Three-dimensional reconstruction of blood vessels from in vivo color Doppler optical coherence tomography images

Optimizing 3D retinal vasculature imaging in diabetic retinopathy using registration and averaging of OCT-A

High resolution visualization of optical coherence tomography (OCT) and OCT angiography (OCT-A) data is required to fully take advantage of the imaging modality's three-dimensional nature. However, artifacts induced by patient motion often degrade OCT-A data quality. This is especially true for patients with deteriorated focal vision, such as those with diabetic retinopathy (DR). We propose a novel methodology for software-based OCT-A motion correction achieved through serial acquisition, volumetric registration, and averaging. Motion artifacts are removed via a multi-step 3D registration process, and visibility is significantly enhanced through volumetric averaging. We demonstrate that this method permits clear 3D visualization of retinal pathologies and their surrounding features, 3D visualization of inner retinal capillary connections, as well as reliable visualization of the choriocapillaris layer.

Removing Subcutaneous Microvessels Using Photo-Mediated Ultrasound Therapy

BACKGROUND AND OBJECTIVES

We have developed a novel anti-vascular technique, termed photo-mediated ultrasound therapy (PUT), which utilizes nanosecond duration laser pulses synchronized with ultrasound bursts to remove the microvasculature through cavitation. The objective of the current study is to explore the potential of PUT in removing subcutaneous microvessels.

STUDY DESIGN/MATERIALS AND METHODS

The auricular blood vessels of two New Zealand white rabbits were treated by PUT with a peak negative ultrasound pressure of 0.45 MPa at 0.5 MHz, and a laser fluence of 0.056 J/cm2 at 1064 nm for 10 minutes. Blood perfusion in the treated area was measured by a commercial laser speckle imaging (LSI) system before and immediately after treatment, as well as at 1 hour, 3 days, 2 weeks, and 4 weeks post-treatment. Perfusion rates of 38 individual vessels from four rabbit ears were tracked during this time period for longitudinal assessment.

RESULTS

The measured perfusion rates of the vessels in the treated areas, as quantified by the relative change in perfusion rate, showed a statistically significant decrease for all time points post-treatment (P < 0.001). The mean decrease in perfusion is 50.79% immediately after treatment and is 32.14% at 4 weeks post-treatment. Immediately after treatment, the perfusion rate decreased rapidly. Following this, there was a partial recovery in perfusion rate up to 3 days post-treatment, followed by a plateau in the perfusion from 3 days to 4 weeks.

CONCLUSIONS

This study demonstrated that a single PUT treatment could significantly reduce blood perfusion by 32.14% in the skin for up to 4 weeks. With unique advantages such as low laser fluence as compared with photothermolysis and agent-free treatment as compared with photodynamic therapy, PUT holds the potential to be developed into a new tool for the treatment of cutaneous vascular lesions. Lasers Surg. Med. © 2020 Wiley Periodicals, LLC.

Optical coherence tomography angiography and photoacoustic imaging in dermatology

Optical coherence tomography angiography (OCTA) is a relatively novel functional extension of the widely accepted ophthalmic imaging tool named optical coherence tomography (OCT). Since OCTA's debut in ophthalmology, researchers have also been trying to expand its translational application in dermatology. The ability of OCTA to resolve microvasculature has shown promising results in imaging skin diseases. Meanwhile, photoacoustic imaging (PAI), which uses laser pulse induced ultrasound waves as the signal, has been studied to differentiate human skin layers and to help in skin disease diagnosis. This perspective article gives a short review of OCTA and PAI in the field of photodermatology. After an introduction to the principles of OCTA and PAI, we describe the most updated results of skin disease imaging using these two optical imaging modalities. We also place emphasis on dual modality imaging combining OCTA and photoacoustic tomography (PAT) for dermatological applications. In the end, the challenges and prospects of these two imaging modalities in dermatology are discussed.

