Biomedical subjects

Victor X D Yang

Publications and source records attributed to Victor X D Yang.

10 recordsLinked to original sources

PubMed2007

Wide dynamic range detection of bidirectional flow in Doppler optical coherence tomography using a two-dimensional Kasai estimator.

We demonstrate extended axial flow velocity detection range in a time-domain Doppler optical coherence tomography (DOCT) system using a modified Kasai velocity estimator with computations in both the axial and transverse directions. For a DOCT system with an 8 kHz rapid-scanning optical delay line, bidirectional flow experiments showed a maximum detectable speed of >56 cm/s using the axial Kasai estimator without the occurrence of aliasing, while the transverse Kasai estimator preserved the approximately 7 microm/s minimum detectable velocity to slow flow. By using a combination of transverse Kasai and axial Kasai estimators, the velocity detection dynamic range was over 100 dB. Through a fiber-optic endoscopic catheter, in vivoM-mode transesophageal imaging of the pulsatile blood flow in rat aorta was demonstrated, for what is for the first time to our knowledge, with measured peak systolic blood flow velocity of >1 m/s, while maintaining good sensitivity to detect aortic wall motion at <2 mm/s, using this 2D Kasai technique.

Algorithms↗

PubMed2007

Ex vivo imaging of chronic total occlusions using forward-looking optical coherence tomography.

BACKGROUND AND OBJECTIVES: Percutaneous coronary interventions (PCI) of chronic total occlusions (CTOs) of arteries are more challenging lesions to treat with angioplasty and stenting than stenotic vessels due primarily to the difficulty in guiding the wire across the lesion. Angiography alone is unable to differentiate between the occluded lumen and the vessel wall and to characterize the content of the occlusion. New technologies to aid in interventional guidance are therefore highly desirable. We sought to evaluate tissue characterization in arterial (CTOs) by imaging ex vivo peripheral arterial samples with optical coherence tomography (OCT). STUDY DESIGN/MATERIALS AND METHODS: Ex vivo arterial samples were obtained from patients undergoing peripheral limb amputation. Samples were imaged in an enface orientation using an OCT system, enabling sequential acquisition of longitudinal images and volumetric reconstruction of cross-sectional views of the occluded arteries. Histology was performed for comparison. RESULTS: OCT imaging reliably differentiated between the occluded lumen and the underlying arterial wall in peripheral CTOs. OCT correctly identified tissue composition within the CTO, such as the presence of collagen and calcium and was also able to identify intraluminal microchannels. CONCLUSIONS: OCT imaging of CTO anatomy and tissue characteristics may potentially lead to substantial improvements in PCI interventions by providing novel guiding capabilities.

Angiography↗

PubMed2006

Doppler optical coherence tomography with a micro-electro-mechanical membrane mirror for high-speed dynamic focus tracking.

An elliptical microelectromechanical system (MEMS) membrane mirror is electrostatically actuated to dynamically adjust the optical beam focus and track the axial scanning of the coherence gate in a Doppler optical coherence tomography (DOCT) system at 8 kHz. The MEMS mirror is designed to maintain a constant numerical aperture of approximately 0.13 and a spot size of approximately 6.7 microm over an imaging depth of 1mm in water, which improves imaging performance in resolving microspheres in gel samples and Doppler shift estimation precision in a flow phantom. The mirror's small size (1.4 mm x 1 mm) will allow integration with endoscopic MEMS-DOCT for in vivo applications.

Computer Systems↗

PubMed2006

Feasibility of interstitial Doppler optical coherence tomography for in vivo detection of microvascular changes during photodynamic therapy.

