Efficient and high accuracy 3-D OCT angiography motion correction in pathology

We describe a novel method for non-rigid 3-D motion correction of orthogonally raster-scanned optical coherence tomography angiography volumes. This is the first approach that aligns predominantly axial structural features such as retinal layers as well as transverse angiographic vascular features in a joint optimization. Combined with orthogonal scanning and favorization of kinematically more plausible displacements, subpixel alignment and micrometer-scale distortion correction is achieved in all 3 dimensions. As no specific structures are segmented, the method is by design robust to pathologic changes. Furthermore, the method is designed for highly parallel implementation and short runtime, allowing its integration into clinical workflow even for high density or wide-field scans. We evaluated the algorithm with metrics related to clinically relevant features in an extensive quantitative evaluation based on 204 volumetric scans of 17 subjects, including patients with diverse pathologies and healthy controls. Using this method, we achieve state-of-the-art axial motion correction and show significant advances in both transverse co-alignment and distortion correction, especially in the subgroup with pathology.

Three-Dimensional Enhanced Imaging of Vitreoretinal Interface in Diabetic Retinopathy Using Swept-Source Optical Coherence Tomography

PURPOSE

To analyze the vitreoretinal interface in diabetic eyes using 3-dimensional wide-field volumes acquired using high-speed, long-wavelength swept-source optical coherence tomography (SSOCT).

DESIGN

Prospective cross-sectional study.

METHODS

Fifty-six diabetic patients (88 eyes) and 11 healthy nondiabetic controls (22 eyes) were recruited. Up to 8 SSOCT volumes were acquired for each eye. A registration algorithm removed motion artifacts and merged multiple SSOCT volumes to improve signal. Vitreous visualization was enhanced using vitreous windowing method.

RESULTS

Of 88 diabetic eyes, 20 eyes had no retinopathy, 21 eyes had nonproliferative diabetic retinopathy (NPDR) without macular edema, 20 eyes had proliferative diabetic retinopathy (PDR) without macular edema, and 27 eyes had diabetic macular edema (DME) with either NPDR or PDR. Thick posterior hyaloid relative to healthy nondiabetic controls was observed in 0 of 20 (0%) diabetic eyes without retinopathy, 4 of 21 (19%) eyes with NPDR, 11 of 20 (55%) eyes with PDR, and 11 of 27 (41%) eyes with DME (P = .0001). Vitreoschisis was observed in 6 of 22 (27%) healthy nondiabetic eyes, 9 of 20 (45%) diabetic eyes without retinopathy, 10 of 21 (48%) eyes with NPDR, 13 of 20 (65%) eyes with PDR, and 17 of 27 (63%) eyes with DME (P = .007). While no healthy nondiabetic controls and diabetic eyes without retinopathy had adhesions/pegs between detached posterior hyaloid and retina, 1 of 21 (4%), 11 of 20 (55%), and 11 of 27 (41%) eyes with NPDR, PDR, and DME, respectively, demonstrated this feature (P = .0001).

CONCLUSION

SSOCT with motion-correction and vitreous windowing provides wide-field 3-dimensional information of vitreoretinal interface in diabetic eyes. This may be useful in assessing progression of retinopathy, planning diabetic vitreous surgery, and predicting treatment outcomes.

En face imaging of the choroid in polypoidal choroidal vasculopathy using swept-source optical coherence tomography

OBJECTIVE

To define morphologic features of polypoidal choroidal vasculopathy (PCV) using en face images from swept-source optical coherence tomography (SS OCT).

DESIGN

Prospective cross-sectional study.

METHODS

The study included 10 eyes from 6 patients with PCV and 10 eyes from 5 age-matched normal subjects. All subjects were prospectively scanned with a prototype SS OCT system. A motion correction algorithm was applied to correct and merge scans into a single volumetric dataset. En face images were generated at intervals of 4.13 μm (1 pixel) relative to the Bruch membrane.

