Ultrasound physics 1

physics principles

1. ULTRASOUND PHYSICS (1) Dr. Kamal Sayed MSc US UAA ok sound/waves/MD us/wave parameters/speed/ frequency/period/power/intensity/amplitude/ FR/resolution/imaging depth/real time/ ok

2. What is the principle of ultrasound? An electric current passes through a cable to the transducer and is applied to the crystals, causing them to deform and vibrate. This vibration produces the  ultrasound  beam. The frequency of the  ultrasound  waves produced is predetermined by the crystals in the transducer. Physics is the branch of science concerned with the nature and properties of matter and energy. The subject matter of physics includes mechanics, heat, light and other radiation, sound, electricity, magnetism, and the structure of atoms. Physics is the natural science that studies matter, its motion and behavior through space and time, and the related entities of energy and force. Physics is one of the most fundamental scientific disciplines, and its main goal is to understand how the universe behaves.  Wikipedia Physics is a science that deals with matter and energy and their interactions. a : the physical processes and phenomena of a particular system. b : the physical properties and composition of something.

3. the father of physics is Galileo Galilei The 7 branches of physics Mechanics. Motion and its causes; interactions between objects. Thermodynamics . Heat and temperature. Vibrations and Waves Phenomena. Specific types of repetitive motions- springs, pendulums, sound. Optics. Light (including mirrors), lenses, colors. Electromagnetism . ... Relativity . ... Quantum Mechanics .

4. To be expert in US yu must be expert in US physics To define medical diagnostic US yu must know what is sound , wave موجات صوتية ؟؟ ماهي الموجة ؟ ماهوالصوت هي موجة wave وفيها صوت sound Any motion which repeats in cycles is called a wave it starts from zero point up to 360 degrees (this is called one cycle) & when repeated it is called a wave Therefore : a wave is a disturbance or variation that transferes energy progressively from point to point in a medium A medium is a substance or region through which a wave is transmitted

5. These are mechanical waves A wave is produced due to a disturbance from a source– eg . (stone dropped into a stagnant water leads to waves propagating from zero point to the end). The stone caused a pressure on water surfae which carried the energy from point zero to the far point. This process results in : 1-wave propagation direction 2- particle motion 3- source of the wave

6. Therefore energy is transferred over distance BUT matter is NOT because water particles move in a vibration motion (all media are composed from many small molecules bound to each other with intermolecular elastic forces/ كلما كانت قوة ربط الجزيئات شديدة كلما كان الوسط اكثر صلابة more stiff & when pressure is applied one molecule presses the next & so on In vibration motion transferring the energy & NOT the water molecules thus producing a wave). This wave can be recorded in a graph shape thereby we can measure the various wave variables (wave length , period, etc A wave can be described by certain variables (parameters) or متغيرات That change over time & space. These variables help to understand how waves behave under various conditions

7. Wave variables are : Amplitude , frequency , & period 1) Amplitude : is the degree of loudness, it Is the sterngth or wave height which increases with magnitude of pressure 2) frequency : (repetition of cycles) is the number of cycles per second. يعنى التردد وعدد الدورات الكاملة في الثانية الواحدة 3) period : the time it takes for a sound wave to complete one cycle Period is the reciprocal of frequency : period = 1/frequency In meters per second or mm/ms or --- At 5 MHz the period is 0.2 ms/ the higher the frequency the shorter the period

8. Ultrasonic sound is a cyclic sound pressure with a high frequency than the upper limit of human hearing equal to 20KHz Seven parameters that describe sound waves: Period /frequency / amplitude /power / speed / intensity / wavelength Acoustic variables identify sound waves Acoustic parameters describe the particular features of sound waves.

9. The 3 main acoustic variables Pressure = Force per unit area or the Pascals (Pa) or pounds concentration of force per square inch (lb/in2) Density = Mass per unit volume Kilograms per centimeter cubed (kg/cm3) Distance = How far apart objects are Feet, inches, centimeters, or miles

10. Period Definition The time required to complete a single cycle. Period can also be described as the time from the start of a cycle to the start of the next cycle. Example The period of the moon circling the earth is 28 days. The period of class in high school may be 50 minutes. Units : microsec , seconds, hours—all units of time Typical Values 0.1 to 0.5microsec 0.0000001 to 0.0000005sec = 1 x 10-7 to 5 x 10-7sec = Determined By Sound source Cannot be Changed by Sonographer . Slide (11)

11. In Microseconds ( μ s), one millonth of a second Period The time it takes for one cycle to occur

12. Frequency The number of certain events that occur in a particular time duration. In diagnostic ultrasound, the frequency of a wave is described as the number of cycles of an acoustic variable that occur in one second Units of frequency : Hz/sec Frequency is Determined By Sound source Cannot be Changed by Sonographer . Slide (13)

