UltraSound - Technology Information PortalWednesday, 24 April 2019



Ultrasound Probes Transducers

  • Intro

A transducer is a device, usually electrical or electronic, that converts one type of energy to another. Most transducers are either sensors or actuators. A transducer (also called probe) is a main part of the ultrasound machine. The transducer sends ultrasound waves into the body and receives the echoes produced by the waves when it is placed on or over the body part being imaged.
Ultrasound transducers are made from crystals with piezoelectric properties. This material vibrates at a resonant frequency, when an alternating electric current is applied. The vibration is transmitted into the tissue in short bursts. The speed of transmission within most soft tissues is 1540 m/s, producing a transit time of 6.5 ms/cm. Because the velocity of ultrasound waves is constant, the time taken for the wave to return to the transducer can be used to determine the depth of the object causing the reflection.
The waves will be reflected when they encounter a boundary between two tissues of different density (e.g. soft tissue and bone) and return to the transducer. Conversely, the crystals emit electrical currents when sound or pressure waves hit them (piezoelectric effect). The same crystals can be used to send and receive sound waves; the probe then acts as a receiver, converting mechanical energy back into an electric signal which is used to display an image. A sound absorbing substance eliminates back reflections from the probe itself, and an acoustic lens focuses the emitted sound waves. Then, the received signal gets processed by software to an image which is displayed at a monitor.
Transducer heads may contain one or more crystal elements. In multi-element probes, each crystal has its own circuit. The advantage is that the ultrasound beam can be controlled by changing the timing in which each element gets pulsed. Especially for cardiac ultrasound it is important to steer the beam.
Usually, several different transducer types are available to select the appropriate one for optimal imaging. Probes are formed in many shapes and sizes. The shape of the probe determines its field of view.
Transducers are described in megahertz (MHz) indicating their sound wave frequency. The frequency of emitted sound waves determines how deep the sound beam penetrates and the resolution of the image. Most transducers are only able to emit one frequency because the piezoelectric ceramic or crystals within it have a certain inherent frequency, but multi-frequency probes are also available.
See also Blanking Distance, Damping, Maximum Response Axis, Omnidirectional, and Huygens Principle.

• View the NEWS results for 'Transducer' (6).Open this link in a new window.

• View the DATABASE results for 'Transducer' (182).Open this link in a new window.

 Further Reading:
Testing Diagnostic Ultrasound Probes For Bad CrystalsOpen this link in a new window
Saturday, 19 September 1998   by www.pamia.org    
  News & More:
Ultrasound beamforming and image formation(.pdf)Open this link in a new window
2007   by dukemil.bme.duke.edu    
Transmission Line Matrix (TLM) modelling of medical ultrasound(.pdf)Open this link in a new window
   by www.era.lib.ed.ac.uk    
Transducer Types 

Transducers can be divided in:
1.) Transducers where the sound wave is transmitted and received by different elements.
2.) Transducers where multiple elements part of the time transmit and part of the time receive sound energy.
The first type of ultrasound transducer is used in detection of blood flow (also called nonimaging transducers). For example, the continuous wave transducer (Pedoff transducer) has two separate elements, where one element is always transmitting while the other element is always receiving.
Probes of the second type are used to image cardiac structures and have the capability to use various Doppler techniques to detect blood flow (also called imaging transducers). For example, continuous wave, pulsed wave, high pulse repetition frequency, color flow, M-mode, and 2D-mode are the various modes that this type of transducer can perform.

Transducers can also be divided in mechanical and electronic or phased scan types.
Mechanical transducers use a combination of single element oscillation, multiple element rotation, or a single element and set of acoustic mirrors to generate the sweeping beam for 2D mode. Caused by the vibration (created as the mirrors rotate or oscillate inside the cover) is this type sometimes called the 'wobbler'. Mechanical transducers are cheaper than electronic transducers.
Different types of electronic or phased array probes can create a linear or rectangular shaped scan plane as well as a sector or pie shaped scan plane. Sector scanners are most useful for cardiac ultrasound examinations where the beam is directed between the ribs to image the heart. A linear array transducer is more useful in abdominal, OB/GYN, and small parts examinations. Electronic transducers are more expensive but they provide dynamic focusing and smaller probe.
See also Rectangular Array Transducer.

• View the DATABASE results for 'Transducer Types' (3).Open this link in a new window.

 Further Reading:
Medical Physics: Ultrasound - extended reading exerciseOpen this link in a new window
   by www.cyberphysics.pwp.blueyonder.co.uk    

In medical ultrasound, probe refers to the ultrasound transducer. The probe covers the elements, backing material, electrodes, matching layer and protective face that both sends and receives the sound waves. The reflected ultrasound waves are received by the probe and generate a signal. Most probes emit only for 10% of time and receive for the remaining 90% of time.
Probes come in different shapes and sizes for use in different scanning situations. The most common mechanical transducers are oscillating probes and the rotating probes driven by a motor. Mechanical probes produce excellent images, but are more subject to wear than electrical probes. Electrical probes are generally more expensive than mechanical probes.
See also Omnidirectional, Probe Cleaning, and Multi-frequency Probe.

• View the NEWS results for 'Probe' (5).Open this link in a new window.

• View the DATABASE results for 'Probe' (123).Open this link in a new window.

 Further Reading:
Medical Physics: Ultrasound - extended reading exerciseOpen this link in a new window
   by www.cyberphysics.pwp.blueyonder.co.uk    
  News & More:
Duke Engineers Develop New 3-D Cardiac Imaging ProbeOpen this link in a new window
Friday, 27 May 2005   by www.sciencedaily.com    
  Probes I top
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