Patent Description:
Optical strain sensing is useful for measuring physical deformation of an optical fiber caused by, for example, the change in tension, compression, or temperature of the optical fiber. A multi-core optical fiber is composed of several independent waveguides or cores embedded within a single fiber. A continuous measure of strain along the length of a core can be derived by interpreting the optical response of the core using swept wavelength inteferometry. With knowledge of the relative positions of the cores along the length of the fiber, these independent strain signals may be combined to gain a measure of a strain profile applied to the multi-core optical fiber. The strain profile of the fiber is a measurement of applied bend strain, twist strain, and/or axial strain along the length of the fiber at a high (e.g., less than <NUM> micrometers) sample resolution. In a technique known as optical position and/or shape sensing detailed in commonly-assigned <CIT>, entitled "Optical Position and/or Shape Sensing", this strain profile information is used to reconstruct the three dimensional position of the fiber.

A tomographic optical system obtains virtual "slices" (a tomographic image) of specific cross-sections of a scanned object. These virtual slices allows a user to see inside an object (e.g., a human anatomical target) without physically cutting it. Tomography involves gathering projection data from multiple directions either transmitted through or reflected from an anatomical target. That projection data is then processed by a reconstruction algorithm to generate the virtual slices. Unfortunately, known tomography approaches require that each of the transmitter locations and detector locations is known with a high degree of accuracy and precision.

Commonly used forms of tomography include CAT scans, PET scans, and MRI scans. For example, CAT scans use multiple x-ray detectors at different locations to measure x-rays from x-ray transmitters located at many different positions. Since the CAT scan machine is large and outside of the anatomical target, it is a relatively easy task to determine the coordinates of these different positions very accurately and precisely.

Optical coherence tomography (OCT) uses visible or near-IR light instead of x-rays and uses reflected light instead of transmitted light. OCT, however, does not penetrate deeply into tissue, and typically, can only scan to a depth on the scale of millimeters, e.g., a few millimeters to a few centimeters. As a result of scanning depth limitations, it is necessary to place OCT probes inside an anatomical target in order to effectively scan tissue inside an anatomical target cavity. It would be desirable to be able to perform OCT scanning at greater depths. It would also be useful to have a greater OCT measuring range so that the surface of tissue can be located and probed from a distance.

Still further, it would be useful to be able to perform topographic measurements where the exterior surface of an anatomical target cavity (such the abdomen, lung, mouth, throat, nose, or ears) is measured. These measurements could then be used to register previously taken CAT scans (or PET scans or MRI scans) to a coordinate frame in which a surgeon is working to provide an "overlay" of the CAT scan image with the currently visible tissue.

Although the distance of a reflection from an OCT source and the relative angle between measurements as a mirror is scanned or a fiber is rotated can be determined, it is difficult to determine the absolution position and angle of the source. Machines such as a "FaroArm" use multiple hinged segments with high-resolution encoders to measure three dimensional locations and angles. But FaroArm machines, like CAT, PET, and MRI machines, are too large to be placed inside a human anatomical target and are even too intrusive to be used outside of the anatomical target in an operating room.

<CIT>discloses a method for measuring bending. The method includes receiving a reflected signal from a strain sensor provided on an optical fiber; determining a spectral profile of the reflected signal; and determining bending of the optical fiber based on a comparison of the spectral profile of the reflected signal with a predetermined spectral profile. <CIT> discloses robust and portable system, apparatus and method for imaging subsurface of specimens. We have described a modular OCDR-OCT system and OFDR-OCT system to obtain high quality images. The instant application also discusses proprietary algorithms that have been modified from existing algorithms and their use as a combination to suit a particular system. The imaging of stationary, moving and combination of both subsurface structures such as retina for diabetic patients is described. Further, <CIT>) discloses another OFDR probe comprising a multi-core optical fiber <NUM> which is split into multiple single-core optical fibers <NUM>, <NUM>. It fails to disclose a combination of single core fibers and multi-core fibers in the same housing.

The inventors recognized that shape sensing fiber and a fiber shape measurement system can be used to provide the desired measurements identified in the introduction with a high degree of accuracy using a small, inexpensive, and unobtrusive device (e.g., a <NUM> micron diameter optical fiber). The technology described in this application uses shape sensing fiber and a fiber shape measurement system to generate information concerning the distribution of tissue at and around an area in which a surgeon is operating. The technology may also perform three dimensional scanning outside and/or inside an anatomical target to map tissue surfaces and/or identify sub-surface features.

