Accession Number : AD0784369

Title :   A Theoretical Evaluation of Ultrasonic Detection of Small Gas Bubbles.

Descriptive Note : Medical research progress rept. no. 4,

Corporate Author : NAVAL MEDICAL RESEARCH INST BETHESDA MD

Personal Author(s) : Carey,William M.

Report Date : MAR 1972

Pagination or Media Count : 40

Abstract : The scattering of ultrasound (such as is commonly used in medical diagnosis) by small bubbles was analyzed. A bubble larger than the acoustic wavelength casts an acoustic shadow as predicted by geometric acoustics; a bubble the same size as the acoustic wavelength imparts strong directionality to the scattered wave. A bubble smaller than the acoustic wavelength radiates a scattered spherical wave of less than 0.1% of the incident energy because of dissipative losses. For a random distribution of these bubbles (of sub-wavelength size) the intensity of the scattered wave is directly proportional to the bubble density. A direct acoustic-optical imaging system (ultrasonic Bragg imaging) is insufficiently sensitive to detect bubbles smaller than an acoustic wavelength. The image detail in acoustic-optical imaging systems is limited by the acoustic wavelength, the numerical aperture of the optics, and spatially abrupt near-field acoustic intensity variations. (Modified author abstract)

Descriptors :   *Acoustooptics, *Gas embolism, *Diagnostic equipment, Decompression sickness, Ultrasonics, Images, Diagnosis(Medicine), Medical equipment, Bioinstrumentation

Subject Categories : Acoustic Detection and Detectors
      Biomedical Instrumentation and Bioengineering

Distribution Statement : APPROVED FOR PUBLIC RELEASE