Ultrasound

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 • 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