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What are the different types of transducers, and why does it matter?

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Hello!

I’m Mike, and I recently joined the Portable Ultrasound Machines (PUM) team. When I started work with PUM, I didn’t have a background in ultrasound. So to help me get up to speed, I kept a note of all the new terms I was coming across along with a short definition.

In the coming weeks and months, I’ll be sharing some of these with you. I hope you’ll find them a useful introduction to the – sometimes confusing! – language used in this sector and that they will help you if you are just beginning your journey with ultrasound and the machines we use.

In an earlier post we introduced the ‘transducer’ (also known as a probe). That article we touched on how the choice of transducer can influence image quality. This post explores in more detail the different types of transducer, and how they can help with different applications in veterinary, breeding and farming contexts.

Transducers: a quick recap

Your transducer, which is also known as the ‘probe’, is the device you will use to transmit and receive the ultrasound waves which will in turn be translated into an image by your machine. The transducer will either be held against the skin of the animal, or carefully inserted rectally. The transducer generates the ultrasound waves using crystals with ‘piezoelectric’ properties, these ultrasound waves are then focused in the required direction by the ‘lens’ of the transducer, and when reflected the energy is translated into electric current to be sent back up the wire to the ‘machine’ to be processed and displayed.

More than one type of transducer…

There is more than just one type of transducer, with each one developed to be particularly good at a particular task. Here I will summarise the four types of transducer used in small, large and exotic animal work. I will focus mainly on their size, shape and the frequency at which they emit ultrasound waves.

The frequency (that is, how many waves are emitted per second) matters because it directly effects what we can see and how clear the image is. At lower frequencies whilst we are able to penetrate further into the animal to see what we need, the image quality reduces. Whereas at higher frequencies we are not able to penetrate as far into the animal, but due to the higher frequency the quality of the image is much higher.

Convex

The head of a convex prove has a relatively large footprint (the area that makes contact with the skin). This means you can see more of the animal at once in a single sweep. It also has a relatively low frequency of between 2.5 – 5 MHz (which means it emits 2.5 – 5 million waves per second depending on your setting). This results in better penetration, but the trade-off is lower resolution. It is therefore particularly appropriate for use with larger animals such as very large dogs, sheep, goats, pigs or cows.

A typical convex transducer

Microconvex

As its name suggests, the head of a microconvex probe is smaller than that of its larger convex relation. This means several sweeps can be required as less of the animal can be seen at once. As it operates at a higher frequency, its penetration is also reduced, meaning it is less suited for use in larger animals. However, it does have several advantages compared to convex probes: its higher frequency range (between 3.5MHz and 7MHz) means it offers a higher image quality, and its small size means manoeuvrability is improved. These combined benefits mean that – whilst it is more expensive than a convex probe – if only scanning small animals this may be the only probe you ever need.

microconvex probe for KX5600v
A typical microconvex transducer

Linear

Whilst convex and microconvex probes are suited to a wide variety of applications, from pregnancy scans to echocardiography, there are also more specialist probes available. Or example, linear probes are particularly good for providing high quality scanning close to the surface. They have a particularly high frequency range of 6-9MHz and are well suited to tendon scanning, or abdominal scanning on slim dogs, cats, and scanning for eggs or follicles in reptiles, particularly snakes. We would not advise this probe be used for general use in small animals, however.

A typical linear transducer

Linear (rectal)

A variation on the linear probe is the linear rectal probe developed for internal scanning of larger animals (for example cows and horses). It shares the linear probe’s high frequency and high image quality close to the surface to which it is applied. Please note that internal scanning of animals is illegal on cows in the UK without a DEFRA-approved exemption and illegal on horses unless you are a qualified veterinarian.

A typical linear (rectal) transducer

Choosing the right transducer

The right transducer for you will depend on how you plan to use it. It will also be important to consider your budget and any existing equipment you have. You will find that many new ultrasound machines are packaged with a transducer, but equally common is that you will need to specify the transducer you require (if any) at time of purchase.

At PUM we offer both options for maximum flexibility. In addition we are delighted to offer great value packages for those just starting out on their ultrasound journey (take a look here, for example) as well as new machines tailored for use with particular animals (whether you are a breeder, vet, work on-farm or with reptiles/exotics).

If you are in any doubt at all please don’t hesitate to contact our friendly team who will be more than happy to provide advice and information to help you make your choice.

What have we learnt?

  • Transducers – also known as ‘probes’ – are the device you will use to transmit and receive the ultrasound waves which will in turn be translated into an image by your machine.
  • Key differences between transduces tend to relate to their size, shape and the frequencies at which they emit ultrasonic waves.
  • Convex probes scan at lower frequencies, are larger, and well suited to larger animals.
  • Microconvex probes scan at medium/high frequencies, are smaller and are ideal for the majority of small animal applications.
  • Linear probes are specifically adapted for applications close to the surface, with particularly high frequencies. They are particularly commonly used when scanning for eggs or follicles in reptiles, or for the scanning of tendons in other animals.
  • Linear (rectal) probes also scan at a high frequency, and are designed for internal use with cows and horses (although note that internal scanning of animals is illegal on cows in the UK without a DEFRA-approved exemption and illegal on horses unless you are a qualified veterinarian).
  • Key factors to consider when purchasing include your planned use, budget and any existing equipment you might have.

What next?

We hope you have found this first article interesting and a helpful ‘starting point’ in thinking about the different types of transducers available. If you would like to discuss any questions you have we would be delighted to speak with you (with no obligation to purchase a scanner from us). We are proud to offer the experience of professional sonographers with a combined experience of over 25 years and should you purchase from PUM will always be available to answer your questions and solve your problems. Free of charge, whenever you need us, we are here to help.

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