Introduction to Ultrasound 1- Sounds energy was discovered before the discovery of X-rays. 2-Curie brothers (Jacques and Pierre) ,first discovered piezoelectric effect that produces ultrasound in 1880. 3- First they discovered the production of an electrical pulse from the application of the mechanical pressure on certain crystals. 4- The reversed piezoelectric was discovered a year later.

Industrial applications 1-The first practical uses of ultrasound failed to locate the Titanic which sank in 1916. 2- Ultrasonics improved during the Second World War with military development of SONAR for detection of submarines. 3- USA and England developed pulse echo ultrasound equipment for flow detection in metals.

Detection of submarines by ultrasound

Profile of the sea bed by echo sounder

Medical applications 1- The first ultrasound unit was designed by Dussik in Austria in 1937. 2- He used two transducers on opposite sides of the head in an attempt to visualize the cerebral ventricles. 3- In 1949 a quartz transducer was made . 4- The picture of the underline anatomy was displayed as dots on the oscilloscope screen. 5- The initial sonograms were made with transducer and objects submerged in water . 6- In 1960s ,the water tank was replaced by a mineral oil as a coupling agent.

What is sound? What is a wave? Sound is a type of wave. Wave is a variation that transfers energy progressively from point to point in a medium.

How do sound waves move from one point to another? Sound waves require matter to exist, travel or propagate from one point to another. All matters are composed of molecules. Sound waves moves through the cyclic vibrations of molecules in the matter. vibrations The sound waves of the musical instruments reach our ears through of air molecules. Sound waves produce a force (pressure) on the molecules of a medium displacing them towards and away from the source in a cyclic fashion.

Fundamental of waves Types: The wave is the co-ordinated disturbance moving at a fixed speed . Types: 1-Electromagnetic waves: --Radiation( X.ray,gamma rays,) --light (visible light, ultraviolet, and infrared light). --Microwaves. --Radio waves. 2-Mechanical waves: --Ocean waves. --Seismic waves. --Sound waves.

Electromagnetic vs mechanical waves EMW 1-The velocity is equal to the speed of light 2-Because it is a transverse wave ,no medium required. 3-The frequency ranges from 100Hz(radio w) to 10 24Hz (gamma rays). 4-Produced by electrical charge. MW 1- The velocity depends on medium 2-Because it is a longitudinal wave a medium is required. 3-The frequency ranges from 20Hz—1MHz. 4- The source must be a vibrating source

Wave direction 1- longitudinal waves :. The direction of travel of the wave is in the same direction as particle motion. e.g. sound wave. 2- Transverse waves : The motion of the particles is perpendicular to the direction of propagation of the wave energy. e.g. wave motion resulting from a stone thrown in the water.

Transverse versus Longitudinal waves

Stone is thrown into a still pond

Compression and rarefaction of air molecules

Mechanical waves sound waves) Definition: It is the propagation of energy through a medium by cyclic pressure vibration. It requires a deformable medium for propagations Wave equation: A(t)=A*sin(ft) where A = amplitude at time t. A*= peak amplitude. f = frequency

Wave Power and Intensity Power is the rate at which work is performed. The unit of power is watts. Intensity is the amount of energy per second (power) that passes through a specified area. The unit of intensity is w/m2. Amplitude: It means a maximum cyclical change in a quantity, such as the pressure in an ultrasound wave. It is the difference between the maximum value and equilibrium of the acoustic variable.

The Decibel Definition The decibel is a unit which used to compare the relative intensities of two ultrasound beams and expressed in logarithms to base 10. Equation Relative intensity level (dB) dB=10log I/I0 Where : I =Intensity of a beam at any point. I0 =initial intensity of a beam Relative signal level (dB) dB=20 log A2/A1

Amplitude and Intensity Amplitude is the quantitative statement regarding the magnitude or strength of a wave. A wave of a higher amplitude is accompanied by a greater pressure amplitude. In case of calculating the biological effects , the intensity is measured as a ratio of pressure amplitude and acoustic impedance of a medium.

Mechanical wave properties Wavelength: Definition: It is the distance between two adjacent bands of compression and rarefactions. Units: Meter

The wave velocity Definition: Units: Velocity is the speed at which the wave moves through the medium . It is often called the speed of propagation. Units: Meter per second. All acoustic waves are transmitted through the same medium at the same velocity even though their frequencies are different.

Velocity of sound in some non-biological material Material Velocity (m/s) Air 330 Water 1480 Lead 2400 Aluminum 6400

Velocity of sound in selected tissues Materials Velocity (m/s) Lung 600 Fat 1460 Aqueous hummer 1510 Liver 1555 Blood 1560 Kidney 1565 Muscle 1600 Lens of eye 1620 Skull bone 4030

The wave Frequency Definition: Units: Frequency is the number of cycles that pass a given point per one second. Units: Hurtz (Hz) One hurtz=One cycle per second

Nature of sound Familiar definition : Fundamental definition: Sound is the sensation perceived by the sense of hearing Fundamental definition: Sound is mechanical energy transmitted by pressure waves in a material medium. Characteristics of sound : 1-It is a form of energy. 2-It is a mechanical energy. 3-It needs a material for transference. 4-It propagates through a material medium.

Sources of sound Sound production require a vibrating objects. Sources include: 1- musical instruments. 2-Human vocal cords. 3-Peizoelectric transducer 4-Certain animal like a bat.

The sound waves need a media to propagate through it

Bats uses ultrasound to detect flying insects

Acoustic variables Acoustic variables include: Acoustic variables are quantities which vary in rhythmic , cyclic fashion in time and in space. Acoustic variables include: 1-Pressure. 2-Density. 3-particle motion. 4-Temprature.

Pressure: Is the concentration of force ,or, Force over a given area. Unit of pressure is pound per square inch. Density: Is the concentration of mass or weight. Unit of density is pound per cubic feet and kilogram per cubic meter. Temperature: Is the concentration of heat energy. Unit of temperature Is a degree of (Fahrenheit, Celsius, or Kelvin scale). Particle motion includes the displacement, speed, velocity, and acceleration of a particle.

Piezoelectric, Piezoelectric effect The prefix Piezo means pressure It describes the formation of electrical charge on the surfaces of the crystal when pressure (mechanical stress) is applied.

The reverse Piezoelectric effect It is the production of ultrasound (mechanical energy) when an electrical signal is applied to the crystal. The crystal undergoes mechanical deformation , contracting or expanding depending on the polarity of the electric signal.

Production of sound waves Ultrasound waves are produced when an electrical signal is applied to a piezoelectric crystal

Piezoelectric crystal

Piezoelectric effect and reverse piezoelectric effect

The microphone (sound to electricity) and loud speaker (electricity to sound)

Sound spectrum Sound is divided into three major categories: 1-Infrasound ( Frequencies below 20 Hrz) 2-Audible sound (F between 20 and 20 KHrz) 3-Ultrasound (F above 20 khz) 4-Medical ultrasound (F above one MHrz) ;