Contrast Agent Enhanced Multimodal Photoacoustic Microscopy and Optical Coherence Tomography for Imaging of Rabbit Choroidal and Retinal Vessels in vivo

Multimodal imaging with photoacoustic microscopy (PAM) and optical coherence tomography (OCT) can be an effective method to evaluate the choroidal and retinal microvasculature. To improve the efficiency for visualizing capillaries, colloidal gold nanoparticles (AuNPs) have been applied as a multimodal contrast agent for both OCT and PAM imaging by taking advantage of the strong optical scattering and the strong optical absorption of AuNPs due to their surface plasmon resonance. Ultra-pure AuNPs were fabricated by femtosecond laser ablation, capped with polyethylene glycol (PEG), and administered to 13 New Zealand white rabbits and 3 Dutch Belted pigmented rabbits. The synthesized PEG-AuNPs (20.0 ± 1.5 nm) were demonstrated to be excellent contrast agents for PAM and OCT, and do not demonstrate cytotoxicity to bovine retinal endothelial cells in cell studies. The image signal from the retinal and choroidal vessels in living rabbits was enhanced by up to 82% for PAM and up to 45% for OCT, respectively, by the administered PEG-AuNPs, which enables detection of individual blood vessels by both imaging modalities. The biodistribution study demonstrated the AuNP accumulated primarily in the liver and spleen. Histology and TUNEL staining did not indicate cell injury or death in the lung, liver, kidney, spleen, heart, or eyes up to seven days after AuNP administration. PEG-AuNPs offer an efficient and safe contrast agent for multimodal ocular imaging to achieve improved characterization of microvasculature.

Multi-wavelength, en-face photoacoustic microscopy and optical coherence tomography imaging for early and selective detection of laser induced retinal vein occlusion

Multi-wavelength en face photoacoustic microscopy (PAM) was integrated with a spectral domain optical coherence tomography (SD-OCT) to evaluate optical properties of retinal vein occlusion (RVO) and retinal neovascularization (RNV) in living rabbits. The multi-wavelength PAM of the RVO and RNV were performed at several wavelengths ranging from 510 to 600 nm. Rose Bengal-induced RVO and RNV were performed and evaluated on eight rabbits using color fundus photography, fluorescein angiography, OCT, and spectroscopic en face PAM. In vivo experiment demonstrates that the spectral variation of photoacoustic response was achieved. The location and the treatment margins of the occluded vasculature as well as the morphology of individual RNV were obtained with high contrast at a laser energy of 80 nJ, which was only half of the American National Standards Institute safety limit. In addition, dynamic changes in the retinal morphology and retinal neovascularization were administered using PA spectroscopy at numerous time points: 0, 3, 7, 14, 21, 28, and 35 days after photocoagulation. The proposed multi-wavelength spectroscopic PAM imaging may provide a potential imaging platform to differentiate occluded retinal vasculature and to improve characterization of microvasculature in a safe and efficient manner.

Optical coherence tomography of the preterm eye: from retinopathy of prematurity to brain development

Preterm infants with retinopathy of prematurity are at increased risk of poor neurodevelopmental outcomes. Because the neurosensory retina is an extension of the central nervous system, anatomic abnormalities in the anterior visual pathway often relate to system and central nervous system health. We describe optical coherence tomography as a powerful imaging modality that has recently been adapted to the infant population and provides noninvasive, high-resolution, cross-sectional imaging of the infant eye at the bedside. Optical coherence tomography has increased understanding of normal eye development and has identified several potential biomarkers of brain abnormalities and poorer neurodevelopment.

In vivo, label-free, three-dimensional quantitative imaging of kidney microcirculation using Doppler optical coherence tomography

