ADGA Presentation – Ultrasound Basics

Each section is transcribed below its respective video, in case you prefer to read than listen. If you are happy listening to the audio, you can scroll past the text and just press ‘play’ on the next video.

About Catherine

 

My name is Catherine, and I’m a Sonographer in the UK. I’ve been scanning animals for 9 years, and I enjoy working with this amazing technology so much that a few years ago I actually took a year out to do my Masters Degree in Medical Ultrasound.

I’ve recently started a new project as a Research Sonographer at Imperial College, looking at ultrasound and artificial intelligence among other things, and that helps to keep me up to date. I do this part-time, and the rest of my time I dedicate to veterinary ultrasound. That can involve working with vets, breeders or farmers on a variety of applications from heart scanning, to meat grading, and most commonly pregnancy scanning.

 

Section 1: Transducers

 

This presentation is going to be a slightly expanded version of the workshops I ran at the American Dairy Goat Association Convention in Idaho. These workshops were practical in nature, so that everybody could try out the controls as we went along, so it may be that you would like to have your scanner with you so that you, too, can find these controls on your machine.

For those who are totally new to ultrasound, I wanted to first explain the different types of transducers (or probes) you can get, because “what probe should I pick?” is a really common question.

The two main probes for abdominal scanning are convex and microconvex. A convex probe will have a larger surface area – called a ‘footprint’ – and it will also use lower frequency ultrasound. This means that its image resolution is poorer than a microconvex probe, but its ultrasound waves will penetrate further. This is the same as in audible sound; you can hear lower pitched sound, the base, through ceilings and walls when you often cannot hear any of the melody.

The microconvex probe is smaller in size and emits higher frequency sound waves. This means that you can achieve sharper, higher resolution images with this probe, but it may struggle to penetrate very large animals. I personally use the microconvex probe for almost everything – I find it so much more maneuverable – but similarly, there are people who are already accustomed to the larger probe from previous machines they have owned who just cannot get along with a smaller one. If you’ve been scanning with a machine bought from somewhere like eBay, it will almost certainly have come with the larger probe, because these are cheaper to manufacture.

Transducers house crystals that vibrate when an electric current is passed across them, sending out wavefronts. The opposite also occurs, so when these sound waves reflect off interfaces in the body and return to the transducer, these sound waves or vibrations are converted back into electrical signals which can then be processed.

All of this work is done inside your ultrasound transducer, and that is why it is such a valuable part of your ultrasound machine. The crystals inside also make it very vulnerable to damage, so you must avoid knocking or dropping it. When a crystal is damaged you will see a black line down your screen, arising from that area of damage. It is simply not cost-effective to repair, so you’ll have to put up with it or keep going until enough crystals drop out that you just have to replace the probe. Unfortunately this will happen naturally over time, but if you care for your probe, it should last many years.

I have a couple of tips to prolong the lifespan of your probe. The first one is to get into the habit of freezing your image between scans. The freeze button is the one with the snowflake. This means that you are not making your transducer work hard scanning the air for several minutes between scans. The second tip is to keep your transducer clean, and do so with an antibacterial rather than an alcohol wipe. Over time, alcohol will dry and crack the transducer’s membrane.

 

Section 2: Probe orientation & good contact

With special thanks to Terry

 

This section is on how to correctly orientate your probe. If you’ve already been scanning for a while, you may wish to skip this section.

Take a close look at your probe and you should notice either a dot or an indentation on one side. Now look at your ultrasound monitor; it will also have some kind of marker on one side, usually a dot or small square. These correspond and help you to orientate yourself correctly. Get into the habit of always holding your transducer the same way – most people will place their thumb on the dot. This way, when you slide across the animal’s body to the left, your image will also move to the left. Being consistent in how you hold your transducer will massively increase the speed at which you brain is able to connect your physical movements to what you are seeing on screen, so that scanning soon becomes natural – something you don’t even need to think about – rather than constant frustration.

The other important thing about scanning technique is achieving good skin contact. This is done with the use of plenty of gel, and gentle pressure. The larger probes can be more difficult for this because the edges often roll off the skin and result in black voids down the sides of your screen where you are not in contact with the skin.

