Ultrasound-Lecture-2.pdf

SHENNA MARIE G. FORRO, RRT, MSRT OBJECTIVES: ▸Explain the concept of key wave properties and its importance in sonography ▸Define ultrasound and describe its behavior ▸To know and understand the physics of ultrasound ACOUSTICS ‣A branch of physics that deals with sound and sound waves TWO WAY...

SHENNA MARIE G. FORRO, RRT, MSRT OBJECTIVES: ▸Explain the concept of key wave properties and its importance in sonography ▸Define ultrasound and describe its behavior ▸To know and understand the physics of ultrasound ACOUSTICS ‣A branch of physics that deals with sound and sound waves TWO WAYS TO DEFINE SOUND: Experiential: ▸What we hear through the human auditory system. Physical: ‣Propagation of pressure variations through a medium from a sound source to a listener. SOUND ‣A form of energy which causes a mechanical disturbance in the form of vibration of molecules within a medium ‣Sound is a mechanical wave that travels in a medium in a LONGITUDINAL WAVE and STRAIGHT-LINE FASHION SOUND ‣ In order to be transmitted, sound requires a medium containing molecules, and therefore cannot travel through a vacuum. ‣ The production of sound requires a vibrating object. TAKE NOTE: ‣ Sound is a travelling variation of acoustic variables ‣ Acoustic variable include pressure, density, and particle motion ULTRASOUND WAVE ‣ Travels in a sinusoidal form ULTRASOUND WAVE TYPES OF ULTRASOUND WAVE ‣ LONGITUDINAL OR COMPRESSED WAVE ‣ Back and Forth TYPES OF ULTRASOUND WAVE ‣ TRANSVERSE WAVE OR SHEAR WAVE ‣ Up and Down WHEN A SOUND TRAVELS THROUGH A MEDIUM ‣ The molecules of that medium are alternately compressed and rarefied. Compression ‣ Regions of high pressure Rarefaction ‣ Regions of low pressure TYPES OF ULTRASOUND WAVE TYPES OF ULTRASOUND WAVE TYPES OF ULTRASOUND WAVE  The phase of the wave when the molecules are pushed together is wave when the molecules are pushed together is called compression, and when called compression, and when apart, rarefaction ULTRASOUND WAVE They oscillate back and forth, forming zones of compression and rarefaction FREQUENCY ‣ Number of cycles per second ‣ Units: Hertz (Hz) ‣ 1 Hz = 1 cycle/second ‣ Ultrasound imaging frequency range: 2-20 MHz ‣ Determines pitch and is crucial for image resolution and penetration. The lower the frequency, the higher the penetration, and lower of resolution PERIOD (T) ‣ The time for a sound wave to complete one cycle ‣ Unit: sec, ms, µs WAVELENGTH / CYCLE LENGTH ‣ Distance over which one cycle occurs ‣ Length of cycle from front to back ‣ Crest to crest / trough to trough PROPAGATION VELOCITY ‣ Speed at which a sound wave travels through a medium (cm/sec) ‣ Determined by density and stiffness of medium A. Slowest in air/gas B. Fastest in solids ‣ Velocity = wavelength x frequency PROPAGATION VELOCITY / SPEED ‣ Largely determined by the resistance of the medium to compression, which in turn is influenced by the density of the medium and its stiffness or elasticity. AMPLITUDE ‣ The strength/intensity of a sound wave at a given time ‣ Represented as hight of the wave ‣ Decreases with increasing depth AMPLITUDE ‣ Defines the brightness of the image ‣ The higher the amplitude the brighter the image POWER ‣ Rate at which the energy is transmitted into the body ‣ It is not contant, the acoustic power varies over time and space ‣ Unit: W, mW INTENSITY ‣ The amount of energy per second that passes through specified area ‣ Intensity of sound measures in bel or decibel ‣ Intensity of wave is proportional to the amplitude of the wave square INTENSITY PRESSURE ‣ Amount of force over a specific area ‣ Unit: Pascal, Megapascal ‣ Proportional to the amount of force and volume of the sound wave ‣ Inversely proportional to the area covered END OF DISCUSSION