Why ultrasound transducers matter
Sonographer Yvette Lovis and I scanned recently some cows at the Museum of Kent Life, having scanned their sheep in 2015.
Afterwards, they asked us if we’d check their pigs for pregnancy. We advised them that we may not be able to see anything, but that we’d it a go anyway. We were not successful.
Yesterday in our Facebook group, I asked those recently trained in pregnancy scanning to explain why it was that we were unable to obtain useful images using the equipment we had brought along for scanning cows. Most people knew it had to be something to do with the probe design, giving the following suggestions:
- The transducer we had with us would give a limited field of view. This is true – our linear probe would give a straight, narrow imaging area, whereas a convex transducer provides a sector image, which widens with depth. However, this would be a mere inconvenience, and is not the reason why our rectal linear probe would not work for abdominal scanning on pigs.
- The transducer is suitable for cattle scanning only. Not so! Linear rectal probes are also excellent for scanning snakes and other small reptiles (as are standard linear probes) – check out the video of a Brazilian Rainbow Boa’s heart below, taken with a linear probe.
The most important reason was to do with frequency. Although cows are clearly very large animals, when scanning rectally, you are only a few centimetres away from the uterus. For this reason, you can afford to use a very high frequency transducer (8MHz and greater), for much greater detail. The transducer we were using for the cows was multifrequency, and did go down to 6MHz. We’d seen some cute pink pigs on the way in, and assuming it was these they wanted scanned, said we would give it a try – 6MHz may have worked.
The pigs the farm actually produced for us to scan were twice the size, and our high frequency probe simply had no chance of penetrating through their layers of fat. We have promised to return with a low frequency large convex probe for the pigs!
February 17, 2022
March 13, 2020