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 'Cavitation' 
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CavitationMRI Resource Directory:<br> - 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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• Related Searches:
    • Acoustic Power
    • Microbubble Scanner Modification
    • Microbubble Shell
    • Coded Excitation
    • Mechanical Index

 Further Reading:
  Basics:
Stone fragmentation by ultrasoundOpen this link in a new window
August 2004   by www.ias.ac.in    
US Resources  
Education - Software - Examinations - 3d UltraSound - Rental - Abdominal
 
Coded ExcitationMRI Resource Directory:<br> - UltraSound Physics -
 
Increasing the frequency of the transmitted power improves the image quality of ultrasound, but the improvement in resolution results in a decreased signal to noise ratio (SNR). Higher acoustic power levels can prevent the loss in SNR, but among other reasons, ultrasound regulations limit this to avoid heating or cavitation.
Coded excitation increase the signal to noise ratio without the loss of resolution by using coded waveforms. Coded excitation allows transmitting a long wide-band pulse with more acoustic power and high penetration of the sound beam.
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 Further Reading:
  News & More:
Coded Pulse Excitation for Ultrasonic Strain Imaging(.pdf)Open this link in a new window
Wednesday, 2 February 2005   by ultrasonics.bioen.uiuc.edu    
US Resources  
Veterinary UltraSound - Doppler UltraSound - Obstetric - Gall Bladder - Rental - Pediatric
 
Mechanical IndexMRI Resource Directory:<br> - Safety -
 
(MI) The mechanical index is an estimate of the maximum amplitude of the pressure pulse in tissue. It is an indicator of the likelihood of mechanical bioeffects (streaming and cavitation). The mechanical index of the ultrasound beam is the amount of negative acoustic pressure within a ultrasonic field and is used to modulate the output signature of US contrast agents and to incite different microbubble responses.
The mechanical index is defined as the peak rarefactional pressure (negative pressure) divided by the square root of the ultrasound frequency.
The FDA ultrasound regulations allow a mechanical index of up to 1.9 to be used for all applications except ophthalmic (maximum 0.23). The used range varies from 0.05 to 1.9.
At low acoustic power, the acoustic response is considered as linear. At a low MI (less than 0.2), the microbubbles undergo oscillation with compression and rarefaction that are equal in amplitude and no special contrast enhanced signal is created. Microbubbles act as strong scattering objects due to the difference in impedance between air and liquid, and the acoustic response is optimized at the resonant frequency of a microbubble.
At higher acoustic power (MI between 0.2–0.5), nonlinear oscillation occurs preferentially with the bubbles undergoing rarefaction that is greater than compression. Ultrasound waves are created at harmonics of the delivered frequency. The harmonic response frequencies are different from that of the incident wave (fundamental frequency) with subharmonics (half of the fundamental frequency), harmonics (including the second harmonic response at twice the fundamental frequency), and ultra-harmonics obtained at 1.5 or 2.5 times the fundamental frequency. These contrast enhanced ultrasound signals are microbubble-specific.
At high acoustic power (MI greater than 0.5), microbubble destruction begins with emission of high intensity transient signals very rich in nonlinear components. Intermittent imaging becomes needed to allow the capillaries to be refilled with fresh microbubbles. Microbubble destruction occurs to some degree at all mechanical indices. A mechanical index from 0.8 to 1.9 creates high microbubble destruction. The output signal is unique to the contrast agent.
Radiology-tip.comIonizing Radiation
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Radiology-tip.comSpecific Absorption Rate
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 Further Reading:
  Basics:
Guidelines for the Safe Use of Diagnostic Ultrasound(.pdf)Open this link in a new window
   by folk.ntnu.no    
  News & More:
Harmonic ImagingOpen this link in a new window
   by www.imasonic.com    
Searchterm 'Cavitation' was also found in the following services: 
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Optison™InfoSheet: - Contrast Agents - 
Intro, 
Historical Development, 
Microbubbles,
etc.MRI Resource Directory:<br> - Contrast Agents -
 
From GE Healthcare;;
Optison is the first 'second generation USCA' marketed in the US.
Ultrasound contrast agents used during an ultrasound imaging procedure, enable more accurate diagnosis of the patient's heart condition. The application of Optison allows to image the endocardial borders of the heart, to see cardiac wall motion abnormalities and to guide the selection and monitoring of treatment.
Optison represents a class of microbubbles with a shell formed by sonicating a solution of capsules filled with a perfluoropropane gas. The high molecular weight slows microbubble dissolution and prolongs the enhancement for several minutes. The human albumin-stabilized cavitation bubbles have a surface tension of 0.9 N/m and a surface dilatational viscosity 0.08 msP.