The technology described in this application provides three dimensional scanning inside and/or outside a human, animal, or other organic or inorganic anatomical target using a paired shape sensing fiber and single-core fiber. The shape sensing fiber provides position and orientation information, and the single-core fiber provides distance or range information to the point(s) on or in the anatomical target being scanned.

The shape sensing fiber allows for the precise determination of the location and pointing direction of the single-core fiber optical transmitter inside or outside an anatomical target using optical frequency domain reflectometry (OFDR) technology. The single-core fiber optical transmitter includes a collimator at its transmitting (distal) end and provides a distance to a current point in or on the anatomical target from light back-scattered into the collimator and processed using OFDR. The position of the current point in or on the anatomical target in three dimensions can be obtained because both the three dimensional position and pointing direction (which can be expressed as a pointing angle, through some other measurement, etc.) of the single-core fiber optical transmitter are known from the shape sensing fiber and the distance from the fiber tip to a current point in or on the anatomical target is known from the single-core fiber. An example reflection-based tomography embodiment of this technology is now described.

<FIG> shows an example cross section of a multi-core shape sensing fiber <NUM> including four optical cores A-D with core B being a center core and cores A, C, and D spaced around core B. <FIG> shows an example cross section of a single-core distance or range sensing fiber <NUM> with a single optical core E.

The single core E may be paired with the multiple cores A-D by including it within the shape sensing fiber <NUM>, such as near the core B or elsewhere in the shape sensing fiber <NUM>. In some instances, the single core E may be included in its own fiber <NUM> that is positioned next to the shape sensing fiber <NUM> in use. An example situation that favors the former approach that includes core E in shape sensing fiber <NUM> is where an integrated fiber is desired for physical dimensions, for alignment between the cores A-E, to provide one fiber to the user of the system, etc. An example situation that favors the latter pairing that configures core E in a fiber <NUM> separate from cores A-D in a fiber <NUM> is when it is preferred for optics for core E; for example, in some configurations, it can be difficult to provide an acceptable termination at the end of the shape sensing fiber <NUM> when the single core E has, or is configured with, collimating optics. Example embodiments below assume a two fiber pair in discussion for ease of description, and these techniques are also applicable to single fiber configurations.

To perform the distance/ranging measurement provided by the single core E, an example embodiment collimates the light transmitted and received at the distal/pointing end of the single core E. Light collimation may be accomplished in a number of ways. One example is shown in <FIG> where the end of the fiber <NUM> is melted and allowed to form a curved surface <NUM> approximating a convex lens that tends to collimate the light (collimated beam <NUM>). This collimator configuration is inexpensive, easy, and small, but not necessarily as effective as other collimators and may or may not be sufficient for particular applications depending on the details of the lens formation process.

<FIG> illustrate example collimators that may be more effective than the one for the example shown in <FIG> shows a micro GRIN (gradient-index) lens <NUM> collimator with its collimated beam <NUM>, and <FIG> shows a ball-lens-type collimator <NUM> with its collimated beam <NUM>.

The single-core fiber <NUM> may be bonded, for example, to the multicore shape sensing fiber <NUM> at their respective ends such that all six degrees of freedom (x, y, z, roll, pitch, and yaw) of the single-core fiber <NUM> may be determined from the multicore shape sensing fiber <NUM> to provide the position and pointing direction (e.g. as a pointing angle, some other measurement, etc.) of the distal end. <FIG> shows an example of a multi-core shape sensing fiber positioned together with a single-core fiber <NUM> having a collimator <NUM>. Together they are referred to as the fiber pair.

