HK1157169B - Imaging system for combined full-color reflectance and near-infrared imaging - Google Patents

Description

Imaging system for combined full color reflectance and near infrared imaging

Technical Field

The present invention is directed to medical imaging, and in particular to systems and methods for obtaining visible light images and near infrared light images from an observed region, such as living tissue, and in particular for use in endoscopy.

Background

Near Infrared (NIR) imaging has been described in the literature for various clinical applications. Typically, such imaging modalities utilize contrast agents that absorb and/or fluoresce in the NIR (e.g., indocyanine green). Such contrast agents may be bound to a target molecule (e.g., an antibody) for disease detection. Contrast agents may be introduced intravenously or subcutaneously into tissue to image tissue structure and function (e.g., blood/lymph/bile flow in vessels) that are not readily visible with standard visible light imaging techniques.

Independently of clinical applications, endoscopic NIR imaging devices typically include multiple imaging modes as a practical feature. For example, endoscopists utilize visible spectrum colors for both visualization and navigation, and endoscopic imaging devices that provide NIR imaging typically provide simultaneous color images. Such a concurrent imaging apparatus may be implemented, for example, as follows:

one conventional configuration utilizes spectral separation of visible and NIR light, with panchromatic and NIR image signals acquired using separate sensors for different color (e.g., red, green and blue) and NIR spectral bands, or using a single color sensor with integrated filters containing filter elements transparent to different spectral bands (e.g., red, green, blue and NIR). Thus, such multi-mode color and NIR imaging devices provide a dedicated sensor or sensor pixel for each of the two imaging modes. Disadvantageously, this increases the number of image sensors in a multi-sensor implementation, or compromises image resolution when certain sensor pixels are dedicated to NIR imaging while other pixels are used for color imaging on the same sensor.

Another conventional configuration utilizes a single monochromatic image sensor to sequentially image visible and NIR light. Thus, the object is illuminated successively with light in the red, green, blue and NIR spectral bands, wherein a separate image frame is acquired for each spectral band and a composite color and NIR image is generated from the acquired image frames. However, this approach may produce objectionable motion artifacts (i.e., color fringing and "iridescence") in the composite color and NIR images where the image frames are acquired sequentially at different times. These artifacts may be mitigated by increasing the acquisition or frame rate to greater than, for example, 15 frames per second (fps), e.g., up to 90 fps, or even 180 fps. Due to the high data transfer rate, it is difficult to achieve high frame rates for high definition images (e.g., 2 megapixels) or images with large dynamic range (> 10 bits), thus limiting image size and/or resolution.

It is therefore desirable to provide a system and method for simultaneous acquisition of full-color visible and NIR light images that eliminates the above-described disadvantages without compromising image resolution and/or introducing objectionable motion artifacts.

Disclosure of Invention

According to an aspect of the invention, a method for acquiring NIR and full-color images comprises the steps of: the region to be observed is irradiated with continuous blue/green light, and is irradiated with red light and NIR light, wherein at least one of the red light and the NIR light is periodically turned on and off. Blue, green, red and NIR light returning from the region being observed is directed to one or more sensors configured to detect blue, green and combined red/NIR light, respectively. The red spectral component and the NIR spectral component are determined from the combined red/NIR light image signal in synchronism with the switched red and NIR light, respectively. A full color reflected image of the region being viewed is reproduced and displayed from the blue, green and red light, and a NIR image is likewise reproduced and displayed from the NIR light.

According to another aspect of the invention, an imaging system for acquiring NIR images and full-color images includes: a light source that supplies visible light and NIR light to a region to be observed; a camera having one or more image sensors configured to detect blue and green light, respectively, and combined red and NIR light, respectively, returning from the region being viewed; and a controller in signal communication with the light source and the camera. The controller is configured to control the light source to successively illuminate the tissue with blue/green light and the region under observation with red light and NIR light, wherein at least one of the red light and the NIR light is periodically turned on and off in synchronization with the acquisition of red and NIR images in the camera.