INTRODUCTION: Doppler optical coherence tomography (DOCT) is an emerging imaging modality that provides subsurface microstructural and microvascular tissue images with near histological resolution and sub-mm/second velocity sensitivity. A key drawback of OCT for some applications is its shallow (1-3 mm) penetration depth. This fundamentally limits DOCT imaging to transparent, near-surface, intravascular, or intracavitary anatomical sites. Consequently, interstitial Doppler OCT (IS-DOCT) was developed for minimally-invasive in vivo imaging of microvasculature and microstructure at greater depths, providing access to deep-seated solid organs. Using Dunning prostate cancer in a rat xenograft model, this study evaluated the feasibility of IS-DOCT monitoring of microvascular changes deep within a tumor caused by photodynamic therapy (PDT). MATERIALS AND METHODS: The DOCT interstitial probe was constructed using a 22 G (diameter approximately 0.7 mm) needle, with an echogenic surface finish for enhanced ultrasound visualization. The lens of the probe consisted of a gradient-index fiber, fusion spliced to an angle-polished coreless tip to allow side-view scanning. The lens was then fusion spliced to a single-mode optical fiber that was attached to the linear scanner via catheters and driven along the longitudinal axis of the needle to produce a 2D subsurface DOCT image. The resultant IS-DOCT system was used to monitor microvascular changes deep within the tumor mass in response to PDT in the rat xenograft model of Dunning prostate cancer. Surface PDT was delivered at 635 nm with 40 mW of power, for a total light dose of 76 J/cm(2), using 12.5 mg/kg of Photofrin as the photosensitizer dose. RESULTS: IS-DOCT demonstrated its ability to detect microvasculature in vivo and record PDT-induced changes. A reduction of detected vascular cross sectional area during treatment and partial recovery post-treatment were observed. CONCLUSIONS: IS-DOCT is a potentially effective tool for real-time visualization and monitoring of the progress of PDT treatments. This capability may play an important role in elucidating the mechanisms of PDT in tumors, pre-treatment planning, feedback control for treatment optimization, determining treatment endpoints and post-treatment assessments.

Animals↗

PubMed2005

Interstitial Doppler optical coherence tomography.

Doppler optical coherence tomography (OCT) can image tissue structure and blood flow at micrometer-scale resolution but has limited imaging depth. We report a novel, linear-scanning, needle-based Doppler OCT system using angle-polished gradient-index or ball-lensed fibers. A prototype system with a 19-guage (diameter of approximately 0.9 mm) echogenic needle is constructed and demonstrates in vivo imaging of bidirectional blood flow in rat leg and abdominal cavity. To our knowledge, this is the first demonstration of Doppler OCT through a needle probe in interstitial applications to visualize deeply situated microcirculation.

Animals↗

PubMed2005

Endoscopic Doppler optical coherence tomography in the human GI tract: initial experience.

BACKGROUND: Expanding the current endoscopic optical coherence tomography (OCT) system with Doppler capability may augment this novel high-resolution cross-sectional imaging technique with functional blood flow information. The aim of this feasibility study was to assess the clinical feasibility of an endoscopic Doppler OCT (EDOCT) system in the human GI tract. METHODS: During routine endoscopy, 22 patients were imaged by using a prototype EDOCT system, which provided color-Doppler and velocity-variance images of mucosal and submucosal blood flow at one frame per second, simultaneously with high-spatial-resolution (10-25 mum) images of tissue microstructure. The images were acquired from normal GI tract and pathologic tissues. OBSERVATIONS: Subsurface microstructure and microcirculation images of normal and pathologic GI tissues, including Barrett's esophagus, esophageal varices, portal hypertensive gastropathy, gastric antral vascular ectasia, gastric lymphoma, and duodenal adenocarcinoma, were obtained from 72 individual sites in vivo. Differences in vessel diameter, distribution, density, and blood-flow velocity were observed among the GI tissue pathologies imaged. CONCLUSIONS: To our knowledge, this is the first study to demonstrate the feasibility of EDOCT imaging in the human GI tract during routine endoscopy procedures. EDOCT may detect the different microcirculation patterns exhibited by normal and diseased tissues, which may be useful for diagnostic imaging and treatment monitoring.

Adult↗

PubMed2004

Micromachined array tip for multifocus fiber-based optical coherence tomography.

High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels.

Equipment Design↗

PubMed2004

Increased brain tumor resection using fluorescence image guidance in a preclinical model.

