Basic physical principles of ultrasound
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Sound waves
- Ultrasound uses high frequency energy to create sound waves, characterized by
- frequency: number of cycles per second (Hz)
- wavelength: distance between excitations (mm)
- amplitude: height of sound wave (decibels)
Ultrasound and tissue interaction
- reflection
- occurs when an ultrasound wave hits tissue. Part of the wave is reflected back to the transducer
- tissues with greater density reflect a greater portion of the beam
- tissues at a 90 degree angle to the beam reflect a greater portion of the beam
- acoustic impedance
- tissues can be defined by their individual acoustic impedance
- AI = density x acoustic velocity
- scatter
- small structures lead to scattering of the ultrasound signal
- scattering radiates the beam in all directions, very little reaches back to the transducer
- refraction: ultrasound waves can be deflected as they pass into a medium of different acoustic impedance
- attenuation
- when sound travels through a medium, intensity diminishes with distance
- caused by absorption of the energy by the tissues, and conversion to heat
- also affected by acoustic impedance and mismatch in impedance between adjacent structures
Ultrasound set-up
- Energy source
- Transducer: converts electrical pulses to vibrations and returned vibrations back to electrical pulses
- piezoelectric crystals
- found inside the transducer
- compress and expand the electric current that is applied, generating a sound wave
- same crystals also act as receivers. An electric current is generated when a reflected wave hits a crystal
- piezoelectric crystals
Image formation: based on the time interval between the ultrasound transmission and the arrival of the sound wave back to the transducer
Resolution
- axial- along the length of the ultrasound beam
- lateral- side to side resolution of the 2D image
- elevational- the thickness of the tomographic slice
Basics of Echocardiography
Fetal Echocardiography
- Transposition
- A Descriptive Case Presentation
- Fetal Cardiac Myxoma
The Guide to Pediatric Echocardiography
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