The controller is further configured to determine the red spectral component and the NIR spectral component from sensor signals representing the combined red light and NIR light, respectively. The imaging system further includes a display that receives image signals corresponding to blue light, green light, and the separately determined red spectral component and thereby reproduces a full color visible light image of the region being viewed. The display also receives separately determined NIR spectral components and reproduces therefrom a NIR image of the region to be observed.

The video imaging system may use a three-sensor color camera configured to continuously image the blue and green bands and intermittently image the red band, thereby providing continuous high-quality luminance information and full chrominance sufficiently continuous to generate high-quality video images of the observed region, such as living tissue. In such a configuration, the red image sensor may be time-multiplexed to acquire both red and NIR images (i.e., the red image sensor alternately and in rapid succession images both red light for color information required for a color image and NIR light for image information required for an NIR image). Such time multiplexing may be associated with (and synchronized with) an illumination source for providing NIR illumination (for excitation of fluorescence) and red light for color imaging. Then, the resulting image signals are appropriately separated and processed by image processing.

Embodiments of the invention may include one or more of the following features. The region to be observed can be illuminated alternately with red light and NIR light, wherein the duration of the red light can be different from, preferably longer than, the duration of the illumination with NIR light. The illumination may be switched at the video field rate or frame rate.

The fields captured by the image sensor and lacking either the red spectral component or the NIR spectral component may be interpolated from temporally adjacent image fields comprising the respective red spectral component or NIR spectral component. In one embodiment, the NIR spectral component obtained in the absence of red light may be subtracted from the combined red/NIR light to obtain a separate red spectral component. This is particularly advantageous when the detected NIR signal has an intensity comparable to that of the red signal.

In one embodiment, the light source may include an illuminator that emits visible and NIR light of substantially constant intensity over a continuous spectral range, and a plurality of movable filters disposed between the illuminator and the region being viewed for transmitting temporally continuous blue/green light and temporally discontinuous red and NIR light. In one embodiment, the one or more image sensors include a single image sensor having a plurality of pixels, each pixel being responsive to one of blue reflected light, green reflected light, and combined red reflected light/NIR fluorescent light returning from the region being viewed. In one embodiment, the single image sensor includes a mosaic blue/green/red-NIR filter array disposed in front of the sensor pixels.

In another embodiment, the light source may comprise an illuminator emitting visible and NIR light of substantially constant intensity over a continuous spectral range, first dichroic means for separating the visible and NIR light into blue/green and red and NIR light, shutter means for converting the separated red and NIR light into temporally discontinuous red and discontinuous NIR light, and second dichroic means for combining the blue/green light, the temporally discontinuous red light and the temporally discontinuous NIR light for transmission to an area under observation.

In another embodiment, the light source may include a first illuminator that emits green and blue light of substantially constant intensity, a second illuminator that produces switched red light, a third illuminator that produces switched NIR excitation light, and dichroic means for combining the switched red light and switched NIR light with the green and blue light for transmission to the area being viewed. The switched red and NIR light may be generated by interrupting a continuous intensity beam of red and NIR light with a shutter or chopper. Alternatively, the switched red and NIR light may be generated by electrically switching the second and third illuminators on and off.

The image sensor may employ interlaced scanning or progressive scanning.

The imaging system may include an endoscope.

Drawings

The following drawings illustrate certain illustrative embodiments of the invention which should be considered illustrative of the invention and not in any way limiting.

FIG. 1 illustrates an endoscopic system according to one embodiment of the present invention;

FIGS. 2 a-2 d illustrate various exemplary embodiments of a multi-mode light source to be used with the endoscope system of FIG. 1;

FIG. 3a illustrates an exemplary dichroic prism employed by a 3-sensor color camera;

FIG. 3b shows the optical transmission ranges of the spectral components separated by the dichroic prism of FIG. 3 a;

FIG. 3c shows the optical transmission range of a notch filter blocking excitation light from entering the camera;

FIG. 4 shows a timing diagram for a first embodiment for continuous illumination with green/blue light and alternating illumination with red/NIR light;

FIG. 5 shows a timing diagram for a second embodiment for continuous illumination with green/blue light and alternating illumination with red/NIR light;

FIG. 6 shows a timing diagram for a third embodiment for continuous illumination with green/blue/NIR light and alternating illumination with red light; and

fig. 7 illustrates an exemplary CMOS sensor with stacked imaging layers and the corresponding spectral sensitivities of these layers.

