ENGR AHMED A A HASSAN

Introduction of Ultrasound Physics'

Introduction to the Physics of Ultrasound

• Sound?

• Sound is a mechanical, longitudinal wave that travels in a straight line

• Sound requires a medium through which to travel

Amplitude

Cycle• 1 Cycle = 1 repetitive periodic oscillation

Cycle

frequency1 cycle in 1 second = 1Hz

1 second

= 1 Hertz

Wavelength

• The length of one complete cycle• A measurable distance

Wavelength

Wavelength

Amplitude

• The degree of variance from the norm

Amplitude

Spectrum of sound

Frequency range Hz Description Example

0 - 20 Infrasound Earth quake

20 - 20.000 Audible sound Speech, music

> 20.000 Ultrasound , Quartz crystal

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gas liquid solid

Atomic structures

• low density• weak bonding forces

• medium density• medium bonding

forces

• high density • strong bonding forces• crystallographic

structure

Basic formula

AirWaterSteel, longSteel, trans

330 m/s1480 m/s

3250 m/s

5920 m/s

11

Example Sound Speeds

Spring 2006

Medium sound speed (m/s)

air (20C) 343

water 1497

gold 3240

brick 3650

wood 3800–4600

glass 5100

steel 5790

aluminum 6420

What is the Echo?

Repetition of a sound by reflection of sound waves from a surfacer = c * t2

The 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

How the Ultrasound System work?

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 Crystal

Microscopic 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

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An alternating voltage generates crystal oscillations at the frequency f

U(f)

Sound wave with

frequency f

Piezoelectric Effect

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A short voltage pulse generates an oscillation at the crystal‘s resonantfrequency f0

Short pulse ( < 1 µs )

Piezoelectric Effect

Transducer Construction

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Sound reflection

ProbeSound travel path

Work piece

r

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surface = sound entry

backwall Mass

1 2

water delay

0 2 4 6 8 10 0 2 4 6 8 10

IE IEIP IP

BE BEF

1 2

Immersion testing

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 echo's 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.

Liver metastases

Piezoelectric Crystals

• The thickness of the crystal determines the frequency of the scanhead

Low Frequency3 MHz

High Frequency10 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

Resolution– frequency

– Wave Length – resolution

Resolution– frequency

– Wave Length – 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

History

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 on the 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 from the bowel.

Automatic Scanner (1959)

Tom Brown developed the world’s first and only fully automatic scanner in order to give a consistent scanning pattern. Much of the early research was carried out with this machine

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

EMI 4200Static Scanner

System 85Real-time scanners

System 185Diagnostic Sonar Ltd.

The Beginnings of 3D (1976)

• develop the world’s first 3-D ultrasound scanner.

• Sonicaid Multiplanar Scanner

Now a Days: