Can wireless ultrasound probes be used for professional canine pregnancy scanning?
Wireless ultrasound probes (or ‘ultrasound wands’) went through a temporary boom in popularity in the UK, before their limitations quickly became obvious. Now, many people who originally invested in wireless scanners are looking to upgrade to higher quality systems. But is there a role for these wireless probes, and if so, what is it? I put a typical wireless ultrasound probe to the test against the VIS Scan Pad to find out the key differences, and examine why not all 128 element transducers are created equal.
Bladder scan in a Dogue De Bordeaux – Scan Pad
In the below clip, the Scan Pad shows the bladder as a dark, anechoic (echo free) structure. This is because it is fluid-filled (urine), and sound waves pass through fluid without returning reflections.
The walls of the bladder are clearly seen, and the gas-filled colon is also seen below.
Bladder scan in a Dogue De Bordeaux – Wireless Probe
The wireless probe is quick and easy to use, and saving images and video clips to your phone or tablet device is a breeze. However, there are key quality differences between this device and a professional ultrasound scanner like the Scan Pad. These are:
- Frequency. Even in a larger dog like this Dogue De Bordeaux, the higher frequency microconvex probe of the Scan Pad (even when set on ‘Res’ – the higher resolution setting) had no problems with penetration. The lower frequency wireless probe provides a much coarser image, in part due to its lower frequency. Most professional canine scanners opt to scan at higher frequency ranges of 5-7MHz, with the option to adjust frequency up or down depending on the animal, as opposed to being restricted to a 3.5MHz fixed frequency delivered by a wireless probe.
- Dynamic Range. The dynamic range of the wireless probe is very limited when compared with the Scan Pad. On the Scan Pad clip, it is easy to pick out the areas of gas under the bladder. On the wireless probe, it’s much more difficult to discern these from the overall background. Subtle differences in echogenicity cannot be picked up on this machine.
- Filtering. The wireless probe clearly has very little by the way of noise filtering. The random movement you see all around is most likely noise generated by the transducer itself, combined with cheaper casing and poor transducer insulation. It reminds me of the noise or ‘snow’ of old television screens, when they weren’t picking up any signal. Do you also see how wide each of those ‘points’ are? They’re more like horizontal lines, and that also gives some clues as to the probe’s poor lateral resolution.
- Beam width. In a healthy animal, the bladder should be clear and black. This can be seen to be the case in this dog with the Scan Pad. With the wireless probe, however, the bladder looks cloudy – at times, it even appears ‘sludgy’ towards the bottom. This is because the wireless probe’s ultrasound beam is poorly focused and very wide in this plane – its slice thickness – so that structures outside of the bladder are caught in the crossfire and incorrectly ‘placed’ into the bladder by the ultrasound machine. As clear black fluid in early gestation is an indication of a healthy pregnancy and cloudy fluid can indicate resorption or pyometra, extra care should be taken when using a wireless probe for anything other than a yes/no pregnancy confirmation in later pregnancy.
Late pregnancy scan in a Shih Tzu – Wireless Probe
I next performed another comparison scan, this time with a heavily pregnant (and unfortunately quite wriggly!) Shih Tzu. Again, the wireless probe provides a very homogenous image, making it much more difficult to pick out individual structures. Nevertheless, it is perfectly adequate to confirm the presence of a heartbeat, and the spine and rib cage can be seen.
Late pregnancy scan in a Shih Tzu – Scan Pad
By no means a perfect scan on a little dog who had little desire to sit still, the quality provided by the Scan Pad is clearly far more diagnostic. The chambers of the heart can be seen, and the body of the pup can be more easily distinguished from surrounding tissue.
Late pregnancy scan in a Shih Tzu – Apogee 2300
As a final comparison, I scanned again on the Siui Apogee 2300. This is a very high end (over £15,000) machine, and not the type of machine most mobile scanners or dog breeders would use. It was interesting to see that the gap between the Scan Pad and the Apogee 2300 was actually not as large as one might imagine. The subtle differences in tissue characteristics are much clearer on this machine, and yes, the Apogee delivers far higher spatial resolution – the detail you can see in the heart is breathtaking – but from a diagnostic point of view, there is no information that this machine gives you that the Scan Pad does not. This is encouraging for professional mobile dog scanners to know that the same level of diagnostic accuracy for pregnancy detection delivered by a top-of-the-range veterinary grade machine can be achieved with a machine priced under £3000.
The wireless probe is a relatively cost-effective tool for a yes/no pregnancy scan at home on your own animals. It is not recommended as a professional tool for scanning other people’s pets.
It is recommended for use in later pregnancies only (at least 35 days+) as it has the potential to deliver confusing results in early pregnancy, particularly with regard to false positives or false negatives in confirming viability. It is unlikely to have adequate spatial resolution to pick up foetal heartbeats below 35 days’ gestation. It does not have the resolution or quality to confirm the health of an early pregnancy, particularly due to its beam width, and any worried pet owner without access to a professional-grade ultrasound machine in the hands of a well-trained individual should seek the advice of their veterinarian.
Have you had any experience using a wireless ultrasound probe, positive or negative? Contact us to share your story!
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