OCT system development
OCT is now established as the standard clinical imaging modality for screening and diagnosis of several retinal diseases as well as glaucoma. Currently, there are more than a dozen established and start-up companies participating in the growth of the ophthalmology OCT market. Yet, new innovations in OCT system development are made every day leading to several categories of setups depending on the source, beam delivery, and detection techniques. Compared to other optical imaging techniques, OCT systems are fast, label-free (relying on backscattering), and have intrinsic microscale axial sectioning capabilities. Therefore, OCT systems have been used to image a variety of samples. While we have highlighted a few of our recent OCT systems in the next sections, we list the different categories of OCT setups and our contributions to the field.
SPECTRAL DOMAIN OCTSources: LED, Superluminiscent diodes, PCF-pumped ultrafast lasers |
Snapshot OCM: Full-field spectral-domain OCT that uses no moving parts to generate 3D images, using a hyperspectral camera | Paper. Briefcase OCT: An economical and a compact OCT probe that fits in a briefcase for primary care and point-of-care applications | Paper. Dynamic OCE: Measure the mechanical properties of samples noninvasively by tracking the stress-induced displacements using volumetric OCT | Paper. Multimodal systems: An integrated system that combined OCT with multiphoton microscopy | Paper. |
SWEPT-SOURCE OCTSources: Swept-source lasers |
Polarization-sensitive OCT: The polarization-sensitivity of the setup was exploited not only for Biological applications but also to explore the effects of multiple scattering in OCT | Paper. |
ENDOSCOPIC OCTSources: Swept-source lasers |
Endoscopic OCT: Catheter-based OCT inserted into an endotracheal tube to study the efficacy of suctioning | Paper. |
FULL-FIELD OCMSources: LED |
4-phase shifted OCM: Permits capturing single shot phase sensitive imaging through simultaneous acquisition of four phase-shifted images with a single camera using unpolarized light for object illumination | Paper. |
EN FACE OCTDetection in (x,y,t) |
En face Fourier-domain OCT: Creates temporal modulation of the light beam which is later demodulated to yield phase-sensitive OCT images of the retina | Paper. |
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Besides these, we have improved the functionality of these systems by integrating them with adaptive optics, portable systems for point-of-care imaging, polarization-sensitive imaging, spectroscopic imaging, magnetomotive contrasts, etc. for several biological and biomedical applications. |
Ear probes
Nearly everyone has directly experienced or knows someone that has had repeated issues with ear infections. Otitis media, the general clinical name for ear infections, are one of the most common reasons for kids to visit the doctor’s office. Our group has developed an imaging system and handheld imaging probe, based on optical coherence tomography, to visualize the contents of the middle ear noninvasively using infrared light no stronger than sunlight. This imaging system can detect the contents of the middle ear without relying on visualization of the eardrum surface, which is often blocked by earwax or a difficult-to-navigate ear canal. This helps physicians more accurately diagnose and ultimately treat ear infections.
PUBLICATIONS:
- Monroy GL, Pande P, Nolan RM, Shelton RL, Porter RG, Novak MA, Spillman DR, Chaney EJ, McCormick DT, Boppart SA. Noninvasive in vivo optical coherence tomography tracking of chronic otitis media in pediatric subjects after surgical intervention. J Biomedical Optics, 22:121614. 2017.
Snapshot OCM
Prevalent techniques in label-free linear optical microscopy are either confined to imaging in two dimensions or rely on scanning, both of which restrict their applications in imaging subtle biological dynamics. In this paper, we present the theoretical basis along with demonstrations supporting that full-field spectral-domain interferometry can be used for imaging samples in 3D with no moving parts in a single shot. Consequently, we propose a novel optical imaging modality that combines low-coherence interferometry with hyperspectral imaging using a light-emitting diode and an image mapping spectrometer, called Snapshot optical coherence microscopy (OCM). Having first proved the feasibility of Snapshot OCM through theoretical modeling and a comprehensive simulation, we demonstrate an implementation of the technique using off-the-shelf components capable of capturing an entire volume in 5 ms. The performance of Snapshot OCM, when imaging optical targets, shows its capability to axially localize and section images over an axial range of ±10 µm, while maintaining a transverse resolution of 0.8 µm, an axial resolution of 1.4 µm, and a sensitivity of up to 80 dB. Additionally, its performance in imaging weakly scattering live cells shows its capability to not only localize the cells in a densely populated culture but also to generate detailed phase profiles of the structures at each depth for long durations. Consolidating the advantages of several widespread optical microscopy modalities, Snapshot OCM has the potential to be a versatile imaging technique for a broad range of applications.
PUBLICATIONS:
- Iyer RR, Zurauskas M, Cui Q, Gao L, Smith RT, Boppart SA. Full-field spectral domain optical interferometry for snapshot three-dimensional microscopy. Biomedical Optics Express, 11:5903-5919, 2020.
4-phase-shifted full-field optical coherence microscopy
A new method is presented for full-field optical coherence tomography imaging, which permits capturing single shot phase sensitive imaging through simultaneous acquisition of four phase-shifted images with a single camera using unpolarized light for object illumination. Our method retains the full dynamic range of the camera by using different areas of a single camera sensor to capture each image. We demonstrate the performance of our method by imaging phantoms and live cultures of fibroblast, cancer, and macrophage cells to achieve 59 dB sensitivity with isotropic resolution down to 1 μm, and displacement sensitivity down to 0.1 nm. Our method can serve as a platform for developing high resolution imaging systems because when used in conjunction with broadband spatially incoherent light sources, the resolution is not affected by optical aberrations or speckle noise.
PUBLICATIONS:
- Zurauskas M, Iyer RR, Boppart SA. Simultaneous 4-phase-shifted full-field optical coherence microscopy. Biomedical Optics Express, 12:981-992, 2021.
Briefcase OCT
Development of low-cost and portable optical coherence tomography (OCT) systems is of global interest in the OCT research community. Such systems enable utility broadly throughout a clinical facility, or in remote areas that often lack clinical infrastructure. We report the development and validation of a low-cost, portable briefcase spectral-domain optical coherence tomography (SD-OCT) system for point-of-care diagnostics in primary care centers and/or in remote settings. The self-contained briefcase OCT contains all associated optical hardware, including light source, spectrometer, hand-held probe, and a laptop. Additionally, this system utilizes unique real-time mosaicking of surface video images that are synchronized with rapid A-scan acquisition to eliminate the need for lateral scanning hardware, and enable the construction of cross-sectional B-mode images over extended lateral distances. The entire briefcase system weighs 9 kg and costs ∼USD$8000 using off-the-shelf components. System performance was validated by acquiring images of in vivo human skin on the fingertip, palm, and nail fold. The efficiency, portability, and low-cost enable accessibility and utility in primary care centers and low-resource settings.
PUBLICATIONS:
- Dsouza R, Won J, Monroy GL, Spillman DR, Boppart SA. Economical and compact briefcase spectral domain optical coherence tomography system for primary care and point-of-care applications. J Biomedical Optics, 23:096003. 2018.