Detailed Description

Color video images are typically obtained with a three-sensor color camera in which individual red, green and blue image sensors provide simultaneous contiguous arrays of red, green and blue pixel information. A full color video image is generated by combining image information from all three sensors. Color fidelity (i.e., true color reproduction) is extremely important in medical imaging applications, and all three sensors are used to provide complete color information.

However, in order to understand the relative importance of color and spatial information in video images of human tissue, it is useful to consider information in such video images in terms of luminance and chrominance. Luminance refers to the brightness information in an image, and it is this information that provides spatial detail that enables a viewer to recognize the shape. Therefore, the spatial and temporal resolution of the luminance is critical for the perception of video image quality. Chrominance refers to color information in a video image. One characteristic of human vision is that subtle detail changes in the chrominance of image features are not readily perceptible and thus are less critical in the overall assessment of image quality than subtle detail changes in luminance. It is for this reason that video coding of chrominance information is often sub-sampled.

In video images of human tissue obtained with visible light, structural details of the tissue are largely contained in the blue and green wavelength regions of the imaging light. Blue and green light tends to be reflected from the tissue surface, while red light tends to be highly scattered within the tissue. As a result, there is very little fine structure detail in the red light reaching the red image sensor. It is also known from color science that human vision receives most of the spatial information from the green part of the visible spectrum-i.e. green light information contributes disproportionately to brightness. A standard formula for calculating luminance from the color components of gamma correction is Y '= 0.2126R' + 0.7152G '+ 0.0722B'. For this reason, spatial and/or temporal interpolation of the red component of video images of human tissue does not significantly affect the perception of subtle details in those images.

Like red light, NIR light tends to be scattered in tissue, causing NIR image features to be defined diffusely rather than clearly. Furthermore, since NIR images highlight areas of interest (i.e., areas in which contrast agents are located) but do not provide overall visualization or navigation information, it is desirable for NIR endoscopic imaging devices to provide continuous color images as well as a superimposed or side-by-side display of NIR image information. In such a display, NIR light may also contribute less to the spatial information presented to the viewer.

Fig. 1 schematically illustrates an exemplary embodiment of an NIR endoscopic imaging system 10, comprising: a multimode light source 11 providing both visible and NIR radiation and connected to endoscope 12 by a radiation guide, such as a fiber optic cable 17, suitable for transmitting both color and NIR radiation; a color camera 13 mounted to the endoscopic image guide, here illustrated with three different sensors 34, 36, 38 for blue, green and red/NIR imaging, respectively (see fig. 3 a); and a camera controller 14 connected to the camera 13 and the light source 11 for controlling and synchronizing the illumination and image acquisition. The controller 14 may also process the acquired visible and NIR images for display on a monitor 15 connected to the controller 14, for example, by a cable 19. The images may be acquired in real time at a selectable frame rate, such as a video rate.

Fig. 2a to 2d show schematic diagrams of exemplary embodiments of various light sources 11. The illustrated light source is configured to supply visible illumination light that produces a substantially continuous spectral distribution in a normal color imaging mode. The light source may be an arc lamp, a halogen lamp, one or more solid state sources (e.g., LEDs, semiconductor lasers), or any combination thereof, and may be spectrally filtered or shaped (e.g., with bandpass filters, IR filters, etc.). Continuous spectra can be generated as primary colors (RGB) simultaneously or sequentially, for example, using a rotating filter wheel.

In a system according to the present invention, a light source to be used with the system of the present invention and described in detail below is configured to provide continuous, uninterrupted illumination in the blue and green portions of the visible spectrum and discontinuous red and/or NIR light. The blue and green portions of the visible spectrum may be optically filtered out of the emission produced by the continuous source or directly produced by narrow band sources (e.g., blue and green LEDs). Red and NIR light may also be produced by arc lamps, halogen lamps, solid state sources (e.g., red and NIR LEDs or lasers), or any combination thereof.

