CLINICAL APPLICATIONS OF ULTRASOUND

1. CLINICAL APPLICATIONS OF ULTRASOUND • Without reference, identify principles relating to Digital Radiography Clinical Applications with at least 70 percent accuracy.

2. CLINICAL APPLICATIONS OF ULTRASOUND

3. CLINICAL APPLICATIONS OF ULTRASOUND • What is Sound • Mechanical waveform energy • Created by vibrations • Consists of areas of compression and rarefaction • Travels in longitudinal waves

4. CLINICAL APPLICATIONS OF ULTRASOUND • Physical Properties of Sound (Continuous Wave Parameters) • Classify frequency (Hz) sound by frequency • Ultrasound - above 20KHz * • Diagnostic ultrasound frequency range is 1Mhz - 20MHz • Audible sound - 20Hz to 20KHz • Infrasound - below 20Hz

5. CLINICAL APPLICATIONS OF ULTRASOUND • Period (T) • Length of time to complete one cycle • Measured in microseconds for diagnostic ultrasound • Inversely proportional to frequency T = 1/f (Hz) • Wavelength • Length (distance) of one complete cycle • Determined by sound source and medium • Equal to speed of sound / frequency ( = c / f) • Within the body, speed is nearly constants. Frequency adjusts wavelength • Frequency increase = wavelength decrease • Frequency decrease = wavelength increase • Wavelength directly affects image detail (resolution)

6. CLINICAL APPLICATIONS OF ULTRASOUND • Speed (c) • The speed at which sound propagates through a medium • Determined solely by properties of the medium: density and stiffness • Independent of frequency • Speed is inversely proportional to density • Speed is directly proportional to stiffness • Average speed of sound in soft tissue = 1,540 m/s • Speed of sound in other mediums • Air 330m/s • Water 1,480m/s • Liver 1,555m/s • Kidney 1,565m/s • Muscle 1,600m/s • Bone 4,080m/s

7. CLINICAL APPLICATIONS OF ULTRASOUND • Amplitude - describes the magnitude of the sound wave • Express amplitude in decibels • Decreases as wave travels through the body due to attenuation • Power - refers to the strength of the sound wave • Power decreases as the sound wave travels through the body • Power measured in watts • Power is directly proportional to amplitude • Intensity - refers to the concentration of energy in a sound beam • Equal to the power of the beam divided by the cross-section • Unit of measurement - watts/cm2 (squared) • Typical diagnostic ultrasound intensities range from 0.01 mW/cm2 (squared) to 100 watts/cm2 (squared)

8. CLINICAL APPLICATIONS OF ULTRASOUND • Physical Properties of Sound (Pulsed Wave Parameters) • Pulse duration - the length of time from the beginning to the end of the actual sound burst; usually measured in microseconds • Pulse repetition rate (PRP) - the time from the start of one pulse to the start of another pulse. For diagnostic ultrasound (PRP) it ranges from 100 microsec to 1 milliSec • Pulse repetition frequency (PRF) - the number of pulses that occur per second • Duty factor - the percentage or fraction of time that the ultrasound machine is sending out sound • Spatial pulse length (SPL) - the length of a single burst of sound • Piezoelectric Transducers • Transducers convert one form of energy to another • Piezoelectric - literally means pressure electric • Types of transducers • Focused • Linear/curved linear array • Phased array • Annular array

9. CLINICAL APPLICATIONS OF ULTRASOUND • Display Modes • A-Mode (Amplitude Mode) least often used • Data represented as spikes on a line trace • Height of spike represents strength of echo • B-Mode (Brightness Mode) • Echoes represented as dots on a screen that combine to form an image • Echo strength represented as brightness of dot • M-Mode (Motion Mode) • Used to study rhythmically moving structures • M-Mode trace scrolls across the screen • Distance between spikes represents distance between interfaces

10. CLINICAL APPLICATIONS OF ULTRASOUND • Doppler Effect • Doppler shift in medical ultrasound • In ultrasound, Doppler shifts occur when moving objects reflect sound • Reflectors moving toward the sound source (Transducer) send echoes of slightly higher frequency than the original beam • Reflectors moving away from the sound source (Transducer) send echoes of slightly lower frequency than the original beam • The difference between the transmitted frequency and the received frequency represent the Doppler frequency • Doppler frequencies are usually in the audible sound range • Continuous-Wave Doppler sends a continuous wave of sound into the tissue • Uses a separate transducer to "listen" • Can detect flow anywhere in the beam path • Pulsed Doppler allows the sonographer to select signals from a specific depth using principles similar to pulse-echo B-Mode scanning