RESULTS

Age ± standard deviation for the normal group was 62.4 (±12.1) years and for the PCV group was 68.3 (±5.2) years. En face SS OCT imaging of PCV eyes demonstrated the relationship between larger pigment epithelial detachments (PEDs) and small adjoining PEDs that correlated with the polypoidal lesions seen on indocyanine green angiography in all PCV eyes. En face SS OCT demonstrated choroidal vascular abnormalities in 7 out of 7 eyes with PCV, and in 2 out of 3 enrolled fellow eyes in patients with unilateral PCV. Out of 7 PCV eyes, focal choroidal vascular dilation was noted in 3 eyes and diffuse choroidal vascular dilation was noted in 1 eye. In addition, a branching vascular network was noted above the Bruch membrane in 1 eye, below the Bruch membrane within the choriocapillaris in 1 eye, and in the larger choroidal vascular layer in 1 eye.

CONCLUSIONS

En face SS OCT provides an in vivo tool to visualize the pathologic features and the choroidal vasculature in PCV.

Depth-encoded all-fiber swept source polarization sensitive OCT

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of conventional OCT and can assess depth-resolved tissue birefringence in addition to intensity. Most existing PS-OCT systems are relatively complex and their clinical translation remains difficult. We present a simple and robust all-fiber PS-OCT system based on swept source technology and polarization depth-encoding. Polarization multiplexing was achieved using a polarization maintaining fiber. Polarization sensitive signals were detected using fiber based polarization beam splitters and polarization controllers were used to remove the polarization ambiguity. A simplified post-processing algorithm was proposed for speckle noise reduction relaxing the demand for phase stability. We demonstrated systems design for both ophthalmic and catheter-based PS-OCT. For ophthalmic imaging, we used an optical clock frequency doubling method to extend the imaging range of a commercially available short cavity light source to improve polarization depth-encoding. For catheter based imaging, we demonstrated 200 kHz PS-OCT imaging using a MEMS-tunable vertical cavity surface emitting laser (VCSEL) and a high speed micromotor imaging catheter. The system was demonstrated in human retina, finger and lip imaging, as well as ex vivo swine esophagus and cardiovascular imaging. The all-fiber PS-OCT is easier to implement and maintain compared to previous PS-OCT systems and can be more easily translated to clinical applications due to its robust design.

Quantitative 3D-OCT motion correction with tilt and illumination correction, robust similarity measure and regularization

Variability in illumination, signal quality, tilt and the amount of motion pose challenges for post-processing based 3D-OCT motion correction algorithms. We present an advanced 3D-OCT motion correction algorithm using image registration and orthogonal raster scan patterns aimed at addressing these challenges. An intensity similarity measure using the pseudo Huber norm and a regularization scheme based on a pseudo L0.5 norm are introduced. A two-stage registration approach was developed. In the first stage, only axial motion and axial tilt are coarsely corrected. This result is then used as the starting point for a second stage full optimization. In preprocessing, a bias field estimation based approach to correct illumination differences in the input volumes is employed. Quantitative evaluation was performed using a large set of data acquired from 73 healthy and glaucomatous eyes using SD-OCT systems. OCT volumes of both the optic nerve head and the macula region acquired with three independent orthogonal volume pairs for each location were used to assess reproducibility. The advanced motion correction algorithm using the techniques presented in this paper was compared to a basic algorithm corresponding to an earlier version and to performing no motion correction. Errors in segmentation-based measures such as layer positions, retinal and nerve fiber thickness, as well as the blood vessel pattern were evaluated. The quantitative results consistently show that reproducibility is improved considerably by using the advanced algorithm, which also significantly outperforms the basic algorithm. The mean of the mean absolute retinal thickness difference over all data was 9.9 um without motion correction, 7.1 um using the basic algorithm and 5.0 um using the advanced algorithm. Similarly, the blood vessel likelihood map error is reduced to 69% of the uncorrected error for the basic and to 47% of the uncorrected error for the advanced algorithm. These results demonstrate that our advanced motion correction algorithm has the potential to improve the reliability of quantitative measurements derived from 3D-OCT data substantially.

Choroid, Haller's, and Sattler's layer thickness in intermediate age-related macular degeneration with and without fellow neovascular eyes

PURPOSE

To analyze choroidal, Sattler's, and Haller's layer thickness maps in age-related macular degeneration (AMD) patients having eyes with bilateral large drusen and pigment changes (intermediate AMD), in patients having intermediate AMD eyes with neovascular fellow eyes (nAMD), and in healthy subjects using three-dimensional (3D) 1060-nm optical coherence tomography (OCT).

