U.S. patent application number 14/220417 was filed with the patent office on 2014-09-25 for optical coherence tomography with multiple sample arms.
The applicant listed for this patent is Jeffrey Brennan, Sean Caffey, Mark S. Humayun. Invention is credited to Jeffrey Brennan, Sean Caffey, Mark S. Humayun.
Application Number | 20140285811 14/220417 |
Document ID | / |
Family ID | 44628930 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140285811 |
Kind Code |
A1 |
Brennan; Jeffrey ; et
al. |
September 25, 2014 |
OPTICAL COHERENCE TOMOGRAPHY WITH MULTIPLE SAMPLE ARMS
Abstract
A multiplexed OCT imaging system includes a plurality of sample
arms, an imaging engine, and an optical controller. The sample arms
are optically coupled to the imaging engine via the optical
controller; the optical controller multiplexes optical signals from
the sample arms to permit some of the sample arms to operate
sequentially or simultaneously.
Inventors: |
Brennan; Jeffrey; (Los
Angeles, CA) ; Humayun; Mark S.; (Glendale, CA)
; Caffey; Sean; (Hawthorne, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Brennan; Jeffrey
Humayun; Mark S.
Caffey; Sean |
Los Angeles
Glendale
Hawthorne |
CA
CA
CA |
US
US
US |
|
|
Family ID: |
44628930 |
Appl. No.: |
14/220417 |
Filed: |
March 20, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13106388 |
May 12, 2011 |
8711364 |
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14220417 |
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13106391 |
May 12, 2011 |
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13106388 |
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13106393 |
May 12, 2011 |
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13106391 |
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Current U.S.
Class: |
356/479 |
Current CPC
Class: |
H04J 14/02 20130101;
A61B 2562/0233 20130101; A61B 5/04001 20130101; G01B 9/02016
20130101; A61B 5/0073 20130101; G01B 9/02091 20130101; G01N 21/4795
20130101; G01B 9/02027 20130101; G01B 9/02007 20130101; A61B
2562/063 20130101; A61B 3/102 20130101; A61B 5/0066 20130101; A61B
2562/043 20130101; A61F 2009/00851 20130101; G01B 9/02028 20130101;
A61N 1/0551 20130101; A61N 1/3605 20130101; A61N 1/0529
20130101 |
Class at
Publication: |
356/479 |
International
Class: |
G01B 9/02 20060101
G01B009/02 |
Claims
1. A multiplexed OCT imaging system comprising: a plurality of
sample arms; at least one imaging engine; and an optical
controller, wherein the sample arms are optically coupled to the at
least one imaging engine via the optical controller, the optical
controller multiplexing optical signals from the sample arms to
permit at least some of the sample arms to operate simultaneously
and activating a new imaging engine upon detecting a new sample arm
coupled to the newly activated imaging engine.
2. The imaging system of claim 1, wherein the activation occurs
upon a detection of a demand issued by a user.
3. The imaging system of claim 1, wherein the optical controller is
a switch matrix balancing loads among activated imaging engines to
minimize the number of image-engine activations.
4. The imaging system of claim 1, wherein the at least one imaging
engine comprises a broadband light source.
5. The imaging system of claim 4, wherein the at least one imaging
engine further comprises a spectrometer-based OCT interferometer
for separating different bands of the broadband light within the
sample arms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/106,388 (filed on May 12, 2011), Ser. No.
13/106,391 (filed on May 12, 2011), and Ser. No. 13/106,393 (filed
on May 12, 2011), and also claims priority to and the benefit of
U.S. Provisional Patent Application No. 61/334,364, filed on May
13, 2010. The foregoing applications are incorporated herein by
reference in their entireties.
TECHNICAL FIELD
[0002] In various embodiments, the present invention relates
generally to optical coherence tomography (OCT) imaging systems for
use in various medical and veterinary applications.
BACKGROUND
[0003] Advances in the development of novel diagnostic
techniques--including new or improved imaging modalities--provide
surgeons with more information and a better understanding of the
area being treated. This enables surgeon to collect, for example,
real-time and non-destructive biopsies including analysis of
regions that are typically difficult to access. These innovations
have resulted in significant improvements in diagnostic evaluation,
treatment options, and patient outcomes for a variety of
maladies.
[0004] One such useful diagnostic technique is optical coherence
tomography (OCT), an interferometric technique utilizing light
(typically infrared) for noninvasive diagnosis and imaging. OCT is
used to obtain sub-surface images of translucent or opaque
materials at a resolution equivalent to a low-power microscope. OCT
provides tissue morphology imagery at much higher resolution
(better than 10 .mu.m) than other imaging modalities such as MRI or
ultrasound. OCT has transformed the field of ophthalmology and
promises to have a similar impact on a variety of other medical
specialties. A particular mode of OCT, termed "A-scan," provides
one-dimensional axial depth scans of the tissue of interest, thus
providing information on the identity, size, and depth of
subsurface features. A series of spatially adjacent A-scans
(typically lying in a straight line) may be combined to form a
two-dimensional reconstructed image of the imaged area (termed a
"B-scan"), offering surgeons a visual reconstruction of subsurface
features. Likewise, three-dimensional (3D) images, termed
"C-scans," may be formed by "stacking" multiple B-scans.
[0005] OCT systems have become a mainstay in hospitals and
ophthalmology clinics for diagnostic evaluation and imaging
purposes. Despite the clear benefit of the technology to the health
and treatment of the patient, the cost of an OCT system often
prohibits hospitals and clinics from purchasing a sufficient number
of OCT systems to accommodate patient demand. This resource
limitation creates a bottleneck that complicates the examination
process, slows patient throughput, and ultimately reduces the
productivity of the medical staff.
[0006] Consequently, there is an urgent need for OCT systems that
can handle multiple patients simultaneously or nearly so, thereby
reducing costs and increasing patient throughput.
SUMMARY
[0007] In various embodiments, the present invention relates to OCT
systems and methods for performing multiple scans in a multiplexed
fashion. Such OCT systems and methods may sequentially or
simultaneously generate images of the multiple targets through
information collected from the sample arms. The invention thereby
permits high patient throughput by permitting treatment using
multiple OCT probes whose outputs are handled simultaneously or
sequentially. In various embodiments, sequential handling of OCT
output occurs quickly enough that each clinician using an OCT probe
does not experience significant delay.
[0008] Accordingly, in one aspect, the invention pertains to a
multiplexed OCT imaging system comprising a plurality of sample
arms (i.e., OCT probes), at least one imaging engine, and an
optical controller. In various embodiments, the sample arms are
optically coupled to the imaging engine(s) via the optical
controller, which multiplexes optical signals from the sample arms
to permit at least some of them to operate sequentially or
simultaneously. In some embodiments, the sample arms comprise
optical fibers for transmitting light between the at least one
imaging engine and a plurality of targets. For example, the optical
fibers may be single-mode optical fibers.
[0009] In some embodiments, the system comprises display hardware
associated with each sample arm to display images of the target of
interest. In various implementations, the display hardware connects
to the imaging engine(s) directly or via a local area network.
[0010] In some embodiments, the imaging engine(s) comprise(s) a
reference arm for generating an interference pattern with respect
to the radiation from the sample arm. This interference pattern
results from the difference in optical path-length or phase between
the reference arm and the sample arm and encodes the depth
information. In various embodiments, a mechanical element is
included to adjust the relative position between the reference arm
and the sample arm. Alternatively, an optical component may be
included to auto-match the optical path-lengths between the
reference arm and the sample arm. The sample arm and reference arm
may share a common beam path with respect to a target.