According to the invention, the paired fibers <NUM> and <NUM> are embedded in a fiber housing that is inserted into a cavity inside of an anatomical target. <FIG> shows an example. The two fibers <NUM> and <NUM> are included inside of a fiber housing <NUM>, positioned inside a cavity <NUM> of an anatomical target <NUM>. Examples of fiber housing <NUM> include a catheter, a lumen of the catheter, a non-catheter housing, and the like. The light exiting the single-core fiber <NUM> with collimation encounters an interior anatomical target surface <NUM> at a current point and scatters. Some of the scatter will be Lambertian (omnidirectional), and a portion of this light scatters back into the collimating optics associated with the fiber <NUM> and travels back through the single core E of the fiber <NUM>. Although losses may be negligible or significant, OFDR is very sensitive, and the sensing system can be designed such that back scatter is sufficient to resolve the anatomical target surface or sub-surface using OFDR.

<FIG> illustrates an example graph of a time domain response of light sent through the single core fiber <NUM> and into the anatomical target <NUM>. The time delay from the reflection at the collimator <NUM> to the first large reflection is an indication of the distance from the end of the single core fiber <NUM> to the first anatomical target surface. The speed of light in air "c" is used to convert the measured round trip time delay into the distance L from the distal end of the single core fiber <NUM> to the first tissue surface, where the delay = <NUM>/c, c being the speed of light.

<FIG> illustrates in a two-axis coordinate plane an example determination of a reflection point on the surface <NUM> of the anatomical target using: coordinate and orientation information from the multicore shape sensing fiber <NUM>, and distance information from the single core fiber <NUM>. The illustration of <FIG> is similar to a two-dimensional mapping of the example shown in <FIG>. The position and angle of the single core fiber <NUM> tip (distal end) can be determined using the shape sensing fiber <NUM> and the distance from the fiber pair tip to the reflecting point (p,q). The position and angle information of the single core fiber <NUM> tip can be used in determining the location in space of the reflecting point in the anatomical target. In <FIG>, the fiber housing <NUM> is shown moved to four different positions P1-P4 in a scan operation. An actuator such as a robotic arm (e.g., see robotic arm <NUM> of <FIG>) may be controlled to move the fiber housing <NUM> into the anatomical target cavity <NUM> and to point the tip of the fiber housing <NUM> at the different positions P1-P4. Pointing position P2 has a vertical coordinate y and a horizontal coordinate x. A pointing direction is expressed as a pointing angle θ in the x-y plane, and the length from the tip of the fiber housing <NUM> to the current point p, q on the surface <NUM> of the anatomical target is shown as L. In various examples, θ is determined from information obtained from the shape sensing fiber <NUM>, and L is determined as discussed above in conjunction with <FIG>.

<FIG> is like <FIG> and shows multiple positions P1-P4 and orientations of the fiber housing <NUM> tip used to locate multiple points on interior target surface <NUM> of the anatomical target <NUM>.

Appropriate scanning the fiber housing <NUM> tip through different positions and angles generates a three dimensional data set of the scattering surface(s). The three dimensional data set of the scattering surface(s) may be used to generate a three dimensional map of those surface(s) and/or may be used for navigation inside the anatomical target <NUM>.

<FIG> illustrates an example of scatter from surface <NUM> and subsurface <NUM> features of the anatomical target <NUM>. A time domain reflection graph of reflection power v. time delay shown in <FIG> shows detected subsurface scattering beyond the initial tissue surface <NUM>. In various examples, light with a wavelength of <NUM> micron should be able to penetrate several millimeters into the anatomical target tissue and can be used to determine the anatomy beneath the scanned surface <NUM>. Maps of sub-surface features may be generated using a process similar to the process used to find the tissue surface while also accounting for the index of refraction differences within the tissue which cause the collimated beam to refract (bend) and changes the speed of light.

