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Amplitude• The degree of variance from the norm Amplitude
Spectrum of soundFrequency range Hz Description Example 0 - 20 Infrasound Earth quake 20 - 20.000 Audible sound Speech, music > 20.000 Ultrasound , Quartz crystal
Atomic structures gas liquid solid• low density • medium density • high density• weak bonding forces • medium bonding • strong bonding forces forces • crystallographic structure Krautkramer NDT Ultrasonic Systems
Basic formulaAir 330 m/sWater 1480 m/sSteel, long 5920 m/sSteel, trans 3250 m/s
Example Sound Speeds Medium sound speed (m/s) air (20 C) 343 water 1497 gold 3240 brick 3650 wood 3800–4600 glass 5100 steel 5790 aluminum 6420Spring 2006 11
What is the Echo?Repetition of a sound by reflection of sound waves from a surfacer = c * t2The pulse bounces off a target and returns to the receiver after a time interval t.The receiver records the length of this time interval,and calculates the distance travelled r based on the speed of sound c
What that mean?If the sound path from one surface to Another the sound will be reflected Surface 1 Surface 2
What is Ultrasound?• Ultrasound is a mechanical, longitudinal wave with a frequency exceeding the upper limit of human hearing, which is 20,000 Hz or 20 kHz.Medical Ultrasound 2MHz to 16MHz
Piezoelectric material• AC applied to a piezoelectric crystal causes it to expand and contract – generating ultrasound, and vice versa• Naturally occurring - quartz• Synthetic - Lead zirconate titanate (PZT)
Human Hair Single CrystalMicroscopic view of scanhead
Ultrasound Production • Transducer contains piezoelectric elements/crystals which produce the ultrasound pulses (transmit 1% of the time) • These elements convert electrical energy into a mechanical ultrasound wave SoundElectric Signal
The Returning Echo• Reflected echoes return to the scanhead where the piezoelectric elements convert the ultrasound wave back into an electrical signal• The electrical signal is then processed by the ultrasound system Electric Signal Sound
Piezoelectric Effect Sound wave with frequency f U(f)An alternating voltage generates crystal oscillations at the frequency f Krautkramer NDT Ultrasonic Systems
Piezoelectric Effect Short pulse ( < 1 µs )A short voltage pulse generates an oscillation at the crystal‘s resonantfrequency f0 Krautkramer NDT Ultrasonic Systems
Sound reflection r Probe Sound travel path Work piece Krautkramer NDT Ultrasonic Systems
Immersion testing 1 2 surface = water delaysound entry backwall Mass IP 1 IP 2 IE IE BE BE F 0 2 4 6 8 10 0 2 4 6 8 10 Krautkramer NDT Ultrasonic Systems
In ultrasound, the following events happen:1. The ultrasound machine transmits high-frequency (1 to 20 megahertz) sound pulses into the body using a probe.2. The sound waves travel into the body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).3. Some of the sound waves reflect back to the probe, while some travel on further until they reach another boundary and then reflect back to the probe .4. The reflected waves are detected by the probe and relayed to the machine.
5. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (1540 m/s) and the time of the each echos return (usually on the order of millionths of a second).6. The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image.
Piezoelectric Crystals• The thickness of the crystal determines the frequency of the scanhead Low Frequency High Frequency 3 MHz 10 MHz
Frequency and Wavelength therefore are directly proportional- if the frequency increases the wavelength must decrease. if the frequency decreases the wavelength must increase
Frequency vs. Resolution• The frequency also affects the QUALITY of the ultrasound image – The HIGHER the frequency, less penetration the BETTER the resolution – The LOWER the frequency, HIGHER penetration the LESS the resolution
Types of Resolution• Axial Resolution – specifies how close together two objects can be along the axis of the beam, yet still be detected as two separate objects – frequency (wavelength) affects axial resolution – frequency resolution
Types of Resolution• Lateral Resolution – the ability to resolve two adjacent objects that are perpendicular to the beam axis as separate objects – beamwidth affects lateral resolution
Types of Resolution• Spatial Resolution – also called Detail Resolution – the combination of AXIAL and LATERAL resolution - how closely two reflectors can be to one another while they can be identified as different reflectors
Types of Resolution• Temporal Resolution – the ability to accurately locate the position of moving structures at particular instants in time – also known as frame rate
Types of Resolution• Contrast Resolution – the ability to resolve two adjacent objects of similar intensity/reflective properties as separate objects - dependant on the dynamic range
1st who is the 1st sono grapher ?• Bats use a variety of ultrasonic ranging(echolocation) techniques to detect their prey.They able to fly without their vision.They can detect frequencies beyond 100 kHz,possibly up to 200 kHz.This discovered in 1793 by Italian Scientist called Spallanzani.
Sir Francis Galton (1800)• Recognized that by moving the plunger (located inside the whistle) the size of the cavity could be changed to alter the pitch (frequency) of sound• Determined the normal limit of human hearing is around 18 kHz
1st Contact B-Scanner (1956)The first contact B scanner was designed and built by Tom Brown onthe frame of a hospital bed-table. It is seen here with its first picture;this shows echoes from the skin, at the top of the picture, and fromthe bowel.
Automatic Scanner (1959)Tom Brown developed the world’s first and only fullyautomatic scanner in order to give a consistent scanningpattern. Much of the early research was carried out with thismachine
Fetal Cephalometry (1961)• Dr. James Willocks (seated, scanning) developed a technique for fetal cephalometry using A-Scan equipment and electronics.
1st Commercially Produced Medical Scanners (1962)
The Mid ’70s and the Change to Real-time System 185 EMI 4200 System 85 Diagnostic Sonar Static Real-time scanners Ltd. Scanner
The Beginnings of 3D (1976)• develop the world’s first 3-D ultrasound scanner.• Sonicaid Multiplanar Scanner