[0011] In some embodiments, the optical controller, for example,
may be an optical switch, a time-division multiplexer, or a
wavelength-division multiplexer; the wavelength-division
multiplexer may comprise interference or thin film filters for
avoiding overlapping wavelengths between each sample arm.
[0012] The optical controller may activate a new imaging engine
upon detecting a new sample arm; such activation may occur upon the
detection of a demand issued by a user. For example, the optical
controller may be a switch matrix that balances loads among
activated imaging engines in order to minimize the number of
image-engine activations.
[0013] In some embodiments, the imaging engine(s) of the system
comprise(s) a broadband light source and a spectrometer-based OCT
interferometer to separate different bands of the broadband light
within the sample arms.
[0014] In a second aspect, the invention relates to a method of
using a multiplexed OCT imaging system to provide a plurality of
images. In various embodiments, the method comprises emitting light
from each of a plurality of light sources upon one of a plurality
of targets and collecting reflected light from each target, and
sequentially or simultaneously generating OCT images. Each image is
associated with one of the plurality of targets based on the
reflected light.
[0015] In some embodiments, the method further comprises emitting
reference light from the light source upon a reference plane, and
generating OCT images comprises processing and reconstructing
interference patterns between the reflected light from each target
and reflected light from the reference plane. In various
implementations, light is emitted onto the targets sequentially
and/or simultaneously to produce a plurality of OCT signals, which
are multiplexed. The multiplexing may be, for example,
wavelength-division multiplexing or time-division multiplexing.
[0016] These and other objects, along with advantages and features
of the present invention herein disclosed, will become more
apparent through reference to the following description, the
accompanying drawings, and the claims. Furthermore, it is to be
understood that the features of the various embodiments described
herein are not mutually exclusive and can exist in various
combinations and permutations.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the drawings, like reference characters generally refer
to the same parts throughout the different views. Also, the
drawings are not necessarily to scale, with an emphasis instead
generally being placed upon illustrating the principles of the
invention. In the following description, various embodiments of the
present invention are described with reference to the following
drawings, in which:
[0018] FIG. 1 schematically depicts components of an OCT
interferometry system utilizing a swept-source light source, an
interferometer, a sample arm, a balanced photodetector, and data
acquisition and processing hardware.
[0019] FIG. 2 schematically depicts an OCT interferometry system
incorporating an OCT imaging engine and a remotely-located sample
arm.
[0020] FIGS. 3A and 3B schematically depict an OCT imaging system
with the imaging engine and the sample arm located in separate
rooms and with display and control interface available associated
with the sample arm via direct point-to-point electrical
connections and/or a local area network.
[0021] FIG. 4A schematically illustrates an OCT imaging system with
multiple sample arms installed with the imaging engine via an
optical controller. Each of the sample arms are located in
different rooms, separate from the imaging engine.
[0022] FIG. 4B illustrates an OCT imaging system incorporating
multiple imaging engines that couple the assembly arms via the
optical controller.
[0023] FIG. 4C illustrates an OCT imaging system with multiple
sample arms installed in different rooms, separate from the imaging
engine, with displays associated with the sample arm via direct
point-to-point electrical connections and/or a local area
network.
[0024] FIG. 4D illustrates a multiple-sample-arm configuration
using a wavelength-division multiplexer as an optical
controller.
[0025] FIG. 4E depicts a spectrometer used to separate the
wavelength components of a sample arm so that the separate
wavelength components can be sampled by individual sensors in an
array.
[0026] FIG. 4F depicts a single sample arm multiplexed into
multiple wavelength OCT systems.
[0027] FIG. 5A depicts the reference arm in an OCT imaging system
that incorporates a mechanical element for adjusting the reference
arm position to match light path lengths between the sample arms
and the reference arm. The multiple sample arms are connected to
the imaging engine via an optical controller.
[0028] FIG. 5B schematically depicts an interferometer
configuration in which the reference and sample arms share the same
beam path.
[0029] FIGS. 6A and 6B depict an OCT imaging system for providing
A-scan and B-scan images of the target, respectively.
[0030] FIGS. 7A and 7B illustrate an OCT imaging system for A-scan
and B-scan imaging, respectively, coupled to an optical
instrument.
[0031] FIG. 8A depicts a combination, including the scanning
system, the lens system, and the prism, attached on a swivel arm
and an arm assembly joint attached to a mechanical frame of an
optical instrument, thus enabling a user to easily move the OCT
imaging system in and out of the optical path.
[0032] FIG. 8B depicts a therapeutic laser associated with the OCT
imaging engine for providing simultaneous imaging and treatment of
the target.
[0033] FIG. 8C depicts an optical element mounted onto the light
source of the OCT imaging engine for providing illumination of the
target.
[0034] FIG. 9 illustrates the illumination system of a slit
lamp.
[0035] FIG. 10A illustrates the optics of an indirect
ophthalmoscope.
[0036] FIG. 10B illustrates an embodiment of a B-scan capable
OCT-enabled indirect ophthalmoscope.
[0037] FIG. 11 depicts the optical path and components in a typical
binocular microscope.
[0038] FIG. 12 illustrates an IOL showing the center point that may
be identified using OCT to locate and measure concentric ridges or
included fiducials.
[0039] FIG. 13A depicts the working principle of three-dimensional
displays.
[0040] FIG. 13B illustrates dual cameras and a single display
mounted above a supine patient.
[0041] FIG. 14A depicts an OCT-enabled electrode.
[0042] FIG. 14B depicts an OCT-enabled electrode array
incorporating an optical controller to multiplex signals from the
optical fibers.
[0043] FIG. 15 illustrates one particular use of an OCT-enabled
electrode array in brain tissue.
DETAILED DESCRIPTION
[0044] Optical coherence tomography (OCT) is an imaging methodology
that provides three-dimensional images of biological tissues at
sub-micrometer lateral and axial resolution. The advantages of OCT
include high imaging resolution, real-time imaging,
non-invasiveness, and compact size. FIG. 1 depicts an exemplary OCT
interferometry system 100 in accordance with embodiments of the
present invention, although alternative systems with similar
functionality are also within the scope of the invention. As
depicted, OCT interferometry system 100 includes a sample arm 110,
a reference arm 120, a light source 130, a photodetector 140, and
data-acquisition and processing hardware (or a "driver") 150. Light
from light source 130 (which may be, e.g., a swept-source or
tunable laser) travels through optical fibers to sample arm 110 and
reference arm 120. Via sample arm 110, the light illuminates a
sample of interest 160, which may include or consist essentially
of, e.g., biological tissue. In a typical medical imaging
application, the sample arm is the only component of the OCT
imaging system that requires contact with or close proximity to the
area to be imaged (e.g., the eye). Various features of interest of
sample 160 reflect the light in different amounts or from different
depths. The reflected light is combined with light reflected by
reference arm 120 (which typically includes or consists essentially
of a mirror), and the interference pattern thus generated provides
information about the spatial dimensions and location of structures
within sample 160. In OCT, an optical interferometer is used to
detect the reflected coherent light. Most light illuminating the
sample is scattered and no longer coherent with the light emitted
from the light source; therefore, the scattered light can be
effectively filtered out by the interferometer. On the other hand,
light reflected by structures in the sample remains coherent with
the light emitted from the light source and can thus be detected
and processed to create an OCT image.
