FIELD OF INVENTION

In part, this invention relates to imaging systems, and more specifically to image data collection probes, data collection systems, optical coherence tomography and related methods.

BACKGROUND

Optical coherence tomography (OCT) is an interferometric imaging technique with widespread applications in ophthalmology, cardiology, gastroenterology and other fields. In interferometric imaging, light from a known and controlled optical path (the ‘reference path’) is caused to interfere with light returned from an unknown path such that information about this unknown path (the ‘sample path’) may be determined by an analysis of the resulting interferogram. The interferogram contains the depth location information of structures within the sample being analyzed. A particular advantage of OCT is its inherent compatibility with fiber optics making it a nearly ideal imaging modality for non-invasive or minimally invasive medical procedures.

In general, for OCT systems, the lengths of the sample and reference paths are matched to ensure the interference effect being recorded corresponds to a desired scan region within the sample. In the case of relatively long optical catheters required in many procedures (approximately 1.5 to 2 meters is common) such matching can be difficult to achieve. Furthermore, the optical fibers used in these catheters can easily stretch or contract several millimeters during use.

When using OCT, the optical ‘zero-point’ is critical. This defines where, in the image space, the so-called reference plane exists. By convention, surface planes are in the x-y plane, and the depth occurs along the z-axis. In a microscope application for example, it may be beneficial to set the zero point at the surface of the microscope slide, so specimens can be measured against this known surface. For a catheter inserted in a lumen such as a blood vessel, the most useful reference plane is the outer surface of the catheter tip itself, and all distances are measured outward from this location.

OCT systems typically use an adjustable reference path within the optical imaging equipment to adjust to each catheter as it is used. This is generally handled using a reference motor which can move a reflector such as a reference mirror back and forth to adjust the reference path.

A given medical application may use many disposable catheters per day; all interfaced to the same imaging equipment. Thus, while the primary path length adjustment can work quite effectively, it usually requires an initial adjustment by a skilled operator who understands the optical reflection pattern or ‘signature’ of the catheters that will be recorded by OCT to determine how to adjust the reference path to coincide with the outer surface of the catheter tip.

Again, the adjustment of the image zero-point, or reference plane location is performed by adjusting the primary path-length of the reference arm. This adjustment is often termed ‘z-offset’ of the reference arm and is controlled via a motor, called simply the z-offset motor, and a movable reference mirror. By convention, the instrument z-offset is zero when the sample arm length (catheter) is manufactured exactly as designed; is negative when the catheter is too short; and positive when the catheter is too long. Motor movements can be used to adjust the reference path in a consistent manner for different catheters.

OCT catheter-based probes typically include a beam directing structure such as lens or reflector placed at their distal tip to focus and direct light for scanning purposes. The light typically propagates through one or more transparent sheaths that comprise the catheter outer structure with an optical fiber disposed therein and in optical communication with the lens or reflector. Each of the optical interfaces can cause a reflection that will be detected by OCT. Hence, it may be challenging to determine which of those reflections corresponds to the desired optical reference point (‘zero-point’) of the system.

Since measurements are made based on this zero-point setting, setting it correctly can significantly affect the results of a given medical application. Furthermore, because there may be several closely spaced and similar intensity reflections, the use of software to detect the proper zero-offset (‘z-offset’) is problematic and unreliable. Additionally, as a further complexity, because imaging systems and the disposable catheter-based based probes such systems use change over time, software for one system is generally not designed for different OCT probes. Calibration drift and other imaging artifacts can also affect image quality during a review of frames post-pullback.

Therefore, methods, devices and systems suitable for calibrating an OCT system are needed. Given the complexity of optical interface signals, additional techniques, software modules, and devices to address such signals in the context of calibrating a data collection probe or the underlying data are needed. In addition, image processing techniques suitable for dealing with calibration drift and related issues after a pullback is complete are also needed. Further, the methods, devices, and systems should be able to work with different types of disposable data collection probes. The present invention addresses these needs and others.

SUMMARY

In part, the invention relates to various image data collection probe designs that include a calibration feature to distinguish probe types and calibrate a data collection system when using a given type of data collection probe. Methods and systems that are configured to perform continuous calibration using image processing techniques after a pullback is complete that do not rely on motor related offset changes are also embodiments of the invention. The placement or properties of a given calibration feature can be used to identify different types of data collection probes. In turn, the specific calibration steps that can be performed for a given catheter type can be specified upon identifying the type of catheter being used with an OCT system.

