Ultrasound physics and instumentation

Prepared by Yannick NGERAGEZE

Ultrasound physics

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Introduction An ultrasound is machine that uses high

frequency sound waves and their echoes to help determine the size, shape and depth of an abnormality.

It allow various organs in the body to be examined right in the doctor's office or clinic.

prepared by yannick Ngerageze

prepared by yannick Ngerageze3

Physical principles of sound wave A wave is a repeating disturbance or movement

that transfers energy through matter or space Mechanical waves are waves which require a

medium. A medium is a form of matter through which

the wave travels (such as water, air, glass, etc.) Waves such as light, x-rays, and other forms of

radiation do not require a medium.


They are two kinds of mechanical waves

Transverse In a transverse wave the matter in the wave

moves up and down at a right angle to the direction of the wave


They are two kinds of mechanical waves

Longitudinal Waves (Compression Waves)

In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave


Sound wave Sound is a compressional wave which travels

through the air through a series of compressions and rarefactions.

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Compressional

Longitudinal wave

On a compressional wave the area squeezed together is called the compression. The areas spread out are called the rarefaction.

The wavelength is the distance from the center of one compression to the center of the next compression.



The parts of a waveTransverse wave The crest is the highest point

on a transverse wave. The trough is the lowest point on a transverse wave.

The rest position of the wave is called the node or nodal line.

The wavelength is the distance from one point on the wave to the next corresponding adjacent point.


Wavelength and frequency Wavelength is a measure of distance, so the

units for wavelength are always distance units, such as meter, centimeters, millimeters, etc.

Frequency is the number of waves that pass through a point in one second.

The unit for frequency is waves per second or Hertz (Hz). One Hz = One wave per second.

Wavelength and frequency are inversely related


Wavelength and frequency The smaller the wavelength, the more times it

will pass through a point in one second. The larger the wavelength, the fewer times it will pass through a point in one second.


Period Period is the time it takes for one full

wavelength to pass a certain point.

Frequency is waves per second.

Period is seconds per wave.

Tf

periodfrequency

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Speed A wave moving through a medium travels at a

certain speed. This is Wave Speed.

Wave speed is usually measured in meters/second, but may be measured using other distance units (such as centimeters per second).

Wave speed is calculated as the product of a waves frequency and wavelength.


Amplitude The amplitude of a wave is directly related to

the energy of a wave.


Amplitude The amplitude of a transverse wave is

determined by the height of the crest or depth of the trough


The Behavior of sound waves Reflection

When a wave bounces off an object and changes direction, this is reflection.

Refraction

Is the bending of a wave as it passes from one medium to another.

A wave travels at different speeds in different things.

When a wave traveling a certain speed moves into another medium, it will either increase in speed or decrease in speed, resulting in a change in direction


Diffraction

diffraction occurs when passing through a small opening, they diffract and spread out as they pass through the hole.


Sound travels through different media We hear sound which usually travels through

air. Sound travels through other media as well,

such as water and various solids. Sound travels different speeds in different

media. Sound typically travels faster in a solid that a

liquid and faster in a liquid than a gas.


Sound travels through different media

The denser the medium, the faster sound will travel.

The higher the temperature, the faster the particles of the medium will move and the faster the particles will carry the sound.


Sound intensity Sound intensity is the energy that the sound

wave possesses. The greater the intensity of sound the farther

the sound will travel and the louder the sound will appear.

Loudness is very closely related to intensity. Loudness is the human perception of the sound

intensity. The unit for loudness is decibels.


Doppler Effect The Doppler effect is the apparent change in

frequency detected when the sound is moving relative to the hearer.


Principles of instrumentation in ultrasonography All ultrasound scanners consist of similar

components that perform the same key functions.

One of these is a transmitter that sends pulses to the transducer, a receiver and a processor that detects and amplifies the backscattered energy.


The Transmitter

Although the transducer is itself the transmitter of the ultrasound pulses into the body,

It must be energized initially by the transmitter, which applies precisely timed, high-amplitude voltage to the transducer.

The length of an ultrasound pulse is determined by the number of alternating voltage changes applied to the transducer.

Transducers have a range of frequencies which they are able to produce.

This is known as the bandwidth.


Receiver

The receiver not only detects, but differentially amplifies weak signals emanating from different depths.

Different tissue thicknesses attenuate the ultrasound variably, and the difference in echo strength is compensated by time gain compensation (TGC).


Time Gain Compensation TGC is an amplification technique to increase

ultrasound echoes from tissue interfaces that are deeper within the body.

This is to compensate for the increasing attenuation of the echoes returning from these deeper areas.

This is one of the manual controls available to the sonographer to achieve a more uniform grey-scale image.


Display The ultrasound machine use 3 types of display

A-Mode or Amplitude ModeB-Mode (Brightness Mode) M-Mode (Motion Mode)

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A-Mode Each pulse produces a

new a one-dimensional display or image

Line of information on the display

An uncommon display, except in ophthalmologic sonography used for precise intraocular length measurements



B-Mode (Brightness Mode) Basis for gray scale,

two-dimensional (2D) imaging

US unit tracks the position of the transducer to place a dot on the screen corresponding to the transducer position (X, Y locations), creating a 2D image


M-Mode (Motion Mode)

One-dimension image used to investigate moving structures with respect to time

Evaluates motion pattern of moving structures such as in the heart


Different components of US machine

the following parts:

1. Transducer (probe)The probe is the mouth and ears of the

ultrasound machine. In the probe, there are one or more quartz

crystals called piezoelectric crystals. When an electric current is applied to these

crystals, they change shape rapidly.