Turning now to FIG. 2, in one embodiment, light source 11 includes an illuminator 202 that produces visible and NIR light emissions, a collimating lens 204, a filter wheel or reciprocating filter holder 208 that alternately transmits red and NIR light and continuously transmits green and blue light. Alternatively, tunable electro-optical or acousto-optical filters may be used. The filtered light is focused by the lens 206 onto the light guide 17.

Another embodiment of a light source 11b is schematically illustrated in fig. 2 b. The light source 11b includes an illuminator 202 that produces visible and NIR light emissions and a collimating lens 204. The dichroic mirror 212 transmits green/blue light and reflects red/NIR light to another dichroic mirror 214, which dichroic mirror 214 transmits NIR light to an NIR mirror 215 and reflects red light, or vice versa. The green/blue light may be further bandpass filtered by filter 213. The reflected red and NIR light is chopped, for example by chopper wheels 219a, 219b (which may be combined into a single chopper wheel) to produce temporally discontinuous illumination that is then reflected by mirrors 216, 217 and combined with green/blue light by dichroic mirror 218. This combined light is then focused by the lens 206 onto the light guide 17 as previously described.

In another embodiment of the light source 11c, schematically illustrated in fig. 2c, the illuminator 202a produces green and blue light emissions that are collimated by a collimating lens 204 a. Likewise, individual illuminators 202b, 202c produce red and NIR light emissions that are collimated by corresponding collimating lenses 204b and 204c, respectively. As in the embodiment of fig. 2b, red and NIR light is chopped by, for example, chopper wheels 219a, 219b (which may also be combined into a single chopper wheel) to produce illumination that is discontinuous in time, which illumination is then combined with green/blue illumination by dichroic mirrors 222, 228. This combined light is then focused by the lens 206 onto the light guide 17 as previously described.

As previously mentioned, in another embodiment of the light source 11d, schematically illustrated in fig. 2d, the illuminator 202a produces green and blue light emissions that are collimated by the collimating lens 204 a. However, unlike in the embodiment of fig. 2c, the individual illuminators 202d, 202e are here electrically switched to produce red and NIR light emissions with controlled timing. For example, the red and NIR light sources 202d, 202e may be solid state light sources, such as LEDs or semiconductor lasers, which may be rapidly turned on and off with appropriate, preferably electronic, switches. As described above with reference to fig. 2c, red and NIR illumination is collimated by respective collimating lenses 204b and 204c and combined with green/blue illumination by dichroic mirrors 222, 228. This combined light is then focused by the lens 206 onto the light guide 17 as previously described.

The alternating red and NIR illumination is synchronized with the image acquisition of the three sensor camera so that red and NIR images are acquired by the camera in synchronization with the red and NIR illumination of the endoscope.

Fig. 3a shows the three-sensor camera 13 of fig. 1 in more detail, in particular the optical beam splitter used to direct red/NIR, green and blue light to three different image sensors 34, 36 and 38, respectively. For NIR fluorescence applications, the camera preferably also includes an excitation band blocking filter 32. The beam splitter may for example be constituted by a plurality of dichroic prisms, a cube separator, a plate separator or a membrane separator. Fig. 3b shows the spectral composition received from the endoscope according to fig. 3 a. Fig. 3c illustrates the spectral composition 31 of light transmitted through an excitation band blocking filter 32 implemented as a notch filter that blocks the transmission of excitation light but transmits other wavelengths in the visible and NIR spectral range. The transmission characteristics of this filter 32 can be designed to also block undesirable NIR wavelengths that interfere with the visible spectrum, possibly degrading the color image.

