Equis ISSN 2398-2977

Ultrasonography: overview

Contributor(s): Roberta Baxter, Sue Dyson, Chris Whitton

Introduction

  • A diagnostic and therapeutic medium.
  • An ultrasonic image is produced by the reflection of high-frequency sound waves at density interfaces between two tissues.
  • Fluid is an excellent medium for transmission of sound waves and fluid-filled structures appear black or anechoic on the ultrasonographic image.
  • Gas transmits little but produces severe attenuation of the sound beam.
  • Other tissues are seen as various shades of grey depending on their ability to reflect sound waves.
  • Ultrasound is a form of radiant energy at frequencies >20,000 cycles/s (Hertz or Hz).
  • For diagnostic ultrasonography, the reflections of high frequency ultrasonic waves are recorded as they bounce off the target tissues.
  • Lower frequencies   →   greater penetration.
  • Higher frequencies   →   for lower penetration and greater detail.
Print off the Owner factsheet on Diagnostic imaging to give to your clients.

Definitions

A-mode
  • Amplitude modulation, eg ocular ultrasound   Ultrasonography: eye  .
  • ‚ÄčOne axis of the display indicates the depth of the echo-producing structure.
  • Other axis indicates the strength of the echo.
  • Limited usefulness in veterinary medicine.
B-mode
  • Brightness modulation.
  • Position on the display indicates the depth of the echogenic structure.
  • Produces a two dimensional image   Metacarpus: palmar 20 cm transverse ultrasound  .
  • Brightness = strength of the echo.
M-mode
  • Motion mode.
  • Form of B-mode ultrasound.
  • A traced display of the movement of echogenic tissues over time, eg echocardiography   Heart: LAV valve insufficiency - M-mode echocardiograph     .
Real time
  • Scans recorded at a high rate per second (frame rate).
  • The form of B-mode ultrasound currently in use.
Doppler
  • Used to evaluate blood flow.
  • Based on measurement of the shift in frequency of the returning ultrasonic wave.
  • This allows determination of flow velocity and direction within the targeted blood vessels and cardiac chambers   Heart: ventricular septal defect 03 - echocardiograph  .

Physics

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Uses

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Appearance of tissues

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Artifacts

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The thorax

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.
  • Denoix J M, Bertoni L, Heitzmann A G, Werpy N & Audigie F (2011)Ultrasonographic examination of the collateral ligaments of the distal interphalangeal joint in horses. Part A: technique and normal images. Equine Vet Educ23(11), 574-580.
  • Garrett K S et al(2009)Diagnosis of laryngeal dysplasia in five horses using magnetic resonance imaging and ultrasonography. Equine Vet J41(8), 766-771PubMed.
  • Bischofberger A S et al (2006)Magnetic resonance imaging, ultrasonography and histology of the suspensory ligament origin: a comparative study of normal anatomy of Warmblood horses. Equine Vet J38(6), 508-516PubMed.
  • Marr C (1993)Thoracic ultrasonography. Equine Vet Educ.
  • McGladdery A J (1992)Ultrasonography as an aid to the diagnosis of equine colic. Equine Vet Educ4(5), 248-251.
  • Bruck I, Raun K, Synnestvedt B & Greve T (1992)Follicle aspiration in the mare using a transvaginal ultrasound-guided technique. Equine Vet J24(1), 58-59PubMed.

Other sources of information

  • Rantanen N W & McKinnon A O (1998) EdsEquine Diagnostic Ultrasound. 1st edn. Williams & Wilkins, Baltimore. ISBN: 0 683 07123 8.


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