Patent ID: 12201272

DETAILED DESCRIPTION

The beam splitter ofFIG.2receives a beam of light from a carrier lens12. The beam enters the pentaprism8and is partially reflected off a first interface9and then internally reflected back towards a sensor11. The remaining light passing through the interface is reflected off a back surface of a prism10towards the same sensor11. The first interface9can be a half-silvered mirror or semi-reflective coating on one of the prism surfaces.

Each reflection changes the path length and, as a result, the back focal length of each beam is different. The image formed on each portion of the sensor11captures a separate focal plane of the object being observed by the insertion portion of an endoscope. Alternatively, two separate sensors can be used in place of the single sensor11, and the individual sensors can be placed at different distances from the beam splitter.

The beam splitter ofFIG.3includes the beam splitter ofFIG.2along with prisms8and10with an additional rear prism14. This arrangement further splits the remaining light passing through the interface15. The interface15can be ⅔ reflective or 50% reflective and the sensors11, individually detecting each partial beam, can be offset from the prisms at different distances. The additional interface15provides a third beam which is captured by a third sensor11for additional depth of field information.

Each separate sensor11detects a differently focused beam providing an image including information at a particular depth. Each of the beam splitter elements or prisms (8,10and14), can be made of crystal glass, polymers, acrylic, or other light transmissive materials. Also, the interfaces (9,15) can be made partially reflective such that the intensity of each sensed beam is substantially equal. Alternatively, to compensate for surface losses or other differences, the reflective surfaces on the interfaces (9,15) may divide the beams unequally.

The optical arrangement ofFIG.4describes an imaging head for an endoscope, including polarizing beam splitter16with a polarizing function, variable liquid lens20, temporally-switched variable waveplate17, beam splitter19and sensors18. The first beam splitter16separates the light exiting a detachable endoscope into two channels. A focus difference is introduced between the two channels while they are separate using the variable liquid lens20. The two channels are then recombined spatially while maintaining their distinct polarizations.

Both channels pass through a gap in which the variable liquid lens20is disposed. After passing through this gap, both channels enter another beam splitter16recombines the two beams and passes them on to a variable wave plate17for changing the polarization of both beams. The variable wave plate17varies between ON and OFF such that when it is ON, the polarization of the incoming light beam is rotated by 90 degrees.

After the variable wave plate17, the combined beam enters a beam splitter19which once again separates the channels based on polarization such that they are imaged onto different sensors18. Thus, on odd frames, one sensor18captures “s” polarized light and the other sensor18captures “p” polarized light. On even frames, the different sensors18are given the other channel. The collimating lens group22is disposed before the variable wave plate17for further beam manipulation and control.

In this manner, four different images corresponding to four different focal planes can be acquired over the course of two frames. From the plurality of images, a processing unit (not shown) calculates an image with greater depth of field than would be possible with a single sensor and conventional optics. Alternatively, this imaging head could be integrated into a video endoscope that does not detach from a camera head.

The two illustrations inFIG.5show the two beam paths taken by the first channel during separate capture frames, that is on odd/even frames. Likewise, the two illustrations inFIG.6show the two beam paths taken by the second channel during separate capture frames. The beams inFIG.5have different focal planes due to a difference in offset of the sensors18from the beam splitter19. Likewise, beams inFIG.6have different focal planes due to a difference in offset of the sensors18from the beam splitter19.

The focal difference between the first and second channels due to the variable lens20and path length difference is also simultaneously provided to the sensors18. This results in four unique focal planes over two capture periods. Furthermore, the variable lens can change position or focal power to increase the number of focal planes further or simply to adjust focus. The variable lens may have variable curvature or a variable index of refraction.

The camera head may also have a control unit to adjust the focal difference according to the content of the acquired image, the imaging environment, or other application specific needs. In addition, the camera head can be capable of identifying the specific endoscope or endoscope-type being used and adjust focus accordingly. The “s” and “p” polarization described above is exemplary and could be replaced with circular or elliptical polarization.

The camera head ofFIG.7includes a single beam splitter16, a variable lens20, two collimating lens groups22, and two sensors18. The function of the camera head is similar to that ofFIGS.4-6with no recombination of the two channels by an additional beam splitter16. This configuration is easier to manufacture but only acquires two images per acquisition period.

In the arrangement ofFIG.7, the light beam from the endoscope enters the beam splitter16and is divided into two beams. The first beam passes through a collimating lens group22before impinging on the image sensor18. Separately, the second beam passes through a variable lens20and then another separate collimating lens group22before impinging on image sensor18.

The arrangement is also connected to a control device for controlling the variable lens and a processor71that calculates depth from the captured images or segments the in-focus portions for recombination and display. The processor71is also able to model three-dimensional surfaces and build complex tissue models. These models and surfaces can be stored in memory such as RAM or transmitted to a display screen for display to a user.

