Optical coherence tomography OCT

Optical coherence tomography

Optical coherence tomography (OCT) is a technology that uses the coherence of light to image fine structures inside samples. It offers several advantages, including high speed, high resolution, non-invasiveness, and real-time observation. OCT is mainly used for non-invasive inspections in medical and industrial applications.

 

Optical coherence tomography can be further explained at Wikipedia.

Principle and method

OCT is a technology that uses the coherence of light to measure distance in the direction that light travels. Near-infrared light is shone on the sample, and the light scattered and reflected back by the sample is combined with reference light passing through a fixed light path inside the OCT device. By detecting the light interference signal generated in this manner, a one-dimensional signal in the depth direction is obtained. It is possible to obtain tomographic images by continuously scanning the position of light incidence on the sample.

SD-OCT (spectral domain-OCT) method

Light from a broadband wavelength light source is shone on the sample, the interference light spectrally dispersed, then detected by a linear image sensor. An image in the depth direction of the sample is acquired by Fourier transforming the obtained wavelength information.

SD-OCT (spectral domain-OCT) method

SS-OCT (swept source-OCT) method

The wavelength-swept light source sweeps the wavelength temporally and shines its output light on the sample, and the generated interference light is detected with a differential detector. An image in the depth direction of the sample is acquired by Fourier transforming the obtained wavelength information.

SS-OCT (swept source-OCT) method

Sample applications by wavelength

Sample applications by wavelength

Application example: Fundoscopy

The state of the retina including swelling and bleeding can be analyzed by taking tomographic images of the retina and nerve fiber layer. This technology is used for early detection of the symptoms of diseases such as glaucoma, age-related macular degeneration (ARMD), and diabetic retinopathy, as well as follow-up examinations after treatment.

 

Learn more on the application of OCT method to opthalmology.

SD-OCT method

SD-OCT method

SS-OCT method

SS-OCT method

Recommended products

[for SD-OCT/SS-OCT]
It is an electromagnetically driven mirror capable of two-dimensional linear motion. It has a wide optical deflection angle and high mirror reflectivity.

[for SD-OCT/SS-OCT]
It is an electromagnetically driven mirror capable of one-dimensional linear motion. It has a wide optical deflection angle and high mirror reflectivity.

[for SD-OCT]
A CMOS linear image sensor with a readout rate of 40 MHz max. and a line rate of 34 kHz max.

[for SD-OCT]
A high-sensitivity CMOS linear image sensor using a photosensitive area with vertically long pixels (14 × 200 µm).

[for SD-OCT]
Front-illuminated type CCD linear image sensor with a high-speed line rate [40 MHz max. (× 4 ports)]

[for SD-OCT]
Image sensor module with a built-in CCD linear image sensor S15729-01.

[for SD-OCT]
A 1024-pixel high-speed InGaAs linear image sensor with high sensitivity in the near-infrared region (0.9 to 1.7 µm).

[for SS-OCT]
These are differential amplification type photoelectric conversion modules containing two Hamamatsu photodiodes with balanced characteristics.

Application example: Brain neuron imaging

The use of a broadband light source in the 1700 nm band enables high-resolution imaging of deep, highly scattered biological tissue. In particular, SD-OCM (spectral domain - optical coherence microscopy) enables non-invasive deep brain neuronal imaging without craniotomy, and has been applied to in-vivo observation of Alzheimer's lesions.

Measurement system

Sensitivity roll-off in air

OCT sensitivity as a function of skin depth

Axial resolution in air

OCT resolution as a function of skin depth

Result

Example OCT image of Cerebral Neuronal Cell Bodies

Example OCT image of Cerebral Myelinated Axons

Example OCT image of Sub-Cortical layers of the Brain

Provided by Jun Zhu and Vivek J. Srinivasan (University of California Davis)

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It is a compact laser light source that emits broadband near-infrared laser light generated from nonlinear optical phenomenon induced by an ultrashort pulsed laser.