Optical Coherence Tomography (OCT) is a relatively new type of imaging system for medical diagnosis. Because most current OCT systems use a sharply focused beam in tissues, they have a short depth of field (high image resolution is near the focus only). In this paper, limited diffraction beams of different orders are used to increase depth of field and to reduce sidelobes in OCT. Results show that the proposed OCT system has a lateral resolution of about 4.4 wavelengths (the central wavelength of the source is about 940 nm with a bandwidth of about 70 nm) and lower than -60 dB sidelobes over an entire depth of field of 4.5 mm with the diameter of the objective lens of 1 mm.
Optical Coherence Tomography (OCT) is a relatively new type of imaging system for medical diagnosis. Because most current OCT systems use a sharply focused beam in tissues, they have a short depth of field (high image resolution is near the focus only). In this paper, limited diffraction beams of different orders are used to increase depth of field and to reduce sidelobes in OCT. Results show that the proposed OCT system has a lateral resolution of about 4.4 wavelengths (the central wavelength of the source is about 940 nm with a bandwidth of about 70 nm) and lower than -60 dB sidelobes over an entire depth of field of 4.5 mm with the diameter of the objective lens of 1 mm.
Relaxor ferroelectric materials have been studied extensively in both theory and experiments for many years. Their applications to medical ultrasonic transducers have also been investigated. In this paper, we report an experimental study of a composite relaxor ferroelectric transducer and its nonlinear phenomenon at certain bias voltages. Novel applications of the relaxor transducer to diffraction-limited beam production, acoustic power measurement, low speckle medical imaging, and high resolution pulse-echo imaging are discussed.
Diffraction-limited beams were first discovered by Durnin in 1987. These beams are pencil- like and have very large depth of field. Recently, we have discovered new families of diffraction-limited beams which contain some of the diffraction-limited beams known previously, such as, the plane wave and Durnin's Bessel beams, in addition to an infinite variety of new beams, such as X waves. In this paper, we generalize the new diffraction- limited beams to n-dimensional space, review the recent development of the diffraction-limited beams, and describe their applications to medical ultrasonic imaging, tissue characterization and nondestructive evaluation of materials. Advantages and disadvantages of these beams are discussed and their possible applications to other wave related fields are addressed.
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