How we Think

Optical Coherence Tomography: An Emerging Technology for Biomedical Imaging and Optical Biopsy

Background Optical coherence tomography (OCT) is a recently developed medical diagnostic technology that uses back-reflected infrared light to perform in situ micron scale tomographic imaging. In this work, we investigate the ability of OCT to perform micron scale tomographic imaging of the internal microstructure of in vitro atherosclerotic plaques. Methods and Results Aorta and relevant nonvascular tissue were obtained at autopsy. Two-dimensional cross-sectional imaging of the exposed surface of the arterial segments was performed in vitro with OCT. A 1300-nm wavelength, superluminescent diode light source was used that allows an axial spatial resolution of 20 μm. The signal-to-noise ratio was 109 dB. Images were displayed in gray scale or false color. Imaging was performed over 1.5 mm into heavily calcified tissue, and a high contrast was noted between lipid- and water-based constituents, making OCT attractive for intracoronary imaging. The 20-μm axial resolution of OCT allowed small structural details...

Optical Coherence Tomography for Optical Biopsy Properties and Demonstration of Vascular Pathology

BACKGROUND: OCT can image plaque microstructure at a level of resolution not previously demonstrated with other imaging techniques because it uses infrared light rather than acoustic waves. OBJECTIVES: To compare optical coherence tomography (OCT) and intravascular ultrasound (IVUS) imaging of in vitro atherosclerotic plaques. METHODS: Segments of abdominal aorta were obtained immediately before postmortem examination. Images of 20 sites from five patients were acquired with OCT (operating at an optical wavelength of 1300 nm which was delivered to the sample through an optical fibre) and a 30 MHz ultrasonic transducer. After imaging, the microstructure of the tissue was assessed by routine histological processing. RESULTS: OCT yielded superior structural information in all plaques examined. The mean (SEM) axial resolution of OCT and IVUS imaging was 16 (1) and 110 (7), respectively, as determined by the point spread function from a mirror. Furthermore, the dynamic range of OCT was 109 dB compared with 43 dB for IVUS imaging. CONCLUSIONS: OCT represents a promising new technology for intracoronary imaging because of its high resolution, broad dynamic range, and ability to be delivered through intravascular catheters.

https://heart.bmj.com/content/heartjnl/77/5/397.full.pdf

Assessing atherosclerotic plaque morphology: comparison of optical coherence tomography and high frequency intravascular ultrasound.

Optical coherence tomography (OCT) is a method of high-resolution imaging originally developed for the transparent tissue of the eye. Recently, the technology has been advanced toward the difficult challenge of imaging in nontransparent tissue. In the paper, three topics are addressed. First, the principles behind OCT imaging are discussed. Second, the difficulties associated with OCT imaging in nontransparent tissue are outlined. Finally, the feasibility of OCT for medical imaging is discussed. Specifically, OCT demonstrates its greatest potential in situations where conventional biopsy is either dangerous or ineffective.

Optical coherence tomography: high-resolution imaging in nontransparent tissue

An ultrasonic phased array applicator for hyperthermia provides electronic steering of the sound beam rather than mechanical movement of the transducer assembly. An applicator consisting of a stack of linear phased arrays is examined. The effects of various design parameters, including individual array height and length, are discussed. work was supported in part by URI Therm-X, Inc., and in part by the National Institute of Health under NIH Training Gr-ant CA 09067. and Computer Engineering Department, University of Illinois, 1406 West Green St., Urbana, IL 61801. Manuscript received December 20,1983; revised July 17,1984. This The authors are with the Bioacoustics Research Laboratory, Electrical

An Ultrasonic Phased Array Applicator for Hyperthermia

Abstracl-An ultrasonic tapered phased array transducer, consisting of a linear phased array employing elements with a tapered thickness, was developed to study the feasibility of its use for hyperthermic treatment of deep-seated tumors. The cylindrical focal region is generated and steered in two dimensions by controlling the phases of the driving signals on each element and moved in the third dimension by changing the driving frequency. Experimentally obtained field intensity distributions are in good agreement with theoretical predictions. Acoustical power output measurements indicate that tapered phased arrays are capable of providing the intensities necessary for producing therapeutic temperatures in tumors.

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A Tapered Phased Array Ultrasound Transducer for Hyperthermia Treatment

Interest in the use of ultrasound to characterize the structure and composition of blood vessel walls has risen dramatically as a result of the development of intravascular ultrasonic imaging transducers mounted on the tips of small-diameter catheters. A study of the resolution of these tranducers is needed to understand the limitations in the visualization of these structures. Theoretic and experimental studies of the resolution of the two principal designs of intravascular ultrasonic transducers, the mechanically scanned single element and the multielement circular array, were carried out. Comparisons of the two designs reveal that they have similar resolutions. However, the resolutions in two of the three dimensions are shown to decrease linearly with increasing radial distance. Significant errors in image interpretation, particularly in larger diameter vessels, will result if this variation in resolution is not accounted for.

P.J. Benkeser

Papers

An Ultrasonic Phased Array Applicator for Hyperthermia

A Tapered Phased Array Ultrasound Transducer for Hyperthermia Treatment

Resolution limitations in intravascular ultrasound imaging.

Cardiac segmentation by a velocity-aided active contour model

Comparison of septal defects in 2D and 3D echocardiography using active contour models.