METHODS

Automatically generated choroidal thickness (ChT), retinal thickness, and Sattler's and Haller's layer thickness maps were statistically analyzed in 67 subjects consisting of intermediate AMD (n = 21), intermediate AMD (n = 22) with fellow nAMD eyes (n = 22), and healthy eyes (n = 24) with no age and axial eye length difference between groups of eyes (P > 0.05, ANOVA). Eyes were imaged by a prototype high-speed (60,000 A-scans/s) spectral-domain 3D 1060-nm OCT over a 36° × 36° field of view.

RESULTS

The mean ± SD (μm) subfoveal ChT for healthy subjects and for bilateral intermediate AMD, unilateral intermediate AMD, and their nAMD fellow eyes was 259 ± 95 and 222 ± 98, 149 ± 60, and 171 ± 78, respectively. Choroidal thickness maps demonstrated significant submacular thinning in unilateral intermediate AMD in comparison to healthy and bilateral intermediate AMD eyes (P < 0.001, ANOVA, post hoc P < 0.001 and P < 0.05, respectively). Sattler's and Haller's layers were thinnest in intermediate AMDs that presented with nAMD fellow eyes (Kruskal-Wallis test P < 0.01). For the choroid and its sublayers, there was no difference between the intermediate AMD eyes and their fellow nAMD eyes (paired testing, P < 0.05).

CONCLUSIONS

The 3D 1060-nm OCT choroidal imaging visualized significant changes in choroidal, Sattler's, and Haller's layer thickness in relation to the progression of AMD. This may be important for understanding the choroidopathy in the pathophysiology of AMD.

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 Haller's and Sattler's 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. Haller's and Sattler's 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 Haller's and Sattler's 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 Sattler's and Haller's 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 Sattler's and Haller's was 87±56 µm and 141±50 µm, respectively, with a significant relationship for AL (P<.001).

Conclusions

Automated Sattler's and Haller's 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 Sattler's 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.

Choroidal analysis in healthy eyes using swept-source optical coherence tomography compared to spectral domain optical coherence tomography

PURPOSE

To compare analyses of choroidal thickness and volume in healthy eyes measured concurrently with prototype long-wavelength swept-source optical coherence tomography (OCT) and commercially available spectral-domain optical coherence tomography (OCT) with and without enhanced depth imaging (EDI).

DESIGN

Prospective cross sectional study.

METHODS

The study included 19 healthy subjects (19 eyes), who were prospectively recruited to undergo 2 consecutive imaging sessions on the same randomly selected eye using spectral domain OCT and a prototype long-wavelength swept-source OCT. On spectral domain OCT, 2 line scans, 1 with and 1 without EDI, and 1 volumetric scan were obtained. On swept-source OCT, 1 line scan and 1 volumetric scan were obtained. Scan patterns on swept-source OCT were created to simulate those available on Cirrus HD-OCT to keep the time of image acquisition constant. Swept-source OCT volumetric scans were motion corrected using a novel registration algorithm. Choroidal thickness and volume were analyzed.

RESULTS

The choroidoscleral interface was clearly visualized in 19/19 (100%) of eyes imaged by swept-source OCT, compared to 14/19 (73.6%) and 13/19 (68.4%) eyes imaged by spectral domain OCT, with and without EDI, respectively. There was no significant difference in choroidal thickness measurements on the line scans obtained on either system (P = 0.10). Choroidal volume could not be assessed on volumetric scans from spectral domain OCT. Mean choroidal volume from swept-source OCT volumetric scans was 11.77 ± 3.13 mm(3) (6.43 mm(3)-17.15 mm(3)).

CONCLUSION

This is the first study that compares simultaneously a prototype long-wavelength swept-source OCT to a commercially available spectral domain OCT for a detailed analysis of choroid in healthy eyes. Swept-source OCT shows potential for better choroidal analysis. Studies using swept-source OCT in diseased eyes will further define this new technology's utility in chorioretinal diseases.

Optical coherence tomography angiography of optic disc perfusion in glaucoma

PURPOSE

To compare optic disc perfusion between normal subjects and subjects with glaucoma using optical coherence tomography (OCT) angiography and to detect optic disc perfusion changes in glaucoma.