<FIG> is a flowchart illustrating example OFDR-based tomography procedures for determining a location in <NUM>-dimensional space of a reflection point in an anatomical target using the fiber pair and an example OFDR-based distributed strain measurement system. A single-core fiber and collimator are positioned adjacent to the distal end of a multicore shape sensing fiber (step S1). The fiber pair (of the single-core and multicore fibers) is included in a fiber housing (e.g., a lumen of a catheter), and positioned so that the collimated light can exit the end of the fiber housing towards a current point in or on the anatomical target (step S2). Collimated light is projected over a range of multiple frequencies from the single core to the current point in or on the anatomical target (step S3). A distance Lreflection from the tip of the fiber housing to the current point in or on the anatomical target is determined based on return reflections from the end of the fiber housing using an OFDR system and the single-core fiber (see <FIG>) (step S4). Light is also projected, over a range of multiple frequencies, through the multiple shape sensing cores of the multicore shape sensing fiber to the distal end of the fiber housing (step S5). The three dimensional position <MAT> and pointing direction of fiber housing tip are measured using the multicore shape sensing fiber and a multichannel OFDR system (step S6). The pointing direction can be expressed as a unit vector v̂ (magnitude of <NUM> and pointing in the direction of the collimator) (step S7). The vector v̂ is multiplied by the distance Lreflection measured to the reflection point (step S8). This new vector is added to the position of the multicore fiber distal end: <MAT> and gives the location in <NUM> dimensional space of the reflection point (step S9). Determining many locations using this procedure maps out the surface of the anatomical target or cavity. If data from beyond the surface of the anatomical target or cavity (the interior of the tissue) is generated, then a tomographic map may be constructed that is a three dimensional description of the subsurface tissue.

Some technical description of single channel and multichannel OFDR system operation which are used to implement OFDR-based tomography is now provided in conjunction with <FIG>. <FIG> shows an example single channel OFDR-based distributed measurement system that includes a tunable light source <NUM> optically coupled to an interferometric interrogator <NUM> and a laser monitor network <NUM>. A fiber optic sensor comprising a sensing fiber <NUM> is coupled via a circulator to the measurement arm of the interferometric interrogator <NUM>. The reference and measurement arms of the interferometric interrogator <NUM> and the outputs from the laser monitor network <NUM> are coupled to photodiode detectors connected to data acquisition electronics <NUM>. The measurement data is provided from the data acquisition electronics <NUM> to a system controller data processor <NUM>. A single channel corresponds to a single fiber core.

<FIG> is a flowchart illustrating example procedures for operating the OFDR-based distributed measurement system in <FIG>. During an OFDR measurement, a tunable light source <NUM> is swept through a range of optical frequencies (step S11). This light is split with the use of optical couplers and routed to two separate interferometers. The first interferometer serves as an interferometric interrogator <NUM> and is connected to a length of sensing fiber <NUM>. Light enters the sensing fiber <NUM> through the measurement arm of the interferometric interrogator <NUM> (step S12). Scattered light from the sensing fiber <NUM> is then interfered with light that has traveled along the reference arm of the interferometric interrogator <NUM> (step S13). The laser monitor network <NUM> contains a Hydrogen Cyanide (HCN) gas cell that provides an absolute wavelength reference throughout the measurement scan (step S14). A second interferometer, within a laser monitor network <NUM>, is used to measure fluctuations in tuning rate as the light source is scanned through a frequency range (step S15). A series of optical detectors (e.g., photodiodes or other optical detectors) convert the light signals from the laser monitor network <NUM>, gas cell, and the interference pattern from the sensing fiber <NUM> to electrical signals (step S16).

A data processor in a data acquisition unit <NUM> uses the information from the laser monitor network <NUM> interferometer to resample the detected interference pattern of the sensing fiber <NUM> so that the pattern possesses increments constant in optical frequency (step S17). This step is a mathematical requisite of the Fourier transform operation in examples. Once resampled, a Fourier transform is performed by the system controller <NUM> to produce a light scatter signal in the temporal domain (step S18). In the temporal domain, the amplitudes of the light scattering events can be depicted as a function of delay along the length of the fiber.

Using the distance that light travels in a given increment of time, this delay can be converted to a measure of length along the sensing fiber <NUM>. In other words, the light scatter signal indicates each scattering event as a function of distance along the fiber. The sampling period is referred to as the spatial resolution and is inversely proportional to the frequency range that the tunable light source <NUM> was swept through during the measurement.

As the fiber <NUM> is strained, the local light scatters shift as part or all of the fiber <NUM> changes in physical length. These distortions are highly repeatable. Hence, an OFDR measurement of detected light scatter for the fiber <NUM> can be retained in memory that serves as a reference pattern of the fiber in an unstrained state. A subsequently measured scatter signal when the fiber <NUM> is under strain may then be compared to this reference pattern by the system controller <NUM> to gain a measure of shift in delay of the local scatters along the length of the sensing fiber <NUM> (step S19). This shift in delay manifests as a continuous, slowly varying optical phase signal when compared against the reference scatter pattern. The derivative of this optical phase signal is directly proportional to change in physical length of the sensing core of the sensing fiber <NUM> (step S20).