Quite a few people asked me about gel at the ADGA workshops. There’s no one brand I can recommend above all others, so my advice would be to try a few out from eBay and compare them. You don’t want one that’s really watered down and runny. Your local vet practice may be able to recommend the one that they use, or you may know a wholesaler who can also access ultrasound gel. Ultrasound gel is formulated to have the same acoustic properties as water (given that this is also what makes up the majority of the body), so there aren’t many things you can substitute it for, but in an emergency you can use water itself. However, it will quickly evaporate or be absorbed so you will have to keep reapplying it. Water can also be mixed with gel when you have a particularly hairy goat that you cannot shave.

The first landmark you should look for is the bladder, and this also a great way to test that you have good contact and the right amount of pressure. The bladder should be nice and circular; too much pressure and you will squash it into a kidney bean shape, which is a sign that you should ease off a little.

The bladder should appear as a pure black circle area. It is termed “anechoic,” meaning it does not return any echoes. Ultrasound passes freely through it. An exception might be if your goat had cystitis, where the bladder may look cloudy, and/or bladder stones, but these are rare in does. If you are using a lower end scanner you may run into a false positive here, so don’t immediately panic if the bladder looks cloudy or shadowy, particularly if this occurs with multiple animals. We think of ultrasound beams as being paper-thin, but in fact they are three dimensional and there’s a thickness to them that we cannot see. Cheaper transducers have thicker beams that can impinge on surrounding tissue, erroneously placing these reflections inside other structures.

The opposite of an anechoic structure is an echogenic one, and examples of this are bone and gas, which are highly reflective and show up bright white on ultrasound. Ultrasound cannot penetrate very well through them (which is why we avoid the gassy rumen when scanning), and we often see shadows behind them where the ultrasound energy simply cannot penetrate.

 

Section 3: Using the bladder as a landmark

 

The bladder is found by angling your transducer towards the back of the animal. You can use one of two locations; the favorite place is up inside the right leg pit, avoiding the rumen which is located further to the left, but another spot for very early pregnancy is just in front of or behind the udder, again tilting your probe backwards. The success of this does depend on the breed of goat and type of udder, and we encountered a few at the ADGA Convention for whom this wasn’t particularly suitable.

Once you’ve found a good location you don’t need to move your probe around a lot – imagine it as being like a flashlight. You can tilt your wrist and shine it in different directions without actually having to move from that one place.

The bladder is an excellent starting point because early pregnancies will be seen around it. A gestation sac is filled with amniotic fluid so will also be black inside, but it has thicker walls than the bladder. The sac or sacs will also be smaller than the bladder in early pregnancy, and as the pregnancy progresses, you should be able to identify the white spot of an embryo inside. This is the first point at which you can confirm pregnancy; merely seeing fluid is not sufficient, because it could be a false or failed pregnancy. To confirm fetal viability, you must identify a heartbeat or fetal movement.

After around 60 days, the uterus drops, and it will no longer be in such close proximity to the bladder. At this stage, finding the kid through all of the placentomes can be a real challenge!

 

Section 4: Basic controls

 

Gain

Once you manage to get an image, there are a number of controls you can use to optimize it. The one that people tend to become familiar with first is gain. Gain amplifies the returning echoes. Turn it up to make the image appear lighter on your screen, and turn it down to make it appear darker. The idea is to have fluid-filled areas which should be black as black, but everything else should show in various shades of grey. It is a mistake to obsess over the number down the side – for example, that your gain is set at 63. It should never be the same with every scan on every animal. It’s a control you should be adjusting all the time. Use your eyes for this, rather than worrying about a meaningless number.

 

Depth

Another important control to optimize every time is depth. In an early pregnancy, it is likely that your depth will start out too great, with the gestation sacs tiny little things at the top of the screen. This is just making life so much more difficult for yourself. If you reduce your depth and use all of your imaging area to visualize the sac, you will be able to diagnose pregnancy with far greater confidence, as well as see heartbeats much earlier.

In more advanced pregnancies, it is important to increase your depth in order to get as much of the kid on-screen as possible.