DESIGN

Observational, cross-sectional study.

PARTICIPANTS

Twenty-four normal subjects and 11 patients with glaucoma were included.

METHODS

One eye of each subject was scanned by a high-speed 1050-nm-wavelength swept-source OCT instrument. The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was used to compute 3-dimensional optic disc angiography. A disc flow index was computed from 4 registered scans. Confocal scanning laser ophthalmoscopy (cSLO) was used to measure disc rim area, and stereo photography was used to evaluate cup/disc (C/D) ratios. Wide-field OCT scans over the discs were used to measure retinal nerve fiber layer (NFL) thickness.

MAIN OUTCOME MEASURES

Variability was assessed by coefficient of variation (CV). Diagnostic accuracy was assessed by sensitivity and specificity. Comparisons between glaucoma and normal groups were analyzed by Wilcoxon rank-sum test. Correlations among disc flow index, structural assessments, and visual field (VF) parameters were assessed by linear regression.

RESULTS

In normal discs, a dense microvascular network was visible on OCT angiography. This network was visibly attenuated in subjects with glaucoma. The intra-visit repeatability, inter-visit reproducibility, and normal population variability of the optic disc flow index were 1.2%, 4.2%, and 5.0% CV, respectively. The disc flow index was reduced by 25% in the glaucoma group (P = 0.003). Sensitivity and specificity were both 100% using an optimized cutoff. The flow index was highly correlated with VF pattern standard deviation (R(2) = 0.752, P = 0.001). These correlations were significant even after accounting for age, C/D area ratio, NFL, and rim area.

CONCLUSIONS

Optical coherence tomography angiography, generated by the new SSADA, repeatably measures optic disc perfusion and may be useful in the evaluation of glaucoma and glaucoma progression.

Handheld ultrahigh speed swept source optical coherence tomography instrument using a MEMS scanning mirror

We developed an ultrahigh speed, handheld swept source optical coherence tomography (SS-OCT) ophthalmic instrument using a 2D MEMS mirror. A vertical cavity surface-emitting laser (VCSEL) operating at 1060 nm center wavelength yielded a 350 kHz axial scan rate and 10 µm axial resolution in tissue. The long coherence length of the VCSEL enabled a 3.08 mm imaging range with minimal sensitivity roll-off in tissue. Two different designs with identical optical components were tested to evaluate handheld OCT ergonomics. An iris camera aided in alignment of the OCT beam through the pupil and a manual fixation light selected the imaging region on the retina. Volumetric and high definition scans were obtained from 5 undilated normal subjects. Volumetric OCT data was acquired by scanning the 2.4 mm diameter 2D MEMS mirror sinusoidally in the fast direction and linearly in the orthogonal slow direction. A second volumetric sinusoidal scan was obtained in the orthogonal direction and the two volumes were processed with a software algorithm to generate a merged motion-corrected volume. Motion-corrected standard 6 x 6 mm(2) and wide field 10 x 10 mm(2) volumetric OCT data were generated using two volumetric scans, each obtained in 1.4 seconds. High definition 10 mm and 6 mm B-scans were obtained by averaging and registering 25 B-scans obtained over the same position in 0.57 seconds. One of the advantages of volumetric OCT data is the generation of en face OCT images with arbitrary cross sectional B-scans registered to fundus features. This technology should enable screening applications to identify early retinal disease, before irreversible vision impairment or loss occurs. Handheld OCT technology also promises to enable applications in a wide range of settings outside of the traditional ophthalmology or optometry clinics including pediatrics, intraoperative, primary care, developing countries, and military medicine.

Swept source optical coherence microscopy using a 1310 nm VCSEL light source

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.

Ultrahigh speed endoscopic optical coherence tomography using micromotor imaging catheter and VCSEL technology

We developed a micromotor based miniature catheter with an outer diameter of 3.2 mm for ultrahigh speed endoscopic swept source optical coherence tomography (OCT) using a vertical cavity surface-emitting laser (VCSEL) at a 1 MHz axial scan rate. The micromotor can rotate a micro-prism at several hundred frames per second with less than 5 V drive voltage to provide fast and stable scanning, which is not sensitive to the bending of the catheter. The side-viewing probe can be pulled back to acquire a three-dimensional (3D) data set covering a large area on the specimen. The VCSEL provides a high axial scan rate to support dense sampling under high frame rate operation. Using a high speed data acquisition system, in vivo 3D-OCT imaging in the rabbit GI tract and ex vivo imaging of a human colon specimen with 8 μm axial resolution, 8 μm lateral resolution and 1.2 mm depth range in tissue at a frame rate of 400 fps was demonstrated.

