| 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. By using the 1.05 µm central wavelength, instrumentation companies are now developing systems to image deeper through the retina into the blood vessel layer (called the choroid) to diagnose eye diseases and monitor treatment. Developing clinical applications are in Endoscopy, both in the esophagus or in the arteries, and dentistry.
When SWIR wavelengths like 1.04 and 1.31 are used for OCT in tissue, it is because they travel farther in scattering medium than do visible or NIR wavelengths, due to a phenomenon called Raleigh scattering. In one version of OCT, called spectral-domain optical coherence tomography (SD-OCT), linescan 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 capture a 3 dimensional view of the tissue. The Sensors Unlimited line of high speed digital linescan cameras provide the resolution and speed to image up to 150,000 lines per second of 2048 pixels. The speed cuts the time the patient has to hold still while scanning larger 3-D volumes. The pixel count and related spectral resolution enables deeper image capture with the detail that doctors use to make better healthcare decisions.
Read our recent article on OCT imaging with NIR and SWIR cameras from Sensors Unlimited, Inc.
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| A) A Full-range SD-OCT 3-D image showing front of human eye from eye lashes to below the iris and into the lens, an image of 2048 pixels x 2048 lines x 200 frames covering a volume of 12x18x18 mm. B) Across section of the 3-D image from the top of the cornea through to the bottom of the lens, demonstrating the image depth resulting from the combination of the University of Washington Full-Range FFT technology with the Sensors Unlimited GL2048L camera. Provided by Dr. Ruikang Wang of the BAIL lab at the University |
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. Sensors Unlimited high-frame rate imaging cameras, such as the SU640SDWH and the video frame-rate high-resolution GA1280JS-15, both enable FF-OCT methods to capture 2-D images at specific depths in one frame capture.
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| En-face OCT imagery of Capillary network in ON Head taken with the Sensors Unlimited LDH camera. Provided by Professor Kostidika Bizheva, U of Waterloo. | Imagery of a heart stent taken with an ultrasound (left) and through OCT (right). The ultrasound technology sees deeper than OCT, but with far lower resolution. Thus, the SWIR OCT image on the right shows much more detail, including the tissue squeezing through the stent in the upper right quadrant of the vessel. Courtesy of Massachusetts General Hospital, Harvard Medical School, Boston, Mass. |
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