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Biomedical subjects

Andrew M Rollins

Publications and source records attributed to Andrew M Rollins.

16 recordsLinked to original sources
PubMed2006

A feasibility study of optical coherence tomography for guiding deep brain probes.

Deep brain simulation (DBS) is effective for the treatment of various diseases including Parkinson's disease and essential tremor. However, anatomical targeting combined with microelectrode mapping of the region requires significant surgical time. Also, the fine-tipped microelectrode imposes a risk of hemorrhage in the event that the trajectory intersects subcortical vessels. To reduce the operation time and the risk of hemorrhage, we propose to use optical coherence tomography (OCT) to guide the insertion of the DBS probe. We conducted in vitro experiments in the rat brain to study the feasibility of this application. The result shows that OCT is able to differentiate structures in the rat brain. White matter tends to have higher peak reflectivity and steeper attenuation rate compared to gray matter. This structural information may help guide DBS probe advance and electrical measurements.

Animals↗
PubMed2006

Comparison of corneal thickness measured with optical coherence tomography, ultrasonic pachymetry, and a scanning slit method.

PURPOSE: To investigate the relationship between 1310-nm optical coherence tomography (OCT), an ultrasound pachymeter, and the Orbscan II (Bausch & Lomb, Rochester, NY) in corneal thickness measurements before and after LASIK. METHODS: Twenty-eight eyes of 14 patients with a mean age of 39.9 +/- 8.6 years underwent LASIK for correction of myopia with or without astigmatism. Central corneal thickness was measured with real-time 1310-nm OCT and Orbscan preoperatively and 1 day, 1 week, and 1 month postoperatively, and with an ultrasound pachymeter preoperatively and 1 month postoperatively. RESULTS: Measurements of corneal thickness by all instruments correlated well with one another pre- and postoperatively (r value range: 0.87 to 0.94, P<.05); however, there were significant differences among these methods (ANOVA: P<.005). Baseline readings for ultrasound and Orbscan were similar, as were readings 1 month postoperatively for OCT and Orbscan (P>.05). Thickness measured by OCT was thinner than for other instruments preoperatively (P<.005) and thicker than Orbscan postoperatively (P<.005). Significant corneal thinning (P<.001) was found with all study devices 1 day after laser ablation. Significant corneal thinning (P<.005) was found with OCT and Orbscan 1 week compared to 1 day postoperatively, and thickening (post hoc: P<.001) was evident at 1 month compared to 1 week postoperatively. CONCLUSIONS: Although the instruments correlated well in measuring corneal thickness after LASIK, there were significant differences. All instruments indicated corneal swelling and recovery during the first postoperative week and thickening at 1 month.

Adult↗
PubMed2005

Phase-referenced Doppler optical coherence tomography in scattering media.

We present a fiber-based, low-coherence interferometer that significantly reduces phase noise by incorporating a second, narrowband, continuous-wave light source as a phase reference. By incorporating this interferometer into a Doppler OCT system, we demonstrate significant velocity noise reduction in reflective and scattering samples using processing techniques amenable to real-time implementation. We also demonstrate 90% suppression of velocity noise in a flow phantom.

Equipment Design↗
PubMed2005

Comparison of optical coherence tomography and ultrasound biomicroscopy for detection of narrow anterior chamber angles.

