Behrooz Zabihian

Choroidal Haller's and Sattler's Layer Thickness Measurement Using 3-Dimensional 1060-nm Optical Coherence Tomography

Objectives To examine the feasibility of automatically segmented choroidal vessels in three-dimensional (3D) 1060-nmOCT by testing repeatability in healthy and AMD eyes and by mapping Hallers and Sattlers layer thickness in healthy eyes Methods Fifty-five eyes (from 45 healthy subjects and 10 with non-neovascular age-related macular degeneration (AMD) subjects) were imaged by 3D-1060-nmOCT over a 36°x36° field of view. Hallers and Sattlers layer were automatically segmented, mapped and averaged across the Early Treatment Diabetic Retinopathy Study grid. For ten AMD eyes and ten healthy eyes, imaging was repeated within the same session and on another day. Outcomes were the repeatability agreement of Hallers and Sattlers layer thicknesses in healthy and AMD eyes, the validation with ICGA and the statistical analysis of the effect of age and axial eye length (AL) on both healthy choroidalsublayers. Results The coefficients of repeatability for Sattlers and Hallers layers were 35% and 21% in healthy eyes and 44% and 31% in AMD eyes, respectively. The mean±SD healthy central submacular field thickness for Sattlers and Hallers was 87±56 µm and 141±50 µm, respectively, with a significant relationship for AL (P<.001). Conclusions Automated Sattlers and Hallers thickness segmentation generates rapid 3D measurements with a repeatability correspondingto reported manual segmentation. Sublayers in healthy eyes thinnedsignificantly with increasing AL. In the presence of the thinned Sattlers layer in AMD, careful measurement interpretation is needed. Automatic choroidal vascular layer mapping may help to explain if pathological choroidal thinning affects medium and large choroidal vasculature in addition to choriocapillaris loss.

In vivo three dimensional dual wavelength photoacoustic tomography imaging of the far red fluorescent protein E2-Crimson expressed in adult zebrafish

For the first time the far red fluorescent protein (FP) E2-Crimson genetically expressed in the exocrine pancreas of adult zebrafish has been non-invasively mapped in 3D in vivo using photoacoustic tomography (PAT). The distribution of E2-Crimson in the exocrine pancreas acquired by PAT was confirmed using epifluorescence imaging and histology, with optical coherence tomography (OCT) providing complementary structural information. This work demonstrates the depth advantage of PAT to resolve FP in an animal model and establishes the value of E2-Crimson for PAT studies of transgenic models, laying the foundation for future longitudinal studies of the zebrafish as a model of diseases affecting inner organs.

In vivo dual-modality photoacoustic and optical coherence tomography imaging of human dermatological pathologies

Vascular abnormalities serve as a key indicator for many skin diseases. Currently available methods in dermatology such as histopathology and dermatoscopy analyze underlying vasculature in human skin but are either invasive, time-consuming, and laborious or incapable of providing 3D images. In this work, we applied for the first time dual-modality photoacoustic and optical coherence tomography that provides complementary information about tissue morphology and vasculature of patients with different types of dermatitis. Its noninvasiveness and relatively short imaging time and the wide range of diseases that it can detect prove the merits of the dual-modality imaging system and show the great potential of its clinical use in the future.

Dual modality optical coherence and whole-body photoacoustic tomography imaging of chick embryos in multiple development stages

Chick embryos are an important animal model for biomedical studies. The visualization of chick embryos, however, is limited mostly to postmortem sectional imaging methods. In this work, we present a dual modality optical imaging system that combines swept-source optical coherence tomography and whole-body photoacoustic tomography, and apply it to image chick embryos at three different development stages. The explanted chick embryos were imaged in toto with complementary contrast from both optical scattering and optical absorption. The results serve as a prelude to the use of the dual modality system in longitudinal whole-body monitoring of chick embryos in ovo.

Combined multi-modal photoacoustic tomography, optical coherence tomography (OCT) and OCT angiography system with an articulated probe for in vivo human skin structure and vasculature imaging

Cutaneous blood flow accounts for approximately 5% of cardiac output in human and plays a key role in a number of a physiological and pathological processes. We show for the first time a multi-modal photoacoustic tomography (PAT), optical coherence tomography (OCT) and OCT angiography system with an articulated probe to extract human cutaneous vasculature in vivo in various skin regions. OCT angiography supplements the microvasculature which PAT alone is unable to provide. Co-registered volumes for vessel network is further embedded in the morphologic image provided by OCT. This multi-modal system is therefore demonstrated as a valuable tool for comprehensive non-invasive human skin vasculature and morphology imaging in vivo.

In vivo spectroscopic photoacoustic tomography imaging of a far red fluorescent protein expressed in the exocrine pancreas of adult zebrafish

Fluorescent proteins brought a revolution in life sciences and biological research in that they make a powerful tool for researchers to study not only the structural and morphological information, but also dynamic and functional information in living cells and organisms. While green fluorescent proteins (GFP) have become a common labeling tool, red-shifted or even near infrared fluorescent proteins are becoming the research focus due to the fact that longer excitation wavelengths are more suitable for deep tissue imaging. In this study, E2-Crimson, a far red fluorescent protein whose excitation wavelength is 611 nm, was genetically expressed in the exocrine pancreas of adult zebrafish. Using spectroscopic all optical detection photoacoustic tomography, we mapped the distribution of E2-Crimson in 3D after imaging the transgenic zebrafish in vivo using two different wavelengths. With complementary morphological information provided by imaging the same fish using a spectral domain optical coherence tomography system, the E2-Crimson distribution acquired from spectroscopic photoacoustic tomography was confirmed in 2D by epifluorescence microscopy and in 3D by histology. To the authors’ knowledge, this is the first time a far red fluorescent protein is imaged in vivo by spectroscopic photoacoustic tomography. Due to the regeneration feature of zebrafish pancreas, this work preludes the longitudinal studies of animal models of diseases such as pancreatitis by spectroscopic photoacoustic tomography. Since the effective penetration depth of photoacoustic tomography is beyond the transport mean free path length, other E2-Crimson labeled inner organs will also be able to be studied dynamically using spectroscopic photoacoustic tomography.