Fig. 4 shows a timing diagram of a first exemplary embodiment of a simultaneous color and NIR imaging mode using, for example, a three sensor camera. In this embodiment, the camera sensor utilizes an interlaced readout format, which represents an advantageous combination of spatial and temporal resolution for smooth display of motion. Any of the light sources illustrated in fig. 2 a-2 d may be used with the present embodiment. The light source provides continuous blue/green illumination and alternating red and NIR illumination. The fields are exposed alternately on the image sensor, i.e. a first field with even lines (field) alternates with a second field with odd lines (field). In the timing diagram of fig. 4, which shows a full frame rate of 30 fps, one field period (16.7 ms) provides NIR illumination, followed by two field periods (33.3 ms) of red illumination. In other words, the sample or tissue is illuminated with full spectral color (RGB) during the two field periods (33.3 ms) and with GB and NIR during the third field period. To reconstruct a full color visible image, the missing red information is interpolated between fields adjacent to the field illuminated with NIR. The blue and green image information is always available, providing optimal and continuous luminance information. An NIR image is generated from every sixth field in each field, where the missing lines are spatially interpolated. When displaying a fluorescent field, the image is updated every three fields, with the displayed image being interpolated between even and odd lines.

In all figures, the term "IR" is used as an alternative to or interchangeably with "NIR".

Once the color and NIR image data have been processed, the signals are output to a video monitor and may be displayed as two separate, simultaneous views (one color, one fluorescence) or as a combined color and fluorescence image signal (e.g., by assigning the fluorescence signal a color that contrasts with the color naturally present in the tissue).

Fig. 5 shows a timing diagram of a second exemplary embodiment of a simultaneous color and NIR imaging mode. In this embodiment, the camera sensor utilizes a progressive scan sensor readout format in which a complete frame (G/B/R alternating with G/B/NIR) is read out during each field period. Any of the light sources illustrated in fig. 2 a-2 d may be used with the present embodiment. The light source provides continuous blue/green illumination and alternating red and NIR illumination. In the timing diagram of fig. 5, one field period (16.7 ms) provides NIR illumination followed by one field period (16.7 ms) of red illumination. In other words, the sample or tissue is illuminated with full spectral color (RGB) during one field period (16.7 ms) and with GB and NIR during the third field period. In this case, a full visible spectrum color image is available at each pixel in every other frame. In alternate frames, blue and green information is directly acquired, while red information is interpolated between adjacent frames. Unlike the embodiment of fig. 4, no spatial interpolation is required. Further image processing and display may be achieved in a manner similar to that described in the previous embodiments.

Fig. 6 shows a timing diagram of a third exemplary embodiment, in which both the green/blue illumination and the NIR illumination are continuous, while only the red illumination is modulated. Similar to in the embodiment of fig. 4, the fields are alternately exposed on the image sensor, i.e. a first field (field) with even lines is alternated with a second field (field) with odd lines. In the timing diagram of fig. 6, which shows a full frame rate of 30 fps, one field period (16.7 ms) provides (NIR + GB) illumination (red illumination is turned off), followed by two field periods (33.3 ms) (NIR + RGB). If the NIR image signal is small compared to the red reflectance signal, it will not significantly affect the total visible (RGB) image, making it possible to generate color images by conventional color image processing without correction. In addition, the NIR contribution obtained in the red image channel when the red illumination is turned off is subtracted from the (NIR + R) image data by spatial and temporal interpolation to obtain a red image signal, as shown in the second to last row in the timing diagram of fig. 6. Alternatively, a sensor with progressive scan image sensor readouts similar to those illustrated in fig. 5 may be used for RGB and (RGB + IR) image acquisition in alternate frames.

In another exemplary embodiment (not illustrated in the figures), the green/blue illumination and the red illumination are continuous, while the NIR illumination is modulated. This timing scheme can be best applied if the red and NIR image signals have approximately the same amplitude. In this embodiment, the light source provides uninterrupted illumination with the full visible spectrum and intermittent illumination with NIR light. The timing diagram is substantially the same as that shown in fig. 6, with NIR and red illumination interchanged. The intermittent NIR illumination is synchronized to coincide with every second field in the case of an interlaced camera and every second field in a progressive camera. For each field in which NIR illumination is provided, the red image sensor will acquire an (R + NIR) image signal. The NIR image signal may be extracted from the (R + NIR) image signal by interpolating the red signal values from the appropriate preceding and following "red only" image fields and subtracting the red image signal from the (R + NIR) signal. Since the red and NIR image signals have similar amplitudes, such interpolation and subtraction will provide a rather accurate NIR image signal value. The color image is processed by using the acquired and interpolated values of the red image signal in combination with the blue and green image signals. The resulting color and NIR image information may then be displayed or recorded as previously described.