OBJECTIVE: To assess the accuracy of classification of narrow anterior chamber (AC) angles using quantitative imaging by optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM). DESIGN: Observational comparative study. METHODS: A high-speed (4000 axial scans/s) anterior segment OCT prototype was developed using a 1.3-microm light source. Seventeen normal subjects (17 eyes) and 7 subjects (14 eyes) with narrow angle glaucoma were enrolled. All subjects underwent gonioscopy, OCT, and UBM. Quantitative AC angle parameters (angle opening distance, angle recess area, and the trabecular-iris space area [a new parameter we have defined]) were measured from OCT and UBM images using proprietary processing software. MAIN OUTCOME MEASURES: Specificity and sensitivity in identifying narrow angles with image-derived AC angle parameters. RESULTS: Eight of 31 eyes were classified as having narrow angles (Shaffer grade < or =1 in all quadrants). The AC angle parameters measured by both OCT and UBM had similar mean values, reproducibility, and sensitivity-specificity profiles. Both OCT and UBM showed excellent performance in identifying eyes with narrow angles. Areas under the receiver operating characteristic curves for these parameters were all in the range of 0.96 to 0.98. CONCLUSIONS: Optical coherence tomography was similar to UBM in quantitative AC angle measurement and detection of narrow angles. In addition, it was easier to use and did not require contact with the eye. Optical coherence tomography is a promising method for screening individuals at risk for narrow angle glaucoma.

Adult↗
PubMed2005

High-speed optical coherence tomography of laser iridotomy.

PURPOSE: To describe high-speed (4000 axial scans/s) optical coherence tomography (OCT) findings in a patient with narrow angles. DESIGN: Interventional case report. METHODS: A 56-year-old woman was found to have occludable narrow angles on OCT screening. This was confirmed by gonioscopy. Bilateral iridotomy was performed. Imaging of the angles was performed with a high-speed OCT prototype before and after iridotomy. RESULTS: OCT showed narrow angle bilaterally. Cornea, sclera, scleral spur, trabecula, iris, and iris recess were visualized. After iridotomy, the OCT showed reduction of iris concavity and patent iridotomies. Quantitative measurements of trabecula-iris space area on the OCT images showed widening of the angles to nonoccludable values. CONCLUSIONS: A 1.3-microm wavelength OCT allows noncontact quantitative assessment of the angle and may be useful in the management of narrow-angle glaucoma.

Diagnostic Techniques, Ophthalmological↗
PubMed2005

Anterior chamber width measurement by high-speed optical coherence tomography.

OBJECTIVE: To measure anterior chamber (AC) width and other dimensions relevant to the sizing of phakic intraocular lenses (IOLs) with a high-speed optical coherence tomography (OCT) system. DESIGN: Cross-sectional observational study. PARTICIPANTS: Both eyes of 20 normal volunteers. METHODS: A novel high-speed (4000 axial scans/second) OCT prototype was developed for anterior segment scanning. The system uses long wavelength (1310 nm) for deeper angle penetration, rectangular scanning for undistorted imaging, and short image acquisition time (0.125 seconds) to reduce motion error. Three horizontal cross-sectional OCT images (15.5 mm wide and 6 mm deep) of the anterior segment were obtained from each eye with real-time image display to guide centration on the corneal apex. Image processing software was developed to correct for image warping resulting from index transitions. Anterior chamber dimensions were measured using computer calipers by 3 expert raters (ophthalmologists). Analysis of variance was used to determine interrater, interimage, right versus left eye, and intersubject standard deviation (SD) of OCT measurements. MAIN OUTCOME MEASURES: Anterior chamber width (recess to recess), AC depth, and crystalline lens vault as measured by OCT; external white-to-white (WTW) corneal diameter (CD) as measured by Holladay-Godwin gauge. RESULTS: The mean AC width was 12.53+/-0.47 mm (intereye SD), and the mean corneal diameter was 11.78+/-0.57 mm. Optical coherence tomography measurement of AC width has good repeatability from image to image (SD, 0.134 mm), but there was significant difference between raters (SD, 0.215 mm). Estimation of AC width from WTW CD by linear regression was relatively inaccurate (residual SD, 0.41 mm). The mean AC depth was 2.99+/-0.323 mm (intereye SD), with repeatability of less than 0.001 mm (interimage SD), and the mean crystalline lens vault was 0.39+/-0.27 mm with 0.023 mm repeatability. CONCLUSIONS: Reproducible OCT AC biometry was demonstrated using a high-speed OCT prototype. Further improvement in reproducibility may be achieved by automating the measurements with a computer. Direct OCT AC width measurement may improve sizing of angle-supported AC IOLs over conventional estimation by WTW CD. The measurement of AC depth and lens vault also may be useful for other types of phakic AC IOLs.