The invention also includes various image data processing software modules and a modular or encapsulated for such modules as well as processing methods relating to their sequential arrangement. OCT data frames can be prefetched from a database or other data store or memory for use by a first software module, such as a continuous calibration module, and subsequently prefetched for a second software module, such as side branch detection. This prefetching is extendable to a plurality of software modules such as imaging processing and filtering modules.

The use of intravascular imaging probe structural components and their optical properties such as associated intensity patterns in a frame of OCT image data can be used to identify calibration features of interest or instances where features are misidentified as a calibration feature of interest. For example, a dark or low intensity region in an OCT image that maps to a particular structural component and its optical signature regions can be used as part of a filtering or pattern recognition algorithm to screen out erroneous optical interface signals when searching for a calibration feature of interest. In this way, splices having reflections, glass components that are substantially transmissive, and light scattering calibration features can be identified with greater accuracy. In one embodiment, calibration features which move relative to the data collection probe during a pullback are searched to perform continuous calibration after the pullback is complete using imaging processing methods and software modules.

The invention provides, in part, methods of detecting a calibration feature disposed in a vessel having a vessel wall, the vessel scanned using an intravascular imaging probe. The method includes the steps of: 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.

The invention also provides methods of detecting a calibration feature disposed in a vessel having a vessel wall, the vessel scanned using an intravascular imaging probe. The method includes the steps of: 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 a plurality of scan lines; averaging the plurality of 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 expected to appear; identifying candidate pixels of the calibration feature using a first spatial filter; identifying a region defined by the candidate pixels using a second spatial filter having a thickness of at least a portion of the calibration feature; and fitting a curve to the candidate pixels to define a boundary of the calibration feature in the speckle reduced first frame.

In some embodiments, the intravascular imaging probe comprises an optical fiber and a beam director in optical communication with the optical fiber. The calibration feature can be a substantially elliptical cross-section of a substantially transparent curved cover comprising a polymer. The elliptical cross section can have a first annular region and a second annular region, and the second annular region can be doped with a light scattering material. The thickness can be an annular thickness of the second annular region and wherein the second annular region is disposed concentrically within the first annular region.

In some embodiments, the method can include the step of receiving the thickness from a device attached to the intravascular imaging probe.

In some embodiments, the method can include the step of searching for the second annular region using the thickness.

In some embodiments, the method can include the steps of 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 can include a first annular region having a first optical intensity and a second annular region having a second optical intensity, and the second optical intensity brighter than the first optical intensity.

In some embodiments, the method can include the steps of: 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.

In some embodiments, the method can include the steps of: averaging the plurality of 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 expected to appear; identifying candidate pixels of the calibration feature using a first spatial filter; identifying a region defined by the candidate pixels using a second spatial filter having a thickness of at least a portion of the calibration feature; and fitting a curve to the candidate pixels to define a boundary of the calibration feature in the speckle reduced second frame.

In some embodiments, the method can include the steps of: 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.

In some embodiments, the method can include the steps of: identifying a dark region having a first intensity in a plurality of the frames; and excluding optical signals having a second intensity appearing in the dark region if the second intensity is greater than the first intensity.

In some embodiments, one or more of the identifying steps are performed using one or more filters.

In some embodiments, the method can include the step of rejecting image data associated with the boundary of the calibration feature, when a shape of the boundary is irregular or exceeds a shape threshold.

The invention also provides, in part, intravascular image data processing systems. The system can include a memory and a processor in communication with the memory. The memory includes instructions executable by the processor to cause the processor to: continuously calibrate a plurality of frames comprising cross-sectional images using an elliptical calibration feature that changes between two or more frames of the plurality of frames, the plurality of frames comprising data collected during a pullback of a probe through a blood vessel; detect a guidewire in the plurality of frames; and display a plurality of continuously calibrated frames.

In some embodiments, the continuously calibrating includes identifying the elliptical calibration feature in at least a majority of the plurality of the frames.

In some embodiments, identifying the elliptical calibration feature is performed using one or more constraints selected from the group consisting of non-concentric positioning of calibration feature, a circular profile of calibration feature, a perimeter measure of calibration feature, an area measure of calibration feature, a thickness of a brighter annular subset of the calibration feature, a thickness of a brighter annular subset of the calibration feature and thickness of a doped region of the calibration feature.

In some embodiments, the system can include instructions executable by the processor to cause the processor to divide the plurality of frames into a plurality of windows and fit a curve relative to a measurement of the elliptical calibration feature across the plurality of windows.

In some embodiments, the system can include instructions executable by the processor to cause the processor to detect one or more side branches in the continuously calibrated frames and display a side branch on one or more of the continuously calibrated frames.