In any of the foregoing embodiments, the NIR endoscopic imaging system may also be operated such that the light source provides continuous illumination with the full visible spectrum or NIR spectrum, and the camera acquires corresponding color images or NIR (absorption or fluorescence) images in a continuous manner to provide high spatial resolution. The resulting video image of each individual illumination/imaging mode-color or NIR-can then be displayed and/or recorded.

By implementing color and NIR imaging as described in the foregoing embodiments, full color visible and NIR light images may be acquired and displayed at video rates without compromising image resolution and/or introducing objectionable motion artifacts. Furthermore, if any residual color fringing occurs due to rapid movement of sharp edges across the field of view (e.g., in the case of discontinuous acquisition of red or NIR images), these relatively minor effects can be mitigated by temporal interpolation of the missing (red/NIR) video field with minimal additional processing time.

While the present invention has been disclosed in conjunction with the preferred embodiments shown and described in detail, various modifications and improvements thereto will become readily apparent to those skilled in the art. For example, instead of using separate image sensors for the G/B and R/NIR, respectively, or a single color sensor for the RGB image and the NIR fluorescence image, a single direct three-color RGB sensor image sensor with a stacked pixel design, implemented in CMOS technology and available from Foveon corporation of san jose, california, may be used. Such a sensor is schematically illustrated in fig. 7. It will be appreciated that this sensor design can be extended to four colors by adding a NIR sensitive layer. Thus, red, green, blue and NIR images are acquired at different depths of the image sensor. In the case of a 4-layer sensor, multiplexing of red and NIR illumination would not be necessary. However, in the case of a 3-layer sensor, multiplexing of red and NIR illumination is still required, as described above for a 3-sensor conventional camera. For fluorescence imaging applications, appropriate light blocking filters will also be required to block NIR excitation light.

While the invention has been illustrated and described in connection with the presently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiment was chosen and described in order to explain the principles of the invention and the practical application to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by letters patent is set forth in the appended claims and includes equivalents of the elements described therein.

Claims (25)

1. A method for acquiring NIR and full color images, comprising the steps of:

the region to be observed is illuminated continuously with blue and green light,

illuminating the region under observation with red light and NIR light, wherein at least one of the red light and the NIR light is periodically turned on and off,

directing the blue and green reflected light and the combined red reflected light and NIR fluorescent light to one or more sensors configured to detect the blue reflected light, the green reflected light, and the red reflected light, and the NIR fluorescent light, respectively, wherein the red reflected light and the NIR fluorescent light are detected in synchronization with the switched red light and NIR light,

the red reflected light spectral component and the NIR fluorescence spectral component are determined from the combined image signals of red reflected light and NIR fluorescence respectively,

displaying a full-color image of the region being viewed based on the blue and green reflected light and the separately determined spectral components of the red reflected light, an

The NIR image is displayed from the NIR fluorescence spectral components.

2. The method of claim 1, wherein the region to be observed is illuminated alternately with red light and NIR light.

3. The method of claim 2, wherein the duration of red light illumination is different from the duration of NIR light illumination.

4. The method of claim 3, wherein the duration of red light illumination is longer than the duration of NIR light illumination.

5. The method of claim 2, wherein the duration of red light illumination is substantially equal to the duration of NIR light illumination.

6. The method of claim 1, wherein the region under observation is continuously illuminated with red light and periodically illuminated with NIR light.

7. The method of claim 1, wherein the region under observation is illuminated continuously with NIR light and periodically with red light.

8. The method of claim 1, wherein the red or NIR light, or both, is switched at a video rate.

9. The method of claim 2, wherein image fields lacking a red reflected light spectral component or a NIR fluorescence spectral component are interpolated from temporally adjacent image fields comprising the respective red reflected light spectral component or NIR fluorescence spectral component.

