5.24 Ultrasonic Dosimetry
177
Ultrasonic Chemical Action
High intensity ultrasonic waves in solutions can effect the rate of chemical reactions
in several direct ways: (1) By raising the temperature, (2) by increasing the pressure,
(3) by causing a more complete mixture of reactants and (4) by generating vibrations
in long molecular chains and membranes, causing them to be closer to reactants.
Regarding the third effect: Mixtures of immiscible fluids and fluids with insoluble
solids will likely have macroscopic regions within made of one kind of material.
Intense ultrasonic waves will tend to break up these regions into a number of smaller
such regions, allowing reactants to have greater surface areas on which to react.
Moreover, the products of the reactions will not accumulate as much if they are
dispersed once formed.
Fluid Streaming
Ultrasonic streaming: When high-intensity ultrasonic waves pass through a fluid,
non-linear effects may induce macroscopic motion of the fluid. Ultrasonic streaming
has been used to noninvasively carry medicines to the blood stream, to hasten
chemical reactions through its stirring effect, and to study the composition of
heterogeneous fluid mixtures such as contaminated blood.
5.24.3 Ultrasonic Dosimetry Standards
In 1972, The Food and Drug Administration (FDA) (also The World Federation for
Ultrasound in Medicine and Biology (WFUMB)) gave the following guidelines:
• US heating should be restricted to < 1.5 ◦ C
• Peripheral vascular intensities: 730 mW/cm 2
• Ophthalmic US intensities: I < 17 mW/cm 2
• Fetal US intensities: I < 94 mW/cm 2
• Cardiac US intensities: I < 430 mW/cm 2
The American Institute of Ultrasound in Medicine (AIUM) has proposed
guidelines for limits below which ultrasound has been demonstrated to not show
damaging effects. These guidelines include: A diagnostic exposure should cause
less than one degree rise in temperature above normal. Exposure intensity should be
less than 1 W/cm 2 for focused ultrasound beams.
In 1992, the FDA mandated that ultrasonic instruments used for diagnostics
with intensities that can reach 720 mW/cm 2 have on-screen display of Thermal and
Mechanical Acoustic Output Indices, defined below.
Diagnostic ultrasound systems have outputs ranging from 10 mW/cm 2 for imaging to as high as 750 mW/cm 2 for pulsed Doppler ultrasound. The intensity values
177
Ultrasonic Chemical Action
High intensity ultrasonic waves in solutions can effect the rate of chemical reactions
in several direct ways: (1) By raising the temperature, (2) by increasing the pressure,
(3) by causing a more complete mixture of reactants and (4) by generating vibrations
in long molecular chains and membranes, causing them to be closer to reactants.
Regarding the third effect: Mixtures of immiscible fluids and fluids with insoluble
solids will likely have macroscopic regions within made of one kind of material.
Intense ultrasonic waves will tend to break up these regions into a number of smaller
such regions, allowing reactants to have greater surface areas on which to react.
Moreover, the products of the reactions will not accumulate as much if they are
dispersed once formed.
Fluid Streaming
Ultrasonic streaming: When high-intensity ultrasonic waves pass through a fluid,
non-linear effects may induce macroscopic motion of the fluid. Ultrasonic streaming
has been used to noninvasively carry medicines to the blood stream, to hasten
chemical reactions through its stirring effect, and to study the composition of
heterogeneous fluid mixtures such as contaminated blood.
5.24.3 Ultrasonic Dosimetry Standards
In 1972, The Food and Drug Administration (FDA) (also The World Federation for
Ultrasound in Medicine and Biology (WFUMB)) gave the following guidelines:
• US heating should be restricted to < 1.5 ◦ C
• Peripheral vascular intensities: 730 mW/cm 2
• Ophthalmic US intensities: I < 17 mW/cm 2
• Fetal US intensities: I < 94 mW/cm 2
• Cardiac US intensities: I < 430 mW/cm 2
The American Institute of Ultrasound in Medicine (AIUM) has proposed
guidelines for limits below which ultrasound has been demonstrated to not show
damaging effects. These guidelines include: A diagnostic exposure should cause
less than one degree rise in temperature above normal. Exposure intensity should be
less than 1 W/cm 2 for focused ultrasound beams.
In 1992, the FDA mandated that ultrasonic instruments used for diagnostics
with intensities that can reach 720 mW/cm 2 have on-screen display of Thermal and
Mechanical Acoustic Output Indices, defined below.
Diagnostic ultrasound systems have outputs ranging from 10 mW/cm 2 for imaging to as high as 750 mW/cm 2 for pulsed Doppler ultrasound. The intensity values