Calibration and image processing devices, methods, and systems
In part, the invention relates to systems and methods of calibrating a plurality of frames generated with respect to a blood vessel as a result of a pullback of an intravascular imaging probe being pullback through the vessel. A calibration feature disposed in the frames that changes between a subset of the frames can be used to perform calibration. Calibration can be performed post-pullback. Various filters and image processing techniques can be used to identify one or more feature in the frames including, without limitation, a calibration feature, a guidewire, a side branch, a stent strut, a lumen of the blood vessel, and other features. The feature can be displayed using a graphic user interface.
1. A method of detecting a calibration feature disposed in a vessel having a vessel wall, the vessel scanned using an intravascular imaging probe, the method comprising:
storing image data obtained during a pullback through the vessel in a memory device, the image data comprising a plurality of frames, each frame comprising scan lines;
averaging scan lines for a first frame of the plurality of frames to obtain a speckle reduced first frame;
identifying a region in the speckle reduced first frame in which the calibration feature is estimated to appear;
identifying candidate samples of the calibration feature;
identifying a region defined by the candidate samples using a thickness of at least a portion of the calibration feature; and
fitting a curve to the candidate samples to define a boundary of the calibration feature in the speckle reduced first frame.
2. The method of claim 1 wherein the intravascular imaging probe comprises an optical fiber and a beam director in optical communication with the optical fiber.
3. The method of claim 2 wherein the calibration feature is a substantially elliptical cross-section of substantially transparent curved cover comprising a polymer, wherein the elliptical cross section comprises a first annular region and a second annular region, the second annular region doped with a light scattering material.
4. The method of claim 2 further comprising rotating the optical fiber and the beam director within the calibration feature and generating an image of a cross-section of the blood vessel, the image comprising a first annular region having a first optical intensity and a second annular region having a second optical intensity, the second optical intensity brighter than the first optical intensity.
5. The method of claim 3 wherein the thickness is an annular thickness of the second annular region and wherein the second annular region is disposed concentrically within the first annular region.
6. The method of claim 3 further comprising
averaging scan lines for a second frame of the plurality of frames to obtain a speckle reduced second frame;
identifying a region in the speckle reduced second frame in which the calibration feature is estimated to appear;
identifying candidate samples of the calibration feature using a first spatial filter;
identifying a region defined by the candidate samples using a second spatial filter having a thickness of at least a portion of the calibration feature; and
fitting a curve to the candidate samples to define a boundary of the calibration feature in the speckle reduced second frame.
7. The method of claim 5 further comprising receiving the thickness from a device attached to the intravascular imaging probe.
8. The method of claim 7 further comprising searching for the second annular region using the thickness.
9. The method of claim 1 further comprising
identifying a dark region having a first intensity in one or more of the scan lines of a frame; and
excluding optical signals having a second intensity appearing in the dark region if the second intensity is greater than the first intensity.
10. The method of claim 1 further comprising wherein one or more of the identifying steps are performed using one or more filters.
11. The method of claim 1 further comprising rejecting image data associated with the boundary of the calibration feature, when a shape of the boundary is irregular or exceeds a shape threshold.