[0045] Hardware 150 may be a personal-computer-(PC-) based
architecture, and may include a high-speed analog-to-digital
converter (for example, on a PCI bus) that digitizes the output of
photodetector 140 at a sampling rate ranging from several million
samples per second to several billion samples per second. In an
embodiment, the digitized data is processed by the PC processor and
readily available or straightforwardly implemented by software
that, e.g., performs a Fourier transform and signal processing and
reconstruction algorithms on the data. In another embodiment the
data processing is performed in dedicated hardware, e.g., an ASIC,
FPGA, DSP, or combination of these devices. The hardware and/or
associated software derives, e.g., reconstructed images, biometric
measurements, and/or quantitative data from the data produced by
OCT interferometry system 100.
Distributed OCT
[0046] Embodiments of the present invention provide a distributed
OCT imaging system utilizing a sample arm separated from a
remotely-located imaging engine, where the imaging engine includes
one or more of the following: a light source (e.g., a swept-source
laser or a super-luminescent light-emitting diode), an
interferometer (containing various optical components therein), a
reference arm, data-acquisition hardware, signal-processing
hardware, and/or display hardware (e.g., an LCD and driver). In
other words, some or all of these components may be located
remotely from the sample arm, but depending on the design and
application, one or more of these components may be co-located with
the sample arm.
[0047] The data-acquisition hardware and electronic-processing
hardware may be implemented utilizing off the-shelf-hardware such
as a PC, or they may be implemented in dedicated hardware, such as
an application-specific integrated circuit (ASIC),
field-programmable gate array (FPGA), digital signal processor
(DSP), graphical processing unit (GPU), or combination of these
devices. FIG. 2 depicts a sample arm 210 connected to a
remotely-located OCT imaging engine 220 by a length of optical
fiber 230, preferably a single-mode optical fiber. The separation
distance between the imaging engine 220 and the sample arm 210 may
vary and depends on the particular application. For example, in
some facilities the imaging engine and the sample arm may be
located in adjacent rooms, while in other facilities these will be
located on different floors or even different buildings. Utilizing
a single-mode fiber, separation distances of several hundred meters
or more are possible. For example, the sample arm 210 may be
located in an examination room of a doctor's clinic, while the
imaging engine 220 may be placed in another location (e.g., a
server room in the same building or an adjacent one), with the two
linked by an optical fiber 230, preferably single-mode to decrease
dispersive effects. Depending on the configuration, the imaging
engine may constitute the majority of bulk, weight, and noise
(e.g., from fans cooling the electronics) of the system, and it
therefore may be preferable to locate the imaging engine or
portions thereof in a more convenient or less conspicuous location.
Furthermore, locating the bulk of the OCT hardware in another
location may assist in maintaining a sterile field. The imaging
engine may be linked (e.g., via a wired or wireless computer
network) to a low-cost multi-purpose PC or alternate display
technology in the examination room for OCT imaging display
purposes.
[0048] Furthermore, the components that constitute the imaging
engine may be distributed across multiple locations. For example,
with reference to FIGS. 3A and 3B, the sample arm 310 may be
located in the examination room and linked via optical fiber 320 to
the light source 331, interferometer 332, and data-acquisition and
processing hardware 333 located in a second location, which is
electrically linked (e.g., via a direct point-to-point connection
340 or via a wired or wireless network, such as Ethernet 350) to
image-display hardware 360 and control interface 370 located in the
same examination room as the sample arm. In another embodiment, the
image-display hardware 360 and control interface 370 are located in
a separate third location.
Multiple Sample Arm OCT
[0049] Embodiments of the present invention provide an OCT imaging
system utilizing an interferometer with one or more sample arms
each including an optical assembly appropriate for the intended
application. In one embodiment, as illustrated in FIG. 4A, the
light source 401, interferometer 402, and related data-acquisition
and processing equipment 403 are located in a central area or room
405 and each of the multiple sample arms 410 is located in a
separate area 415. For example, each sample arm may be located in a
separate examination room outside area 405, but each sample arm is
linked to the same remotely-located OCT imaging engine 420. In
another embodiment, the multiple sample arms are located in the
same examination room. The multiple sample arms may be interfaced
to the interferometer via an optical controller 425.
[0050] In one embodiment, the optical controller 425 (e.g., a
wavelength-division multiplexer, a time-division multiplexer, or an
optical switch) multiplexes optical signals from the sample arms to
permit at least some of the sample arms to operate substantially
simultaneously and enables a doctor, clinician, or even automated
software to select which sample arm (i.e., which examination room)
is optically linked to the centralized imaging engine. (By
"substantially simultaneously" is meant, in this context, that
users of the sample arms do not experience clinically significant
latency, jitter or delay in the operation of the sample arm that
interferes with their ability to conduct an examination.) A
wavelength-division multiplexer (WDM) joins optical signals
together, i.e., it multiplexes multiple optical signals of
different wavelengths from the sample arms onto a single optical
fiber connected to the imaging engine. The wavelengths of the
multiplexed signals are band-separated sufficiently to avoid
interference or crosstalk. In time-division multiplexing (TDM), two
or more signals are transferred in an optical fiber, but are
partitioned among timeslices; that is, the signals physically "take
turns" on a divided time domain of the signal channel. Both WDM and
TDM enable multiplication of optical fiber capacity for
transmitting optical signals from sample arms simultaneously to one
or more imaging engines, and thus it is not necessary to optically
switch the sample arms into and out of the system.
[0051] As noted below, depending on the implementation, the amount
of time required to obtain an image with a sample arm--i.e., the
duration of the communication between the sample arm and the
imaging engine--may be small, i.e., on the order of seconds.
Moreover, most of the time involved in capturing an image is
expended in positioning and preparing the patient. As a result,
operational simultaneity among sample arms and true multiplexing
may not be necessary as a practical matter. Optical controller 425
may simply accord the various sample arms access to a single
imaging engine 420 on a sequential basis, or invoke additional
image-processing applications and balance loads as needed. So long
as no clinician experiences excessive delays, relatively
inexpensive systems configured for sequential operation can be
employed, and this operation may be substantially simultaneous as
understood herein.
[0052] In various embodiments, as depicted in FIG. 4B, more than
one imaging engine 420 may be deployed to handle the signals from
the multiple sample arms 410. How many imaging engines are deployed
for a given (and changing) number of sample arms depends on system
configuration. If, as shown in FIG. 4B, each imaging engine 420
includes a light source 401 and interferometer 402 as well as
processing hardware 403, then the optical controller 425 may
activate an imaging engine which was previously off upon detection
of a newly active sample arm, which is coupled to the activated
imaging engine. Similarly, optical controller 425 may de-activate
imaging engines upon detecting that the associated sample arms are
no longer in use. In these implementations, the optical controller
425 acts as a simple switch matrix whose operation is governed by
user demand. In more sophisticated implementations, the processing
system 403 may be virtualized so that multiple software-based
image-processing applications can be separately launched and run on
a single computer, up to the limit of the computer's capacity to
execute them. In such implementations, the light sources 401 and
interferometers 402 may be collectively located in area 405 or
instead in the various examination rooms 415. Optical controller
425 executes a queue management and/or load-balancing function that
distributes demand from active sample arms to actively running
image-processing applications, and launches new instances of the
image-processing applications as these become necessary to
accommodate demand. The system may include multiple computers
(e.g., in a cloud configuration) so that once the multi-application
limit of a particular computer is reached, a new computer (or new
cloud-based computational capacity) is activated and
image-processing applications launched thereon as necessary.