Doppler optical coherence tomography (DOCT) is a functional extension of optical coherence tomography (OCT) and is currently being employed in several clinical arenas to quantify blood flow in vivo. In this study, the objective was to investigate the feasibility of DOCT to image kidney microcirculation, specifically, glomerular blood flow. DOCT is able to capture three-dimensional (3D) data sets consisting of a series of cross-sectional images in real time, which enables label-free and non-destructive quantification of glomerular blood flow. The kidneys of adult, male Munich-Wistar rats were exposed through laparotomy procedure after being anesthetized. Following exposure of the kidney beneath the DOCT microscope, glomerular blood flow was observed. The effects of acute mannitol and angiotensin II infusion were also observed. Glomerular blood flow was quantified for the induced physiological states and compared with baseline measurements. Glomerular volume, cumulative Doppler volume, and Doppler flow range parameters were computed from 3D OCT/DOCT data sets. Glomerular size was determined from OCT, and DOCT readily revealed glomerular blood flow. After infusion of mannitol, a significant increase in blood flow was observed and quantified, and following infusion of angiontensin II, a significant decrease in blood flow was observed and quantified. Also, blood flow histograms were produced to illustrate differences in blood flow rate and blood volume among the induced physiological states. We demonstrated 3D DOCT imaging of rat kidney microcirculation in the glomerulus in vivo. Dynamic changes in blood flow were detected under altered physiological conditions demonstrating the real-time imaging capability of DOCT. This method holds promise to allow non-invasive imaging of kidney blood flow for transplant graft evaluation or monitoring of altered-renal hemodynamics related to disease progression.

Applications of a new In vivo tumor spheroid based shell-less chorioallantoic membrane 3-D model in bioengineering research

The chicken chorioallantoic membrane (CAM) is a classical in vivo biological model in studies of angiogenesis. Combined with the right tumor system and experimental configuration this classical model can offer new approaches to investigating tumor processes. The increase in development of biotechnological devices for cancer diagnosis and treatment, calls for more sophisticated tumor models that can easily adapt to the technology, and provide a more accurate, stable and consistent platform for rapid quantitative and qualitative analysis. As we discuss a variety of applications of this novel in vivo tumor spheroid based shell-less CAM model in biomedical engineering research, we will show that it is extremely versatile and easily adaptable to an array of biomedical applications. The model is particularly useful in quantitative studies of the progression of avascular tumors into vascularized tumors in the CAM. Its environment is more stable, flat and has a large working area and wider field of view excellent for imaging and longitudinal studies. Finally, rapid data acquisition, screening and validation of biomedical devices and therapeutics are possible with the short experimental window.

Statistical properties of phase-decorrelation in phase-resolved Doppler optical coherence tomography

Decorrelation noise limits the ability of phase-resolved Doppler optical coherence tomography systems to detect smaller vessels exhibiting slower flow velocities, which limits the utility of the technique in many clinical and biological settings. An understanding of the statistical properties of decorrelation noise can aid in the optimal design of these systems and guide the development of noise mitigating strategies. In this work, the statistical properties of decorrelation noise are derived from the underlying statistics of the coherent imaging system and validated through comparison with empirical results and Monte Carlo modeling. Expressions for the noise distribution and the noise variance as a function of relevant imaging system parameters are given, and the implications of these results on both system and algorithm design are discussed.

Enhanced detection of early-stage oral cancer in vivo by optical coherence tomography using multimodal delivery of gold nanoparticles

Contrast in optical coherence tomography (OCT) images can be enhanced by utilizing surface plasmon resonant gold nanoparticles. To improve the poor in vivo transport of gold nanoparticles through biological barriers, an efficient delivery strategy is needed. In this study, the improved penetration and distribution of gold nanoparticles were achieved by microneedle and ultrasound, respectively, and it was demonstrated that this multimodal delivery of antibody-conjugated PEGylated gold nanoparticles enhanced the contrast in in vivo OCT images of oral dysplasia in a hamster model.

Optical coherence tomography: a potential tool for unsupervised prediction of treatment response for Port-Wine Stains

BACKGROUND

Treatment of Port-Wine Stains (PWS) suffers from the absence of a reliable real-time tool for monitoring a clinical endpoint. Response to treatment varies substantially according to blood vessel geometry. Even though optical coherence tomography (OCT) has been identified as a modality with potential to suit this need, it has not been introduced as a standard clinical monitoring tool. One reason could be that - although OCT acquires data in real-time - gigabyte data transfer, processing and communication to a clinician may impede the implementation as a clinical tool.

OBJECTIVES

We investigate whether an automated algorithm can address this problem.

METHODS

Based on our understanding of pulsed dye laser treatment, we present the implementation of an unsupervised, real-time classification algorithm which uses principal components data reduction and linear discriminant analysis. We evaluate the algorithm using 96 synthesized test images and 7 clinical images.

RESULTS

The synthesized images are classified correctly in 99.8%. The clinical images are classified correctly in 71.4%.

CONCLUSIONS

Principal components-fed linear discriminant analysis (PC-fed LDA) may be a valuable method to classify clinical images. Larger sampling numbers are required for a better training model. These results justify undertaking a study involving more patients and show that disease can be described as a function of available treatment options.

Imaging of intradermal tattoos by optical coherence tomography

BACKGROUND/PURPOSE

Tattoos have become increasingly popular followed by a growing demand for tattoo removal, and yet there is little knowledge and monitoring of tattoo pigment deposition in skin layers. The purpose of this pilot study is to describe optical coherence tomography image characteristics of intradermal tattoos.

METHODS

We included five black tattoos in 3 female volunteers, 39, 35 and 30 years old. In vivo imaging of tattoo pigments in the skin is possible with optical coherence tomography (OCT), a novel non-invasive, in vivo optical imaging technology with a resolution and a penetration in skin high enough for visualization of tattoo pigment in the dermis.

RESULTS

In optical coherence tomography images tattoo pigments clusters appear as dark, homogenous vertical columns and structures in the papillary dermis. OCT-scanned normal skin (without tattoos) appeared to be free of this dark structure.

CONCLUSION

We have demonstrated that OCT can be used to visualize clusters of light absorbing pigments in a predictable manner.

The validation of the Depth Measurement Videomicroscope (DMV) as a noninvasive tool for the assessment of capillary vascular malformations

The assessment of capillary vascular malformation (CM) morphology can be performed using videomicroscopy. Previously only the type of capillary pattern could be demonstrated. The Depth Measurement Videomicroscope (DMV) allows both depth and diameter of CM vessels to be measured. The aim of this study was to examine how videomicroscope recordings correlated with biopsy recordings and to investigate pressure-related changes in recordings when using the device. For the first part of the study, 10 patients with CMs resting in a temperature-controlled room were assessed with the DMV. Following this a 3mm punch biopsy of the area was taken. The depth and diameter measurements taken with the DMV were compared to those obtained histologically. For the second part of the study, pressure measurement was used to determine the amount of pressure required on the tip of the DMV to alter the results obtained. Five recordings were taken on the forearm of one volunteer. When the DMV and biopsy measurements are compared using a Bland and Altman Test to determine their relationship there is a close agreement with the diameter measurements and a correction factor of -0.100mm for the depth measurements. The pressure required to alter the skin microcirculation when placing the DMV on the skin surface was found to be 62mmHg. This corresponds closely with other studies of pressure effects on the skin microcirculation and exceeds the pressure used when using the DMV. The DMV thus provides a useful tool for assessing CM capillary structure.

Optical coherence angiography

Noninvasive angiography is demonstrated for the in vivo human eye. Three-dimensional flow imaging has been performed with high-speed spectral-domain optical coherence tomography. Sample motion is compensated by two algorithms. Axial motion between adjacent A-lines within one OCT image is compensated by the Doppler shift due to bulk sample motion. Axial displacements between neighboring images are compensated by a correlation-based algorithm. Three-dimensional vasculature of ocular vessels has been visualized. By integrating volume sets of flow images, two-dimensional images of blood vessels are obtained. Retinal and choroidal blood vessel images are simultaneously obtained by separating the volume set into retinal part and choroidal parts. These are corresponding to fluorescein angiogram and indocyanine angiogram.

Noninvasive imaging of oral premalignancy and malignancy

Early detection of cancer and its precursors remains the best way to ensure patient survival and quality of life. Our specific aim is to test a multimodality approach to noninvasive diagnostics of oral premalignancy and malignancy. In the hamster cheek pouch model (120 hamsters), in vivo optical coherence tomography (OCT) and optical Doppler tomography (ODT) map epithelial, subepithelial, and vascular change throughout carcinogenesis. In vivo multiwavelength multiphoton (MPM) and second-harmonic generated (SHG) fluorescence techniques provided parallel data on surface and subsurface tissue structure, specifically collagen presence and structure, cellular presence, and vasculature. Images are diagnosed by two blinded, prestandardized investigators using a scale from 0 to 6 for all modalities. After sacrifice, histopathology is evaluated on a scale of 0 to 6. Imaging data are reproducibly obtained with good accuracy. Carcinogenesis-related structural and vascular changes are clearly visible to tissue depths of 2 mm. Sensitivity (OCT/ODT alone, 71 to 88%; OCT+MPMSHG, 79 to 91%) and specificity (OCT alone, 62 to 83%; OCT+MPMSHG, 67 to 90%) compare well with conventional techniques. Our conclusions are that OCT/ODT and MPM/SHG are promising noninvasive in vivo diagnostic modalities for oral dysplasia and malignancy.

Optical probes and techniques for molecular contrast enhancement in coherence imaging

Optics has played a key role in the rapidly developing field of molecular imaging. The spectroscopic nature and high-resolution imaging capabilities of light provide a means for probing biological morphology and function at the cellular and molecular levels. While the use of bioluminescent and fluorescent probes has become a mainstay in optical molecular imaging, a large number of other optical imaging modalities exist that can be included in this emerging field. In vivo imaging technologies such as optical coherence tomography and reflectance confocal microscopy have had limited use of molecular probes. In the last few years, novel nonfluorescent and nonbioluminescent molecular imaging probes have been developed that will initiate new directions in coherent optical molecular imaging. Classes of probes reviewed in this work include those that alter the local optical scattering or absorption properties of the tissue, those that modulate these local optical properties in a predictable manner, and those that are detected utilizing spectroscopic optical coherence tomography (OCT) principles. In addition to spectroscopic OCT, novel nonlinear interferometric imaging techniques have recently been developed to detect endogenous molecules. Probes and techniques designed for coherent molecular imaging are likely to improve the detection and diagnostic capabilities of OCT.

Imaging of the ovary

Epithelial ovarian cancer has the highest mortality rate among the gynecologic cancers and spreads beyond the ovary in 90% of the women diagnosed with ovarian cancer. Detection before the disease has spread beyond the ovary would significantly improve the survival from ovarian cancer, which is currently only 30% over 5 years, despite extensive efforts to improve the survival. This study describes initial investigation of the use of optical technologies to improve the outcome for this disease by detecting cancers at an earlier and more treatable stage. Women undergoing oophorectomy were recruited for this study. Ovaries were harvested for fluorescence spectroscopy, confocal microscopy, and optical coherence tomography. Fluorescence spectroscopy showed large diagnostic differences between normal and abnormal tissue at 270 and 340 nm excitation. Optical coherence tomography was able to image up to 2mm deep into the ovary with particular patterns of backscattered intensity observed in normal versus abnormal tissue. Fluorescence confocal microscopy was able to visualize sub-cellular structures of the surface epithelium and underlying cell layers. Optical imaging and/or spectroscopy has the potential to improve the diagnostic capability in the ovary, but extended systematic investigations are needed to identify the unique signatures of disease. The combination of optical technologies supported by modern molecular biology may lead to an instrument that can accurately detect early carcinogenesis.

Two-dimensional and 3-dimensional optical coherence tomographic imaging of the airway, lung, and pleura

BACKGROUND

Methods for obtaining real-time in vivo histologic resolution by means of noninvasive endoscopic optical imaging would be a major advance for thoracic surgical diagnostics and treatment. Optical coherence tomography is a rapidly evolving technology based on near-infrared interferometry that might provide these capabilities. The purpose of this study is to investigate the feasibility of real-time 2- and 3-dimensional optical coherence tomographic imaging of airway, pleural, and subpleural lung tissues in normal, inflammatory, and malignant animal models and patients with known or suspected airway malignancy.

METHODS

Freshly excised lungs and pleural tissue obtained from rabbits with inhalation lung injury and induced empyema, metastatic sarcomas, and pleural sarcomas and from patients with airway disease were imaged by using 2- and 3-dimensional optical coherence tomography with a prototype superluminescent diode optical coherence tomographic system constructed in our laboratory. Lungs and pleural tissue were subsequently processed for standard hematoxylin and eosin histology for comparison with optical coherence tomography.