In vivo imaging of the rodent eye with swept source/Fourier domain OCT

Swept source/Fourier domain OCT is demonstrated for in vivo imaging of the rodent eye. Using commercial swept laser technology, we developed a prototype OCT imaging system for small animal ocular imaging operating in the 1050 nm wavelength range at an axial scan rate of 100 kHz with ~6 µm axial resolution. The high imaging speed enables volumetric imaging with high axial scan densities, measuring high flow velocities in vessels, and repeated volumetric imaging over time. The 1050 nm wavelength light provides increased penetration into tissue compared to standard commercial OCT systems at 850 nm. The long imaging range enables multiple operating modes for imaging the retina, posterior eye, as well as anterior eye and full eye length. A registration algorithm using orthogonally scanned OCT volumetric data sets which can correct motion on a per A-scan basis is applied to compensate motion and merge motion corrected volumetric data for enhanced OCT image quality. Ultrahigh speed swept source OCT is a promising technique for imaging the rodent eye, proving comprehensive information on the cornea, anterior segment, lens, vitreous, posterior segment, retina and choroid.

Automated lamina cribrosa microstructural segmentation in optical coherence tomography scans of healthy and glaucomatous eyes

We demonstrate an automated segmentation method for in-vivo 3D optical coherence tomography (OCT) imaging of the lamina cribrosa (LC). Manual segmentations of coronal slices of the LC were used as a gold standard in parameter selection and evaluation of the automated technique. The method was validated using two prototype OCT devices; each had a subject cohort including both healthy and glaucomatous eyes. Automated segmentation of in-vivo 3D LC OCT microstructure performed comparably to manual segmentation and is useful for investigative research and in clinical quantification of the LC.

Automated three-dimensional choroidal vessel segmentation of 3D 1060 nm OCT retinal data

A fully automated, robust vessel segmentation algorithm has been developed for choroidal OCT, employing multiscale 3D edge filtering and projection of "probability cones" to determine the vessel "core", even in the tomograms with low signal-to-noise ratio (SNR). Based on the ideal vessel response after registration and multiscale filtering, with computed depth related SNR, the vessel core estimate is dilated to quantify the full vessel diameter. As a consequence, various statistics can be computed using the 3D choroidal vessel information, such as ratios of inner (smaller) to outer (larger) choroidal vessels or the absolute/relative volume of choroid vessels. Choroidal vessel quantification can be displayed in various forms, focused and averaged within a special region of interest, or analyzed as the function of image depth. In this way, the proposed algorithm enables unique visualization of choroidal watershed zones, as well as the vessel size reduction when investigating the choroid from the sclera towards the retinal pigment epithelium (RPE). To the best of our knowledge, this is the first time that an automatic choroidal vessel segmentation algorithm is successfully applied to 1060 nm 3D OCT of healthy and diseased eyes.

Motion correction in optical coherence tomography volumes on a per A-scan basis using orthogonal scan patterns

High speed Optical Coherence Tomography (OCT) has made it possible to rapidly capture densely sampled 3D volume data. One key application is the acquisition of high quality in vivo volumetric data sets of the human retina. Since the volume is acquired in a few seconds, eye movement during the scan process leads to distortion, which limits the accuracy of quantitative measurements using 3D OCT data. In this paper, we present a novel software based method to correct motion artifacts in OCT raster scans. Motion compensation is performed retrospectively using image registration algorithms on the OCT data sets themselves. Multiple, successively acquired volume scans with orthogonal fast scan directions are registered retrospectively in order to estimate and correct eye motion. Registration is performed by optimizing a large scale numerical problem as given by a global objective function using one dense displacement field for each input volume and special regularization based on the time structure of the acquisition process. After optimization, each volume is undistorted and a single merged volume is constructed that has superior signal quality compared to the input volumes. Experiments were performed using 3D OCT data from the macula and optic nerve head acquired with a high-speed ultra-high resolution 850 nm spectral OCT as well as wide field data acquired with a 1050 nm swept source OCT instrument. Evaluation of registration performance and result stability as well as visual inspection shows that the algorithm can correct for motion in all three dimensions and on a per A-scan basis. Corrected volumes do not show visible motion artifacts. In addition, merging multiple motion corrected and registered volumes leads to improved signal quality. These results demonstrate that motion correction and merging improves image quality and should also improve morphometric measurement accuracy from volumetric OCT data.