Adult↗
PubMed2005

Correlation of endoscopic optical coherence tomography with histology in the lower-GI tract.

BACKGROUND: Optical coherence tomography (OCT), a noninvasive optical imaging technique, provides high-resolution cross-sectional images of tissue microstructure. We developed a system for real-time endoscopic OCT (EOCT) of the human GI tract. During clinical trials, the structure of mucosa and submucosa, glands, blood vessels, pits, villi, and crypts was observed in a range of GI organs. Although EOCT images are thought to accurately depict actual histologic features, there are few data to support this assumption. Therefore, the present study correlated images acquired with an EOCT imaging system in vitro to corresponding histologic sections. METHODS: EOCT images were obtained of fresh specimens of ileum, colon, and rectum that then were fixed in formalin and were processed for microscopic evaluation by using standard methods. The thickness of mucosa and of submucosa was determined for both EOCT images and histologic slides. RESULTS: The first hyper-reflective layer in the EOCT images was identified as mucosa. A close correlation (R 2=0.84) was observed between EOCT and histology. Furthermore, the submucosa and the muscularis propria could be identified as the next deepest hyporeflective band and a hyper-reflective layer, respectively, in EOCT images. The submucosa was found to be more compressible than mucosa, and its EOCT appearance was dependent on its content of adipose tissue. CONCLUSIONS: EOCT provides images that precisely correlate with the histologic structure of the mucosa and the submucosa of the GI tract.

Colon↗
PubMed2005

Optical coherence tomography: a new method to assess aneurysm healing.

OBJECT: Aneurysmal subarachnoid hemorrhage affects approximately 10/100,000 people per year. Endovascular coil embolization is used increasingly to treat cerebral aneurysms and its safety and durability is rapidly developing. The long-term durability of coil embolization of cerebral aneurysms remains in question; patients treated using this modality require multiple follow-up angiography studies and occasional repeated treatments. METHODS: Optical coherence tomography (OCT) is an emerging imaging modality that uses backscattered light to produce high-resolution tomography of optically accessible biological tissues such as the eye, luminal surface of blood vessels, and gastrointestinal tract. Vascular OCT probes in the form of imaging microwires are presently available--although not Food and Drug Administration-approved--and may be adapted for use in the cerebral circulation. In this study the authors describe the initial use of OCT to make visible the neck of aneurysms created in a canine model and treated with coil embolization. Optical coherence tomography images demonstrate changes that correlate with the histological findings of healing at the aneurysm neck and thus may be capable of demonstrating human cerebral aneurysm healing. CONCLUSIONS: Optical coherence tomography may obviate the need for subsequent follow-up angiography studies as well as aid in the understanding of endovascular tissue healing. Data in this study demonstrate that further investigation of in vivo imaging with such probes is warranted.

Animals↗
PubMed2004

Polarization-resolved second-harmonic-generation optical coherence tomography in collagen.

We describe a novel imaging technique, second-harmonic-generation optical coherence tomography (SHOCT). This technique combines the spatial resolution and depth penetration of optical coherence tomography (OCT) with the molecular sensitivity of second-harmonic-generation spectroscopy. As a consequence of the coherent detection required for OCT, polarization-resolved images arise naturally. We demonstrate this new technique on a skin sample from the belly of Icelandic salmon, acquiring polarization-resolved SHOCT and OCT images simultaneously.

Animals↗
PubMed2004

Group index of the human cornea at 1.3-microm wavelength obtained in vitro by optical coherence domain reflectometry.