Load-balancing software and virtualization and cloud architectures
are very well known in the art and are straightforwardly adapted to
the present context without undue experimentation.
[0053] In various embodiments the optical controller 425 and/or
processing system 403 may be provided as either software, hardware,
or some combination thereof. For example, the system may be
implemented on one or more server-class computers, such as a PC
having a CPU board containing one or more processors such as the
Core Pentium or Celeron family of processors manufactured by Intel
Corporation of Santa Clara, Calif. and POWER PC family of
processors manufactured by Motorola Corporation of Schaumburg,
Ill., and/or the ATHLON line of processors manufactured by Advanced
Micro Devices, Inc., of Sunnyvale, Calif. The processor may also
include a main memory unit for storing programs and/or data
relating to the methods described above. The memory may include
random access memory (RAM), read only memory (ROM), and/or FLASH
memory residing on commonly available hardware such as one or more
application specific integrated circuits (ASIC), field programmable
gate arrays (FPGA), electrically erasable programmable read-only
memories (EEPROM), programmable read-only memories (PROM), or
programmable logic devices (PLD). In some embodiments, the programs
may be provided using external RAM and/or ROM such as optical
disks, magnetic disks, as well as other commonly used storage
devices.
[0054] For embodiments in which the optical controller 425 and/or
processing system 403 are provided as a software program, the
program may be written in any one of a number of high level
languages such as FORTRAN, PASCAL, JAVA, C, C++, C#, LISP, PERL,
BASIC, PYTHON or any suitable programming language. Additionally,
the software can be implemented in an assembly language and/or
machine language directed to the microprocessor resident on a
target device.
[0055] Referring to FIG. 4C, in some embodiments, a display 430 and
control interfaces 435 may also be located in each examination room
via point-to-point wiring 440 or a network interface 445. The
display 430 and control interfaces 435 may also be included in the
OCT system, thus allowing a user to view and manipulate the
diagnostic images. The display 430 and control interfaces 435 may
be provided as one integral unit or separate units and may also
include one or more user input devices 450 such as a keyboard
and/or mouse. The display can be passive (e.g., a "dumb" CRT or LCD
screen) or in some cases interactive, facilitating direct user
interaction with the images and models through touch-screens
(using, for example, the physician's finger as an input device)
and/or various other input devices such as a stylus, light pen, or
pointer. The actual time required to capture an image in the OCT
imaging system is minimal. Depending on the imaging application and
the sample arm implementation, a particular sample arm may only
need to be interfaced to (or communicate with) the imaging engine
for several seconds or less in order to capture sufficient data for
imaging or diagnostic purposes. Depending on the design of the
interferometer, the total path length of light propagation in the
reference arm is generally carefully matched (i.e., equal to within
a coherence length) to that of the sample arms to ensure proper
functionality of the interferometer. In one embodiment, the
reference arm incorporates any of a variety of approaches to linear
actuation (e.g., motor, servo, piezo drive, and/or other mechanical
element) that is controlled by the imaging-engine hardware and
software, which auto-adjusts the reference arm position to match
path lengths between the sample and reference arms.
[0056] With reference to FIG. 4D, for example, using a
spectrometer-based OCT interferometer configuration, including a
broadband light source 461 (such as one or multiple
super-luminescent diodes or a super-continuum laser with a
bandwidth sufficient for the number of desired sample arms), a
spectrometer 462, and properly chosen filters 463 in the WDM 464
(e.g., thin films or interference filters with sharp cutoffs), each
sample arm 465 operates over a different range of wavelengths
(e.g., 50-150 nm wide each). The spectrometer 462 isolates and
samples the bandwidth of each discrete band within the wavelength
range of each sample arm 465. FIG. 4E depicts a spectrometer 471
containing multiple sensors 472 in an array, with different sensors
optimized for different wavelengths 473, and/or gratings 474 for
separating the wavelength components for each sample arm 475. The
cutoff filters that have roll-off or slope and a finite wavelength
gap (e.g. 10-20 nm) between sample arms are desirable for avoiding
overlap wavelength between the sample arms. The spectral bandwidth
of the light source, the number of sample arms, and the spectral
bandwidth of each sample arm dictate the resolution of the OCT
imaging. The slope of the cutoff for each filter can be optimized
for system performance.
[0057] In one embodiment, a single sample arm is
wavelength-division multiplexed to multiple interferometers or
components of an interferometer optimized for a particular optical
spectrum. This embodiment enables a single instrument to perform
OCT imaging at multiple wavelengths, for example, any combination
of 830 nm, 1050 nm, 1310 nm, and 1550 nm wavelengths. There are
both advantages and disadvantages for imaging at different
wavelengths: for example, 830 nm light provides a better imaging
resolution than longer wavelength light, but it does not penetrate
certain biological tissues as deeply as longer wavelengths. On the
other hand, 1310 nm light exhibits better penetration into tissue
(e.g., the retina), providing a deeper imaging capability, but it
is strongly absorbed by water and thus cannot be effectively used
for imaging the retina externally through the cornea. FIG. 4D
depicts a single sample arm 481, including an A-scan, B-scan, or
C-scan capability connected to an OCT system that incorporates a
broadband light source 482, data-acquisition, processing and
display hardware 483, filters or wavelength-division multiplexer
484, a wavelength-division multiplexer 485, and multiple
interferometers 486 and/or spectrometers 487, each optimized for a
particular bandwidth. The broadband light source 482 may include
multiple light sources with narrow bandwidths (e.g., 100 nm) at
different wavelengths or a single broadband (e.g., 1000 nm) light
source, such as a super-continuum laser.
[0058] Multiple fiber-based interferometers may be used to ensure
single-mode operation at a broad range of wavelengths. For example,
a 1310 nm light source utilizes a fiber with a core size of
approximately 9 .mu.m whereas an 830 nm light source uses a fiber
with a core size approximately 4.5 .mu.m for single mode operation.
Likewise, different sensor technologies (e.g. Si vs InGaAs) are
preferred for different wavelengths. The optical properties and the
optical path length of the sample arm can be optimized to reduce
the effects of modal and chromatic dispersion at the different
wavelengths implemented, for example, by minimizing the optical
path length of the sample arm.
[0059] In another embodiment, the WDM is eliminated altogether and
the sample arms for each imaging wavelength are all arranged
separately (i.e., not sharing a common optical path) within the OCT
instrument.
[0060] FIG. 5A depicts an exemplary system in which a reference arm
510 incorporates a mechanical element 520 for adjusting a position
thereof to select a light-path length between the reference arm and
a light source 501 to match a light-path length between the light
source 501 and the sample arms 530. A fiber-based optical delay
line, composed of fiber-optic components (e.g., an optical cavity
or two linearly chirped fiber Bragg gratings, fiber optic coupler,
and circulator) can be used to replace the mechanical element 520
to manually or automatically match the path lengths as well. In an
alternate embodiment, a common-path interferometer configuration,
wherein the sample and reference arms share a common beam path with
a reference plane defined by an optical surface near the front
surface of a target, is used to eliminate the requirement of one or
multiple reference arms and decrease sensitivity to path-length
mismatches. Referring to FIG. 5B, the common-path configuration can
be implemented by integrating the reference arm into the sample arm
assembly. In some embodiments, the integration is implemented by
incorporating, for example, an optical coupler 560 or a prism 565
and a reflector 570 (e.g., a mirror) to couple the reference arm
575 and sample arm 580 into a single fiber 585. Signals in the
single fiber 858 are then delivered to the interferometer 590. The
foregoing components form an integration system that can be very
small (e.g., on the order of a few millimeters), where both
reference arm and sample arm share an effectively common path, or
very large if implemented in a large instrument (e.g., an
ophthalmoscope), where the integrated reference arm is designed to
properly match the length of the sample arm. The integration system
can be handhold or mounted on an instrument.
[0061] A variety of sample-arm configurations (e.g., an OCT
scanning ophthalmoscope, an OCT-enabled slit lamp, a
minimally-invasive OCT probe, etc.) may be accommodated in each
examination room by means of an optical-fiber connector that allows
different sample arms to be readily connected to and disconnected
from the remotely-located imaging engine.
OCT-Enabled Ophthalmic Instruments
[0062] A number of instruments are commonly used during ophthalmic
examinations and surgical procedures to view both the anterior
(e.g., the cornea) and posterior (e.g., the retina) segments of the
eye, as well as external regions and structures related to and
surrounding the eye (including but not limited to the eyelids,
eyelashes, tear ducts, etc.). These instruments include but are not
limited to the slit-lamp, the indirect ophthalmoscope, and the
binocular microscope. Embodiments of the present invention
incorporate an OCT imaging system with or into any of these
instruments. Embodiments may provide a visual image of the target
in the ophthalmic instrument simultaneously with a real-time OCT
image of the target; the visual image and OCT image are generated
in a time-synchronized and, in some cases, superimposed manner.
Embodiments include imaging systems in which the OCT engine is
remotely located, as well as imaging systems in which the OCT
engine is located adjacent to the sample arm (e.g., in the same
enclosure or in the same room).
[0063] An A-scan provides one-dimensional axial depth scans of the
tissue of interest, thus providing information on the identity,
size, and depth of subsurface features. FIG. 6A depicts a system
600 having a lens system 610 (e.g., for collimation or focusing)
integrated into the OCT system 620 and a target 630. This system
600 enables one-dimensional single OCT A-scans to be obtained at
the central point of the target; it may also provide B-scan or
C-scan imaging by tracking the manually moved system 600 using,
e.g., a gyroscope, an accelerometer, or an optical tracking system,
and subsequently combining the consecutive and spatially adjacent
A-scans in software. A series of spatially adjacent A-scans
(typically lying in a straight line) may be combined to form a
B-scan, which provides a two-dimensional reconstructed image of the
imaged area. In various embodiments, the ophthalmic instrument
includes or is used in conjunction with an OCT sample arm assembly
that includes a method for scanning (e.g., raster scanning) the OCT
laser in one or two dimensions, producing an A-scan or B-scan,
respectively. FIG. 6B shows how a scanning system 640 may be
coupled to the lens system 650 to produce a two-dimensional,
cross-sectional view of the target 660. Suitable scanning systems,
include but are not limited to, a single-axis or double-axis
scanning-minor galvanometer, a MEMS scanning mirror, a
piezoelectric scanner, an electro-optic crystal (e.g., KTN or
lithium niobate) whose refractive index changes upon an applied
electric field, or an optical phased array (e.g., LCD-based). Light
traces 665 indicate the position of a single scanning laser beam at
different times, instead of multiple concurrent light beams.
[0064] In one embodiment, an A-scan OCT imaging system is coupled
to an ophthalmic instrument. Referring to FIG. 7A, light emitted
from the optical instrument 710 upon a target 715 creates an
optical path 720. An OCT system 725 including or used in
conjunction with an optical fiber 730, a lens system 735 (e.g., for
collimation or focusing), and an optical element 740 is coupled to
the optical path 720. The optical element, for example, may be a
prism coated with a thin film that reflects infrared wavelengths
used for OCT but that transmits visible light used for illumination
during the examination, depending on the prism configuration, or
other suitable optical elements that may be used to couple the OCT
light into the optical path of the examination instrument
non-destructively, i.e., without degrading operation of the latter.
The illustrated embodiment enables single OCT A-scans to be
obtained at the central point of the area under examination by a
surgeon. In additional A-scan embodiments, the fiber 741 is
connected directly to the ophthalmic instrument 710 via use of, for
example, the fiber connector 742 employed in a therapeutic
laser-treatment system. An optical filter 743, located between the
illumination source of the ophthalmic instrument 710 and the
optical element 740, may be included to eliminate undesirable
wavelengths created by the illumination source. For example, an
infrared filter can be used to eliminate infrared wavelength that
may interfere with the OCT signal (e.g., by saturating the sensor);
a short-wavelength filter can be utilized to filter out shorter
wavelengths (e.g., light in the 400 nm range) that may damage the
retina. In another embodiment, a B-scan OCT imaging system is
coupled to the ophthalmic instrument. With reference to FIG. 7B,
the OCT system 750 is coupled to the light path 755 via a lens
system 760, a scanning system 765, and an optical element 770.
Utilizing the scanning system 765, this embodiment provides a
two-dimensional reconstructed image of the imaged area, offering
surgeons a visual reconstruction of subsurface features. In another
embodiment, the B-scan OCT imaging system 750 is coupled to or
integrated into the ophthalmic instrument 780 that delivers a
therapeutic laser via a fiber 781 and a fiber connector 782 on the
ophthalmic instrument 780. In another embodiment, an imaging system
with C-scan capabilities is implemented by incorporating a scanning
system capable of controlling the beam deflection in two
dimensions.
[0065] The A-scan and B-scan sample-arm assemblies may be held in
the optical path by hand (e.g., by a surgeon or nurse), or they may
be mounted in a fashion that enables automatic (e.g., actuated by
the imaging system) or manual (e.g., positioned by the doctor)
insertion or removal of the assembly from the optical path. One
embodiment, as depicted in FIG. 8A, incorporates the combination
815, including the scanning system, the lens system, and the prism,
on a swivel arm 820 or jointly attaches the arm assembly 810 to the
mechanical frame 830 of the examination instrument 840, thus
enabling the doctor to easily move the OCT imaging system 835 in
and out of the optical path 850.
[0066] In one embodiment, an optical fiber used to carry the OCT
laser light to the OCT imaging engine may also provide therapeutic
laser capabilities (e.g., 532 nm photocoagulation). FIG. 8B
illustrates how a therapeutic laser 860 may be integrated with the
imaging engine 865; alternatively or in addition, a therapeutic
laser 870 may be installed adjacent to the imaging engine 865. The
therapeutic lasers 860 and 870 may share the same optical path 866
and scanning system 867 as the imaging engine 865 or may instead
have their own optical paths 868 and 869, respectively, to the
target. The scanning capabilities of the OCT sample arm may be used
to direct the focal point of the treatment laser to the appropriate
location on the target 875. This may significantly improve the
precision of the treatment, eliminate image registration errors,
and/or streamline the procedure by enabling the surgeon to examine
the region of interest using multiple imaging modalities
simultaneously (e.g., visual, topographic, or OCT) and to treat the
relevant areas at the same time. Furthermore, the surgeon may
verify the quality of the treatment burn in real time.
[0067] In another embodiment, white light or broadband light over
the visible spectrum that is sourced from the adjacent or
remotely-located imaging engine may be incorporated into the
combined instrument to provide illumination of the region under
examination. FIG. 8C illustrates white light or broadband light 880
emitted from the light source 881 of the imaging engine 885 and
propagating along a separate, larger diameter optical fiber 890
(e.g., multi-mode fiber), rather than the single-mode fiber, for
providing sufficient intensity for white-light illumination on the
target 895. Another option is the use of multi-clad or photonic
crystal fiber having multiple waveguides that may be designed and
optimized for the intended purpose (e.g., containing both
single-mode for OCT and multi-mode for white light).
[0068] It should be noted that although the above descriptions
relate to an OCT-enabled ophthalmic instrument, other imaging
modalities that rely on similar optical configurations
(particularly in the use of optical fiber and optical components
similar to those described herein for illumination and/or light
collection, and also modalities involving scanning mechanisms) may
be used in accordance with the teachings hereof. For example,
two-photon microscopy, two-photon excited fluorescence, scanning
laser ophthalmoscopy (SLO), and/or confocal microscopy can all be
used in the manner described herein, i.e., in lieu of or in
conjunction with OCT capabilities.
OCT-Enabled Slit-Lamp
[0069] Slit lamps are the ophthalmologist's most frequently used
and most universally applicable examination instrument. Slit lamps
are used in the examination of the anterior segment of the eye
(e.g., crystalline lens) as well as the posterior segments (e.g.
retina) with supplementary optics, such as contact lenses. The
illumination system of slit lamps is intended to produce a
uniformly bright, accurately focused slit of light whose dimensions
can be adjusted. With reference to FIG. 9, the illumination system
900 of a representative slit lamp includes a light source 910 (e.g.
halogen), a reflector 920 (e.g., a minor) positioned behind the
light source to maximize illumination, condensing lenses 930 (e.g.
a pair of aspheric plano-convex lenses), a slit aperture 940, and a
projector lens 950. The light source 910 is positioned at principle
focus of the first condensing lens. The projector lens 950 projects
the focused light at the slit 940 to a target 960. An observation
system, which has a design analogous to a telescopic lens system,
is then coupled to the illumination system 900 for magnifying and
viewing the target.
[0070] Embodiments of the present invention incorporate an OCT
imaging system 970 to couple non-destructively to the light path
980. The illustrated embodiment includes an OCT-enabled slit lamp
designed to provide a doctor with both magnified visualization of
the structure of interest as well as real-time OCT reconstructed
images. A sample-arm assembly including a prism (e.g., with a
thin-film coating that reflects OCT-wavelength light and transmits
visible wavelengths) or other arrangement for combining the output
of a single fiber and collimating lens with the light from the slit
lamp may provide A-scan capability of a single point of interest,
as depicted in FIG. 7A. Embodiments may also includes a scanning
mechanism in the slit lamp that enables B-scan functionality, as
shown in FIG. 7B.
[0071] In addition, variable-focus capabilities may be included by
providing a means to adjust the spacing of lens components, such as
the condensing lenses 930 and/or the projector lens 950, in the
optical path and the distance to the eye to adjust the focal point.
For example, variable focus may be used to alternate between OCT
imaging of the anterior and posterior segments of the eye.
[0072] The sample arm assembly may be incorporated into the slit
lamp frame, or it may be mounted externally for easy insertion into
and removal from the optical path as shown in FIGS. 7A and 7B. In
various embodiments, the reconstructed OCT image is displayed on a
small monitor 745, 785 located adjacent to the slit-lamp for
displaying a real-time OCT image of the target proximate a
visualization of the target displayed on the slit-lamp. Although
the OCT and slit-lamp images display different perspectives (e.g.,
topographical/surface vs. cross-section), in some embodiments the
two images may be combined into a single composite image with
enhanced visual features.
OCT-Enabled Indirect Ophthalmoscope
[0073] An ophthalmoscope is an instrument for inspecting the
interior of the eye; it allows a better view of the fundus of the
eye, even if the lens is clouded by cataracts. An indirect
ophthalmoscope can be either monocular or binocular; it provides a
wide angle, bright, binocular view of the retina, while allowing
the observer to maintain an arms-length distance from the patient.
Referring to FIG. 10A, an indirect ophthalmoscope constitutes a
light source 1010 (e.g., halogen) attached to a headband 1015, in
addition to a small hand-held lens 1020. The hand-held condensing
lens (e.g., aspheric convex lens) gathers light coming from the
ophthalmoscope's light source 1010 to illuminate the retina 1025,
and gathers it again for the benefit of the observer after it has
left the subject eye. Light coming from a point on an emmetropic
subject's retina leaves that eye as a bundle of parallel rays. The
condensing lens focuses that bundle to a position 1030 closer to
the observer, who therefore perceives an inverted image of the
retina closer to his eye than the lens in the hand. In case the
observer is presbyopic, the ophthalmoscope is fitted with reading
glasses, so that focusing will not be necessary to see this image,
which is about as far away as the observer's wrists.
[0074] Embodiments of the present invention include an OCT system
1031 coupled to the optical path 1035 of the indirect
ophthalmoscope system. Embodiments of the invention incorporate the
sample arm in the doctor's ophthalmoscope headset, for example, by
utilizing the same optical path as the illumination light source
(e.g., halogen) and/or therapeutic laser from the ophthalmoscope.
The therapeutic laser may be a high-power solid-state laser, such
as a Nd:YAG 532 nm solid-state green laser, with a wide range of
emission modes: single, repeat, continuous, and painting. The
therapeutic laser may deliver multiple wavelengths to enhance the
therapeutic effect. FIG. 10B depicts an exemplary B-scan-enabled
indirect ophthalmoscope implementation. In typical usage, the
doctor holds the assembly 1040 containing the condensing lens 1050,
prism 1060, lens system 1070 and scanning system 1080 in the
optical path 1090, adjusts the axial and lateral position of the
assembly to bring the image into focus, and views and images the
specific region of interest. The prism 1060 combines the
transmitted OCT light with the visible light as it propagates into
the eye and separates the reflected OCT signal from the visible
light as it emanates from the eye. In alternative embodiments, the
OCT sample arm assembly 1095 (including a prism, a lens system,
and, in embodiments with B-scans, a scanning mechanism) is
integrated into the indirect ophthalmoscope 1097 (e.g., doctor's
headset) and utilizing the same optical path 1090 as the
illumination light source and/or therapeutic laser; a standard
condensing lens 1050 is used in normal fashion.
[0075] In addition, variable magnification may be implemented by
using condensing lenses 1050 with different levels of
magnification. In one embodiment, the reconstructed OCT image is
displayed on a small monitor 1099 located within viewing distance
of the doctor.
OCT-Enabled Binocular Microscope
[0076] A binocular microscope is an instrument that magnifies the
image of a target and provides a clear view of small and
inaccessible parts of the target. With reference to FIG. 11, light
from a light source 1100 (e.g., halogen) in a binocular microscope
1110 is collected and focused onto a target 1120 via a condenser
system 1130. An objective 1140 is used to collect the light from
the target 1120 and magnify the image of the target. The image is
further magnified by eyepieces 1150 and projected onto human eyes
1160.