Change in physical length is useful to measure a number of different parameters, e.g., it may be scaled to strain producing a continuous measurement of strain along the sensing fiber. The high resolution and high sensitivity required to make these measurements of a fiber core allow the OFDR system to make very sensitive and high resolution measurements of scattering events that take place in media other than optical fibers, such as tissue surfaces and sub-surfaces.

<FIG> shows an example reflection OFDR-based tomography system which is similar to the single channel OFDR-based distributed sensing system in <FIG> but uses multiple channels and a single-core distance/ranging fiber along with a multicore shape sensing fiber. A reflection based OFDR shape sensing system is described in detail in commonly-assigned <CIT>.

Instead of one interferometric interrogator as in <FIG>, there are four interferometric interrogators referenced generally at <NUM> corresponding to four core waveguides A, B, C, and D in the fiber. Although the term "core" is used below, the technology applies to other types of waveguides that can be used in a spun fiber. Each of the interferometric interrogators is connected to the tunable light source <NUM> via optical couplers. Each independent waveguide core within the multi-core optical fiber is then connected to an interferometric interrogator channel. Each pairing of an interferometric interrogator channel with a core in the multi-core fiber <NUM> or the single-core fiber <NUM> is referred to as an acquisition channel. As the tunable light source <NUM> is swept through a range of frequencies, each acquisition channel is simultaneously measured, and the resulting interference pattern from each channel is routed to the data acquisition electronics <NUM> adapted for the additional interferometers. Each channel is processed independently and identically as described in the flowchart in <FIG>. The system controller data processor <NUM> interprets the signals of the four optical cores and produces a measurement of both position and orientation along the length of the shape sensing fiber <NUM>. The measurement data is then exported from the system controller for display <NUM> and/or other use, such as correlating position for single core fiber <NUM>.

Shape sensing using a multi-core fiber includes detecting a total change in optical length in ones of the cores in the multi-core fiber that reflects an accumulation of all of the changes in optical length for multiple fiber segment lengths up to a point on the multi-core fiber. A location and pointing direction at that point on the multi-core fiber is then determined based on the detected total change in optical length. The data from the single-core fiber channel is processed similarly to the data for each of the shape sensing cores up to the step in which the time-domain response is calculated (S18 in <FIG>). After this step, the data from the single-core fiber is used to determine the distance to any detected reflection as illustrated in <FIG>.

Returning to the human or animal anatomical target example described above, if a portion of tissue is observed over time, then motion due to breathing or changes in blood pressure (e.g., due to heart beat) is detectable in some examples as relative optical phase shifts in the OFDR signal. Since the interrogator network can perform measurements at rates much higher than breathing or heartbeat rates, these variations can be measured by observing the phase changes through scans and between scans. For example, changes in path-length as small as <NUM> can be measured in some examples. Also, measuring OFDR data in both directions of a tunable laser sweep allows detection of relative constant motion (e.g., blood flowing in an artery) due to its Doppler shift. If a reflection is moving toward the source (the tip of the fiber), then the reflection will appear closer than its actual distance when the laser is sweeping up, and the reflection will appear farther than its actual distance when the laser is sweeping down. The scatter pattern from an arterial blood flow, for example, will therefore appear to alternate between two apparent positions, centered about the actual position. By measuring the distance between these two scatter patterns from the up and down scan, and by knowing what the laser sweep rates, the velocity of the scatterer (i.e., the flowing blood) may be calculated.