"August 06, 2001 Molecular Biosystems Inc., a subsidiary of Alliance Pharmaceutical Corp, announced the amendment of the Optison Product Rights Agreement (OPRA) dated May 9, 2000 with Mallinckrodt Inc, a unit of Tyco Healthcare. Optison, an intravenous ultrasound contrast agent, was developed by MBI and is being marketed by Mallinckrodt in the U.S. and Europe. Under the amended agreement, MBI will receive an immediate cash payment plus additional unspecified royalties for a two-year period. The amendment of OPRA coincides with an announcement by Nycomed Amersham Imaging that Nycomed and Mallinckrodt will terminate their joint commercialization and development agreement for ultrasound contrast agents, including Optison, effective Dec. 31, 2001. Effective Jan. 1, 2002, all selling and marketing activities will be resumed solely by Nycomed Amersham." (by EDGAR Online)

Drug Information and Specification:
RESEARCH NAME FS069
DEVELOPER Molecular Biosystems Inc.
INDICATION -
DEVELOPMENT STAGE
LVO -
For sale
APPLICATION intravenous/oral
TYPE microbubbles
SHELL Albumin N-acetyltryptophan, Caprylic acid
CHARGE Slight Negative
GAS Octafluoropropane
MICROBUBBLE SIZE 93% < 10µm
PRESENTATION Five 3 ml vials
STORAGE Refrigerate 2–8°C
PREPARATION Hand agitate
DO NOT RELY ON THE INFORMATION PROVIDED HERE, THEY ARE NOT A SUBSTITUTE FOR THE ACCOMPANYING PACKAGE INSERT!

Distribution Information:
TERRITORY DISTRIBUTOR
USA, EU GE Healthcare

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 Further Reading:
  Basics:
Optison? Prescribing Information(.pdf)Open this link in a new window
  News & More:
CONTRAST ECHOCARDIOGRAPHY: NEW AGENTSOpen this link in a new window
   by eurheartj.oxfordjournals.org    
molecular imaging using ultrasoundOpen this link in a new window
   by bjr.birjournals.org    
American Society of Echocardiography Consensus Statement on the Clinical Applications of Ultrasonic Contrast Agents in EchocardiographyOpen this link in a new window
November 2008   by www.asecho.org    
Nycomed Amersham and Mallinckrodt Agree on Ultrasound Patent Settlement and Announce Joint Development of Existing Ultrasound ProductsOpen this link in a new window
   by www.prnewswire.com    
US Resources  
Examinations - Breast - 3d UltraSound - Calculation - Heart - Abdominal
 
Side EffectMRI Resource Directory:<br> - Safety -
 
Diagnostic ultrasound imaging has no known risks or long-term side effects. Discomfort to the patient is very rare if the sonogram is accurately performed by using appropriate frequencies and intensity ranges. However, the application of the ALARA principle is always recommended.
There are reports of low birth weight of babies after applying more than the recommended ultrasound examinations during pregnancy. Women who think they might be pregnant should raise this issue with the doctor before undergoing an abdominal ultrasound, to avoid any harm to the fetus in the early stages of development.
Since ultrasound is energy, sensitive tissues like the reproductive organs could possibly sustain damage if vibrated to a high degree by too intense ultrasound waves. In diagnostic ultrasonic procedures, such damage would only result from improper use of the equipment.

Possible ultrasound bioeffects:
list_point Ultrasonic heating of tissues can be created by absorption of the ultrasound energy.
list_point Due to increasing of temperature, dissolved gases from microbubbles come out of the contrast solution.
The thermal effect is controlled by the displayed thermal index and the mechanical index indicates the risk of cavitation.
An ultrasound gel is applied to obtain better contact between the transducer and the skin. This has the consistency of thick mineral oil and is not associated with skin irritation or allergy.
Specific conditions for which ultrasound may be selected as a treatment may be attached with higher risks.
See also Ultrasound Imaging Procedures, Fetal Ultrasound and Obstetric and Gynecologic Ultrasound.
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 Further Reading:
  Basics:
International guidelines and regulations for the safe use of diagnostic ultrasound in medicine(.pdf)Open this link in a new window
   by www.radiologymalaysia.org    
  News & More:
Ultrasound: Weighing the Propaganda Against the FactsOpen this link in a new window
   by www.midwiferytoday.com    
Ultrasound Produces Less Unwanted EffectsOpen this link in a new window
2004   by www.annieappleseedproject.org    
US Resources  
Obstetric - UltraSound Reimbursement - Rental - Portable UltraSound - Hospitals - History of UltraSound
 
Related Searches:
 • Acoustic Power
 • Microbubble Scanner Modification
 • Microbubble Shell
 • Coded Excitation
 • Mechanical Index
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