T1, T3, T4, T6

April 27, 2013

Review of how sound propagatesLongitudinal wave (consisting of

compression and rarefaction areas)Speed of sound is dependent on the

properties of the media it is traveling through

Frequency=rate of oscillations, so a frequency of 50Hz= 50 compressions a second.

Ultrasound

o Utilizes sound waves of very high frequency way above the human hearing rangeo (2MHz- 17MHz).o Human hearing

range: Approximately 20 kHz

o Similar to sonar or echolocation in bats

o It is propagated from waves of compression and rarefaction, and requires a tissue to travel.

o Noninvasive, safe, painless, and dye free procedure.

o The higher the frequency, the less depth penetration but the resolution is improved.

o Imaging technique used primarily in medical practices.

How Ultrasounds Work• A transducer creates sound waves

and receives echoes using the piezoelectric effect

• Piezoelectric crystals within the probe change shape when an electric current is applied

– This causes vibrations and the production of sound waves

– Needs a gel couplant to travel into tissues since the high-frequency sound cannot travel through air.

• Some sound reflects off of internal structures while some sound refracts further into the tissue

– A reflection occurs at the boundary between two materials provided that a certain property of the materials is different

• Sound waves are transformed into electric signals then turned into an image stating where reflection occurred in the body

A probe that sends and receives the sound waves, the inside of the probe is cluster of quartz crystals.

Quartz crystals have a physical characteristics that if an electric current is applied, will change shape and vibrate to create sound wave, also in reverse if sound vibrate of off it will convert that sound waves into electric current.

Physics Behind Ultrasound• The machine uses echolocation

to perceive the image in the computer

• The machine sends out millions of pulses per second and calculates how long it takes for the echoes to return back

• Waves reflect off of internal surfaces

• Computer receives echoes and uses time it takes to echo as well as speed of sound to create image/depth.

Applications of PhysicsAttenuation – A decrease of the

amplitude and frequency of a wave as it travels through a medium, in this case the medium is human tissue. Occurs with:Conversion of mechanical energy of

waves to thermal energy.Reverberation off of dense tissuesDispersion when reverberating.

Applications of PhysicsEnhancement – Sound does not attenuate as it

flows through fluid-filled mediums (blood, for example).

Velocity – Speed of sound depends on its medium, so the speed at which the waves return determines the density and type of tissue.For example, sound travels at 1540 m/s in soft

tissue at 37°C.Doppler shift – Change in frequency of waves

can be used to determine velocity of blood flow.Equation: v = Δf*C/2f*cos(ϑ)Where v = velocity of blood, Df = returning

frequency by Doppler shift, c = speed of sound, and q = angle of sound beam and direction of blood cell travel.

Doppler UltrasoundUltrasound can be used to

examine blood flow in vesselsThe sound waves striking the

moving blood will cause a frequency shift in the echo and the computer can detect this and create an image from it.

High Doppler frequencies = Low blood flow

Low Doppler frequencies = High blood flow

Equation: v = Δf*C/2f*cos(ϑ)Where v = velocity of blood, Df

= returning frequency by Doppler shift, c = speed of sound, and q = angle of sound beam and direction of blood cell travel.

Bats using echolocation

Bats transmit Ultrasound frequencies. They produce very short wavelength and high frequency pitches between 14,000 Hz and 100,000 Hz (Most are well above 20,000 Hz)1) - Ultrasound waves are generated either by the larynx or nasal cavity2) – Waves are sent out at regular intervals until the bat detects a moving object3) – Ultrasound waves bounce off an object and the emitted pulse returns to the bat’s ears.

Bats using echolocation4) – The ears of the bat determine the location of the echo based on the subtle difference in time it takes for the sound to reach 1 ear and then the other

5) – The bat determines if the object is getting closer or farther away by the speed at which the echo returns

6) – Once a moving object is detected, the bat increases the number of waves so that it can track it’s prey faster

7) – The bat moves to intercept and adjusts it’s trajectory in the direction where the echoes are returning fastest

Uses of UltrasoundHuman medical purposes:

Obsterics/gynecologyCardiologyUrologyLook for abnormal lumps in the breasts ,

ovaries, or prostate in early stages of cancer

Killing bacteriaAs an antibioticIn sewers

WeldingCleaning jewelry and surgical instrumentsUsed by many animals, including bats and

dolphins.

Ultrasound in PregnancyThe machine measures the intensity of the waves by the number of echoes that are received in an area.

Random waves that are reflected back by various tissues and fluid are less intense so they do not compare to the intensity of the waves that display the fetus

The machine calculates the distance from the probe to the tissue or organ using the speed of sound in tissue (1,540 m/s)

The machine displays the distances and intensities of the echoes on the screen and forms a two dimensional image

Ultrasound in PregnancyProbe transmit ultrasound waves at frequencies of 1 – 5 MHzWaves travel into the body until they hit a boundary between tissue and are reflected backMultiple waves are sent out every secondThe reflected waves that bounce back are received by the probe and transmitted to the machine

Babies!

Being able to see if the baby is male or female

Abnormalities with the heart

Umbilical cord in the correct place

Size and growing cart

3D ultrasound• Transducer is run along the

body surface at various angles rather than just directly sending the sound waves straight in• Allows multiple angles and

depth levels of the echoes to be created

• Advanced computers are able to detect the multiple reflected sound waves

• Provides greater depth of image so doctors can more accurately detect normal development

Why do physicians prefer Ultrasound over any other medical treatment?

Physicians prefer to use Ultrasound because it is consider as a safe test over x-rays, MRI’s, or CT’s. It is much cheaper, and does not

expose the patient to any form of radiation.

Ultrasound can cause a minor physical pain due to cavitation, which is when gases contained in the tissue cell nuclei are heated. This cause a burning feeling.Only real drawback

Differences in High and Low FrequenciesPhysicians decide whether

to use high or low frequencies based on what they are using the Ultrasound for.When they are looking

more at the surface of the body it is preferred to use high frequenciesProduce better images

Low frequencies are used when they are trying to look deeper into the body.

Ultrasonic Images

Ultrasonic Delivery of Medication• Intravenous injections of microbubbles are

administered into the patient• Certain properties of the microbubble

allow it to attach drugs and peptides with high affinity

• The microbubbles bind to specific receptors on tissue at a target site and begin to accumulate

• (Research has shown that these microbubbles enhance the permeability of cellular membranes)

Ultrasonic Delivery of Medication

High intensity ultrasound pulses are created by a probe

The pulse targets the accumulated microbubbles and causes them to lyse

The bound drug or peptide is released into the vasculature at the target site