Time-domain Optical Coherence Tomography System Research Articles

Imaging a spiral dissection of the superficial femoral artery in high resolution with optical coherence tomography—Seeing is believing

Optical coherence tomography (OCT) offers an alternative to intravascular ultrasound (IVUS) for endovascular imaging. Clinical and research applications for OCT have emerged in percutaneous coronary intervention (PCI), however, OCT has not found similar utility in peripheral arterial interventions. Early generation time-domain OCT systems required arterial occlusion to create the blood free environment needed for image acquisition and could not reliably scan vessel diameters encountered in the peripheral circulation. However, the frequency-domain OCT (FD-OCT) system currently FDA approved for use in the United States does not require arterial occlusion to generate images and permits a greater scan diameter allowing for exploratory use in peripheral arteries. To our knowledge, this is the first report using non-occlusive OCT imaging to serve as an adjunct to endovascular intervention for femoropopliteal disease. We illustrate the feasibility of acquiring high resolution images of a spiral dissection of the superficial femoral artery following balloon angioplasty that was not adequately visualized by angiography.

Comparison of Contrast Media and Low-Molecular-Weight Dextran for Frequency-Domain Optical Coherence Tomography

Although an intracoronary frequency-domain optical coherence tomography (FD-OCT) system overcomes several limitations of the time-domain OCT (TD-OCT) system, the former requires injection of contrast media for image acquisition. The increased total amount of contrast media for FD-OCT image acquisition may lead to the impairment of renal function. The safety and usefulness of the non-occlusion method with low-molecular-weight dextran L (LMD-L) via a guiding catheter for TD-OCT image acquisition have been reported previously. The aim of the present study was to compare the image quality and quantitative measurements between contrast media and LMD-L for FD-OCT image acquisition in coronary stented lesions. Twenty-two patients with 25 coronary stented lesions were enrolled in this study. FD-OCT was performed with the continuous-flushing method via a guiding catheter. Both contrast media and LMD-L were infused at a rate of 4 ml/s by an autoinjector. With regard to image quality, the prevalence of clear image segments was comparable between contrast media and LMD-L (97.9% vs. 96.5%, P=0.90). Furthermore, excellent correlations were observed between both flushing solutions in terms of minimum lumen area, mean lumen area, and mean stent area. The total volumes of contrast media and of LMD-L needed for OCT image acquisition were similar. FD-OCT image acquisition with LMD-L has the potential to reduce the total amount of contrast media without loss of image quality.

Postnatal Elongation of Eye Size in DBA/2J Mice Compared with C57BL/6J Mice: In Vivo Analysis with Whole-Eye OCT

To characterize postnatal changes in eye size in glaucomatous DBA/2J (D2) mice and in nonglaucomatous C57BL/6J mice (B6) in vivo by means of whole-eye optical coherence tomography (OCT). D2 (n = 32) and B6 (n = 36) mice were tested between 2 and 20 months of age in eight age bins. A custom time-domain OCT system with a center wavelength of 825 nm and an axial scan length of 7.1 mm produced axial A-scan interferograms at a rate of 20 A-lines/s with a resolution of 8 μm. Axial length (AL), corneal thickness (CT), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and retinal thickness (RT) were measured in the optical axis and adjusted with corresponding refractive indices. Corneal curvature (CC) and IOP were also measured. AL increased (P < 0.001) more in the D2 (21%) than in the B6 (9%) mice. There was an interaction effect (two-way ANOVA, P < 0.001) between age and strain for AL, CT, ACD, and VCD. In the D2 mice, the lens became dislocated posteriorly. Multiple regression analysis in the D2 mice revealed an independent effect of age and IOP (P ≤ 0.01) on axial length. CC steepened in the older D2 mice, whereas it flattened in the B6 mice. In D2 mice, postnatal elongation of AL is larger than that in B6 mice and is associated with a greater increase in ACD and IOP, which seems to be a causal factor. The ease of use, short acquisition time, and noninvasiveness of whole-eye OCT make it suitable for routine use in longitudinal studies of mouse models.

