Dynamic optical coherence elastography (OCE) tracks elastic wave propagation speed within tissue, enabling quantitative three-dimensional imaging of the elastic modulus. We show that propagating mechanical waves are mode converted at interfaces, creating a finite region on the order of an acoustic wavelength where there is not a simple one-to-one correspondence between wave speed and elastic modulus. Depending on the details of a boundary's geometry and elasticity contrast, highly complex propagating fields produced near the boundary can substantially affect both the spatial resolution and contrast of the elasticity image. We demonstrate boundary effects on Rayleigh waves incident on a vertical boundary between media of different shear moduli. Lateral resolution is defined by the width of the transition zone between two media and is the limit at which a physical inclusion can be detected with full contrast. We experimentally demonstrate results using a spectraldomain OCT system on tissue-mimicking phantoms, which are replicated using numerical simulations. It is shown that the spatial resolution in dynamic OCE is determined by the temporal and spatial characteristics (i.e., bandwidth and spatial pulse width) of the propagating mechanical wave. Thus, mechanical resolution in dynamic OCE inherently differs from the optical resolution of the OCT imaging system.

We report a novel design and operation of a highly integrated miniature handheld OCT probe, with high-speed angiography function that can be used in clinical settings for young children and infants, providing rapid, non-invasive structural and angiographic imaging of the retina and choroid. The imaging system is operated at 200 kHz, with 3D OCT and OCTA scan time of 0.8 and 3.2 seconds, respectively, and the scanning angle on the pupil is ± 36°, covering the full perifoveal region. Operator assisting features of the direct-view iris camera and on-probe display are integrated into the hand-held probe, and the fixation target can display animations to attract the attention of young subjects. Compared to conventional OCT systems, the high-speed hand-held OCT system significantly improves the operator's experience and scanning efficiency, which is important for imaging infants. Imaging results indicate a significant reduction in total time consumption in pediatric ophthalmic imaging sessions, as well as the image quality of OCT angiography.

Background: Retinopathy of prematurity (ROP) can lead to retinal detachment and severe vision loss and is a common cause of childhood blindness. Optical coherence tomography angiography (OCTA) is a noninvasive imaging modality that can be used to detect potential abnormalities in the microvasculature in this population. The objective of this study is to assess the feasibility of a newly developed handheld swept source OCT (SS-OCT) device to successfully acquire structural vitreoretinal and retinal microvascular images in awake premature infants.Methods: OCT and OCTA images were acquired at the time of routine ROP examinations from awake, unsedated preterm infants in the Neonatal Intensive Care Unit using a clinical research prototype handheld probe integrated with an SS-OCT system working at 1,060 nm wavelength and an imaging speed of 200,000 A-scans per second (200 kHz), enabling volume OCT and OCTA scans. Each volume was acquired with approximately 36˚ field of view (~6.3×6.3 mm in infants) in 4.8 s. Quality of acquired OCT and OCTA volume images, microvascular information, and vitreoretinal features were determined by 3-masked grader consensus.Results: Twelve infants (5 females, mean gestational age 28.3 weeks, median birth weight 901 g, stages 0 to 3 ROP) underwent a total of 73 individual eye imaging sessions. High-quality OCT images of the fovea and the optic nerve were present in 69/73 (94.5%) and 56/73 (76.7%) scans, respectively. Vitreous bands were observed in 10/73 (13.7%); punctate hyperreflective vitreous opacities in 47/73 (64.4%); epiretinal membrane (ERM) in 6/73 (8.2%); and cystoid macular edema (CME) in 12/73 (16.4%) scans. Mild vessel elevation was noted in 3/73 (4.1%) images, and severe vessel elevation in 4/73 (5.5%) scans. OCTA images obtained in 8 awake infants revealed good quality images of the foveal microvasculature in 11/19 (58%) eye imaging sessions for 6/8 (75%) infants; and peripapillary microvasculature in 14/19 (74%) eye imaging sessions for 5/8 (63%) infants. Conclusions:The SS-OCTA handheld device can capture important vitreoretinal characteristics such as peripapillary and foveal microvasculature, as well as hyperreflective punctate vitreous opacities and tractional vitreous bands, which may predict ROP severity. These images were captured in awake, premature infants without the use of direct ocular contact, an eyelid speculum, or sedation.

