This week we resume with the series of articles about imaging techniques commonly used in general practice, moving on from X-rays to something else most people are familiar with: ultrasound examinations.
If nothing else, many of us have peered happily at printed out scan pictures of grey blobs while proud new parents-to-be delight in informing us it clearly shows a genius in the making.
In very basic terms, an ultrasound machine works by sending sound waves, of much higher frequency than we can hear, into the body in a beam. These sound waves bounce back and are returned to the machine when they hit the interface between two different tissues (as the tissues are of different densities). The size of difference in density between the tissues determines the strength of the sound wave returned.
For example, where soft tissues (such as the organs) meet bone the difference in the density between the two is great, so large amounts of sound are returned. This information is then used by the machine to formulate an image on the monitor to look at. As sound waves will travel through fluid with none being bounced back, structures such as the bladder or fluid inside the womb show up as black on the monitor.
Within soft tissue structures (like the liver or spleen) there are lots of little changes in tissue density, so the picture will show these in various shades of grey. When the ultrasound hits bone, it is nearly all reflected so appears white (and doesn’t allow you to view anything beyond it).
Unlike with an X-ray, which captures a single picture of a static moment, the ultrasound is continuously gathering data as you move the probe so produces more of a movie. This enables us to visualise, for example, a heart beating and even focus on an individual heart valve opening and closing. Therefore not only can information be gathered about the size, shape and structure of an organ but also, in certain cases, we can learn something about its function.
A special type of ultrasound known as Doppler can be used to measure the speed of blood flow in vessels. Again, pregnant ladies and those involved will be familiar with this. The “whoosh, whoosh, whoosh” when the midwife places a probe on your tummy in a routine later pregnancy check is to pick up the blood flow in the baby’s heart.
When used in conjunction with a larger machine it can be incorporated with the visual image and used to look in detail at the heart for problems such as a leaking heart valve.
Another advantage of ultrasounds is that, unlike most X-rays, in pets the majority of ultrasound examinations can be done without the need for sedation. In addition, they do not carry the safety risks that X-rays do. Ultrasounds are increasingly being used more and more in general practice to examine both the heart and abdominal organs. However, there are still limitations, such as looking at bony structures like the spine and some gut problems, and often a combined approach of both ultrasound and X-ray are used to complement each other and provide the most comprehensive information.
Next week we finish this series by looking briefly at the most common general conditions in practice where an ultrasound might be used.