Conventional methods to increase depth of field fundamentally decrease the resolution. Thus, typically systems are forced to make a tradeoff between depth of field and resolution. However, combining several image sensors to provide depth information preserves resolution and can even improve it. Furthermore, the images can be segmented to provide the in-focus portion of each captured image and recombine the in-focus segments for a clearer image with more depth information and depth of field.

Additionally, the camera head ofFIG.7can include an aperture stop smaller than the exit pupil of the endoscope. This increases the depth of field but also reduces the resolution. Alternatively, the camera head could provide a fixed offset between focal planes. However, to provide a fixed offset across different endoscopes, the camera head would need to adjust to each endoscope type. The camera head can be integrated into or detachable from a video-endoscope.

The camera head can also be simplified by replacing the variable liquid lens20with a simple movable focusing lens23as shown inFIG.8. This movable lens23can change the focus position or adjust the focal plane but cannot vary in focal power as can variable liquid lens20. Otherwise, the system ofFIG.8is substantially the same as that ofFIG.7with similar capabilities.

Another optical arrangement for providing depth of field, as in the previous arrangements, is shown inFIG.9. In this configuration, the variable liquid lens20are placed after a single beam splitter19. Thus, the light beam received from the endoscope first passes through a collimating lens group22and a variable wave plate17then into the beam splitter19where the light beam is divided into two beams. The first beam passes straight through the beam splitter and a spectral filter21to the image sensor18and is captured. The second beam is deflected at a right angle and passes through the variable liquid lens20where the focal plane of the beam is changed. The second beam is then received and captured by a separate image sensor18.

The arrangement inFIG.9is capable of imaging two or more images of different focal planes per acquisition period. Additional focal planes can be acquired subsequently by adjusting the variable liquid lens20between each image capture. Furthermore, the position of each image sensor18ofFIG.7-9can be adjusted based on the endoscope being attached, environmental variables or object distance.

The camera head can identify the endoscope being attached and store in memory or adjust automatically based on a detection of a specific endoscope type, where the variable liquid lens20or the relative positions of the sensors18are adjusted. In either case, the adjustment preferably optimizes the focal offset introduced by these elements. Furthermore, the ray bundles at the focal planes should be telecentric.

The larger system diagram ofFIG.10illustrates how any of the camera heads disclosed herein would interact with an endoscope optical head24. In the illustrated case, the variable liquid lens20is placed after the beam splitter19. In addition, two collimating lens groups22are placed downstream of the beam splitter19. The rod lens endoscope24could be any conventional endoscope or one specially adapted to identify with the disclosed camera head. In addition, a collimating lens group22is disposed upstream from the beam splitter19to control and adapt the light beam received from the endoscope.

An alternative arrangement without variable liquid lenses20is provided inFIG.11for a simpler structure and cheaper camera head of an endoscope. The incoming light beam is split into two beams by a beam splitter19. Each beam then passes through an aperture stop13, each aperture stop13having a different diameter. The difference in diameters produces images with distinct depth of field and resolution characteristics. Each beam then passes through carrier lenses before being collimated and reflected by the respective mirrors25onto the sensors18. Lenses can also be disposed immediately upstream of the mirrors25to differently focus the light beams so that the sensors18can be mounted directly to the mirror blocks25at equal distances.

Additionally, variable apertures could be used to vary the attributes, namely the depth of field and resolution of the captured images at a given focal plane from one acquisition period to the next. From a manufacturing perspective, fixed apertures, and even variable apertures, can be less expensive and faster to position than variable liquid lenses.

The alternate optical configuration ofFIG.12focuses incoming light via objective lens40(or collects relayed light from an attached endoscope) and passes the light beam through an aperture stop13and an aspheric or positive lens27and a collimating or carrier lens26. The light beam is then split by beam splitter19and captured by sensors18. Since each sensor18is offset from the beam splitter at different distances, two focal planes can be captured. The aperture stop13can also be a variable aperture stop and thus additional depth of field and resolution information when varied over multiple acquisition periods. Alternatively, the aperture stop13can be the variably-polarized aperture stop shown inFIG.14and further discussed below.

Digital image processing can combine each of the differently focused and separately captured images by selecting and extracting the sharp areas of each image and combining them into a single full resolution image. Additionally, the color information from the blurred areas can be reconstructed using the contrast information of the sharp areas or the combined image such that the colors are accurately reproduced.

First the fusion method generates a contrast weight map, a saturation weight map and an exposure weight map for each captured image. Then these maps are applied to select the best pixels from each image. Finally, the separate weighted images containing the selected or weighted pixels are combined with pyramid-based image fusion to generate a combined image.

By interpolating the color information, both resolution and contrast are slightly reduced. This, however, should not present a problem since the resolution of the sensors and combined image exceeds the resolution of the best endoscopes. On the other hand, the increased depth of focus allows for certain errors in the optics such as image field curvature to be compensated. Image field curvature often occurs in endoscopes with a very long inversion system.