Mapping diurnal changes in choroidal, Haller’s and Sattler’s layer thickness using 3-dimensional 1060-nm optical coherence tomography

PurposeTo test the significance of diurnal changes in choroidal, Haller’s and Sattler’s layer thickness in healthy subjects using spatial analysis of three-dimensional (3D) 1060-nm optical coherence tomography (OCT) scans.MethodsAutomatically generated choroidal, Haller’s and Sattler’s layer thickness maps were statistically analyzed for 19 healthy subjects at two time points (8 a.m. and 6 p.m.) that represent the currently proposed ChT peak and nadir. All subjects were imaged by high-speed 1060-nm OCT over a 36° × 36° field of view. Spatial distribution of layer thickness was analyzed using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid.ResultsThe choroid was significantly thicker at 8 a.m. than at 6 p.m. (p < 0,0125, paired t-test, Bonferroni correction). Diurnal variation of mean choroidal thickness (ChT) for all ETDRS subfields was 12 μm. Haller’s layer thickness showed no significant diurnal variation (P > 0.0125), but Sattler’s layer was thicker in the morning than in late afternoon (P < 0.0125).ConclusionsOur measurements indicate that diurnal ChT variation may exist, but is less relevant than previously proposed by studies using single location imaging. Sattler’s layer shows diurnal variation in line with ChT.

Nonequispaced grid sampling in photoacoustics with a nonuniform fast Fourier transform.

Abstract. To obtain the initial pressure from the collected data on a planar sensor arrangement in photoacoustic tomography, there exists an exact analytic frequency-domain reconstruction formula. An efficient realization of this formula needs to cope with the evaluation of the data’s Fourier transform on a nonequispaced mesh. We use the nonuniform fast Fourier transform to handle this issue and show its feasibility in three-dimensional experiments with real and synthetic data. This is done in comparison to the standard approach that uses linear, polynomial, or nearest neighbor interpolation. Moreover, we investigate the effect and the utility of flexible sensor location to make optimal use of a limited number of sensor points. The computational realization is accomplished by the use of a multidimensional nonuniform fast Fourier algorithm, where nonuniform data sampling is performed both in frequency and spatial domain. Examples with synthetic and real data show that both approaches improve image quality.

Mapping Retinal and Choroidal Thickness in Unilateral Nongranulomatous Acute Anterior Uveitis Using Three-Dimensional 1060-nm Optical Coherence Tomography

Purpose To analyze retinal thickness (RT) and choroidal thickness (ChT) changes in patients with unilateral nongranulomatous acute anterior uveitis (AAU) using three-dimensional (3D) 1060-nm optical coherence tomography (OCT). Methods Retinal and choroidal thickness maps were statistically analyzed for 24 patients with newly diagnosed unilateral AAU before therapy. A total of 17 patients were followed until resolution of inflammatory activity (twice in the first week, then weekly). Resolution occurred in all subjects within 6 weeks after the initial diagnosis. After resolution, thickness maps were again generated. All patients were imaged by high-speed spectral-domain (SD) 3D 1060-nm OCT over a 10 × 10-mm field of view. The spatial distribution of retinal and choroidal thickness was mapped and analyzed using the Early Treatment Diabetic Retinopathy Study (ETDRS) grid. Results The choroid was significantly thicker in eyes affected by AAU than in fellow eyes before therapy with a mean thickness difference of 37 ± 11.44 μm (mean ± SD, Bonferroni correction, α = 0.0125). Following therapy, ChT significantly decreased with a mean change of 24 ± 6.9 μm (mean ± SD, Bonferroni correction, α = 0.0125). There was no significant difference in RT between AAU and fellow eyes before therapy or in AAU eyes before and after therapy. Conclusions Eyes affected by AAU demonstrate an increase in ChT before and a subsequent decrease after therapy while retinal thickness seems unaltered by disease and therapy. ChT might be a useful biomarker in monitoring posterior involvement and response to therapy in patients with AAU.

Comprehensive vascular imaging using optical coherence tomography-based angiography and photoacoustic tomography

Abstract. Studies have proven the relationship between cutaneous vasculature abnormalities and dermatological disorders, but to image vasculature noninvasively in vivo, advanced optical imaging techniques are required. In this study, we imaged a palm of a healthy volunteer and three subjects with cutaneous abnormalities with photoacoustic tomography (PAT) and optical coherence tomography with angiography extension (OCTA). Capillaries in the papillary dermis that are too small to be discerned with PAT are visualized with OCTA. From our results, we speculate that the PA signal from the palm is mostly from hemoglobin in capillaries rather than melanin, knowing that melanin concentration in volar skin is significantly smaller than that in other areas of the skin. We present for the first time OCTA images of capillaries along with the PAT images of the deeper vessels, demonstrating the complementary effective imaging depth range and the visualization capabilities of PAT and OCTA for imaging human skin in vivo. The proposed imaging system in this study could significantly improve treatment monitoring of dermatological diseases associated with cutaneous vasculature abnormalities.