How does an Ultrasound Transducer work?


Ultrasound is a noninvasive medical procedure that uses sound waves to produce images of what is going on inside the body of a patient.  The ultrasound transducer is the device at the heart of the system that produces the sound waves and receives echoes used to generate the data.

What is an ultrasound transducer?

An ultrasound transducer is the handheld device that the technician or doctor moves on or over the body of the patient. A cord connects it to a computer. The device sends sound waves and receives the echoes as they bounce off the body tissue and organs of the patient. These echoes are used by the computer to create an image.

Transducers (probes) come in different sizes and shapes for use in different parts of the body. Some are placed on or over the body part. Others are designed to be inserted into an opening like the vagina or rectum so they can get closer to the organ for a more detailed view.

The basic principle of ultrasound

Ultrasound or sonography is based on the same basic principle used by bats. An ultrasound machine measures the echoes bouncing back to the transducer from the body of the patient to form an image. Bats ‘hear’ echoes and measure them to determine how far away the object is that caused the echo. They use what’s called ‘echolocation’ to fly around at night without bumping into anything.

In the transducer probe are piezoelectric crystals that change shape when an electrical current is applied to them. The vibrations or shape changes create sound waves that move outward. When they are directed at the human body, they pass right through the skin and into the internal anatomy.

As the waves encounter tissues with different characteristics and densities, they produce echoes that reflect back to the crystals. This happens more than a thousand times a second. The returning echoes are converted to electrical signals, and the computer uses them as points of brightness on the image, corresponding to the anatomic position and strength of the reflecting echoes.

A transducer contains a large array of crystals which allow it to make a series of image lines that together form a complete image frame called a sonogram.  All the crystals are repeatedly activated many times in such a way that a complete image frame is formed around 20 times per second. This means that ‘real-time- motion is displayed in the ultrasound image.

As images are captured in real-time, they can show how the blood is moving through the vessels and how an internal organ is moving. This is why they are useful during pregnancy as they can be used to observe the structure and movement of the fetus. They are especially useful when it comes to seeing the interface between spaces that are solid and those that are filled with fluid. The field of view depends on the shape of the probe, and the frequency of the emitted sound waves determines the depth to which they penetrate.  

The uses and benefits 

The technician or doctor operating the device is able to set and change the duration and frequency of the pulses. 

The reason why a gel is used on a patient’s skin is to prevent any distortion of the sound waves. It is a conductive medium that forms a tight connection between the probe and the skin and reduces static.

The person using the transducer must be trained in how to operate the device and understand the human anatomy to obtain the best results. When it is done correctly, it can determine the shape, size, and consistency of the organs and soft tissues.

The fact that transducers don’t use radiation means they don’t carry the risks associated with x-rays. They also provide a better image of soft tissue than seen on an x-ray.

We tend to associate ultrasound with monitoring of the fetus during pregnancy, but it has many other uses. It can be used to detect changes in the appearance of organs, tissues, and vessels or abnormal masses, so it is a great diagnostic tool. It can even help to provide real-time imaging during procedures such as biopsies.

A Doppler ultrasound measures movement of blood cells through the vessels and can help a physician to see blockages, blood clots and narrowing of the vessels. An echocardiogram is used to see images of the heart. A vascular transducer is normally used for carotid arteries and veins. An abdominal transducer is used in organs such as the stomach, kidney, spleen, and liver. A cardiac transducer is typically the smallest type; followed by the vascular and then the abdominal transducer which has a larger footprint. Transvaginal transducers are long and thin with a small head. 

Two-dimensional (2-D), three-dimensional (3-D) and even four-dimensional (4-D) ultrasound is now possible, with 4-D ultrasound offering a moving image. 

COMPARISON OF THREE ULTRASOUND PROBES/TRANSDUCERS

Acuson, SonoSite, and Philips are leading manufacturers of ultrasound equipment. The ultrasound probes/transducers in the following table all have various uses.   

Acuson has been in business since the late 1970s and was eventually acquired by Siemens who has continued to support Acuson transducers. The Acuson 4V1 Ultrasound Probe/transducer is high-resolution and features Hanafy lens technology. This offers thin slice thickness with uniformity throughout the view and great contrast and resolution.  

SonoSite stand behind the durability of their products and the SonoSite C60e Ultrasound Probe/Transducer is no exception.

The Philips X6-1 Ultrasound Probe/Transducer uses xMATRIX Pure Wave technology that allows remarkable clarity of viewing and full exploration. It makes exams easier for clinicians and patients, allowing for quick and easy volume acquisition and supporting multiple interrogation capabilities.

Transducers differ in array (the array is the way piezoelectric crystals are grouped inside).  As seen below the Philips Transducer has a phased array with 9,212 elements.  In a linear sequential array, crystals are side by side and create a single scan line. In a phased array, each crystal is able to produce multiple scan lines.

ACUSON

4V1 Ultrasound

Probe/Transducer

SONOSITE
C60e Ultrasound Probe/Transducer

PHILIPS
X6-1 Ultrasound Probe/Transducer

Array type

Vector Wideband multihertz imaging 

Broadband Curved

Fully-sampled matrix phased array with 9,212 elements

Frequency range

2-4 MHz

5-2 MHz

6-1 MHz

Dimensions

28 mm

66mm

Technology

29

xMATRIX Pure Wave

Lens and aperture

Hanify Lens

Proprietary aperture

Depth and field of view

 

Max  Depth: 30 cm

100° field of view:
90° x 90° volume of field of view

Applications

  • Abdominal
  • Obstetrics
  • Gynecology
  • Fetal Heart 
  • Abdominal
  • Obstetrics
  • Gynecology
  • Musculoskeletal 
  • Abdominal,
  • Obstetrics 
  • Gynecology
  • Fetal
  • Vascular

Ultrasound Compatibility

Acuson Aspen Acuson Sequoia Acuson S2000 Acuson S3000

SonoSite M-Turbo Portable  

 Philips IE33

Modes

2D, 3D and 4D 

2D, 3D and 4D

2D, M-Mode, Color Doppler, Color Power Angio, PW Doppler, 3D, 4D, XRES, Harmonic Imaging