An example transmission-based tomography example of the technology is now described. <FIG> illustrates a simplified example of a transmission-based OFDR tomography system. The fiber housing <NUM> is inserted into an anatomical target cavity and moved to a plurality of different positions (five are shown as P1-P5). The interior surface <NUM> of the anatomical target <NUM> includes a subsurface feature <NUM>. Multiple receiving fibers <NUM> are shown on the opposite surface or outside the anatomical target. Each receiver fiber <NUM> can be an individual channel as shown in <FIG> where the location is determined using a suitable method. The single-core fiber <NUM> in the fiber housing <NUM> functions as a point transmitter. As the fiber housing <NUM> moves to different positions, light from different origination points P1-P5 travels through the tissue to arrive at one or more of the multiple detecting fibers <NUM>. These detecting fibers <NUM> collect light into a single-core that then directs the light for OFDR interferometric detection via photodiodes <NUM>. The interferometric detection allows highly sensitive detection of the light and allows the transit time from the single-core fiber <NUM> to be precisely measured using the swept wavelength processing described in <FIG> (S11-S18) except that S13 is changed so that light transmitted from the source fiber to the receiving fiber is interfered with light that has travelled through the reference path of the interrogator. This processing results in measurement of the amplitude and the delay through the path. By measuring the time of flight between the transmitting single-core fiber <NUM> and each receiving single-core fiber <NUM>, and by knowing the locations of all of the transmitting and receiving positions, the average group index along the path connecting the transmitting fiber <NUM> and the detecting fibers <NUM> is measured. The average group index can be calculated by dividing the measured delay between the transmitter and each detector by the delay calculated by dividing the distance between the transmitter and detector by the speed of light in a vacuum. Light that has been multiply scattered can be distinguished from light that takes the direct path to the detector based on the arrival time of the light. By making measurements at multiple locations P1-P5, a three dimensional distribution of the group index of the tissue may be reconstructed.

<FIG> illustrates an example single-transmitter/single-receiver transmission-based tomography system where a single-transmitter/single-receiver fiber pair is moved to different scanning positions. <FIG> shows two such single-transmitter/single-receiver pairs. Specifically, <FIG> shows two multicore shape sensing networks A and B that share a tunable light source <NUM>, laser monitor network <NUM>, and system controller <NUM>. In addition, there is a single interferometric channel where the transmitter single-core fiber 12A is associated with one multicore shape sensing fiber 10A, and the receiver single-core fiber 12B is associated with the other multicore shape sensing fiber 10B. Because the associated transmitter and receiver fibers remain the same length as their respective tip locations are moved around, any changes in light travel time through the transmitter fibers, the space being probed, and the receiving fibers are due to changes in the time-of-flight between the transmitter and receiver fiber tips.

<FIG> shows an example robotic application of an OFDR-based tomography system in a surgical context. A surgical robot <NUM> includes a robotic arm <NUM> coupled to fiber housing (e.g., a catheter or other fiber housing) <NUM> inserted through an incision <NUM> in an anatomy <NUM> into an anatomical target cavity <NUM>. The robot <NUM> includes actuators and control circuitry (not shown) for moving the arm <NUM> and fiber housing <NUM> to effect the surgical procedure. The surgeon can control the fiber housing <NUM> position and pointing direction and, by sweeping the pointing direction of the fiber housing appropriately, map out one or more surfaces, such as surface <NUM>, of the tissue. Alternatively, the scan could be computer controlled and sweep out an orderly raster scan or other scan pattern. In either case, an accurate map of some or all of the dimensions of the cavity <NUM> can be determined. In some examples, subsurface scatter events can measure and present other features not readily visible with normal image techniques to the surgeon or other personnel as overlays.

<FIG> shows side and front view of another example application of the OFDR-based tomography technology to determine a location of an anatomical target in space. Here, the exterior surface <NUM> of a patient <NUM> is measured using one or more OFDR sensing fibers <NUM> (three are shown in <FIG>). Once an accurate measurement of the surface <NUM> of the patient's anatomical target is made in a known coordinate system (i.e. the coordinate system that a surgical robot is working in), then previously-taken CAT scans, PET scans, and/or MRI scans can be registered against the measured patient surface <NUM> and brought into the known coordinate system. Because infrared light can pass through many textiles, a patient may be clothed and/or under a sheet when these measurements are made.

The above description sets forth specific details, such as particular embodiments for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other embodiments may be employed apart from these specific details. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using optical components, electronic components, hardware circuitry (e.g., analog and/or discrete logic gates interconnected to perform a specialized function, ASICs, PLAs, etc.), and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Moreover, certain aspects of the technology may additionally be considered to be embodied entirely within any form of computer-readable memory, such as, for example, solid-state memory, magnetic disk, optical disk, etc. containing an appropriate set of computer instructions that may be executed by a processor to carry out the techniques described herein.

