Prospects And Limitations Of Diagnostic Ultrasound

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Abstract
The current state of medical diagnostic ultrasound imaging is analyzed including discussions of present limitations and possible solutions of these problems. Ultrasound is unique in that tomographic images are formed from mechanical energy reflected from tissue interfaces of differing acoustic impedance. The low propagation velocities of ultrasound (1540 m/sec) coupled with the range of diagnostic frequencies (1-30 MHz) result in excellent image resolution (2mm x 2mm) and permit electronic signal processing to achieve portable real time dynamically focused scanning systems at relatively low cost. Diagnostic ultrasound is applied in obstetrics, cardiology, abdominal imaging and ophthalmology but it versatility is limited by the physical characteristics of tissue. The relative impenetrability of bone and tissue containing air hinder its use in the head, lung and intestines. Tissue inhomogeneities throughout the entire body make it impossible to achieve diffraction limited resolution, and the slow propagation velocities of sound place an upper limit on the image data acquisition rate. Research is ongoing to improve resolution by adaptive imaging techniques, and parallel processing will hopefully increase data acquisition. These improvements depend heavily on advances in electronics technology.

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