The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward.

The sound waves travel into the patient being scanned.

The sound waves bounce back at various intervals depending on the type of material they pass through.



2. Central Processing Unit (CPU) The CPU is the brain of an ultrasound machine. The CPU is a computer that contains the

microprocessor, memory, amplifiers and power supplies for the microprocessor and transducer probe.

The transducer receives electrical currents from the CPU and sends electrical pulses that are created by returning echoes.



3. Transducer pulse controls The operator, called the ultrasonographer,

changes the amplitude, frequency and duration of the pulses emitted from the transducer probe



4. Display Displays the image from the ultrasound data

processed by the CPU. This image can be either in black-and-white

or color, depending upon the model of the ultrasound machine



5. Keyboard/Cursor Ultrasound machines have a keyboard and

a cursor. The keyboard allows the operator to add

notes and to take measurements of the image.



6. Disk Storage The processed data and/or images can be

stored on disks. These disks can be hard disks, floppy

disks, compact disks (CDs), or digital video disks (DVDs).

Most of the time, ultrasound scans are filled on floppy disks and stored with the patient's medical records.


Different components of US machine Printers

Most ultrasound machines have printers which are thermal. These can be used to capture a printed picture of the image from the monitor.


Images


Clinical application of ultrasound

Sonography is effective for soft tissues imaging of many different systems

Anesthesiology Ultrasound is commonly used by

anesthesiologists to guide injecting needles when placing local anaesthetic solutions near nerves


Clinical application of ultrasound CardiologyEchocardiography is an essential tool in

cardiology, to diagnose e.g. dilatation of parts of the heart and function of heart ventricles and valves


Clinical application of ultrasound Emergency MedicineUltrasound has many applications in the

Emergency Department,For ex. the focused assessment for Trauma

exam for assessing significant hemoperitoneum.

Evaluation of right upper quadrant abdominal pain for patients who may have gallstones or cholecystitis



NeonatologyFor basic assessment of intracerebral structural

abnormalities, bleeds, ventriculomegaly or hydrocephalus

For soft spots in the skull of a newborn infant (Fontanelle) until these completely close at about 1 year of age.

NeurologyFor assessing blood flow and stenoses in the

carotid arteries


Clinical application of ultrasound Gastroenterology In abdominal sonography, the solid organs of

the abdomen The pancreas, aorta, inferior vena cava, liver,

gall bladder, bile ducts, kidneys, and spleen are imaged.

The appendix can sometimes be seen when inflamed (as in e.g.: appendicitis


Clinical application of ultrasound ObstetricsObstetrical sonography is commonly used

during pregnancy to check on the development of the fetus.


Clinical application of ultrasound UrologyTo determine, for example, the amount of fluid

retained in a patient's bladder. In a pelvic sonogram, organs of the pelvic

region are imaged. This includes the uterus and ovaries or urinary

bladder.


Clinical application of ultrasound Males are sometimes given a pelvic sonogram

to check on the health of their bladder, the prostate, or their testicles (for example to distinguish epididymitis from testicular torsion).

MusculoskeletalTendons, muscles, nerves, ligaments, soft

tissue masses, and bone surfaces



Cardiovascular systemTo assess patency and possible obstruction of

arteries Arterial sonography, diagnose DVT (Thrombosonography) and determine extent and severity of venous insufficiency (venosonography


Clinical application of ultrasoundGynecology Gynecologic sonography is used extensively:To assess pelvic organs,To diagnose and manage gynecologic problems

including, leiomyoma, ovarian cysts and lesions,

To Identify ectopic Pregnancy,To Diagnose Gynecologic Cancer


Conclusion

A basic ultrasound machine has 7 main parts: transducer, CPU, keyboard, display, storage, printer, and transducer control.

Sonography is effective for soft tissues imaging of many different systems.


Conclusion Sound is a compressional wave which travels

through the air through a series of compressions and rarefactions; it has different interactions such as reflection, refraction, doppler effect, diffraction.

All ultrasound scanners consist of similar components that perform the same key functions, among them we have transmitter, transducer, receiver and display


References C.R.Hill, J.C.Bamber, G. R. ter Haar John Wiley &Sons

physical Principles of Medical Ultrasonics, 2004

K. Kirk Shung Taylor & Francis Diagnostic Ultrasound Imaging and Blood Flow Measurements2006

F.A. Duck, A.C. Baker, H.C.Starritt Institute of Physics Ultrasound in Medicine ,1997

Principles of Medical Imaging K.K.Shung, M.B.Smith, B.M.W. Tsui Academic Press 1992

http://en.wikipedia.org/wiki/Gynecologic_ultrasonography

http://en.wikipedia.org/wiki/Gynecologic_ultrasonography

Ultrasound physics and instumentation

Health & Medicine

sound wave sound

yannick ngerageze

wave speed

wave tothe

atransverse wave

compressional wave

whichthe wave travels

intensity of sound