Understanding ultrasound machines for use with animals: An introduction to transducers

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 this short beginner\’s article I’ll be introducing ‘transducers’ to you. Specifically: what are they and how do they work; why we don’t have just one standard transducer, and how you can find out more if you have any questions.

What’s a transducer and how does it work?

When you look at an ultrasound machine set-up, you’ll see that there is the ‘machine’ which will often not only include the system itself but also either a black and white or colour display. This is the ‘brain’ of the system, with the computing power to process the images captured, interrogate (for example, measure) and display them. This will either run from a battery or plug into the mains.

An equally vital component of the set-up is your transducer, which is also known as the ‘probe’. Plugged into the machine, this 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 are found in the head of the transducer, and vibrate when an electronic current is passed over them, creating ultrasonic waves. These ultrasound waves are then focused in the required direction by the ‘lens’ of the transducer.

Similarly when the sound waves are reflected back from the objects they have been directed toward, the crystals vibrate again, with their energy being translated into electric current to be sent back up the wire to the ‘machine’ to be processed and displayed.

Different transducers for different jobs

In the same way that there is more than one type of screwdriver, shoe, or coat, each one developed for a different purpose, so there is more than just one type of transducer. Each one is developed to be particularly good at a particular task.

Some (eg convex probes) are particularly appropriate for use with larger animals. Others (for example micro-convex probes) can be used for small and medium-sized animals as large as a big dog. Some are designed for specific tasks, such as the linear probe which is particularly good for scanning close to the surface, or the linear rectal probe developed for internal scanning of larger animals.

Apart from the size and shape of the transducers, the main thing that makes them particularly suited for one task rather than another is the frequency at which they emit ultrasound waves. Frequency simply refers to the number of ultrasound waves emitted by the transducer per second.

The frequency 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.

For example the convex probe generally operates between 2.5 – 5 MHZ (which means it emits 2.5 – 5 million waves per second depending on your setting). This is quite low but combined with its larger head it will allow us to scan larger animals. Whereas a micro-convex probe operates at a higher frequency (3.5 MHZ – 7 MHZ) with a smaller head, meaning it will be appropriate for the vast majority of smaller to medium sized animal work.

Mechanical or electronic transducers?

You may have heard about the debate in our industry regarding the benefits of mechanical, compared to electronic, transducers. If the transducer has a high crystal count, and is made with high quality components from a true ultrasound manufacturer, electronic ultrasound transducers will give you higher image quality than mechanical sector probes because of their beam-focusing capabilities. However, it is important to balance this with the lower purchase cost of a mechanical transducer compared to an electronic model. PUM continue to stock systems which use mechanical transducers as well as more expensive electronic probes as we believe that within their price bracket they offer an unbeatable cost/quality balance.

What have we learnt?

• Transducers (also known as probes) are the devices which – when applied to an animal internally or externally – transmit and receive ultrasound waves which are processed by the ultrasound machine to produce an image;
• There are a range of transducers, each designed for a particular function;
• They vary based on their size, shape and frequency range;
• This in turn influences the size of the animal they are most useful for, the purpose of the scan, and the likely image quality they will produce;
• Transducers can be divided into two categories: mechanical and electronic. Whilst a high quality electronic transducer will likely offer you better image quality, a mechanical probe from a reputable company may offer sufficient quality for your purposes at a more accessible price.

What next?

We hope you have found this first article interesting and a helpful ‘starting point’ in thinking about transducers. There are lots of terms and topics mentioned here which we will return to in more detail, including: convex probes; micro convex probes; linear probes; frequency and image quality.

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.