11. CLINICAL APPLICATIONS OF ULTRASOUND

12. CLINICAL APPLICATIONS OF ULTRASOUND • Duplex instruments allow both B-Mode scanning and Doppler scanning and are called duplex ultrasound machines • Other Items of Medical Equipment that Incorporate Ultrasound Include • Ultrasonic cleaners • Ultrasonic muscle stimulators • Heat therapy machines • Flow detectors • Vaporizer/humidifier • Laboratory mixers, just to name a few

13. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • What is Ultrasound? • Ultrasound is a medical imaging technique that uses high frequency sound waves and their echoes • The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines • In ultrasound, the following events happen • The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into the body using a probe • The sound waves travel into the body and hit a boundary between tissues (e.g , between fluid and soft tissue, soft tissue and bone) • Some of the sound waves reflected back to the probe, while some travel on further until they reach another boundary and reflect • The probe picks up the reflected waves and relays them to the machine • The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of each echo's return (usually on the order of millionths of a second) • The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image • A typical ultrasound sends and receives millions of pulses and echoes each second

14. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Principal Components • Transducer probe • The component of the system in direct contact with the patient • Two functions • Produces the ultrasound pulse • Receives the returning echoes • Piezoelectric crystal • Active element of the transducer • Electrical pulses causes the crystal to expand and contract • The vibrations of the crystals produce the ultrasonic waves that travel outward • Conversely, when the echo of sound or pressure waves hit the crystals, it will vibrate • The vibration of the crystal will produce electrical pulses • This principle is the Piezoelectric Effect

15. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Backing block • Dampens the movement of the crystal • Remove the electric stimulus and the crystal will cease motion immediately • Acoustic lenses - focus ultrasonic beams • Pulse generator • Allow the operator to set and change the frequency and duration of the ultrasound pulses • Apply the commands from the operator that translate into changing electric currents to the piezoelectric crystals in the transducer probe • CPU • Contains the microprocessor, memory, amplifiers and power supplies for the microprocessor and transducer probe • Sends electrical currents to the transducer probe to emit sound waves • Also receives the electrical pulses from the probes created from the returning echoes • Does all of the calculations involved in processing the data • The CPU forms the image on the monitor after the processing of the raw data • Can also store the processed data and/or image on disk

16. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Display • Shows the processed data from the CPU • Can be black-and-white or color • Can be 2-D or 3-D • Ultrasound Characteristics • Ultrasound is a longitudinal wave - molecules are compressed and decompressed • Frequency • Rate of the vibration back and forth • Determined by the electrical pulses applied to the transducer • Higher-frequency results in better resolution but shallower penetration • As frequency increases, the wavelength decreases • Wavelength • Distance sound travels during the period of one vibration • It has an effect on image quality • Determined by the frequency and velocity

17. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Velocity • Rate at which the vibrations move through the tissue • Determines the depth location of structures of the body • Determined by the characteristics of the material it passes through • Most systems are set up to determine distances using as assumed velocity of 1540m/sec • Approximate velocity of sound in various materials (see slide) • Amplitude • Related to the energy (or loudness) of the ultrasound pulses • Determined by how hard the electrical pulse strikes the crystal • Interactions with Matter • When an ultrasound pulse passes through matter, it interacts with the matter in several different ways • These interactions are necessary to form an ultrasound image • Absorption • Reflection • Refraction

18. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Major Uses of Ultrasound • The main advantage of ultrasound is that certain structures can be observed without using radiation • Ultrasound is much faster than x-rays or other radiographic techniques • Here is a short list of some uses for ultrasound • Obstetrics and gynecology • Measuring the size of the fetus to determine the due date • Determining the position of the fetus to see if it is in the normal head down position or breech • Checking the position of the placenta to see if it is improperly developing over the opening to the uterus (cervix) • Seeing the number of fetuses in the uterus • Checking the sex of the baby (if the genital area can be clearly seen) • Checking the fetus's growth rate by making many measurements over time • Detecting ectopic pregnancy, the life-threatening situation in which the baby is in the mother's fallopian tubes instead of in the uterus • Determining whether there is an appropriate amount of amniotic fluid cushioning the baby • Monitoring the baby during specialized procedures • Helpful in seeing and avoiding the baby during amniocentesis (sampling of the amniotic fluid with a needle for genetic testing) years ago, doctors use to perform this procedure blindly; however, with accompanying use of ultrasound, the risks of this procedure have dropped dramatically • Seeing tumors of the ovary and breast

19. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS

20. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Cardiology • Seeing the inside of the heart to identify abnormal structures or functions • Measuring blood flow through the heart and major blood vessels

21. DIAGNOSTIC ULTRASOUND IMAGING CLINICAL APPLICATIONS • Urology • Measuring blood flow through the kidney • Detecting prostate cancer early • Seeing kidney stones