The group index of the cornea, rather than the phase refractive index, is required for thickness calculations with optical coherence tomography. Recent advances with high-speed optical coherence tomography at 1.3 microm make index measurement at this wavelength of great interest. Group indices of three human corneas from an eye bank were measured in vitro with optical coherence domain reflectometry. Measurements were made in a calibrated cuvette filled with a preservation medium to maintain proper corneal hydration. Group indices were calculated from the optical path lengths measured. The corneal group index was 1.389 +/- 0.004 (average +/- standard deviation). The average group index of a balanced salt solution, an approximation to aqueous humor, was 1.343 +/- 0.001.

Chondroitin Sulfates↗
PubMed2003

Molecular contrast in optical coherence tomography by use of a pump-probe technique.

We describe a novel technique for contrast enhancement in optical coherence tomography (OCT) that makes possible molecular-specific imaging for what is believed to be the first time. A pump-probe technique is employed in which a pulsed pump laser is tuned to ground-state absorption in a molecule of interest. The location of the target molecule population is derived from the resulting transient absorption of OCT sample-arm light acting as probe light. A signal processing technique for three-dimensional localization of the transient absorption signal is described, and preliminary results exhibiting OCT contrast from methylene blue dye in multilayer and scattering phantoms are presented.

Contrast Media↗
PubMed2003

In vivo imaging of human retinal flow dynamics by color Doppler optical coherence tomography.

BACKGROUND: Color Doppler optical coherence tomography (CDOCT) combines laser Doppler velocimetry and optical coherence tomography for simultaneous micron-scale resolution cross-sectional imaging of tissue microstructure and blood flow. Recently, CDOCT was adapted to a slitlamp biomicroscope for imaging structure and blood flow in the human retina. OBJECTIVE: To demonstrate feasibility of CDOCT for imaging retinal hemodynamics. DESIGN: Enabling CDOCT to measure retinal blood flow pulsatility in humans. SETTING: Laboratory. MAIN OUTCOME MEASURES: Time-resolved flow profiles and images of retinal blood flow dynamics for measurement of pulsatility within retinal vessels. RESULTS: Rapid sequences of images were acquired over selected vessels near the optic nerve head. From these images, retinal blood flow profiles were extracted and synchronized to an external reference obtained with a photoplethysmograph. Each profile was acquired in less than 10 milliseconds. CONCLUSIONS: Our results indicate that CDOCT provides laser Doppler information in addition to conventional optical coherence tomography, allowing the observation of blood flow dynamics simultaneous to imaging retinal structure. CDOCT is a promising technology for research and clinical studies of retinal blood flow dynamics. CLINICAL RELEVANCE: Blood flow dynamics, such as pulsatility and autoregulation, have been shown to change throughout the progression of diabetic retinopathy and glaucoma. Enabling CDOCT to observe retinal dynamics improves its potential as a clinical diagnostic tool.

Blood Flow Velocity↗
PubMed2002

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.

Animals↗
PubMedDate not supplied

Computer-aided diagnosis of dysplasia in Barrett's esophagus using endoscopic optical coherence tomography.

Barrett's esophagus (BE) and associated adenocarcinoma have emerged as a major health care problem over the last two decades. Because of the widespread use of endoscopy, BE is being recognized increasingly in all Western countries. In clinical trials of endoscopic optical coherence tomography (EOCT), we defined certain image features that appear to be characteristic of precancerous (dysplastic) mucosa: decreased scattering and disorganization in the microscopic morphology. The objective of the present work is to develop computer-aided diagnosis (CAD) algorithms that aid the detection of dysplasia in BE. The image dataset used in the present study was derived from a total of 405 EOCT images (13 patients) that were paired with highly correlated histologic sections of corresponding biopsies. Of these, 106 images were included in the study. The CAD algorithm used was based on a standard texture analysis method (center-symmetric auto-correlation). Using histology as the reference standard, this CAD algorithm had a sensitivity of 82%, specificity of 74%, and accuracy of 83%. CAD has the potential to quantify and standardize the diagnosis of dysplasia and allows high throughput image evaluation for EOCT screening applications. With further refinements, CAD could also improve the accuracy of EOCT identification of dysplasia in BE.

Adenocarcinoma↗