Determination of the scattering anisotropy with optical coherence tomography

In this work we demonstrate measurements with optical coherence tomography (OCT) of the scattering phase function in the backward direction and the scattering anisotropy parameter g. Measurements of the OCT attenuation coefficient and the backscattering amplitude are performed on calibrated polystyrene microspheres with a time-domain OCT system. From these measurements the phase function in the backward direction is determined. The measurements are described by the single scattering model and match Mie calculations very well. Measurements on Intralipid demonstrate the ability to determine the g of polydisperse samples and, for Intralipid, g = 0.35 ± 0.03 is measured, which is well in agreement with g from literature. These measurements are validated using the Intralipid particle size distribution determined from TEM measurements. Measurements of g and the scattering phase function in the backward direction can be used to monitor changes in backscattering, which can indicate morphological changes of the sample or act as contrast enhancement mechanism.

Miniature endoscopic optical coherence tomography probe employing a two-axis microelectromechanical scanning mirror with through-silicon vias

We present the design and experimental results of a new MEMS-based endoscopic optical coherence tomography (OCT) probe. The uniqueness of this miniature OCT imaging probe is a two-axis MEMS mirror with through-silicon vias (TSVs) for interconnecting. The TSV interconnection enables ultracompact probe design, successfully reducing the probe size to only 2.6 mm in diameter. The MEMS mirror is actuated by an electrothermal actuator that is capable of scanning ± 16° at only 3.6 V DC. Two-dimensional and three-dimensional OCT images of microspheres embedded in PDMS and acute rat brain tissue have been obtained with this miniature probe in a time-domain OCT system.

Miniature 10 kHz thermo-optic delay line in silicon

The scanning delay line is a key component of time-domain optical coherence tomography systems. It has evolved since its inception toward higher scan rates and simpler implementation. However, existing approaches still suffer from drawbacks in terms of size, cost, and complexity, and they are not suitable for implementation using integrated optics. In this Letter, we report a rapid scanning delay line based on the thermo-optic effect of silicon at λ = 1.3 μm manufactured around a generic planar lightwave circuit technology. The reported device attained line scan rates of 10 kHz and demonstrated a scan range of 0.95 mm without suffering any observable loss of resolution (15 µm FWHM) owing to depth-dependent chromatic dispersion.

Corneal power measurement with Fourier-domain optical coherence tomography

To study the accuracy and repeatability of anterior, posterior, and net corneal power measured by Fourier-domain optical coherence tomography (OCT). Doheny Eye Institute, Los Angeles, California, USA. Cross-sectional study. A Fourier-domain OCT system (RTVue) was used to scan normal eyes, eyes after myopic laser in situ keratomileusis (LASIK), and keratoconic eyes. After the corneal surfaces were delineated, the system calculated anterior and posterior corneal powers by curve fitting over the central 3.0 mm diameter area. Net corneal power was calculated using a thick-lens formula. The repeatability of the calculations was evaluated by the pooled standard deviation of 3 measurements from the same visit. The net corneal power values were compared with standard automated keratometry measurements (IOLMaster). The repeatability of Fourier-domain OCT net corneal power was 0.19 diopters (D), 0.26 D, and 0.30 D in the normal, post-LASIK, and keratoconus groups, respectively. The Fourier-domain OCT net corneal power was significantly lower than keratometry by a mean of -1.21 D, -2.89 D, and -3.07 D, respectively (P<.001). The anterior-posterior curvature ratio was lower in post-LASIK and keratoconic eyes than in normal eyes (P<.001). Corneal power measured by Fourier-domain OCT achieved good repeatability in all 3 groups. The repeatability was better than slower time-domain OCT systems. Because Fourier-domain OCT directly measures both anterior and posterior corneal surfaces, it may produce more consistent results than standard keratometry in post-LASIK and keratoconic eyes in which the anterior-posterior corneal curvature ratios are altered by surgery or disease.

Automatic segmentation of clinical OCT images for the determination of epithelial thickness changes in laryngeal lesions

Automated classification of laryngeal lesions using optical coherence tomography data can be helpful in making a faster and safer diagnosis. A change in the epithelial layer thickness seems to be an effective indicator for laryngeal cancer and its precursors. Lesions with different grades of malignancy were scanned with a time domain OCT system during microlaryngoscopy. Every diagnosis was confirmed by performing a biopsy. Each OCT image was separately segmented, manually by an expert and automatically by a segmentation algorithm. Values for the maximal and average epithelial thickness as well as the standard deviations were compared for both segmentations. The results show a thickening of the epithelium from normal over dysplastic to cancerous tissue. The values for the automatic segmentation are in good agreement with expert segmentation. In conclusion, automatic segmentation can be used for epithelial thickness measurements as a promising indicator for laryngeal cancer. It would also be possible to extract other characteristics like standard deviation or signal attenuation within the segments. Thus, we laid the foundation for computer-aided diagnosis of laryngeal lesions.

