Frequency Domain Optical Coherence Tomography

(FDOCT)Joon S Kim

IMSURE Summer Research Fellow At Beckman Laser Institute

University of California at IrvineIrvine, CA 92612

Email: jkim627@mail.umd.edu

OCT

• Optical Coherence Tomography– New field of imaging technology that can

complement conventional imaging techniques – Based on interference of EM wave– Provide high spatial resolution cross-sectional

view of tissues without excision– Endless potential biomedical applications

• Non-invasive Diagnostics

OCT vs. Conventional Imag. Tech

1 mm 1 cm 10 cm

Penetration depth (log)

1 m

10 m

100 m

1 mm

Resolution (log)

OCT

Confocalmicroscopy

Ultrasound

Standardclinical

Highfrequency

Two kinds of OCT

• TDOCT– Time Domain OCT– Use of Scanning Mirror

• FDOCT– Fourier (Frequency) Domain OCT– Use of laser source over band of optical

frequency– Advantages over TDOCT

My research experience with FDOCT are in 2 phases…

• First phase: – Understanding and Replicating FDOCT

experimental setting from scratch

• Second phase: – Learning the physical and mathematical

reasoning behind the magical DSP algorithm which extract images out of OCT data!

Part 1• FDOCT experiment set upSwept source

Phase Modulator

Sample

Probe

Detector1

Detector2

2 x 2 CouplerGrating

Mirror

Collimator

Attenuator

Fiber Fabry-Perot

interferometer

Current FDOCT System

• No human intervention required

• Everything controlled from execution module in host computer

• Host computer – houses NI-6112: A2D Conversion of OCT

data– performs digital signal processing– controls peripherals

Scanning sample

• Surface of sample is divided into imaginary grid.

• Each block in grid: Pixel

• Scanning in X direction– Lateral scan

• Scanning in Z direction– A scan

Z

XY

Scanning sample (cont.)

• 1600 samples / A-scan (pixel)

• 400 A-scan / Lateral scan

• Lateral scanning Frequency: 2 KHz

• A-scanning Frequency: 10 MHz– Limited by A2D converter (NI-6112)

• Pixel size: 10 micron

• Slow process => not applicable in Vivo

With NI-5122

• Max. Sampling Frequency: 100 MS/sec

• A-scanning Frequency: 100 MHz– More time for DSP – Boost lateral scanning frequency to 20 KHz– One step closer to in Vivo application of

FDOCT