RESULTS

Optical coherence tomographic imaging achieved an ex vivo resolution of 10 microm and an in vivo resolution of about 30 microm with a depth penetration of 1 to 2 mm with 2- and 3- dimensional reconstruction capabilities. Tumors as small as 500 microm were detectable with optical coherence tomography. The acquired images closely matched histologic images, demonstrating details at the level of mucosal layers, glands, alveoli, and respiratory bronchioles.

CONCLUSIONS

Optical coherence tomography with near-infrared interferometric methods enables near real-time in vivo near-histologic resolution optical imaging. With further advances, optical coherence tomography has the potential for real-time accurate and early pleural and subpleural diagnostics by using small-diameter flexible fiberoptic endoscopic probes for a wide range of thoracic surgical applications.

Design and processing of high-density single-mode fiber arrays for imaging and parallel interferometer applications

The design and fabrication procedures for implementing a high-density (16-microm center spacing) single-mode fiber (SMF) array are described. The specific application for this array is a parallel optical coherence tomography system for endoscopic imaging. We obtained fiber elements by etching standard single-mode SMF-28 fibers to a diameter of 14-15 microm. We equalized 1-m lengths of fiber to within 1 mm by using a fiber interferometer setup, and we describe a method for packaging arrays with as many as 100 fibers.

Imaging of non-parabolic velocity profiles in converging flow with optical coherence tomography

The optical coherence tomography method was explored for two-dimensional flow mapping of a highly scattering fluid in flow with complex geometry. Converging flow (capillary entry) with 4:1 constriction was used for demonstration of non-invasive and remote methods of mapping varying velocity profiles. Downstream of the geometry was scanned with approximately 10 x 10 x 10 microm3 spatial resolution and structural imaging of the lumen and images of one particular velocity were acquired. Stable concave, blunted and parabolic profiles are obtained at different distances of the inlet length. Application of the technique for the blood circulation is also discussed.

Onset of pulsatile pressure causes transiently increased filtration through artery wall

Convective fluid motion through artery walls aids in the transvascular transport of macromolecules. Although many measurements of convective filtration have been reported, they were all obtained under constant transmural pressure. However, arterial pressure in vivo is pulsatile. Therefore, experiments were designed to compare filtration under steady and pulsatile pressure conditions. Rabbit carotid arteries were cannulated and excised from male New Zealand White rabbits anesthetized with pentobarbitol sodium (30 mg/kg iv administered). Hydraulic conductance was measured in cannulated excised rabbit carotid arteries at steady pressure. Next, pulsatile pressure trains were applied within the same vessels, and, simultaneously, arterial distension was monitored using Optical coherence tomography (OCT). For each pulse train, the volume of fluid lost through filtration was measured (subtracting volume change due to residual distension) and compared with that predicted from steady pressure measurements. At 60- and 80-mmHg baseline pressures, the experimental filtration volumes were significantly increased compared with those predicted for steady pressure ( P < 0.05). OCT demonstrated that the excess fluid volume loss was significantly greater than the volume that would be lost through residual distension ( P < 0.05). After 30 s, the magnitude of the excess of fluid loss was reduced. These results suggest that sudden onset of pulsatile pressure may cause changes in arterial interstitial hydration.

Doppler optical coherence imaging of converging flow

The experimental methods of Doppler optical coherence tomography are applied for two-dimensional flow mapping of highly scattering fluid in flow with complex geometry. Converging flow (die entry) is used to demonstrate non-invasive methods to map varying velocity profiles before and after the entry. Complex geometry flow is scanned with approximately 10 x 10 x 10 microm3 spatial resolution. Structural images of the phantom and specific velocity images are demonstrated. A variety of velocity profiles have been obtained before and after the entry. Concave, blunted, parabolic and triangular profiles are obtained at different distances after the entry. Application of the technique to the study of blood circulation is discussed.