Correlation of fundus autofluorescence with photoreceptor morphology and functional changes in eyes with retinitis pigmentosa

To assess and correlate fundus autofluorescence (FAF) characteristics with photoreceptor morphology and functional features in eyes with retinitis pigmentosa (RP). Thirty-four eyes of 17 patients with RP were examined. We compared FAF images obtained by confocal scanning laser ophthalmoscopy with Spectral-domain optical coherence tomography (SD-OCT) and retinal function assessed by microperimetry. Normal FAF surrounded by a ring of increased FAF at the macular area was detected in 32 (94%) eyes. The diameter of the normal FAF was correlated significantly with the preserved area of the photoreceptor inner segment and outer segment (IS/OS) junction on SD-OCT (R=0.939, p<0.001). The area outside the ring was associated with loss of IS/OS junction and external limiting membrane (ELM). The ring of increased FAF demarcated the border between the central retina with preservation of the IS/OS junction and ELM, and the adjacent eccentric retina with loss of these bands. In two eyes of one patient, there was no preservation of normal FAF at the macula and the photoreceptor IS/OS junction was not detected on SD-OCT. The mean retinal sensitivity derived from microperimetry was correlated significantly with the area of normal FAF (R=0.929, p=0.007) and the preserved area of the IS/OS junction (R=0.851, p=0.032). Ten eyes had progressive reduction in size of the normal FAF inside the ring accompanied by decreased area of preserved IS/OS during 3.1 years. FAF appears to reflect the integrity of the photoreceptor layer. It may serve as a secondary outcome measure for novel therapeutic strategies for RP.

High-speed time-domain optical coherence tomography with an imaging speed of ten frames per second with 2000 A-scan

We report on a high-speed time-domain optical coherence tomography (TD-OCT) technology that is capable of imaging 10 fps with 2000 A-scan. A duplex scanning optical delay line that is driven by a 1-kHz sinusoidal wave function was implemented and characterized. The reference and sample arms in a Michelson interferometer were simultaneously scanned using two identical piezoelectric transducers (PZTs). We adopted a sinusoidal wave function with constant voltages as the input functions for the PZTs. A recalibration of the measurement depth was necessary for the sinusoidal wave function operation. A recalibration with a spatial transformation was performed on the A-scan. We achieved an A-scan speed of 6 m/s. To the best our knowledge, this is the highest speed achieved in conventional TD-OCT systems to date.

Repeatability of Retinal Thickness Measurements Between Spectral-Domain and Time-Domain Optical Coherence Tomography Images in Macular Disease

To evaluate and compare the intra-session repeatability of retinal thickness measurements from the Topcon 3D OCT 1000 (Topcon Medical Systems; Paramus, NJ), a spectral-domain optical coherence tomography (SD-OCT) system, with the Stratus (Carl Zeiss Meditec, Inc., Dublin, CA), a time-domain OCT (TD-OCT) system, in eyes with retinal diseases. Repeated scans with both SD-OCT and TD-OCT were taken. Thickness measurements from high-quality scans were used to assess repeatability and compare measurements between the two instruments. Paired scans from 127 eyes were evaluated, of which 63 pairs were of high quality. Coefficients of repeatability and variation for the central subfield were 20.1 μm (2.6%) with SD-OCT and 27.4 μm (4%) with TD-OCT (P = .38). The mean difference in central subfield thickness between the two instruments was 24.5 μm (standard deviation = 20.9). Repeatability of retinal thickness measurements with the Topcon 3D OCT 1000 is comparable to the Stratus. The measurements of the two machines differ significantly and cannot be used interchangeably.

A rapid method of measuring dispersion in low coherence interferometry and optical coherence tomography systems

A method of using multiple spectral channels to measure dispersion mismatch in optical coherence tomography (OCT) and low coherence interferometry systems is presented. The method is tested on a time domain OCT system in comparison to the measurement of the auto-correlation profile. The method is quicker to implement and is more sensitive than the measurement of the auto-correlation profile.