One-step continuous synthesis of biocompatible gold nanorods for optical coherence tomography

We present a novel one-step flow process to synthesize biocompatible gold nanorods with tunable absorption and biocompatible surface ligands. Photothermal optical coherence tomography (OCT) of human breast tissue is successfully demonstrated using tailored gold nanorods designed to have strong absorption in the near-infrared range.

Split-spectrum amplitude-decorrelation angiography with optical coherence tomography

Amplitude decorrelation measurement is sensitive to transverse flow and immune to phase noise in comparison to Doppler and other phase-based approaches. However, the high axial resolution of OCT makes it very sensitive to the pulsatile bulk motion noise in the axial direction. To overcome this limitation, we developed split-spectrum amplitude-decorrelation angiography (SSADA) to improve the signal-to-noise ratio (SNR) of flow detection. The full OCT spectrum was split into several narrower bands. Inter-B-scan decorrelation was computed using the spectral bands separately and then averaged. The SSADA algorithm was tested on in vivo images of the human macula and optic nerve head. It significantly improved both SNR for flow detection and connectivity of microvascular network when compared to other amplitude-decorrelation algorithms.

Piezoelectric-transducer-based miniature catheter for ultrahigh-speed endoscopic optical coherence tomography

We developed a piezoelectric-transducer- (PZT) based miniature catheter with an outer diameter of 3.5 mm for ultrahigh-speed endoscopic optical coherence tomography (OCT). A miniaturized PZT bender actuates a fiber and the beam is scanned through a GRIN lens and micro-prism to provide high-speed, side-viewing capability. The probe optics can be pulled back over a long distance to acquire three-dimensional (3D) data sets covering a large area. Imaging is performed with 11 μm axial resolution in air (8 μm in tissue) and 20 μm transverse resolution, at 960 frames per second with a Fourier domain mode-locked laser operating at 480 kHz axial scan rate. Using a high-speed data acquisition system, endoscopic OCT imaging of the rabbit esophagus and colon in vivo and human colon specimens ex vivo is demonstrated.

Total retinal blood flow measurement with ultrahigh speed swept source/Fourier domain OCT

Doppler OCT provides depth-resolved information on flow in biological tissues. In this article, we demonstrate ultrahigh speed swept source/Fourier domain OCT for visualization and quantitative assessment of retinal blood flow. Using swept laser technology, the system operated in the 1050-nm wavelength range at a high axial scan rate of 200 kHz. The rapid imaging speed not only enables volumetric imaging with high axial scan densities, but also enables measurement of high flow velocities in the central retinal vessels. Deep penetration in the optic nerve and lamina cribrosa was achieved by imaging at 1-µm wavelengths. By analyzing en-face images extracted from 3D Doppler data sets, absolute flow in single vessels as well as total retinal blood flow was measured using a simple and robust protocol that does not require measurement of Doppler angles. The results from measurements in healthy eyes suggest that ultrahigh speed swept source/Fourier domain OCT could be a promising technique for volumetric imaging of retinal vasculature and quantitation of retinal blood flow in a wide range of retinal diseases.

Total retinal blood flow measurement with ultrahigh speed swept source/Fourier domain OCT

Doppler OCT provides depth-resolved information on flow in biological tissues. In this article, we demonstrate ultrahigh speed swept source/Fourier domain OCT for visualization and quantitative assessment of retinal blood flow. Using swept laser technology, the system operated in the 1050-nm wavelength range at a high axial scan rate of 200 kHz. The rapid imaging speed not only enables volumetric imaging with high axial scan densities, but also enables measurement of high flow velocities in the central retinal vessels. Deep penetration in the optic nerve and lamina cribrosa was achieved by imaging at 1-µm wavelengths. By analyzing en-face images extracted from 3D Doppler data sets, absolute flow in single vessels as well as total retinal blood flow was measured using a simple and robust protocol that does not require measurement of Doppler angles. The results from measurements in healthy eyes suggest that ultrahigh speed swept source/Fourier domain OCT could be a promising technique for volumetric imaging of retinal vasculature and quantitation of retinal blood flow in a wide range of retinal diseases.