In some embodiments, the system can include instructions executable by the processor to cause the processor to detect a lumen of a blood vessel on a per frame basis for the continuously calibrated frames and to display the lumen of the blood vessel in the continuously calibrated frames.

In some embodiments, the system can include instructions executable by the processor to cause the processor to detect a guide catheter on a per frame basis for the continuously calibrated frames.

In some embodiments, the system can include instructions executable by the processor to cause the processor to detect a stent strut and to display a stent strut on one or more of the continuously calibrated frames.

In some embodiments, the system can include instructions executable by the processor to cause the processor to: detect one or more side branches on a per frame basis in the continuously calibrated frames; detect one or more stent struts in the continuously calibrated frames on a per frame basis; detect a lumen of a blood vessel on a per frame basis for the continuously calibrated; and display a side branch, one or more stents struts, and the lumen on one or more of the continuously calibrated frames.

In some embodiments, the elliptical calibration feature includes a first border, and the border changes between the two or more frames.

In some embodiments, the elliptical calibration feature includes a second border disposed within the first border, and the second border changes between the two or more frames.

In some embodiments, continuously calibrating a plurality of frames includes calibrating each scan line prior to generating a frame of calibrated scan lines.

In some embodiments, the system can include instructions executable by the processor to cause the processor to: generate an alert in response to a shape of the first border or a loss of calibration feature tracking.

In one embodiment, one or more filter kernels are configured to identify one or more intensity patterns or data collection probe features including without limitation: a calibration feature such as an intensity pattern from an annular doped region of a sheath, a region of low intensity such as a dark ring or band associated with a glass or other substantially non-reflective structure a reflection from a splice between a first section of an optical fiber and a second section of an optical fiber, a reflection from a potting layer, and a calibration feature disposed in the imaging field which is imaged at different locations as a probe rotates.

In one embodiment, a filter kernel can be applied on a per scan line basis. In one embodiment, a filter kernel can be configured to match a high or a low region of a ring along a given scan line. In one embodiment, the first section and the second section are sections of a sample arm of an interferometer. In one embodiment, the selection of a particular filter kernel is triggered based upon a thickness of a doped annular calibration feature. In one embodiment, a thickness of a doped annular calibration feature, a scattering particle concentration of a doped annular calibration feature, or other probe-specific calibration features can be encoded using a tag which can be read by a scanner and transmitted to a calibration software module for selecting a particular filter kernel in response to the encoded thickness. In one embodiment, the tag is a near field tag or an RFID tag. The scanner can be part of a probe interface unit in one embodiment.

In one embodiment, a filter kernel such as a convolution matrix is implemented as a matrix including rows and columns and elements configured to perform image processing for performing intensifying, sharpening, pattern identification, detection, tracking and other image processing tasks. The filter kernel can be used in various preprocessing and other processing stages to perform image processing on OCT image data or other image data. In one embodiment, the term “prefetch” means to obtain data from one source in advance of such data being requested or processed by another system or process. Notwithstanding the foregoing, the scope of the terms discussed herein is not intended to be limiting, but rather to clarify their usage and incorporate the broadest meaning of the terms as known to those of ordinary skill in the art.

In one embodiment, calibration of frames of image data can be performed after a pullback is complete using image processing techniques rather than using motor position to affect a calibration. In one embodiment, different optical fiber changes following a motor-based calibration can be handled in software and performed on a per frame basis. For example, error associated with optical fiber stretching or blood vessel movement, such as due to a heart muscle contraction, can be corrected for on a per frame basis using a continuous calibration processes such as an image processing module. Tracking of moving or otherwise deforming calibration features on a per frame basis and accounting for false signals that can mimic calibration features are embodiments of the invention.

In one embodiment, an elongate sheath having a substantially circular or elliptical cross-section is doped with a plurality of scattering elements in a pattern such as a ring, a band, or other annular region or multiple annular regions. An optical probe can be pulled back with respect to the doped sheath such that image frames of data are generated in which the appearance of the pattern of the doped region changes, moves, or deforms in one or more frames along the pullback.

In one embodiment, the elongate sheath is configured to transmit light suitable for generating an image of a blood vessel or a component thereof. In one embodiment, substantially circular or elliptical cross-section includes a first substantially annular region that includes scattering elements and a second substantially annular region that is substantially free of scattering particles. In one embodiment, a calibration feature includes a ring that defines a first annular subset and a second annular subset. In one embodiment, the scattering particles are TiO2particles.

A calibration feature can include one or more filters use to track a one-dimensional or a two-dimensional feature that appears across a plurality of frames of image data. Optical signatures of catheters can be identified based on the back scattering signals received from calibration features or other sheaths used in a probe.