The extended camera head ofFIG.13with a first segment including elements26and27, second segment28and third segment29. The first segment includes an aperture13, an aspheric lens27and a collimating lens26as may the camera head inFIG.12. The beam splitter19at the end of the first segment splits one third of the light onto a sensor18and allows two-thirds of the light to pass through. Or, to compensate for surface losses or other differences, the reflective surfaces inside the beam splitters19may divide the beams unequally.

The second segment28is an inversion system carrying the remaining light beam to a second beam splitter19which splits half or some fraction of the remaining light onto another sensor18in a different focal plane. The remaining one-third of the light beam passes through the third segment29which is an inversion system like that in the second segment28. The remaining light is deflected by mirror30and imaged by sensor18, which is also in a different focal plane. Each inversion system flips the image or changes the parity of the image resulting in various captured image orientations which must be corrected optically or digitally.

The three sensors18inFIG.13are oriented such that all three can be soldered on the same board72. In this way a very compact construction is possible which can be accommodated in a video endoscope without changing the housing or form factor of the device. Where appropriate, the deflecting mirror30can be replaced with another beam splitter19to pass on some of the beam to an additional inversion system for further imaging, and so on. In this case, the reflectance of each beam splitter19in the chain can be adjusted to equalize the light intensity imaged by each of the sensors18.

The loss of light due to the distribution of the light beam onto various sensors may be compensated in that the system can have a higher numerical aperture than an equivalent system, that is a system which covers the same depth of focus with a single sensor as this system does with multiple sensors.

With the higher numerical aperture, overall a higher resolution is achieved while in conventional systems this high resolution requires a trade-off of lower depth of field. Due to the fact that in the various optical arrangements above the same image is captured by various sensors at the same time on different focal planes, the sharp areas of the individual sensors can be combined into one image.

The camera head for an endoscope shown inFIG.12can further include a specialized variably-polarized aperture stop13such as that shown inFIG.14. This aperture stop13includes an outer opaque annular region31, an inner polarizing annular filter32, and an innermost circular opening33with no filter. This graduated aperture provides different f-numbers for beams of polarized and non-polarized light.

A beam exiting the aperture13ofFIG.14is a separable beam including two overlapping beams propagating together until divided by a polarized beam splitter. After separation, one beam has a higher f-number than the other beam. Thus, one beam can be imaged at high resolution and the other beam can be image at a high depth of field. A processing unit can then calculate a single image with a higher depth of field and/or higher resolution than would be possible with a single sensor and conventional optical arrangements. The effect can be increased if the sensors18are in different focal planes. Alternatively, the polarizing filter32can be a spectral filter. In addition, more levels or annular regions within the graduated aperture ofFIG.14are also advantageous.

The outlined device inFIG.15shows an exemplary camera head with a specialized Radio Frequency Identification (RFID) reader unit36for detecting an RFID identifier (or tag)38for a specific endoscope type34. The camera head is surrounded by a handle structure35for easy handling by the operator. The digital signals from the sensors are then sent via connecting line37to a processing unit or display unit. Alternatively, the digital processing of the sensor images can be performed in the handle with only a combined image being sent to the display.

Advantageously, one or more of the image sensors18can be connected to a small actuator39that can adjust the focal plane position. This allows the focal plane difference between the two sensors to be adjusted for a particular situation without a variable liquid lens. The actuator39can also be combined with these other modes to provide larger ranges of focal plane differences.

Upon the identification of the specific endoscope34from the tag38on the proximal end of the endoscope, the actuator39adjusts the focal planes of the sensors18to an optimal focal plane offset. Alternatively, the identification can be done via the camera head with a QR code, bar code, or a specific color scheme on the endoscope end. Additionally, the endoscope could be identified by direct connection via a data bus or by analysis of electrical resistance or a magnetic field direction of the endoscope end.

The actuator39can be a piezo-electric motor or other small motor. Upon identification of the endoscope tag38, a RFID reader36of a camera head like that inFIG.12signals a controller for the variable aperture stop13. The variable aperture stop13is preferably disposed before the beam splitter19for adjustment to an optimal focal plane offset. Alternatively, the controller could be linked to a variable liquid lens20if the shown camera head was replaced with the camera head ofFIG.4.

It is also noted that any of the camera heads and optical arrangements disclosed herein may be implemented into the device ofFIG.15. The combined image from the several sensors of any of the camera heads will preferably be calculated in real time for an image with increased depth of field and increased resolution. If this is not possible, then a real time average value of the images super-imposed on each other can be generated with the calculated image being available later. In addition, three-dimensional modeling from the different focal planes can be calculated either in real time and displayed on a three-dimensional display or calculated and generated later for analysis and diagnosis.

The invention being thus described, it will be obvious that the same may be varied in many ways. For instance, capabilities, components or features from each of the optical arrangements above are combinable or transferrable to any of the other optical arrangements disclosed herein. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.