the dichroic reflector  172  and is reflected to generate a ring shape radiation pattern. Photoacoustics imaging is obtained by the phased array ultrasound transducers  174  located in a ring-shape on the probe  112 . With this design, a 360 degree photoacoustics image can be obtained by ultrasound using one laser pulse excitation. The rotation stage  110  is used for acquiring 360 degree OCT images. Thus, the image probe  112  can be moved by the linear/rotation stage  110  to obtain and reconstruct 3D cross-sectional images. 
     The integrated biomedical multimodality image probe  112  can be used to obtain tissue surface and cross-sectional image, from the surface to a few centimeters with superior image resolution, deeper imaging depth, and high contrast in blood vessel imaging. This device has potential applications which include but are not limited to: (a) pre-cancer screening: in gastrointestinal and urogential tracts and on skin; (b) diagnosis and management cardiovascular diseases with intravascular procedures: monitoring aneurysms, stents, atherosclerosis, and plaque build-up; (c) noninvasive blood vessel monitoring such as port wine stain depth and location evaluation, and other blood vessel related tissue imaging and monitoring; (d) tissue perfusion and viability monitoring: determination of burn depth in skin, determination of tissue injury and wound closure, and evaluate blood vessel status; (e) blood vessel imaging: image 3D blood vessel distribution, evaluation of micro-vessel distribution density. (f) monitoring tumor development: monitoring superficial tumor grow and its blood vessel developments, monitoring tumor and its blood vessel reactions to chemotherapy or other tumor therapies. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following invention and its various embodiments. 
     Therefore, it must be understood that the illustrated embodiment has been set forth only for the purposes of example and that it should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different elements, which are disclosed in above even when not initially claimed in such combinations. A teaching that two elements are combined in a claimed combination is further to be understood as also allowing for a claimed combination in which the two elements are not combined with each other, but may be used alone or combined in other combinations. The excision of any disclosed element of the invention is explicitly contemplated as within the scope of the invention. 
     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification structure, material or acts beyond the scope of the commonly defined meanings. Thus if an element can be understood in the context of this specification as including more than one meaning, then its use in a claim must be understood as being generic to all possible meanings supported by the specification and by the word itself. 
     For example, instead of using a GRIN lens and prism for light beam focusing and reflection, a lensed fiber with a 45-degree polished ball lens can also be used to achieve the same purpose. This embodiment of OCT probe  10  uses a lensed fiber  176  with a 45-degree polished ball lens  178  for the purpose of both focusing and reflecting light beam as shown in  FIGS. 22   a  and  22   b . A lensed fiber  176  without angle polish can also be used for forward viewing. The lensed fiber OCT probe  10  of  FIGS. 22   a ,  22   b  can be used to replace the GRIN lens and prism in any one of the embodiments described above. 
     To reduce the size of the integrated probe  30 , a membrane transducer  180  made of flexible thin film piezoelectric materials such as PVDF-TrFE copolymer can be used, as shown in  FIGS. 23   a  and  23   b . The thin film transducer  180  can be attached to the OCT probe  10  and provides side-viewing. This embodiment offers decreased overall diameter (&lt;1 mm) of the integrated probe  30 , which is preferred when the luminal area of interested organ is small. 
     The embodiments of  FIGS. 22   a ,  22   b ,  23   a  and  23   b  can be combined in the embodiment of  FIGS. 24   a  and  24   b . As shown a lensed fiber with a 45-degree polished ball lens  178  is used in place of the GRIN lens and prism. The single element membrane transducer  180  is attached to optical fiber  176  to provide side-viewing. The integrated OCT lensed fiber and thin film transducer rotates inside of a flexible or rigid housing  182 . 
     The embodiment of  FIGS. 25   a  and  25   b  uses the same 45-degree polished lensed fiber  176 , while a membrane transducer array  184  with multiple elements is attached to the housing outer wall  182  and is stationary when acquiring images. The transducer array  184  is integrated into the inner wall of the outmost tube  182  (not shown), although other methods of embodiment can also be used. Instead of side-viewing, forward viewing can be achieved using a lensed fiber without 45-degree polish. The integration of the lensed fiber OCT probe  10  and membrane transducer  184  further reduces the overall size of the probe  30 , which is necessary in the application such as intra-coronary imaging when miniaturization of probe is critical. Instead of lensed fiber OCT probe, a GRIN lens and prism based OCT probe can also be used in these configurations. 
     The definitions of the words or elements of the following claims are, therefore, defined in this specification to include not only the combination of elements which are literally set forth, but all equivalent structure, material or acts for performing substantially the same function in substantially the same way to obtain substantially the same result. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptionally equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention.