# US 2014/0207418 A1 · Real-Time Resampling of Optical Coherence Tomography Signals Using a Field Programmable Gate Array

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- Number: US 2014/0207418 A1
- Document ID: US20140207418A1
- Status: Published application
- Kind: A1
- Application number: 13/748,702
- Filed: 2013-01-24
- Published: 2014-07-24
- Earliest claimed: 2013-01-24
- Assignees: National Instruments Corporation
- Applicants: National Instruments Corporation
- Inventors: Kalyanramu Vemishetty
- Web page: https://patentgrep.com/patent/US20140207418A1

## CPC

- G01B 9/02004: using frequency scans
- G01B 9/02069: {Synchronization of light source or manipulator and detector}
- G01B 9/02091: Tomographic interferometers, e.g. based on optical coherence
- G01N 21/4795: {spatially resolved investigating of object in scattering medium (in vivo A61B)}
- A61B 5/0066: {Optical coherence imaging}
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

A signal processing system implemented on a Field Programmable Gate Array (FPGA) operates according to a low frequency K-Clock to sample Optical Coherence Topography (OCT) signals, as opposed to relying on a high frequency K-Clock to obtain the same information. A resampler is used to resample the OCT signal uniformly in the optical frequency domain. The resampling may be performed by extracting instantaneous phase information from a low-frequency digitized K-Clock signal, unwrapping the extracted phase information, multiplying the unwrapped extracted phase information with an interpolation factor to obtain recalculated phase information, determining one or more integer crossing points corresponding to the recalculated phase information, and interpolating one or more values of the OCT signal based on the one or more integer crossing points. The integer crossing points may represent points in phase divisible by 360 degrees, within the range of points in phase defined by the recalculated phase information.

## Claims

### Claim 1

A method for performing optical coherence tomography (OCT), the method comprising:
extracting phase information of a control signal;
unwrapping the extracted phase information;
multiplying the unwrapped extracted phase information with an interpolation factor to obtain recalculated phase information;
determining one or more integer crossing points corresponding to the recalculated phase information;
interpolating one or more values of an OCT signal according to the determined one or more integer crossing points.

### Claim 2 (depends on 1)

The method of claim 1, wherein the control signal is a discrete signal;
wherein the method further comprises obtaining the control signal by digitizing an analog signal that has varying frequency in time.

### Claim 3 (depends on 1)

The method of claim 1, wherein said extracting the phase information of the control signal comprises filtering the control signal.

### Claim 4 (depends on 3)

The method of claim 3, wherein said filtering the control signal comprises one or more of:
performing a Hilbert transformation on the control signal;
phase shifting the control signal; or
reducing distortion and noise in the control signal.

### Claim 5 (depends on 1)

The method of claim 1, further comprising performing said extracting, said unwrapping, said multiplying, said determining, and said interpolating in real-time.

### Claim 6

A field programmable gate array (FPGA) comprising:
a plurality of logic gates interconnected to:
extract normalized phase information from a control signal;
unwrap the extracted normalized phase information;
multiply the unwrapped extracted normalized phase information with an interpolation factor to obtain recalculated phase information;
identify one or more integer values within a range of phase values defined by the recalculated phase information; and
interpolate one or more values of an incoming signal according to the identified one or more integer values.

### Claim 7 (depends on 6)

The FPGA of claim 6, wherein the control signal is a discrete signal representative of an analog signal having varying frequency with time.

### Claim 8 (depends on 6)

The FPGA of claim 6, wherein the plurality of logic gates are further interconnected to:
extract the phase information from the control signal by filtering the control signal.

### Claim 9 (depends on 8)

The FPGA of claim 8, wherein as part of filtering the control signal, the plurality of logic gates are further interconnected to perform one or more of:
a Hilbert transformation on the control signal;
phase shifting the control signal; or
reducing distortion and noise in the control signal.

### Claim 10

A method for processing a data signal, the method comprising:
identifying equally spaced points in phase of a control signal representative of an analog signal that has varying frequency in time, wherein each identified point in phase of the identified equally spaced points in phase corresponds to a respective pair of values of the signal; and
resampling the data signal according to the identified equally spaced points in phase of the control signal, said resampling comprising:
for each identified point in phase, linearly interpolating a corresponding value of the data signal between the respective pair of values of the data signal corresponding to the identified point in phase.

### Claim 11 (depends on 10)

The method of claim 10, wherein said identifying comprises:
extracting phase information from the control signal;
obtaining points in phase from the extracted phase information;
multiplying each obtained point in phase of the obtained points in phase with an interpolation factor to obtain recalculated points in phase, wherein the recalculated points in phase define a range of recalculated points in phase; and
identifying desired points in phase within the range of recalculated points in phase, wherein each desired point of the desired points in phase:
is evenly divisible by a specified number; and
has a value that falls between respective values of a corresponding pair of recalculated points in phase within the range of recalculated points in phase;
wherein the identified desired points in phase are the identified equally spaced points in phase.

### Claim 12 (depends on 11)

The method of claim 11, wherein the specified number is 360 degrees.

### Claim 13 (depends on 10)

The method of claim 10, further comprising:
generating the analog signal using an interferometer and a balanced detector; and
obtaining the control signal by digitizing the analog signal.

### Claim 14 (depends on 10)

The method of claim 10, wherein said identifying comprises filtering the control signal.

### Claim 15 (depends on 14)

The method of claim 14, wherein said filtering the control signal comprises one or more of:
performing a Hilbert transformation on the control signal;
phase shifting the control signal; or
reducing distortion and noise in the control signal.

### Claim 16 (depends on 10)

The method of claim 10, wherein said identifying and said resampling are performed in real-time.

### Claim 17 (depends on 10)

The method of claim 10, wherein said identifying comprises performing a portion of said identifying concurrently with said resampling.

### Claim 18

A system comprising:
a first logic element configured to extract phase information from a control signal;
a second logic element configured to obtain phase points from the extracted phase information;
a third logic element configured to multiply each obtained phase point of the obtained phase points with an interpolation factor to obtain recalculated phase points;
a fourth logic element configured to identify desired phase points within a range defined by the recalculated phase points, wherein each desired phase point of the desired phase points:
is evenly divisible by a specified number; and
has a value that falls between respective values of a corresponding pair of recalculated phase points within the range defined by the recalculated phase points; and
a fifth logic element configured to resample an incoming signal according to the identified desired phase points.

### Claim 19 (depends on 18)

The system of claim 18, wherein the first logic element comprises one or more of:
a Hilbert Transform finite impulse response filter; or
a bandpass filter.

### Claim 20 (depends on 18)

The system of claim 18, wherein to extract the phase information, the first logic element is configured to:
obtain a representation of the control signal as a complex-function;
obtain the phase information based on an imaginary component of the representation of the control signal and a delayed version of the control signal.

### Claim 21 (depends on 18)

The system of claim 18, further comprising:
circuitry configured to generate the control signal.

### Claim 22 (depends on 21)

The system of claim 21, wherein the circuitry comprises:
a first signal generator configured to generate an analog signal having varying frequency with time; and
an analog-to-digital converter configured to generate the control signal by digitizing the analog signal.

### Claim 23 (depends on 18)

The system of claim 18, wherein the incoming signal is an optical coherence tomography (OCT) signal.

### Claim 24 (depends on 18)

The system of claim 18, wherein the first, second, third, fourth, and fifth logic elements are configured on a field programmable gate array (FPGA).

### Claim 25 (depends on 24)

The system of claim 24, further comprising:
circuitry external to the FPGA, and configured to generate the control signal.

### Claim 26 (depends on 18)

The system of claim 18, wherein the first, second, third, fourth, and fifth logic elements are configured to operate in real-time.