Transducer of ultrasound machine

A device that converts one form of energy to another
Piezoelectric crystal: a crystal that produces (+) and (-) electrical charges when it contracts or expands
Crystal of quartz, barium titanate, lead zirconate, or titanate housed within transducer
Reverse (indirect) piezoelectric effect: occurs when an alternating current is passed through a crystal resulting in contraction & expansion of the crystal
US is produced through the reverse piezoelectric effect
Vibration of crystal results in high-frequency sound waves
Fresnal zone (near field) – area of the ultrasound beam on the transducer used for therapeutic purposes
Longitudinal waves – molecular displacement is along direction in which waves travel (bungee cord)
Compression – regions of high molecular density (molecules in high pressure areas compress)
Rarefraction – regions of low molecular density (molecules in low pressure areas expand)
Transverse waves – molecular displacement in direction perpendicular to wave (guitar string)


Influences on the Transmission of Energy:-
Reflection – occurs when the wave can’t pass through the next density

Refraction – is the bending of waves as a result of a change in the speed of a wave as it enters a medium with a different density

Absorption – occurs by the tissue collecting the wave’s energy
Decrease in a wave’s intensity resulting from absorption, reflection, & refraction
 as the frequency of US is  because of molecular friction the waves must overcome in order to pass through tissues

US penetrates through tissue high in water content & is absorbed in dense tissues high in protein

 Absorption =  Frequency (3 MHz) , and
 Penetration =  Absorption (1 MHz) , so
 Penetration =  Frequency +  Absorption (1 MHz)

Tissues  water content = low absorption rate (fat)
Tissues  protein content = high absorption rate (peripheral nerve, bone)
Muscle is in between both
Spatial Average Temporal Peak Intensity (SATP): average intensity during the “on” time of the pulse
Output meter displays the SATP intensity

Spatial Peak Intensity (SPI): max. output (power) produced within an ultrasound beam

Spatial Average Temporal Average Intensity (SATA) or Temporal (time) Average Intensity:
Power of US energy delivered to tissues over a given period of time
Only meaningful for Pulsed US
SAI x Duty Cycles
Ratio between the spatial peak intensity (SPI) to the average output as reported on the unit’s meter
The lower the BNR, the more uniform the beam is
A BNR greater than 8:1 is unsafe
Because of the existence of high-intensity areas in the beam (hot spots), it is necessary to keep the US head moving
Soft tissue healing & repair
Joint contractures & scar tissue
Muscle spasm,Neuroma,Trigger areas,Warts

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Ultrasound in Medicine

Ultrasound is simply sound that has a very high frequency.
Humans are not able to hear ultrasound, though some animals can hear them.
Sounds with frequencies above 20 000 hertz are called ultrasounds.Ultrasound is used for examining soft tissue inside the body.
Parts of the body that may be examined include muscles and unborn babies.
Blood flow can also be monitored using ultrasound.Modern ultrasound equipment can produce 3D images The images so far have been of static images, ultrasound captures movement.
This baby is so pleased to see you it’s waving!Ultrasound is very safe. There is no firm evidence that it does any harm to the body (or the baby in the case of pregnancy scans).
X-rays are potentially dangerous, particularly to young children and pregnant women (they damage the unborn baby).Medical ultrasound systems use very high frequencies – several megahertz (mega means million or 106).
A sound is a wave it has all the usual wave properties (reflection, refraction, diffraction). Ultrasound imaging makes use of the fact that sound can be reflected.
The idea is just like that used in radar and sonar.
A thin layer of jelly is placed between the probe and the skin to make sure all the sound enters the body.
The probe contains a transmitter and a receiver.
A pulse of ultrasound is sent out by the transmitter.
The pulse is reflected from a surface and returns to the receiver.The ultrasound machine measures how long it takes for the pulse to return
Colour enhancement to show blood flow
Digital files for examination on computers

Millions of sound waves are transmitted every second.
As the waves reflected at different times, the computer in the ultrasound machine calculates how far the wave travelled before being reflected (using d=vt).
Using this information the computer builds up an image of the inside of the patient.
Ultrasound is sound with a frequency above 20 000 Hz. If you have just said that it is a sound we cannot hear, that is not quite accurate enough.
Ultrasound can be used for examining soft tissue inside the body. For example, muscle, the heart and unborn babies.
The following are ultrasound frequencies:
23 000 Hz, 36 kHz, 4 MHz, 0.58 MHz, 600 000 Hz
Ultrasound does not have any damaging effect on the body. It is entirely safe to use, even on very young foetuses. X-rays are harmful, particularly on young and unborn children.
Most of the problems involving ultrasound need you to use v=d/t or v=fl
Things to look out for:
Units- time will often be in milliseconds (ms). Take care not to get this confused with metres per second (m/s or ms-1). and distances may be in mm or cm
There will often be an echo (or reflection involved. This means that you will need to think carefully about the times and distances involved.

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Ultrasound Imaging System

The Ultrasound Machine A basic ultrasound machine has the following parts: Transducer probe – probe that sends and receives the sound waves Central processing unit (CPU) – computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe Transducer pulse controls – changes the amplitude, frequency and duration of the pulses emitted from the transducer probe Display – displays the image from the ultrasound data processed by the CPU Keyboard/cursor – inputs data and takes measurements from the display Disk storage device (hard, floppy, CD) – stores the acquired images Printer – prints the image from the displayed data

The basic functional components of an ultrasound imaging system are shown below. THE ULTRASOUND IMAGING SYSTEM
Modern ultrasound systems use digital computer electronics to control most of the functions in the imaging process. Transducer Pulse Generator Amplification Scan Generator Scan Converter Image Processor Display We will now consider some of these functions in more detail and how they contribute to image formation.

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