The depth measuring videomicroscope (DMV): A non-invasive tool for the assessment of capillary vascular malformations

BACKGROUND AND OBJECTIVES

The response of capillary vascular malformations (CVMs) to laser treatment is believed to be due to the pattern of capillary ectasia, the depth, diameter, and flow through these capillaries and the amount of competing chromophores within the skin. Videomicroscopy has successfully been used to determine CVM capillary pattern and diameter of vessels. The depth measuring videomicroscope (DMV) allows the depth of capillaries to be measured also. The aim of this study is to examine how capillary depths within a CVM are affected by dye laser treatment using DMV.

STUDY DESIGN/MATERIALS AND METHODS

Thirteen previously untreated patients were examined in a temperature-controlled room. A DMV examination was carried out prior to and 6 weeks following a treatment with pulsed dye laser. A further cohort of 11 resistant CVM patients, who had all received over five treatments, was also examined for comparison.

RESULTS

Using a Wilcoxon Signed rank test, the results showed that the remaining vessels within the CVM as measured using DMV were more deeply located and smaller (P < 0.01 and P < 0.02 respectively), following the laser treatment. Also in the resistant patients the vessels were again more deeply placed and smaller.

CONCLUSIONS

The hypothesis that smaller and more deeply placed CVM vessels respond poorest to laser treatment is supported by these findings. Moreover, the DMV provides a simple non-invasive technique for demonstrating this.

Vasoconstrictive effect of topical applied corticosteroids measured by laser doppler imaging and reflectance spectroscopy

Topical application of corticosteroids induces blanching of the skin, based on changes of the underlying microcirculation of the skin. Usually the intensity of blanching after topical application of corticosteroids is measured subjectively by a trained observer using a visual score. In order to obtain an objective determination of the blanching effect and to assess the underlying effect of the skin perfusion, it is necessary to use noninvasive bioengineering techniques. The aim of this study was to compare changes in the vascular plexus during 72 h after topical application of corticosteroids of different potencies with control sites by two noninvasive techniques: laser Doppler imaging (LDI) and diffuse reflectance spectroscopy (DRS). We used the most potent vasoconstrictor, Clobetasol-di-propionate. After 8 h (1.49 Rm (mean reflectance) +/- 0.6 SEM) and after 30 h (0.52 Rm +/- 0.36) DRS showed significant changes in blood flow (during blanching and reactive hyperemia). LDI showed a slight change after 8 h (-0.04 aU (arbitrary units) +/- 0.02 blanching) and a second, significant reaction after 30 h (LDI: 0.18 aU +/- 0.04 reactive hyperemia). In LDI after 30 h higher values were found in men than in women (clobetasol-17-propionate under occlusion Deltat(30)-t(0) men: 0.47 aU +/- 0.18; n = 7; Deltat(30)-t(0) women: 0.14 aU +/- 0.02; n = 10; P = 0.025). This leads to the conclusion that DRS is of more value for the detection of blanching than LDI, which has its sensitivity in the hyperperfused skin. Measurement with both devices showed clear differences in men and women, which means that sex differences should be taken into account.

Video-rate three-dimensional optical coherence tomography

Most current optical coherence tomography systems provide two-dimensional cross-sectional or en face images. Successive adjacent images have to be acquired to reconstruct three-dimensional objects, which can be time consuming. Here we demonstrate three-dimensional optical coherence tomography (3D OCT) at video rate. A 58 by 58 smart-pixel detector array was employed. A sample volume of 210x210x80 m3 (corresponding to 58x58x58 voxels) was imaged at 25 Hz. The longitudinal and transverse resolutions are 3 m and 9 m respectively. The sensitivity of the system was 76 dB. Video rate 3D OCT is illustrated by movies of a strand of hair undergoing fast thermal damage.

Spectral interferometric optical coherence tomography with nonlinear beta-barium borate time gating

A high-speed, all optical coherence tomography system was designed and constructed. This tomography system employs spectral interferometry and optical Fourier transformation to reduce the number of mechanical scanning dimensions required for multidimensional profilometry. The system also employs a time gate comprising a beta -barium borate crystal driven by a femtosecond laser pulse to improve measurement time. This system has 43-mum depth resolution and 150-fs temporal resolution and is capable of taking 1000 cross-sectional image frames per second.