Advantage of next‐generation frequency‐domain optical coherence tomography compared with conventional time‐domain system in the assessment of coronary lesion

Intracoronary optical coherence tomography (OCT) is a high-resolution imaging modality used for evaluation of coronary lesion morphology. However, current time-domain OCT (TD-OCT) have a number of limitations with regard to both procedural usage and safety in the clinical setting. The next-generation frequency-domain OCT (FD-OCT), which has a much faster frame rate and pullback speed than TD-OCT, is expected to overcome these limitations. The aim of this study was to evaluate the feasibility and usability of next generation FD-OCT in the assessment of coronary lesions. A comparison study was performed between FD-OCT and TD-OCT from the aspect of usability (set-up time), qualitatively (rate of clear image segment), and safety (adverse event) in 14 ischemic heart disease patients with 20 previously implanted coronary stents. The mean time of the OCT procedure in this study from setup to completion of image acquisition was 3.2 +/- 0.8 min for FD-OCT and 11.2 +/- 2.5 min for TD-OCT (P < 0.01). In qualitative image assessment, FD-OCT has the potential to yield a higher rate of clear image segments (CIS) than TD-OCT (99.4% vs. 80.8%, respectively; P < 0.01). In addition to these improved characteristics, there were no ischemic ECG changes or arrhythmia associated with FD-OCT. The next-generation intracoronary FD-OCT has better performance in the clinical setting and the potential to overcome several limitations of conventional TD-OCT systems.

Structural and optical properties of wood and wood finishes studied using optical coherence tomography: application to an 18th century Italian violin

Optical coherence tomography (OCT) is especially attractive for the study of cultural heritage artifacts because it is noninvasive and nondestructive. We have developed an original full-field time-domain OCT system dedicated to the investigation of varnished and painted artifacts: an interferometric Mirau objective allows one to perform the scan without moving the works of art. The axial and transverse high resolution (respectively, 1.5 and 1 microm) are well adapted to the detection of the investigated structures (pigment grains, wood fibers, etc.). The illumination spectrum is in the visible range (centered at 630 nm, 150 nm wide) to potentially allow us to perform spectroscopic OCT on pigment particles. The examination of wood samples coated with a traditional finish, demonstrates the ability of the system to detect particles, characterize layers thickness, and image the three-dimensional wood structures below the varnishes. OCT has finally been applied to study in situ the coated wood surface of an 18th century Italian violin and provides important information for its conservation treatment.

Comparison of retinal nerve fibre layer measurements from time domain and spectral domain optical coherence tomography systems

Objective: To compare retinal nerve fibre layer (RNFL) thickness measurements acquired using spectral domain (SD) and time domain (TD) optical coherence tomography (OCT) systems. Study Design: Prospective clinical study. Participants: Twenty eyes of 20 healthy volunteers. Methods: All patients underwent 3 sets of circular OCT scans around the optic disc using both a TD OCT system, and a new SD OCT system. RNFL thickness measures within each of 4 quadrants, as well as overall mean RNFL thickness, were compared. Bland-Altman plots were also used to assess agreement. Results: Using the RTVue-100, RNFL measurements in the superior quadrant were, on average, 20 μm greater than those obtained from the Stratus (151.8 μm vs 131.7 μm, p < 0.0001). RNFL measures within other quadrants and overall mean RNFL thickness were not significantly different between systems. Bland-Altman plots indicated large differences between Stratus and RTVue-100 for all variables, with 95% limits of agreement spanning clinically important ranges of >50 μm for all RNFL variables. Conclusions: Significant differences exist between RNFL measurements obtained from the TD and SD OCT systems used in this study. These related, but distinct, technologies are not interchangeable. Further studies will be required to allow for appropriate clinical use of new SD OCT systems.

Optical coherence tomography

Optical coherence tomography (OCT) with micron-scale resolution has become a key intracoronary imaging modality in vivo, providing insights not only into mechanisms of atherosclerotic coronary artery disease, but also into the understanding of vascular response following stent implantation. Although the time-domain OCT system has some technical limitations to acquire images, the recently developed frequency-domain OCT with faster pullback speeds has simplified the procedural requirements with elimination of an occlusion balloon. This article outlines the current and future developments in OCT technology for clinical use and research.

