Tissue contrast imaging systems

1. An imaging catheter, comprising:

a flexible catheter suitable for intravascular advancement;

an imager in proximity to a distal end of the catheter, wherein the imager is positioned to visualize a tissue region adjacent to the distal end;

a sensor in proximity to the distal end wherein the sensor is configured to detect fluorescence from the tissue region;

an excitation source that is configured to activate the fluorescence from the tissue region and is electrically modulated at a rate that is higher than a video frame rate of the imager; and

a hood attached to the distal end of the catheter and also defining an open area when the hood is in an expanded configuration, wherein the open area is in fluid communication with a fluid lumen defined through the catheter and with a blood-filled environment through an opening defined by the hood.

2. The catheter of claim 1 further comprising a hood attached to the distal end of the catheter and also defining an open area when the hood is in an expanded configuration, wherein the open area is in fluid communication with a fluid lumen defined through the catheter and with a blood-filled environment through an opening defined by the hood.

3. The catheter of claim 1 wherein the excitation source comprises one or more LEDs.

4. The catheter of claim 1 further comprising a dye containing one or more fluorophores for infusion into the tissue region.

5. A method of identifying perfusion in a tissue region, comprising:

positioning a distal end of a flexible catheter in proximity to a tisane region of interest, the positioning comprising positioning a hood attached to the distal end of the flexible catheter, the hood having an expanded configuration which defines an open area which is in fluid communication with a fluid lumen through the catheter and with an environment external to the hood through an opening defined by the hood;

illuminating the tissue region of interest adjacent to the distal end of the catheter via an excitation source such that any fluorophores in the tissue region fluoresce, the excitation source being electrically modulated at a rate that is higher than a video frame rate of an imager used to image the tissue region; and

detecting a presence of perfusion in the tissue region upon an indication of fluorescence emitted from the tissue region.

6. The method of claim 5 further comprising introducing a transparent fluid into the open area via the fluid lumen such that an opaque fluid within the open area is displaced through the opening of the hood and into the environment.

7. The method of claim 5 further comprising detecting a fluorescence from the tissue region via a detector.

8. The method of claim 7 further comprising characterizing a physiological parameter of the tissue region from the detected fluorescence.

9. The method of claim 8 wherein characterizing comprises determining a degree of ablation transmurality of the tissue region.

10. The method of claim 8 wherein characterizing comprises distinguishing portions of ablated tissue relative to portions of non-ablated tissue.

11. The method of claim 10 further comprising ablating the non-ablated tissue.

12. The method of claim 6 further comprising visualizing the tissue region of interest via an electronic imager.

13. The method of claim 12 wherein the electronic imager comprises a CCD or CMOS imager.

14. The method of claim 5 further comprising introducing a dye into the tissue region of interest prior to illuminating the tissue region, where the dye is selected from the group consisting of endoscein, fluorescein, fluorescein derivatives, Methylene blue, and indocyanine green.

15. A method of enhancing a visual image of a tissue region, comprising:

positioning a hood attached to a flexible catheter in proximity to a tissue region of

interest, the hood having an expanded configuration which defines an open area which is in fluid communication with a fluid lumen through the catheter and with an environment external to the hood through an opening defined by the hood;

introducing a transparent fluid into the open area via the fluid lumen such that an opaque fluid within the open area is displaced through the opening of the hood and into the environment;

illuminating the tissue region of interest over a visual spectrum;

visualizing the tissue region of interest through the transparent fluid via an imager positioned within or adjacent to the open area; and,

enhancing an illumination of the tissue region at a first wavelength of the spectrum and at a second wavelength of the spectrum in contrast to the first wavelength such that a difference in an image of the tissue region is increased.

16. The method of claim 15 wherein enhancing an illumination comprises enhancing the illumination at the first wavelength in a deep blue region of the spectrum.

17. The method of claim 16 wherein enhancing an illumination comprises enhancing the illumination at the second wavelength in a deep red region of the spectrum.

18. The method of claim 17 further comprising enhancing the illumination in a green region of the spectrum to preserve a white balance of the image.

19. The method of claim 15 wherein illuminating the tissue region comprises illuminating via one or more LEDs.

20. The method of claim 19 further comprising electrically modulating the one or more LEDs at a rate above a frame rate of the imager.

21. The method of claim 15 further comprising applying a pattern of one or more filters with transmission peaks corresponding to one or more of the wavelengths over one or more pixels of the imager such that a difference in the image of the tissue region is further increased.

22. The method of claim 15 wherein visualizing comprises increasing a frame rate of the imager to a rate greater than about 30 Hz.

23. The method of claim 15 further comprising introducing a dye into the tissue region of interest prior to illuminating the tissue region, where the dye is selected from the group consisting of endoscein, fluorescein, fluorescein derivatives, Methylene blue, 20 and indocyanine green.

24. A method of enhancing a visual image of a tissue region, comprising:

positioning a hood attached to a flexible catheter in proximity to a tissue region of interest, the hood having an expanded configuration which defines an open area which is in fluid communication with a fluid lumen through the catheter and with an environment external to the hood through an opening defined by the hood;

introducing a transparent fluid into the open area via the fluid lumen such that an opaque fluid within the open area is displaced through the opening of the hood and into the environment;

illuminating the tissue region of interest over a visual spectrum;

visualizing the tissue region of interest through the transparent fluid via an imager positioned within or adjacent to the open area; and,

applying one or more filters to the imager such that a responsivity of the imager is enhanced at one or more wavelengths such that a difference in an image of the tissue region is increased.

25. The method of claim 24 wherein applying one or more filters comprises enhancing the responsivity at a first wavelength in a deep blue region of the spectrum.

26. The method of claim 25 wherein applying one or more filters comprises enhancing the responsivity at a second wavelength in a deep red region of the spectrum.

27. The method of claim 26 further comprising enhancing the responsivity in a green region of the spectrum to preserve a white balance of the image.

28. The method of claim 24 wherein the one or more filters are applied in a pattern over one or more pixels of the imager.

29. The method of claim 24 further comprising introducing a dye into the tissue region of interest prior to illuminating the tissue region, where the dye is selected from the group consisting of endoscein, fluorescein, fluorescein derivatives, Methylene blue, and indocyanine green.