13. The number of cycles per second in Hz,KHz,MHz

14. The relationship between frequency and period. period = 1/frequency (T = 1/F) increasing the frequency will reduce the period & vice versa Formula for frequency. frequency = propagation speed/wavelength = F= C/Lambda Propagation speed = elasticity (stiffness) / density Propagation speed = The speed by which sound wave travels through media in Meters per second (m/s) or millimeteres per microsecond (mm/ microsec )

15. TWO types of waves : There are 1- mechanical waves : eg sound , ocean & seisemic waves These waves are longitudina & cannot propagate in vaccum . longitudinal waves carrying energy & need a physical medium to be transferred through it. molecules are displaced horizontally parallel to the wave direction So : sound is a M echanical L ongitudinal Pressure wave transmitted in a / M edium (medium is a must) sound is able to converge & diverge * only certain sound frequencies are audible to human ear. slide (16) يعني التردد المسموع للاذن البشرية ويساوي 20 الي 20،000 HERTZ Typically The audible range for human ear hearing is : 20 & 20000 HERTZ

16. (LONGITUDINAL WAVE ) If a gust of wind blows over a field of tall grass , the stalks bend back and forth in the same direction the wind is blowing

17. 2- electromagnetic waves : eg X ray , gamma rays radio & light Electromagnetic wave is a transverse wave & can propagate in vaccum . They are transverse waves. Molecules move up & down ie perpendicular to the wave direction (90 degrees to the wave direction) this represents electromagnetic waves like light, X-rays, gamma rays. slide (18/19)

18. (TRANSVERSE WAVE) spectators in a stadium dot the wave by moving arms up & down at Right angles 90 degrees ie perpendicular to the horizontal direction

19. Transverse Wave  Particles move in a direction perpendicular (at right angles) to the direction of the wave (upper image) Longitudinal Wave  Particles move in the same direction as the wave ( lower image) :

20. The intensity (strength)of sound we hear depends on the 1ST pressure applied (source of sound) A very strong Earthquake in tusanami south east acia in 2010 deep in the center of the ocean caused strong vibrations in water molecules lead to very high waves which covered up to the 3 RD floor of the towers.

21. On earth air is a good medium for propagation of Sound. Sound propagates in air with a speed different than in other media depending on the properties of each medium. Frequency is the number of cycles per second & measured in units called Hertz (1 Hz = 1 cycle per second) 10 to power 3 = 1000 KHz 10 to power 6 = 1000000 = MHz (one million) 10 to power 9 = billion ( miliard ) = GHz = = one thousand million=1000,000,000 10 t0 the power 12 = Tera = THz A 3 MHz probe gives 3 million cycles per second

22. Velocity of Sound in Various Materials Material # Velocity (m/s) ---------------- _______ air 331 fat 1450 water (50°C) 1540 human soft tissue 1540 brain 1541 liver 1549 kidney 1561 blood 1570 muscle 1585 lens of eye 1620 skull-bone 4080 brass 4490 aluminum 6400

23. Air molecules are far apart with week intermolecular elastic bonds & so air medium is compressible & not stiff The molecules move in vibration motion & when pressure is applied it becomes compressed & pushed together so that due to temporary increase in density & the area is called area of compression When pressure is released that area of the wave becomes more dense & called area of rarefaction due to temporary change in density

24. After wave moves through the medium the medium particles return to their resting position Sound is a mechanical wave moves fast & generally doesnot produce visible changes in the medium & is difficult to visualise . Sound wave is propagated by the same concept as the previous example of the stone thrown into water : Sound is a mechanical wave causes medium molecules to vibrate & sound energy is transferred from point to point. Sound needs a medium to be transferred & cannot be transferred through vacuum

25. Anything related to sound is described as acoustic Acoustic pressure is the local pressure deviation from the ambient (normal) pressure caused by the sound wave or to quantify the pressure of the wave . Maximum pressure elevation is called the amplitude, & the greater the pressure the highest is the amplitude & magnitude of the wave. Amplitude is measured in units of pascal .

26. Sound Is A type of wave that carries energy from place to place. • Created by the vibration of a moving object. • Sound waves are comprised of compressions (increases in pressure or density) and rarefactions (decreases in pressure or density ). • Sound cannot travel through a vacuum—sound must travel through a medium.  • Sound is a mechanical, longitudinal wave. • Sound travels in a straight line. Sound is a form of radiant energy. Sound is NOT ionizing radiation.

27. What Is Sound? Sound is a form of energy. It is a pressure wave, created by a mechanical action, and is therefore called a mechanical wave. Sound is produced when a vibrating source causes the molecules of a medium to move back and forth. This backward and forward movement of the molecules creates waves of sound energy that travel, or propagate, through the medium. A medium is

28. A medium is any form of matter: solid, liquid, or gas. Sound requires a medium in which to propagate; therefore, it cannot travel in a vacuum. When sound energy propagates through a medium, it does so in longitudinal waves, meaning that the molecules of the medium vibrate back and forth in the same direction that the wave is traveling . In summary, sound is a mechanical, longitudinal wave. Longitudinal waves should not be confused with transverse waves where molecules in a medium vibrate at 90 to the direction of the traveling wave

29. Acoustic variables are changes that occur within a medium as a result of sound travelling through that medium The three primary acoustic variables are : pressure, density, and distance . As stated in the previous section, when sound energy propagates through a medium, it causes the molecules to move back & forth. Each back and forth movement completes one wave or one cycle of movement.