 

Frequency

I discussed frequency with regard to transducer selection earlier, but most modern transducers will also allow you to adjust your frequency within a set bandwidth. The type of transducer that won’t is the mechanical sector transducer, the type that you feel vibrating in your hand as you scan.

With the Scan Pad, simply press ‘Freq’ which is a touch screen button on the bottom left. You can choose from ‘Pen’ (for greater penetration), ‘Gen’ for general, and ‘Res’ for high resolution. The Scan Pad also has tissue harmonic imaging, prefixed with TH, which in summary means that you can send out lower frequency ultrasound that will penetrate, but your transducer only processes signals which return at a higher frequency – called harmonics.

 

Focal zone

The last control I wanted to emphasize is your focal zone. The Scan Pad applies quite a lot of auto-focusing, so this is not as important on this machine, but on other systems it can make a huge difference. The focal point is usually marked by a small arrow, and the beam narrows at the level of the focal point, improving your spatial resolution in this area. After this point, the beam then rapidly diverges and resolution deteriorates.

If you are scanning quite deep, you therefore need to adjust your focal point further down your screen. It should always be set at or just below your level of interest. If you leave your focal point permanently stuck at the top, you’re always scanning out of focus – never getting the most out of your machine.

There are, of course, many more controls that you can adjust – such as your dynamic range and grey scale maps – so feel free to get in touch if you need help with any of these once you’ve mastered the ones I’ve already discussed.

 

Section 5: Ultrasonic Safety

 

The final section is on ultrasound safety. It’s not a popular topic – in fact, it’s rarely discussed at all. We all like to think of ultrasound as being totally harmless, and indeed it does enjoy a fantastic safety record, but that’s only because it’s historically adhered to international safety regulations and been used by people who have been trained to use it safely. That is starting to change – you can now buy ultrasound equipment online from companies located in areas of the world that do not have the same standards as North America and Europe, and start using it without either training or support.

We know that ultrasound has the potential for harm because animals from mice to chimpanzees have sadly been experimented on in the past and demonstrated evidence of tissue damage, particularly hemorrhage. While this is unlikely to cause lasting damage to a healthy adult, there is one group that is particularly vulnerable – the unborn. The blood supply of a fetus is not as well developed as that of an adult, and it cannot dissipate heat as easily. It is also particularly vulnerable to heat rises – if you think back to when I mentioned acoustic shadowing behind bone, this is due not only to bone’s high reflectivity but also due to the fact that it strongly attenuates ultrasound energy, converting it into heat. Once the fetus develops further and bone begins to harden, we are scanning directly over that bone.

To reduce the risk, particularly to the unborn, the FDA stipulated in the 1990s that two indices be displayed on screen at all times: the mechanical index, which will be displayed on your monitor as ‘MI,’ and the thermal index, displayed as ‘TI.’ This allows users of ultrasound to monitor the level of energy they are putting into the body, and control the risks. If your scanner does not display these values onscreen, not only is it in breach of FDA regulations, but it also means that you cannot prove that you are doing your legal duty – because, ultimately, the law in the UK, USA and Canada, rightly or wrongly, all put the legal responsibility with the user. If you’re scanning your own goats, it’s your choice if you want to do so blinded to any potential risk – you’re not going to sue yourself. But if it’s legal to scan the animals of others in your State and you intend to do so, or if you’re a veterinarian, you leave yourself in a very vulnerable position were anyone ever to accuse you of doing harm to their animal, because you are unable to prove otherwise.

This is not said to scare people, and in reality, the amount of energy imparted by entry level scanners is likely to be very low. But the main question I would ask myself when buying a scanner is – if the seller is willing to sell me something that breaks the safety regulations of my country, is that really a company I want to be doing business with?

If you do already have one of these machines, there are things you can do to reduce the risk – somewhere on your machine should be a control called ‘power’ or ‘acoustic power.’ Keep this as low as possible. If you can get a good image at 60%, there’s no need to have it at 100%. Avoid prolonged scanning times, particularly over fetal bone, but with goats, you’re unlikely to have a mother patient enough that you can keep your probe in the exact same spot for several minutes anyway.

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