[0077] Embodiments of the present invention include an OCT-enabled
binocular microscope that provides a surgeon with intra-operative
OCT capabilities without impacting the use of the binocular
microscope. In various embodiments, B-scan capabilities are enabled
by an OCT sample-arm assembly 1180 (the arrangement of which has
previously been described above) that is mounted on the microscope
1110 and which may be positioned in and out of the optical path
1170 of the microscope by the surgeon. Anterior segment scanning or
retinal scanning may be selected by the insertion or removal of,
for example, a binocular indirect ophthalmomicroscope (BIOM) lens,
located in the optical path between the microscope and the
patient's eye and mounted typically on a movable arm that can be
swiveled into or out of the optical path, or a corneal-contact
lens, placed in contact with the patient's eye, that changes the
focal point of the optical system.
IOL Alignment
[0078] In one particular embodiment utilizing a binocular
microscope, an OCT-enabled visualization and imaging system enables
the surgeon to properly align an intraocular lens during
implantation. Embodiments of the present invention include a
scanning mechanism coupled to an OCT imaging system (either locally
or remotely located) that is placed in proximity to (but not
necessarily in contact with) the eye. The scanning mechanism
enables OCT imaging of both the anterior chamber and the posterior
chamber (using a wavelength such as 830 nm) either by varying the
position of the scanning mechanism (i.e., moving closer to or
further from the eye) or varying the focal point of the laser
through standard optical means. Furthermore, the imaging system
includes software capabilities for identifying the precise center
of the IOL by any or all of the following methods, as shown in FIG.
12: [0079] 1. Identifying the thickest region of the IOL 1200
(which typically corresponds to the central axis of a lens) based
on the reflectance profile of the OCT signal to determine the
maximum distance between detected reflections in the IOL; [0080] 2.
Identifying the concentric ridges and grooves 1210 that encircle
the IOL (similar to a Fresnel lens) that are present in some IOLs
to provide focusing and variable length focal capabilities, and
identifying the center of the IOL as the equidistant point centered
within the innermost concentric ring; and/or [0081] 3. Using IOLs
that contain fiducials 1220 or registration markers that may be
identified by the OCT imaging system using conventional
object-recognition algorithms (e.g., implemented in software along
with OCT image reconstruction).
[0082] Any or all of the above methods may be used in conjunction
with OCT imaging of the retina to identify the foveal pit (e.g., by
switching between anterior and posterior focal points) to assist
the surgeon in aligning the center of the IOL with the foveal pit
(e.g., with overlaid images displayed on a monitor). The foveal pit
may be identified either visually by the surgeon (e.g., by aligning
crosshairs over the center of the foveal pit) or through computer
vision and object-recognition algorithms programmed to identify the
indentation at the foveal pit.
[0083] Additional embodiments simplify the system by replacing the
scanning mechanism with a single fiber incorporating a focusing
lens (e.g., a GRIN lens) for the purpose of capturing A-scans. A
single A-scan may be used to identify the center of the lens and
the foveal pit in combination with the previously described
algorithms designed to identify the center of the IOL and the
foveal pit. In such embodiments, the surgeon manually scans the
optical fiber across the region of interest and is alerted to the
proper alignment (e.g., via audio or visual cues).
[0084] Additional embodiments of the present invention include an
A-scan- or B-scan-capable probe (e.g., including a scanning
mechanism such as a side-scanning probe with a sub-millimeter probe
tip diameter) for insertion into the anterior segment during the
IOL implantation to provide similar imaging for the purpose of
alignment.
[0085] While the foregoing descriptions focus primarily on
ophthalmic applications, these technologies can be generally
applied to any of a number of other medical fields that utilize
imaging technologies, including orthopedics, dermatology,
cardiology, gastroenterology, etc.
[0086] OCT and combination systems in accordance with embodiments
of the present invention may incorporate any of a variety of
features described in U.S. patent application Ser. Nos. 12/718,186,
12/718,188, 12/718,193, 12/718,266, and 12/718,272, the entire
disclosures of which are incorporated by reference herein.
Image Capture and Display Technologies
[0087] The above-described implementations of different imaging
systems typically provide for display of the reconstructed OCT
image for viewing by a surgeon or clinician either in real-time or
replayed at a later time. Embodiments of the invention include one
or multiple displays (e.g., LCD or projection-based displays) for
displaying OCT and other images. Additional embodiments incorporate
one or multiple video cameras (e.g., digital cameras containing
CMOS or CCD imaging sensors) that in conjunction with one or
multiple displays provide substantially the same functionality and
therefore replace a variety of imaging systems used by the surgeon,
including but not limited to slit-lamps, indirect ophthalmoscopes,
and binocular microscopes. The camera(s) are positioned to enable
image capture of the region of interest and the display(s) are
positioned to enable optimal viewing by the surgeon or clinician.
For example, the camera(s) may be mounted on a fixture located
above or in front of the patient or the camera(s) may be mounted in
a headset worn by the surgeon or clinician.
[0088] Various embodiments display camera-captured images (e.g., in
lieu of slit-lamp, binocular microscope, or ophthalmoscope usage),
OCT captured data (e.g., A-scans, B-scans, and C-scans), or both.
The OCT data may be displayed on the screen adjacent to or overlaid
on the visible image(s) captured by the camera(s). The displayed
image may be user-selectable between different image sources (e.g.,
OCT console and one or multiple cameras). The described imaging
system may incorporate one or more of low-light, three-dimensional
display, and high-resolution capabilities.
Low Light
[0089] In one embodiment, the imaging system incorporates low-light
capabilities that enable the surgeon to visualize the structures of
interest in a low-light setting or even in the absence of light
(which is conducive to pupil dilation in the patient without using
topical drugs). For example, low-lux cameras that exhibit high
sensitivity to low light levels may be employed. Ambient light
levels present from external sources (e.g., light leakage through
window blinds, LCD backlight emissions, or light leakage through
door cracks) may be sufficient for low-lux imaging. Alternately,
the examination or operating room may be illuminated by a dim
source of illumination in the visible spectrum to provide
sufficient light for the desired low-light imaging capabilities. In
another embodiment, the cameras are infrared-capable (e.g., the
cameras are CMOS or CCD which is sensitive to infrared light and
the cameras possess no infrared filters). An infrared illumination
source is placed in the room to illuminate the structure of
interest. This is advantageous because the patient's eye is not
sensitive to infrared light and therefore the eye under examination
can be brightly illuminated while fully dilated in the dark setting
with no need for topical dilation drugs. An additional advantage is
that the infrared OCT laser beam and the path it traverses (e.g.,
on the retina) is visible to the surgeon on the display, thus
eliminating the need for a separate visible spectrum alignment
beam.
3D Imaging
[0090] Current display technologies used in medical imaging and
diagnostics display 3D structures in a 2D representation, resulting
in a lack of depth information. Much of the detail gathered from a
3D imaging modality is lost in a 2D representation. There is a
clear benefit for surgeons to be able to visualize imaged
structures in 3D space. Embodiments of the present invention
therefore can include multiple cameras positioned and aligned to
capture 3D real-time video. The cameras can be mounted, for
example, in the surgeon's headset or in a fixture positioned above
or adjacent to the upright or supine patient. Implementations also
include a display to provide 3D image reconstructions to the
surgeon. In one embodiment, the surgeon wears a headset that
contains two separate displays, one for each eye, each of which
displays the image captured from a separate camera to provide a 3D
image to the viewer.
