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Result : Searchterm 'Propagation' found in 2 terms [] and 18 definitions [])
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PropagationMRI Resource Directory: - UltraSound Physics -
 
Ultrasound waves propagate poorly through a gaseous medium that result usually in inadequate imaging.
The effect of propagation through dense zones is that nearly all of the ultrasound waves are reflected. Structures below dense zones, for example bone, calcium, metal are also poorly imaged.
See also Signal Coupling.
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 Further Reading:
  Basics:
An Introduction to UltrasoundOpen this link in a new window
   by www.cis.rit.edu    
A brief introduction to ultrasoundOpen this link in a new window
   by dukemil.egr.duke.edu    
  News & More:
Transmission Line Matrix (TLM) modelling of medical ultrasound(.pdf)Open this link in a new window
   by www.era.lib.ed.ac.uk    
Non-Linear PropagationMRI Resource Directory: - UltraSound Physics -
 
The propagation of high amplitude ultrasound waves is inadequate described by a linear wave equation. Non-linear propagation is to expect if the power levels are high enough to make non-linear effects significant. A non-linear propagation results in the distortion of the transmitted waveforms, resulting in the generation of harmonics of the initial frequency components transmitted by the transducer.
In the near field of ultrasound probes, the occurring diffraction and focusing effects make this process complex. The distortion of a wavefront propagating in a medium in which the compressional phase moves slightly faster than the rarefactional phase, results is the conversion of some wave energy into higher harmonics of the fundamental frequency. The effect increases strongly with increasing wave amplitude.
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 Further Reading:
  Basics:
Nonlinear propagation applied to the improvement of resolution in diagnostic medical ultrasoundOpen this link in a new window
   by lib.ioa.ac.cn    
  News & More:
Transmission Line Matrix (TLM) modelling of medical ultrasound(.pdf)Open this link in a new window
   by www.era.lib.ed.ac.uk    
US Resources  
3d UltraSound - Ultrasound Guided Interventions - Universities - Pediatric - Heart - Distributors
 
CavitationMRI Resource Directory: - UltraSound Physics -
 
Cavitation is any activity of highly compressible transient or stable microbubbles of gas and/or vapour, generated by ultrasonic power in the propagation medium. Cavitation can be described as inertial or non-inertial. Inertial cavitation has the most potential to damage tissue and occurs when a gas-filled cavity grows, during pressure rarefaction of the ultrasound pulse, and contracts, during the compression phase. Collapses of bubbles can generate local high temperatures and pressures. Transient cavitation can cause tissue damage.
The threshold for cavitation is high and does not occur at current levels of diagnostic ultrasound. The introduction of contrast agents leads to the formation of microbubbles that potentially provide gas nuclei for cavitation. The use of contrast agents can lower the threshold at which cavitation occurs.

Types of cavitation:
point Acoustic cavitation - sound in liquid can produce bubbles or cavities containing gas or vapour.
point Stable cavitation - steady microbubble oscillation due to the passage of a sound wave.
point Transient cavitation - short-lived cavitation initiated by the negative pressure of the sound wave.
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 Further Reading:
  Basics:
Stone fragmentation by ultrasoundOpen this link in a new window
August 2004   by www.ias.ac.in    
  News & More:
THERAPEUTIC ULTRASOUND TEAM(.pdf)Open this link in a new window
   by www.icr.ac.uk    
DecibelMRI Resource Directory: - UltraSound Physics -
 
(dB) A customary logarithmic measure most commonly used (in various ways) for measuring sound. Decibel is a way to express the ratio of two sound intensities: dB=10log10I1/I2 being I1 the reference. If one sound is 1 bel (10 decibel) 'louder' than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibel corresponds to an increase of 10 x 10 or 100 times in intensity.
The intensity of ultrasound decreases during the propagation and is measured in db/cm.
For sound pressure (the pressure exerted by the sound waves) 0 decibel equals 20 microPascal (µPa), and for ultrasonic power 0 decibel sometimes equals 1 picoWatt.
See also dB/dt, Phon, and Logarithms.
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 Further Reading:
  News & More:
Ultrasound in diagnostic and therapyOpen this link in a new window
   by www.anst.uu.se    
DivergenceMRI Resource Directory: - UltraSound Physics -
 
The divergence is an ultrasound beam characteristic of the far field. The beam divergence angle, q, depends on the transducer frequency and diameter according to the following approximation:
sin q º 1.22 ld
where l is the wavelength of the ultrasound in the medium of propagation and d is the diameter of the transducer element.
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 Further Reading:
  Basics:
Physics Tutorial: Ultrasound PhysicsOpen this link in a new window
   by www.physics247.com    
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