1. Ultrasound
T1, T3, T4, T6
April 27, 2013

2. Review of how sound propagates
Longitudinal 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.

3. Ultrasound
Utilizes sound waves of very high frequency way above the human hearing range
(2MHz- 17MHz).
Human hearing range: Approximately 20 kHz
Similar to sonar or echolocation in bats
It is propagated from waves of compression and rarefaction, and requires a tissue to travel.
Noninvasive, safe, painless, and dye free procedure.
The higher the frequency, the less depth penetration but the resolution is improved.
Imaging technique used primarily in medical practices.

4. 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

5. Transducer Probe
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.

6. 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.

7. Applications of Physics
Attenuation – 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 tissues
Dispersion when reverberating.

8. Applications of Physics
Enhancement – 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.

9. Doppler Ultrasound Equation: v = Δf*C/2f*cos(ϑ)
Ultrasound can be used to examine blood flow in vessels
The 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.

10. 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 cavity
2) – Waves are sent out at regular intervals until the bat detects a moving object
3) – Ultrasound waves bounce off an object and the emitted pulse returns to the bat’s ears.

11. Bats using echolocation
4) – 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

12. Uses of Ultrasound Human medical purposes: Obsterics/gynecology
Cardiology
Urology
Look for abnormal lumps in the breasts , ovaries, or prostate in early stages of cancer
Killing bacteria
As an antibiotic
In sewers
Welding
Cleaning jewelry and surgical instruments
Used by many animals, including bats and dolphins.

13. Ultrasound in Pregnancy
The 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

14. Ultrasound in Pregnancy
Probe transmit ultrasound waves at frequencies of 1 – 5 MHz
Waves travel into the body until they hit a boundary between tissue and are reflected back
Multiple waves are sent out every second
The reflected waves that bounce back are received by the probe and transmitted to the machine

15. 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

16. 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

17. 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

18. Differences in High and Low Frequencies
Physicians 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 frequencies
Produce better images
Low frequencies are used when they are trying to look deeper into the body.

19. Ultrasonic Images
Used in modern medicine to create images of inside the human body
Transmits ultrasonic wave into the body
Interprets the intensity of the echoes to create image
Black images: ultrasonic waves were able to diffuse through tissue
Muscle tissue and fluid
White images: ultrasonic waves were NOT able to diffuse through tissue
Skin and bone

20. 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)

21. 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