[0091] In a second embodiment, the 3D image is created using
conventional stereoscopic technology, which utilizes a pair of
glasses or a headset (e.g., similar to a binocular indirect
ophthalmoscope headset) that surgeons wear. In one embodiment, the
stereoscopic effect is achieved through the use of glasses with
different polarizing filters for each lens. The image presented to
the display is a superposition of the two camera images through
different polarization filters, each matched to one of the lenses
in the glasses. In another embodiment, the glasses incorporate
shutter technology (typically a LCD), wherein each lens can be
independently and rapidly switched from visible to opaque. The
glasses are synchronized to the refresh rate of the display; the
display alternates images intended for one or the other eye and the
synchronized shutters block the other eye.
[0092] In a third 3D display configuration, the 3D image is created
via an autostereoscopic approach, which has the advantage of not
requiring the viewer to wear a specialized pair of glasses. In one
type of autostereoscopic display, a lenticular lens covers the
display. Alternating pixel columns in the display are intended for
the left eye and right eye; the shape of the lenticular lens
ensures the light from each column of pixels refracts towards the
proper eye. Referring to FIG. 13A, an alternate and potentially
more cost-effective approach is to incorporate parallax barrier
masks 1310 over the display 1320; this achieves a similar effect as
the lenticular lens 1330. FIG. 13B illustrates an embodiment with
dual cameras 1340 and an LCD display 1350 mounted above a supine
patient 1360, appropriate for both use as a binocular indirect
ophthalmoscope (in conjunction with a condenser lens) as well as a
binocular microscope. A handheld sample arm assembly, as previously
described, can be held in the optical path to enable OCT imaging
(or, for example, two-photon fluorescence imaging). The display(s)
and/or camera(s) may also be integrated into a headset.
[0093] The arrangement of multiple cameras can also provide
benefits over single-camera optical-tracking systems that track the
position and orientation of an instrument held by the surgeon; for
example, a multiple-camera arrangement can be used to facilitate
image reconstruction (for example, to stitch multiple A-scans
together into a B-scan image). This is accomplished in one
embodiment via using fiducial markers or indicators (easily
recognized by the cameras, for example, as distinct colors, shapes,
or infrared LEDs). Multiple cameras provide multiple angles at
which to identify these fiducial markers and eliminate ambiguities
in certain positions, thereby increasing the overall accuracy of
the tracking system and reducing the computational requirements in
some cases.
High Resolution
[0094] The use of high-resolution and high-definition display
technologies offer benefits to surgeons, particularly
ophthalmologists and other surgeons who image, diagnose, and treat
biological structures that are invisible to the unaided eye.
Embodiments of the systems described herein, including normal,
low-light, and 3D imaging and for both visible and infrared light
imaging, incorporate high-definition and high-resolution camera and
display systems to provide increased clarity and resolving ability
when visualizing small structures.
OCT-Enabled Electrodes
[0095] Current and emerging neural prostheses and therapies based
on nerve stimulation and recording may involve electrodes
chronically interfaced to the central and peripheral nervous
systems. Electrical stimulation initiates a functional response by
depolarizing the membranes of excitable cells. Depolarization is
achieved by a current flow between two or more electrodes, at least
one of which is in close proximity to the target tissue. In most
neural applications, electrical stimulation is applied as a series
of biphasic (i.e., cathodal and anodal) current pulses. The
activity of neurons is recorded as an extracellular potential, or
action potential, when the recorded signal identifies the firing of
a single neuron (single-unit). Action potentials are recorded with
electrodes implanted in close proximity to the target neurons. In
general, the objective with single-unit neural recording is to
measure action potentials with a useful signal-to-noise ratio,
.about.5:1 or greater, and to do this chronically.
[0096] Neurobiological research has used single-wire or glass
micropipette electrodes to stimulate and/or record individual
neuron waveforms in acute experiments. However, the need to access
populations of neurons and the desire of researchers to monitor
neural networks over time has led to development of arrays of
wires, silicon shafts and other, more complex micro-machined
silicon recording systems capable of high-density sampling. The
efficacy of multiple electrodes used to stimulate or record neural
activity in the brain, spine, and other regions of the body is
typically heavily dependent upon accurate positioning of the
electrodes. Additionally, the act of surgically placing the
electrodes may introduce significant risk, especially if the
electrodes are to be placed in a sensitive region such as the brain
or spine. Many studies have attributed biologically induced
electrode failure to the initial trauma of implantation, leading to
a variety of strategies to minimize this early trauma in the hope
of limiting the subsequent complications. Approaches include
optimizing the speed of electrode insertion, the method of
insertion, and the depth of insertion. Incorporating an OCT imaging
system with electrodes may provide more accurate and detailed
information about the accuracy and depth of insertion upon
including the electrode in the tissue, thereby enhancing
operational efficacy and decreasing risk to the patient.
[0097] Embodiments of the present invention incorporate an OCT
imaging system into a neural stimulation- and/or neural
activity-recording electrode or electrode array. FIG. 14A
illustrates an electrode array containing an electrode carrier
1410, including two electrode leadwires 1420 and a single electrode
channel 1430 with a single fiber 1440, associated with the
electrode leadwires; the array is capable of A-scan OCT as
described below. FIG. 14B shows multiple electrode channels 1450
with multiple A-scan-capable fibers 1460 (constituting a
multiple-sample-arm configuration, as described above). Each
individual optical fiber, which serves as an individual sample arm,
has an end face capable of providing A-scan data of the region
directly in front of the tip of the fiber. Each fiber is positioned
in close proximity to a particular electrode contact 1470, such
that the A-scan data captured by the optical fiber provides
information regarding the tissue directly adjacent to the
associated electrode contact 1470. The multiple electrode contacts
1470 are located at different positions along the distal end of the
electrode carrier 1310; the electrode carrier thus captures optical
information from the tissues adjacent to the contacts along the
distal end of the carrier. A variety of configurations are possible
depending on the application. In this particular example, the
electrodes are made from a biocompatible electrically-conductive
material such as platinum, while the flexible surrounding structure
is made from parylene or another biocompatible polymer. In one
embodiment, an optical controller 1480 (e.g., a wavelength-division
multiplexer, a time-division multiplexer, or an optical switch) is
incorporated to multiplex optical signals from some or all of the
optical fibers to enable their convenient operation by and optical
linkage to a centralized imaging engine 1490.
[0098] In some embodiments of the invention, as depicted in FIG.
15, the OCT-enabled electrode carrier 1510 including OCT fibers
1520 is used to differentiate between gray matter 1530, which is
adjacent to the electrode carrier at the electrical contacts, and
the surrounding tissue, e.g., white matter 1540, to optimally
position electrodes in the brain tissue 1550. In another
embodiment, the captured and processed A-scan data is used to
identify the presence of specific structures forward of the
electrodes. For example, the A-scan data may be used during the
placement of electrodes to identify the presence of blood vessels
1560 before they are disturbed by the tunneling and positioning of
the electrode. Furthermore, the optical fiber(s) may be used to
propagate other wavelengths of laser light, e.g., for ablation
purposes or to optically stimulate neuronal tissue.
[0099] The terms and expressions employed herein are used as terms
and expressions of description and not of limitation, and there is
no intention, in the use of such terms and expressions, of
excluding any equivalents of the features shown and described or
portions thereof. In addition, having described certain embodiments
of the invention, it will be apparent to those of ordinary skill in
the art that other embodiments incorporating the concepts disclosed
herein may be used without departing from the spirit and scope of
the invention. Accordingly, the described embodiments are to be
considered in all respects as only illustrative and not
restrictive.
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