Thalamic integrity underlies executive dysfunction in traumatic brain injury

OBJECTIVE

To quantify the effects of traumatic brain injury on integrity of thalamocortical projection fibers and to evaluate whether damage to these fibers accounts for impairments in executive function in chronic traumatic brain injury.

METHODS

High-resolution (voxel size: 0.78 mm x 0.78 mm x 3 mm(3)) diffusion tensor MRI of the thalamus was conducted on 24 patients with a history of single, closed-head traumatic brain injury (TBI) (12 each of mild TBI and moderate to severe TBI) and 12 age- and education-matched controls. Detailed neuropsychological testing with an emphasis on executive function was also conducted. Fractional anisotropy was extracted from 12 regions of interest in cortical and corpus callosum structures and 7 subcortical regions of interest (anterior, ventral anterior, ventral lateral, dorsomedial, ventral posterior lateral, ventral posterior medial, and pulvinar thalamic nuclei).

RESULTS

Relative to controls, patients with a history of brain injury showed reductions in fractional anisotropy in both the anterior and posterior corona radiata, forceps major, the body of the corpus callosum, and fibers identified from seed voxels in the anterior and ventral anterior thalamic nuclei. Fractional anisotropy from cortico-cortico and corpus callosum regions of interest did not account for significant variance in neuropsychological function. However, fractional anisotropy from the thalamic seed voxels did account for variance in executive function, attention, and memory.

CONCLUSIONS

The data provide preliminary evidence that traumatic brain injury and resulting diffuse axonal injury results in damage to the thalamic projection fibers and is of clinical relevance to cognition.

Effects of the dopaminergic agent and NMDA receptor antagonist amantadine on cognitive function, cerebral glucose metabolism and D2 receptor availability in chronic traumatic brain injury: A study using positron emission tomography (PET)

PRIMARY OBJECTIVE

This study was performed to assess effects of amantadine (AMH), a dopaminergic agent and NMDA antagonist, on chronic traumatic brain injury (TBI). The primary hypotheses were that amantadine treatment would result in executive function improvement and increased activity in pre-frontal cortex.

RESEARCH DESIGN

An open-label design was used.

METHODS

Twenty-two subjects underwent neuropsychological testing pre- and post-12 week treatment. Six subjects also underwent PET scanning.

INTERVENTION

Amantadine 400 mg was administered per day.

RESULTS

Significant improvements on tests of executive function were observed with treatment. Analysis of PET data demonstrated a significant increase in left pre-frontal cortex glucose metabolism. There was a significant positive correlation between executive domain scores and left pre-frontal glucose metabolism.

CONCLUSIONS

This is the first known study to assess amantadine in chronic TBI using PET and the data are consistent with the hypotheses. The conduction of further studies is warranted.

The combined use of amantadine and l-dopa/carbidopa in the treatment of chronic brain injury

The frontal lobes are particularly vulnerable to injury during trauma. The syndrome commonly attributed to frontal lobe dysfunction includes problems with impulsivity, perseveration, disinhibition, amotivation, attention, planning, and problem solving. These symptoms can respond to certain pharmacologic interventions, such as the dopaminergic agents. The case of a 50-year-old woman who showed persistent frontal dysfunction 5 years post-injury is described. After treatment with amantadine alone, she showed decreased impulsivity and perseveration and improved executive function. Further positive response was obtained with the addition of l-dopa/carbidopa, with additional improvements in constructional praxis, divided auditory attention, and cognitive flexibility. Her improved functioning following treatment demonstrates the potential for increasing effectiveness through a combination of dopaminergic agents. No side effects were observed, and the patient maintained gains at follow-up. The rationale for using dopaminergic agents alone and in combination is discussed.