10. The method of claim 7, wherein NIR fluorescence spectral components obtained in the absence of illumination by red light are subtracted from the combined red reflected light and NIR fluorescence to obtain individual red reflected light spectral components.

11. The method of claim 1, wherein the spatial information of the observed region is derived primarily from blue and green reflected light.

12. An imaging system for acquiring NIR and full-color images, comprising:

a light source that provides visible light and NIR light to a region being viewed,

a camera having one or more image sensors configured to detect blue reflected light, green reflected light, and combined red reflected light and NIR fluorescence, respectively, returning from an observed region,

a controller in signal communication with the light source and the camera for

The region to be observed is illuminated continuously with blue and green light,

illuminating the region to be observed with red light and NIR light, wherein at least one of the red light and the NIR light is periodically switched on and off, and

determining from the combined red reflected light and NIR fluorescence light, a red reflected light spectral component and an NIR fluorescence spectral component, respectively, synchronously with the switched red and NIR light, and

a display receiving image signals corresponding to the blue reflected light, the green reflected light and the separately determined red reflected light spectral components and thereby reproducing a full color reflected image of the region being observed, the display also receiving the separately determined NIR fluorescent spectral components and thereby reproducing an NIR image of the region being observed.

13. The imaging system of claim 12, wherein the region under observation is illuminated alternately by a light source having red light and NIR light.

14. The imaging system of claim 12, wherein the light source comprises

An illuminator emitting visible and NIR light of substantially constant intensity over a continuous spectral range, an

A plurality of filters disposed between the illuminator and the region being viewed to transmit temporally continuous blue and green light and temporally discontinuous red and temporally discontinuous NIR light.

15. The imaging system of claim 12, wherein the light source comprises

An illuminator emitting substantially constant intensity visible and NIR light over a continuous spectral range,

a first dichroic means for separating visible and NIR light into blue and green and red light and NIR light,

a shutter device for converting the separated red light and NIR light into temporally discontinuous red light and temporally discontinuous NIR light, an

A second dichroic means for combining the blue and green light, the temporally discontinuous red light, and the temporally discontinuous NIR light for transmission to an area being viewed.

16. The imaging system of claim 12, wherein the light source comprises

A first illuminator emitting green and blue light of substantially constant intensity,

a second illuminator that generates switched red light,

a third illuminator that generates switched NIR light, an

Dichroic means for combining the switched red light and the switched NIR light with the green and blue light for transmission to an area under observation.

17. The imaging system of claim 16, wherein the switched red and NIR light is produced by interrupting a continuous intensity beam of red and NIR light with a shutter or chopper.

18. The imaging system of claim 16, wherein the switched red and NIR light is produced by electrically turning the second and third illuminators on and off.

19. The imaging system of claim 12, wherein the image sensor employs interlaced scanning.

20. The imaging system of claim 12, wherein the image sensor employs progressive scanning.

21. The imaging system of claim 12, further comprising a dichroic prism assembly that spectrally separates blue reflected light, green reflected light, and combined red reflected light and NIR fluorescent light returning from the viewed area and directs the separated light to different exit faces of the dichroic prism assembly, wherein the one or more image sensors comprise three image sensors, each mounted on a different exit face.

22. The imaging system of claim 12, wherein the one or more image sensors comprise a single image sensor having a plurality of pixels, each pixel responsive to one of blue reflected light, green reflected light, and combined red reflected light and NIR fluorescent light returning from an observed region.

23. The imaging system of claim 22, wherein the single image sensor comprises a mosaic blue, green, red-NIR filter array disposed in front of the sensor pixels.

24. The imaging system of claim 12, wherein the one or more image sensors comprise a single image sensor having a plurality of stacked layers, each layer having a plurality of pixels responsive to one of blue reflected light, green reflected light, and combined red reflected light and NIR fluorescent light returning from an observed region.

25. The imaging system of claim 12, wherein the imaging system is configured as an endoscope.