30. Each cycle consists of two parts: a compression, where the molecules are pushed closer together, and a rarefaction, where they are spread wider apart. The molecules, as they are squeezed together and separated, cause changes in the pressure within the medium.

31. Similarly, molecules undergoing compression and rarefaction show variations in density. Density is defined as mass per unit volume. This movement of molecules, or particle motion, is due to propagating sound energy. Distance is defined as how far apart objects are, and it is the measurement of particle motion. Distance may also be referred to as vibration or displacement

32. Acoustic parameters (variables) These are measureable quantities describing sound & include: period, frequency, amplitude, power, intensity, propagation speed, and wavelength. Period and Frequency Period ( T ) is defined as the time it takes for ohttps://www.slideshare.net/KamalEldirawine cycle to occur Since period is measured in time units, it is most often described in microseconds ( μs ), or one millionth of a second Frequency ( f ) is defined as the number of cycles per second . Frequency is measured in hertz (Hz), kilohertz (kHz), or megahertz (MHz)

33. Frequency and period are inversely related. Therefore, as frequency increases, the period decreases, and as frequency decreases, the period increases Their relationship is also said to be reciprocal . When two reciprocals are multiplied together, the product is 1. Consequently, period multiplied by frequency equals 1.

34. One cycle consists of one compression & one rarefaction. Propagation Speed Propagation speed ( c) is defined as the speed at which a sound wave travels through a medium . All sound, regardless of its frequency, travels at the same speed through any particular medium. Therefore, a 20-Hz sound wave and a 20-MHz sound wave travel at the same speed in a given medium

35. Propagation speeds tend to be the fastest in solids, such as bone, and slowest in gases or gas-containing structures, such as the lungs In the body, sound travels at slightly different speeds through the various organs and tissues. The units for propagation speed are meters per second (m/s) or millimeters per microsecond (mm/ μs ). The average speed of sound in all soft tissue is considered to be 1540 m/s or 1.54 mm/ μs . This number was derived by averaging all of the actual propagation speeds of the tissues in the body.

36. Amplitude, Power, and Intensity Amplitude, power, and intensity all relate to the size or strength of the sound wave All three of these decrease as sound travels through a medium. Amplitude ( A) is defined as the maximum or minimum deviation of an acoustic variable from the average value of that variable For example, on a road trip, an average velocity may be 55 mph, but occasional increases of speed of up to 60 mph or decreases of speed down to 50 mph may occur.

37. In this situation, the amplitude would be 5 mph, because that is the maximum and minimum variation from the average velocity. Note that the amplitude is not the difference between the maximum and the minimum extremes. As sound propagates through a medium, the acoustic variables (distance, density, and pressure) will vary, and therefore, they may increase or decrease.

38. To measure amplitude (the maximum variation of an acoustic variable)is from baseline to peak. With respect to sound resonance frequency of an ultrasound transducer is determined by the peizoelectric crystal thickness So thin crystals vibrate at a higher high frequency & vice versa. Sound frequency is of 3 categories : 1- ultrasound : frequency above 20 KHz 2- infrasound : frequency beow 20 KHz 3- audible sound is between 20 Hz & 20 KHz (20,000 Hz) Medical diagnostic US uses frquenices per mega hertz (MHz)

39. The amplitude of these changes can be measured. When amplitude is discussed in ultrasound physics, it is commonly the pressure amplitude that is being referenced. The units of amplitude are Pascals (Pa).

40. Power (P) is defined as the rate at which work is performed or energy is transmitted . As a sound wave travels through the body, it loses some of its energy. Therefore, power decreases as the sound wave moves through the body. The power of a sound wave is typically described in units of watts (W) or milliwatts ( mW ). Power is proportional to the amplitude squared . Therefore, if the amplitude doubles, the power quadruples.

41. The intensity ( I ) of a sound wave is defined as Intensity  is the rate at which energy passes through unit area. Average  intensity  of a sound beam is the total power in the beam divided by the cross-sectional area of the beam. Power is the rate at which energy is transferred. the power of the wave divided by the area (a) over which it is spread, or the energy per unit area. Intensity is proportional both to power ( I P) and to amplitude squared ( I A2). Intensity is measured in units of watts per centimeter squared (W/cm2) or milliwatts per centimeter squared ( mW /cm2). Intensities typically range from 0.01 to 100 mW /cm2 for diagnostic ultrasound. Intensity is discussed in more detail later in this chapter (See section “More about Intensity”).

42. Amplitude. This schematic illustrates how sound can be depicted as a sine wave whose peaks and troughs correspond to areas of compression and rarefaction, respectively. As sound energy propagates through tissue, the wave has a fixed wavelength that is determined by the frequency and amplitude that is a measure of the magnitude of pressure changes. slide (43/44)