The term "signal" as used herein to encompass any signal that transfers information from one position or region to another in an electrical, electronic, electromagnetic, optical, or magnetic form. Signals may be conducted from one position or region to another by electrical, optical, or magnetic conductors including via waveguides, but the broad scope of electrical signals also includes light and other electromagnetic forms of signals (e.g., infrared, radio, etc.) and other signals transferred through non-conductive regions due to electrical, electronic, electromagnetic, or magnetic effects, e.g., wirelessly. In general, the broad category of signals includes both analog and digital signals and both wired and wireless mediums. An analog signal includes information in the form of a continuously variable physical quantity, such as voltage; a digital electrical signal, in contrast, includes information in the form of discrete values of a physical characteristic, which could also be, for example, voltage.

Unless the context indicates otherwise, the terms "circuitry" and "circuit" refer to structures in which one or more electronic components have sufficient electrical connections to operate together or in a related manner. In some instances, an item of circuitry can include more than one circuit. A "processor" is a collection of electrical circuits that may be termed as a processing circuit or processing circuitry and may sometimes include hardware and software components. In this context, software refers to stored or transmitted data that controls operation of the processor or that is accessed by the processor while operating, and hardware refers to components that store, transmit, and operate on the data. The distinction between software and hardware is not always clear-cut, however, because some components share characteristics of both. A given processor-implemented software component can often be replaced by an equivalent hardware component without significantly changing operation of circuitry, and a given hardware component can similarly be replaced by equivalent processor operations controlled by software.

Hardware implementations of certain aspects may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g., digital or analog) circuitry including but not limited to application specific integrated circuit(s) (ASIC) and/or field programmable gate array(s) (FPGA(s)), and (where appropriate) state machines capable of performing such functions.

Circuitry can be described structurally based on its configured operation or other characteristics. For example, circuitry that is configured to perform control operations is sometimes referred to herein as control circuitry and circuitry that is configured to perform processing operations is sometimes referred to herein as processing circuitry.

In terms of computer implementation, a computer is generally understood to comprise one or more processors or one or more controllers, and the terms computer, processor, and controller may be employed interchangeably. When provided by a computer, processor, or controller, the functions may be provided by a single dedicated computer or processor or controller, by a single shared computer or processor or controller, or by a plurality of individual computers or processors or controllers, some of which may be shared or distributed.

Claim 1:
A method of operating an interferometric system to use multiple shape-sensing optical cores (A, B, C, D) and a single optical core (E) in a fiber housing (<NUM>) to generate a three-dimensional data set for at least a portion of an anatomical target (<NUM>) based on distance measurements of multiple points of the target (<NUM>) from a distal end of the fiber housing (<NUM>) and measurements of respective three-dimensional positions and pointing directions of the distal end, the multiple shape-sensing optical cores (A, B, C, D) located alongside the single optical core (E), the method comprising:
(a) projecting, over a first range of multiple frequencies, collimated light from the single optical core (E) to a current point of a target (<NUM>) while the distal end of the fiber housing (<NUM>) is directed toward the current point;
(b) using optical frequency domain reflectometry to detect reflected light scattered from the current point and to process the reflected light to determine a distance of the distal end to the current point;
(c) projecting, over a second range of multiple frequencies, light through the multiple shape-sensing optical cores (A, B, C, D) to the distal end of the fiber housing (<NUM>);
(d) using optical frequency domain reflectometry to obtain a measurement of light reflected from the distal end of the fiber housing (<NUM>) back through the multiple shape-sensing optical cores (A, B, C, D) and to process the measurement of light reflected to determine a position in three-dimensional space of the distal end of the fiber housing (<NUM>) and a pointing direction of the distal end of the fiber housing (<NUM>);
(e) using the determined position in three-dimensional space of the distal end of the fiber housing (<NUM>), the pointing direction of the distal end of the fiber housing (<NUM>), and the determined distance to determine a position in three-dimensional space of the current point; and
repeating (a)-(e) multiple times for multiple additional current points of the target (<NUM>) to generate the three-dimensional data set for at least the portion of the target (<NUM>),
wherein, to generate the three-dimensional data set, the single optical core is used to determine distances of the distal end to the multiple points of the target, and wherein generating the three-dimensional data set requires combining the distances with the respective three-dimensional positions and pointing directions of the distal end.