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Application: Near/Short wave Infrared Sensors for Optical Coherence Tomography (OCT) High Resolution Imaging in Tissue


Optical Coherence Tomography (OCT), a low-coherence interferometry technique, is well established as a non-invasive clinical tool for high resolution ophthalmic imaging of the retina. Researchers are now developing systems to image tissue to several millimeters depth with micron resolution. The technique already finds cellular changes years before cancer appears and has applications for finding cancers in skin, and gastrointestinal tissue, or in finding plagues in arteries.

The 1.3 µm SWIR wavelength is used for Optical Coherence Tomography in tissue because this wavelength travels farther in the scattering medium than visible or NIR wavelengths, due to a phenomenon called Raleigh scattering. In one version of Optical Coherence Tomography, called spectral domain optical coherence tomography (SD-OCT), line scan cameras capture one line of depth information for each readout cycle (known as an axial line or as an "A-line"). Moving the light probe over the tissue in both X and Y directions results in capture of a 3 dimensional view of the tissue. The LDH family of high speed digital linescan cameras allows users to boost line acquisition rates by a factor of ten to 47,000 lines per second; this cuts the time the patient has to hold still by an order of magnitude.

Read our recent article on OCT imaging with NIR and SWIR cameras from Sensors Unlimited, Inc.


3 dimensional OCT image of a fingertip, showing detail beneath the skins' surface and therefore invisible to the human eye, imaged with a high speed linescan camera.
Rotating image of Optical Coherence Tomography tomogram of a fingertip, depicting stratum corneum. At the bottom are superficial parts of the dermis. Sweatducts are clearly visible. Provided by medOCT group, Medical University Vienna, Austria.

An alternative method using two InGaAs cameras provides full-field optical coherence tomography (FF-OCT) by use of heterodyne techniques. The tissue section is fully illuminated and en-faced imaged to capture the data at one depth. Then, the reference mirror is shifted to add images at successive depths, building the 3-D reconstruction of the tissue block. Goodrich high-frame rate imaging cameras, such as the SULDH, SU320MSW and SU640SDWH, enable OCT methods to capture changing blood flows with high time resolution.


OCT techniques can be used to image through tissue. For example, a scan of the tissue beneath the skin's surface can be imaged with a laser and a high speed linescan camera.


OCT imagery of a fingertip taken with the SUI LDH camera. The graph on the right shows an A-scan intensity plot corresponding to the location marked with an arrow on the fingertip image. Provided by Professor Kostidika Bizheva, U of Waterloo.
The advantages of SWIR are clear here in SD-OCT imaging where the SUI camera can image the heart stent more clearly than the ultrasound.
Imagery of a heart stent taken with an ultrasound (left) and through OCT (right). Courtesy of Massachusetts General Hospital, Harvard Medical School, Boston, Mass.



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