BACKGROUND AND OBJECTIVES: Fluorescence image-guided brain tumor resection is thought to assist neurosurgeons by visualizing those tumor margins that merge imperceptibly into normal brain tissue and, hence, are difficult to identify. We compared resection completeness and residual tumor, determined by histopathology, after white light resection (WLR) using an operating microscope versus additional fluorescence guided resection (FGR). STUDY DESIGN/MATERIALS AND METHODS: We employed an intracranial VX2 tumor in a preclinical rabbit model and a fluorescence imaging/spectroscopy system, exciting and detecting the fluorescence of protoporphyrin IX (PpIX) induced endogenously by administering 5-aminolevulinic acid (ALA) at 4 hours before surgery. RESULTS: Using FGR in addition to WLR significantly increased resection completeness by a factor 1.4 from 68+/-38 to 98+/-3.5%, and decreased the amount of residual tumor post-resection by a factor 16 from 32+/-38 to 2.0+/-3.5% of the initial tumor volume. CONCLUSIONS: Additional FGR increased completeness of resection and enabled more consistent resections between cases.

Aminolevulinic Acid↗

PubMed2003

A multispectral fluorescence imaging system: design and initial clinical tests in intra-operative Photofrin-photodynamic therapy of brain tumors.

BACKGROUND AND OBJECTIVES: Intra-operative identification of tumor by fluorescence may improve surgical resection or photodynamic therapy (PDT). A novel instrument was designed, constructed, and tested for this purpose. STUDY DESIGN/MATERIALS AND METHODS: The instrument was designed to provide high-resolution, multi-spectral (five band) fluorescence imaging, and non-contact point spectroscopy, with long working distance ( approximately 50 cm), large field-of-view ( approximately 3 cm diameter), large depth of view ( approximately 2 cm), and 'point-and-shoot' operation. Its performance was determined in tissue-simulating phantoms and in pilot studies in brain tumor resection patients, with or without intra-operative Photofrin-PDT. RESULTS: In phantoms the imaging resolution was approximately 150 microm, while Photofrin concentrations as low as 0.05 or 0.1 microg/g could be detected at the tissue surface or at 0.5 mm depth, respectively. Red Photofrin fluorescence could be clearly visualized post radical resection in all PDT patients, with biopsy confirmation of residual tumor tissue in regions that were not seen as tumor under white light. Photobleaching of Photofrin during PDT was also demonstrated. CONCLUSIONS: The system performed to specification under realistic operating conditions and could reveal unresected residual tumor tissue. It may be used for either PDT dosimetry/monitoring and/or for surgical guidance.

Adult↗

PubMed2003

In vivo Doppler optical coherence tomography of mucocutaneous telangiectases in hereditary hemorrhagic telangiectasia.

BACKGROUND: Hereditary hemorrhagic telangiectasia is characterized by mucocutaneous telangiectases and visceral arteriovenous malformations. Knowledge is limited concerning the development hemodynamics of mucocutaneous telangiectases. Doppler optical coherence tomography can demonstrate microvascular blood flow at flow rates as low as 20 microm/second, which is up to approximately 100 times more sensitive than Doppler US. The aims of this study were to collect in vivo Doppler optical coherence tomography images of mucocutaneous telangiectases and normal surrounding mucosa and skin, and to gain experience for an in vivo GI endoscopic study. It was hypothesized that visibly normal areas may have occult telangiectases and that mucocutaneous telangiectases that have bled may have a higher rate of blood flow than mucocutaneous telangiectases with no history of bleeding. METHODS: Twelve patients with hereditary hemorrhagic telangiectasia and mucocutaneous telangiectases were studied. Two to 3 visible mucocutaneous telangiectases on the digits, lips, and tongue were imaged with Doppler optical coherence tomography, along with visually normal surrounding areas at each site. The Doppler optical coherence tomography images were obtained in 0.5 second by using 1310 nm light. RESULTS: A total of 67 mucocutaneous telangiectases from the 12 patients were imaged (38 digit, 16 lip, 13 tongue). Blood flow was demonstrated within every mucocutaneous telangiectasis imaged. Doppler optical coherence tomography did not identify any abnormal vasculature within visually normal areas. Mucocutaneous telangiectases with a history of bleeding (n = 18) were situated closer to the surface, compared with mucocutaneous telangiectases with no bleeding history (n = 49), but there was no difference in the Doppler flow appearance. CONCLUSIONS: Visually normal areas in patients with hereditary hemorrhagic telangiectasia did not appear to have abnormal vasculature. Mucocutaneous telangiectases with a history of bleeding were more superficial but were otherwise similar to mucocutaneous telangiectases with no bleeding history.

Adult↗