Photonics, especially optical coherence elastography (OCE) and second harmonic generation (SHG) imaging are novel high-resolution imaging modalities for characterisation of biological tissues. Following our preliminary experience, we hypothesized that OCE and SHG imaging would delineate the microstructure of prostate tissue and aid in distinguishing cancer from the normal benign prostatic tissue. Furthermore, these approaches may assist in characterisation of the grade of cancer, as well. In this study, we confirmed a high diagnostic accuracy of OCE and SGH imaging in the detection and characterisation of prostate cancer for a large set of biopsy tissues obtained from men suspected to have prostate cancer using transrectal ultrasound (TRUS). The two techniques and methods described here are complementary, one depicts the stiffness of tissues and the other illustrates the orientation of collagen structure around the cancerous lesions. The results showed that stiffness of cancer tissue was approximately 57.63% higher than that of benign tissue (Young’s modulus of 698.43 ± 125.29 kPa for cancerous tissue versus 443.07 ± 88.95 kPa for benign tissue with OCE. Using histology as a reference standard and 600kPa as a cut-off threshold, the data analysis showed sensitivity and specificity of 89.6% and 99.8% respectively. Corresponding positive and negative predictive values were 99.5% and 94.6% respectively. There was a significant difference noticed in terms of Young’s modulus for different Gleason scores estimated by OCE (p value < 0.05). For SHG, distinct patterns of collagen distribution were seen for different Gleason grade disease with computed quantification employing a ratio of anisotropic to isotropic (A: I ratio) and this correlated with disease aggressiveness.

Elastography has the ability of quantitatively evaluating the mechanical properties of soft tissue; thus it is helpful for diagnosis and treatment monitoring of many diseases, for example, skin diseases. Surface acoustic waves (SAWs) have been proven to be a non-invasive, non-destructive method for accurate characterization of tissue elastic properties. Current SAW elastography using high-energy laser pulse or mechanical shaker still have some problems. In order to improve SAW elastography in medical application, a new technique was proposed in this paper, which combines high-intensity-focused ultrasound as a SAWs impulse inducer and phase-sensitive optical coherence tomography as a SAWs detector. A 2% agar-agar phantom and ex-vivo porcine skin were tested. The data were processed by a new algorithm based on the Fourier analysis. The results show that the proposed method has the capability of quantifying the elastic properties of soft tissue-mimicking materials. The lateral resolution of the elastogram has been significantly improved and the different layers in heterogeneous material could also been distinguished. Our improved technique of SAW elastography has a large potential to be widely applied in clinical use for skin disease diagnosis and treatment monitoring.

Purpose To compare retinal vascular parameters acquired by handheld swept-source optical coherence tomography angiography (SS-OCTA) between nonsedated preterm and full-term infants. Methods Preterm and full-term infants at the University of Washington Medical Center were enrolled. Retinal angiograms (nominal size ∼7 × 7 mm 2 ) were obtained at each routine retinopathy of prematurity (ROP) screening session for preterms and once during the first 72 hours of life for full-terms. Macular vessel area density and nonperfusion area were evaluated on the binarized vasculature map in both small (1.5 × 1.5 mm) and large (3 × 3 mm) quadrants. Average vessel diameter and tortuosity values were obtained from each large vessel branch (length >200 µm). All vascular analyses used previously published algorithms. Results Handheld SS-OCTA captured 31 of 55 (56%) high-quality volumes on 8 awake preterm infants (gestational age 28 ± 4 weeks, birth weight 891 ± 314 g, postmenstrual age at first imaging session 37 ± 2 weeks) and 48 of 54 (89%) volumes on 12 awake full-term infants (gestational age 39 ± 1 weeks, birth weight 3405 ± 329 g). Signal-to-noise ratio was 5.08 ± 1.52 dB in preterm and 4.90 ± 1.12 dB in full-term infants. Preterm infants had higher mean large vessel tortuosity compared to full-term infants ( P = 0.004). The large nasal quadrant vessel area density of infants with stage 3 and/or pre-plus or worse ROP was higher than other preterm infants ( P = 0.007). Conclusions Although inadequate image quality limited usable imaging sessions, handheld SS-OCTA achieved adequate signal-to-noise ratio in nonsedated infants for quantitative retinal vascular parameter analysis. Translational Relevance Large- and small-vessel parameters were associated with prematurity and ROP severity, respectively.

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