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ULTRA SOUND IMAGING

Prepared by : Abhijith Prabha , L6A ,roll no : 6 ,

ECE Department , SNGCE.

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INTRODUCTION An ultrasound imaging device is a machine that is

commonly used to examine underlying features of the human body.

Its advantages are that no surgery is needed in order to obtain a clear picture of entities such as kidney stones.

The main parts of an ultrasound equipment are the ultrasound transducer or probe, the electrical control of the probe (including "beam former") and the visualization system. This section will focus particularly on the visualization system.

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Principle The ultrasound machine transmits high-frequency

(1 to 5 megahertz) sound pulses into your body using a probe.

The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone).

Some of the sound waves get reflect back to the probe, while some travel on further until they reach another boundary and get reflected.

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Fig : schematic diagram of principle of Ultra Sound imaging

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Principle The reflected waves are picked up by the probe

and relayed to the machine. The machine calculates the distance from the

probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second).

The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image

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Relation between attenuation and frequency in body.

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Attenuation coefficient of different body tissues

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Ultra Sound Machine

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The Ultrasound Machine

A basic ultrasound machine has the following parts:

transducer probe - probe that sends and receives the sound waves

central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe

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

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display - displays the image from the ultrasound data processed by the CPU

keyboard/cursor - inputs data and takes measurements from the display

disk storage device (hard, floppy, CD) - stores the acquired images

printer - prints the image from the displayed data

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Fig : working of Ultrasonic Machine

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Ultrasound generator

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Fig: block diagram of Ultra Sound generator

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Ultrasound receiver

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Fig : ckt diagram of a typical Ultrasound Receiver

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Modes of operation A MODE A stands for Amplitude. Information of the

reflected signal in a single ultrasound beam is continually displayed distance from the transducer and intensity are shown by position and amplitude in a line on an oscilloscope. This mode is mainly of historical interest, may be rarely used in gynaecology or ophthalmology.

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Modes of operation B MODE

B stands for Brightness. In this case A-mode information from many beams, typically forming a sector in a plane of the body, is shown as pixel intensity on a monitor. B mode is often referred to as 2D, and is the most important modality for anatomic assessment and orientation in the body, also for localising and as a background for display of other information such as Doppler signals.

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Modes of operation

M MODE M stands for motion. This approach is used

for the analysis of moving organs. It is based on A-mode data from a single ultrasound beam that are represented as function of time. This does not require a sweep through many ultrasound beams which allows for high temporal resolution.

Abhijith Prabha20Fig : illustration of Ultrasound image in Mode M

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Modes of operation

Doppler mode Doppler mode exploits the frequency shift due to

relative motion between two objects. With this approach information regarding blood velocity and cardiac valves can be obtained.

Doppler mode can be obtained by continuous or pulsed wave (PW); in addition, velocity data can be shown as overlaying colour on B-mode images (colour Doppler, power Doppler and Tissue Doppler).

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Transducers Mechanical Probe: seldom used now. Electronic Probe: – Linear array transducers • piezoelectric elements linearly arranged • sequentially activated to produce an image – Phased array transducers • smaller scanning surface (foot print) • good for echocardiography • more expensive • elements are activated with phase

differences to allow steering of the ultrasound signal

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Applications Obstetrics and Gynaecology

measuring the size of the foetus to determine the due date

determining the position of the foetus to see if it is in the normal head down position or breech

checking the position of the placenta to see if it is improperly developing over the opening to the uterus (cervix)

seeing the number of foetuses in the uterus checking the sex of the baby (if the genital area

can be clearly seen) checking the foetus's growth rate by making many

measurements over time

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Applications Cardiology

seeing the inside of the heart to identify abnormal structures or functions

measuring blood flow through the heart and major blood vessels

Urology measuring blood flow through the kidney seeing kidney stones detecting prostate cancer early

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Advantages Ultrasonic can be easily focused, i.e., they

are directional. They are inaudible. It is possible to investigate the properties

of very small structures. Information obtained by US , particularly in

dynamic studies, cannot be acquired by other more convenient technique.

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Limitations development of heat - tissues or water absorb the

ultrasound energy which increases their temperature locally

formation of bubbles (cavitations) - when dissolved gases come out of solution due to local heat caused by ultrasound

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END