Effect of amantadine hydrochloride on symptoms of frontal lobe dysfunction in brain injury: case studies and review

Symptoms consistent with dysfunction of the frontal lobes can occur following traumatic brain injury (TBI) or other types of acquired brain injury (stroke, aneurysm). These symptoms can include problems with short-term memory, attention, planning, problem solving, impulsivity, disinhibition, poor motivation, and other behavioral and cognitive deficits ("frontal lobe syndrome"). These symptoms may respond to certain drugs, such as dopaminergic agents. This case series describes results of using amantadine in 7 patients with this type of symptom profile (6 with TBI, 1 with meningitis following sinus surgery). Patients received neuropsychiatric examinations and serial neuropsychological testing. All patients showed some degree of positive response. One had side effects that resolved upon discontinuation of drug. The rationale for using dopaminergics is discussed, and pertinent literature is reviewed.

Guidelines for the use of tacrine in Alzheimer's disease: clinical application and effectiveness. Johns Hopkins Dementia Research Clinic

The efficacy of tacrine for treatment of Alzheimer's has been demonstrated in several clinical trials but has not been assessed in cases complicated by medical and psychiatric comorbidities. Additionally, the benefit-risk ratio of tacrine is small, so it is best administered with carefully developed guidelines that specify this ratio for patients and families. On the basis of guidelines developed for the Johns Hopkins Dementia Research Clinic, tacrine treatment was offered to 162 patients with probable Alzheimer's. Only 35 accepted, and only 22 continued on tacrine beyond 3 months. The latter group declined by 1.36 points over 1 year on the Mini-Mental State Examination, significantly less than expected. The authors conclude that, if used in the context of clinical guidelines, tacrine is an effective treatment for Alzheimer's.

Neuropsychiatric sequelae of stroke and traumatic brain injury: the role of psychostimulants

OBJECTIVE

The primary purpose of this article is to review certain neuropsychiatric sequelae of stroke and traumatic brain injury (TBI), and the role of the psychostimulants methylphenidate (MPD) and dextroamphetamine (DAMP) in their treatment.

METHOD

A general review of the topic is presented. Controlled and uncontrolled studies involving the use of the psychostimulants are discussed. These consist of 11 studies listed with Medline 2000 that deal specifically with stroke or head injury, with the oldest study reviewed dating back to 1984. Studies concerning the use of psychostimulants in the medically or neurologically ill are reviewed to the extent that they are pertinent.

RESULTS

The current literature consists primarily of uncontrolled case studies. However, these are reviewed and found to suggest a role for the use of the psychostimulants, which is discussed.

CONCLUSIONS

In general, these drugs appear to be a reasonable treatment choice for certain types of mood, behavior, and cognitive symptoms following brain injury. However, it is noted that larger scale controlled studies are needed to adequately assess the clinical usefulness of these drugs.

The frontal lobes and traumatic brain injury

The authors review 1) the pathophysiological, neuroimaging, and neurobehavioral evidence for frontal lobe involvement in closed head injury; 2) studies elucidating the cognitive deficits and behavioral disturbance related to frontal lobe lesions associated with head injury; and 3) pharmacologic treatment of the neuropsychiatric manifestations of frontal lobe injury, including emerging therapies.

Methylphenidate hydrochloride as an antidepressant: controversy, case studies, and review

The use of psychostimulants as antidepressants remains controversial in the field of psychiatry. While methylphenidate hydrochloride (MPH) and dextroamphetamine (DA) are often considered to be equivalent drugs, differences in their neurobiologic mechanism of action may account for different clinical response patterns. Hence, clinical trials and literature reviews that examine the antidepressant efficacy of psychostimulants without distinguishing between MPH and DA may reach inaccurate conclusions. This paper is a critical review of controlled and uncontrolled studies examining the use of MPH as an antidepressant. We discuss the methodologic limitations of existing placebo-controlled trials that have reached mixed conclusions about the efficacy of MPH as an antidepressant. These studies are offset by uncontrolled open trials and clinical case reports that endorse the drug's effectiveness in alleviating depressive symptoms. The series of patients we treated with MPH demonstrates the safety and efficacy of this drug in alleviating depressive symptoms in the medically ill elderly with a variety of mood disorders. Reviewing these six cases and balancing the positive and negative reports in the literature, we provide practical guidelines for identifying patients who are potential candidates for treatment with MPH.