Anterior segment imaging: Fourier-domain optical coherence tomography versus time-domain optical coherence tomography

To compare anterior segment measurements and morphology of 2 optical coherence tomography (OCT) systems. Department of Ophthalmology, District Railway Hospital, and the Nursing Department and Social Medical Issues, Health Care Division, Silesian Medical University, Katowice, Poland. In normal eyes and in eyes with corneal and trabecular-iris angle disorders, the central corneal thickness (CCT), trabecular-iris angle, and angle-opening distance at the nasal and temporal angles were measured 3 times during 1 visit using the Visante time-domain OCT system and the RTVue-100 Fourier-domain corneal anterior module OCT system. Anterior segment morphology was assessed and compared. Fifty-four eyes were evaluated. The mean values (+/-SD) by time-domain OCT and Fourier-domain OCT were, respectively, automatic CCT, 535 +/- 33.07 microm and 538 +/- 31.82 microm; manual CCT, 545 +/- 30.91 microm and 542 +/- 30.57 microm; nasal trabecular-iris angle, 34.7 +/- 9.5 degrees and 35.2 +/- 8.9 degrees; temporal trabecular-iris angle, 35.3 +/- 8.5 degrees and 35.5 +/- 9 degrees; nasal angle-opening distance, 435 +/- 95 microm and 444 +/- 98 microm; and temporal angle-opening distance, 443 +/- 103 microm and 452 +/- 99 microm. There was no significant difference between mean values, and they were highly correlated. On morphologic analysis, time-domain OCT had lower resolution; however, all anterior chamber structures were visible on 1 image. Fourier-domain OCT provided precise information about small areas of the anterior chamber. Fourier-domain OCT provided accurate anterior eye segment measurements that agreed with those obtained with time-domain OCT.

In-vivo retinal imaging by optical coherence tomography using an RSOD-based phase modulator

Fourier-domain rapid scanning optical delay line (RSOD) was introduced for phase modulation and depth scanning in a time-domain optical coherence tomography (TD-OCT) system. Investigation of parameter optimization of RSOD was conducted. Experiments for RSOD characterization at different parameters of the groove pitch, focal length, galvomirror size, etc. were performed. By implementing the optimized RSOD in our established TD-OCT system with a broadband light source centered at 840 nm with 50 nm bandwidth, in vivo retina imaging of a rabbit was presented, demonstrating the feasibility of high-quality TD-OCT imaging using an RSOD-based phase modulator.

Multimodality bonchoscopic imaging of tracheopathica osteochondroplastica

Results of a commercial optical coherence tomography system used as part of a multimodality diagnostic bronchoscopy platform are presented for a 61-year-old patient with central airway obstruction from tracheopathica osteochondroplastica. Comparison to results of white-light bronchoscopy, histology, and endobronchial ultrasound examination are accompanied by a discussion of resolution, penetration depth, contrast, and field of view of these imaging modalities. White-light bronchoscopy revealed irregularly shaped, firm submucosal nodules along cartilaginous structures of the anterior and lateral walls of the trachea, sparing the muscular posterior membrane. Endobronchial ultrasound showed a hyperechoic density of 0.4 cm thickness. optical coherence tomography (OCT) was performed using a commercially available, compact time-domain OCT system (Niris System, Imalux Corp., Cleveland, Ohio) with a magnetically actuating probe (two-dimensional, front imaging, and inside actuation). Images showed epithelium, upper submucosa, and osseous submucosal nodule layers corresponding with histopathology. To our knowledge, this is the first time these commercially available systems are used as part of a multimodality bronchoscopy platform to study diagnostic imaging of a benign disease causing central airway obstruction. Further studies are needed to optimize these systems for pulmonary applications and to determine how new-generation imaging modalities will be integrated into a multimodality bronchoscopy platform.

Analyses and calculations of noise in optical coherence tomography systems

Significant progress has been made in the study of optical coherence tomography (OCT) - a non-invasive, high resolution, and in vivo diagnostic method for medical imaging applications. In this paper, the principles of noise analyses for OCT systems have been described. Comparisons are made of signal-to-noise ratios for both balanced and unbalanced detection schemes under the ideal no-stray light situation as well as the non-ideal situation where residual reflections and scatterings are presented. Numerical examples of noise calculation accompanied by detailed comparison of the main characteristics of both time-domain and frequency-domain OCT systems are also presented. It is shown that a larger dynamic range can be achieved for a Fourier-domain OCT system even under the circumstances of high-speed image acquisition. The main results presented in this paper should be useful for the development of high performance OCT systems.