Optical Coherence Tomography (OCT)

Question 1

What is OCT?

Answer 1

Optical Coherence Tomography: a 3D, non-contact, high resolution, cross-sectional in-vivo imaging that shows microstructures

Question 2

What is COHERENCE?

Answer 2

The measure of how in phase light is from a source.
Two light waves are coherent when their frequencies and waveforms are identical.
Lasers are coherent while a lightbulb is incoherent

Question 3

What is INTERFERENCE?

Answer 3

The superposition of multiple waves
Constructive interference is when the waves are in phase and results in a wave with a larger amplitude
Destructive interference is when the waves are out of phase and cancel one another out

Question 4

What is COHERENCE LENGTH?

Answer 4

The path lengths that can be used for interference - if the path length > coherence length no interference will occur.

Question 5

What is the CENTRAL WAVELENGTH?

Answer 5

The midpoint of a wave

Question 6

What is a waves BANDWIDTH?

Answer 6

The spectral bandwidth of an OCT system is Full Width Half Maximum (FWHM) of the spectrum

Question 7

What is LINE RATE?

Answer 7

The number of a-scans acquired in one second, in Hz.
The speed with which a B-scan is collected depends on the line rate

Question 8

What is the AXIAL RESOLUTION of OCT?

Answer 8

Delta Z: the depth resolution, determined by the coherence length of the light source

Question 9

What is the LATERAL (TRANSVERSE) RESOLUTION of OCT?

Answer 9

Delta X: determined by the minimum spot size of the focusing beam (scan lens)

Question 10

What is the SENSITIVITY of an OCT system?

Answer 10

The minimum reflectivity required to achieve signal-to-noise ratio (SNR) of 1

Question 11

What is A-SCAN OCT?

Answer 11

1D OCT image obtained by completing one trip along the reference arm

Question 12

What is B-SCAN OCT?

Answer 12

2D OCT image comprised of a series of A-scans obtained by scanning at incremental steps or multiple longitudinal locations of the sample

Question 13

What is C-SCAN OCT?

Answer 13

3D OCT image comprised of multiple B-scans obtained by having multiple depth scans with beam propagating at two orthogonal directions

Question 14

What properties does TIME-DOMAIN OCT (TD-OCT) have?

Answer 14

• Slow (complicated opto-mechanics)
• Low SNR
• Acquisition rate of ~16kHz

Question 15

What properties does SPECTRAL-DOMAIN OCT (SD-OCT) have?

Answer 15

• High SNR
• Spectrometer based
• Fast
• Low cost (in silicone detector range)
• Acquisition line rate of ~ 300kHz

Question 16

What properties does SWEPT SOURCE OCT (SS-OCT) have?

Answer 16

• Very fast
• Larger imaging depth range
• Expensive (swept source and fast digital sampling electronics required)
• Acquisition line rate of ~5MHz

Question 17

What LIGHT SOURCE and DETECTOR does TD-OCT use?

Answer 17

Light Source: Broadband light source
Detector: Photodetector

Question 18

What LIGHT SOURCE and DETECTOR does SD-OCT use?

Answer 18

Light Source: Broadband light source
Detector: Spectrometer

Question 19

What LIGHT SOURCE and DETECTOR does SS-OCT use?

Answer 19

Light Source: Tuned narrowband laser
Detector: Photodetector