Visualization of subsurface blood vessels by color Doppler optical coherence tomography in rats: before and after hemostatic therapy

BACKGROUND

The ability to visualize subsurface blood vessels and measure flow may be useful in certain experimental and clinical settings.

METHODS

Color Doppler optical coherence tomography was used to visualize and measure blood flow in subsurface vessels in vivo in a rat skin flap model. Local "hemostatic" interventions (epinephrine or sclerosant injection, heat probe, and laser) were then applied and imaging was repeated. The skin flap was evaluated histologically.

RESULTS

Subsurface blood vessels were easily visualized in cross-section, and vessel diameter and bidirectional blood flow velocity were readily measured. Color Doppler optical coherence tomography demonstrated that flow was significantly reduced after epinephrine injection and became undetectable after the other interventions. This correlated with pathologic evidence of vessel damage in all interventions, except for epinephrine injection. Although vessel response was as predicted to most interventions, the response to epinephrine was only temporary, and limited application of heat alone from the heat probe halted flow without visually apparent surface injury.

CONCLUSIONS

Color Doppler optical coherence tomography provides high-resolution, cross-sectional flow imaging in subsurface blood vessels. Color Doppler optical coherence tomography is potentially a better technique for the study of existing and new hemostatic intervention in the laboratory. Potential future clinical applications include monitoring of the response to hemostatic modalities.

Real-time in vivo color Doppler optical coherence tomography

Color Doppler optical coherence tomography (CDOCT) is a functional extension of optical coherence tomography (OCT) that can image flow in turbid media. We have developed a CDOCT system capable of imaging flow in real time. Doppler processing of the analog signal is accomplished in hardware in the time domain using a novel autocorrelation technique. This Doppler processing method is compatible with a high speed OCT system capable of imaging in real time. Using this system, we demonstrate cross-sectional imaging of bidirectional flow with CDOCT at four frames per second in a tissue-simulating phantom consisting of intralipid solution flowing in glass capillaries. As a demonstration of real-time imaging of blood flow in vivo we imaged pulsatible blood flow in a rat femoral artery at eight frames per second. Issues of velocity sensitivity, imaging speed, and range of velocity measurement are discussed, as well as potential applications of real-time CDOCT.

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

Challenges in small animal noninvasive imaging

The current status and challenges of small animal non-invasive imaging is briefly reviewed. The advantages of non-invasive studies on living animals versus post-mortem studies are evaluated. An argument is advanced that even in post-mortem situations, non-invasive imaging may play an important role in efficiently characterizing small animal phenotypes as well as pathology. Issues of data interpretation under anesthetized conditions in live animal studies are also reviewed. The five imaging technologies covered include CT, PET, ultrasound, MRI and optical imaging. The structural and physiological information content of these different modalities is reviewed along with the ability of these techniques to scale down for use in small mammals such as mice and rats. In general, it was found that most of these technologies scale favorably to the study of small mammals, generally providing more physiological information than when used on the larger human scale. This suggests that these types of small mammal imaging capabilities will play a very significant role in the full utilization of these important animal models in biomedical research.

Methods for imaging the structure and function of living tissues and cells: 1. Optical coherence tomography

This is the first in a series of review articles which aim to present a concise and systematic overview of the principles, limitations, advantages, and uses of some of the more important recently developed techniques capable of imaging living histology. Optical coherence tomography (OCT) is now an established optical biopsy method, imaging 2-3 mm into opaque tissue. It is analogous to optical 'ultrasound' but has an outstanding resolution, being capable of imaging single cells in the intact animal via a surface, intravascular or endoscopic approach. Both two-dimensional (2D) and three-dimensional (3D) image datasets can be acquired and studied over time (4D imaging) in the live animal or human subject without the need to remove tissue or perform any tissue processing or staining. It has been used in ophthalmology, gastrointestinal tract (GI) studies, gynaecological tract investigation, and endovascular imaging, to name but a few areas. A degree of differential tissue contrast information can also be gleaned, since different tissue components give different OCT reflectivity signals such that adipose, muscle, collagen, and elastic components may all be resolved without staining. Continuing developments include faster data acquisition for real-time recording and Doppler OCT for more functional imaging.