What are those lines traveling down my screen?

Scan lines from interference

The main components of an ultrasound probe are all encased within its physical housing. As well as being shaped into a tool that you can comfortably hold in your hand, the physical housing also acts as an insulator against electrical and acoustic interference. Lower quality transducers using cheaper, thinner insulation, are therefore more prone to interference.

This is not to say that high-end transducers do not suffer from interference. The most expensive £30,000 GE 3D/4D probe and the Scan Pad’s £1000 microconvex probe are all high-quality equipment in their own right, yet both can suffer from interference when placed too close to an electrical or acoustic source. Interference is commonly encountered as lines or waves traveling horizontally down the screen, and it’s one of the most frequently encountered phenomenons during scanning, often causing people to worry that their equipment may be faulty. By simply relocating the machine away from emitters of radio or other signals (televisions, mobile phones), the problem is invariably solved instantly.


Scan lines from interference

Above: Scan lines can be seen as waves across the overgained (lower) portion of the above Scan Pad image, due to electrical interference, which have been amplified by turning up the gain too high. Reducing the gain, or moving the machine away from the source of interference, would rectify this problem.


Interference is a problem more frequently encountered by mobile scanners or those who perform pregnancy scanning within their own home, since veterinarians, sonographers and doctors tend to work in an environment which is customised specifically for scanning, free from the usual sources of interference.


What about vertical lines?

Static vertical dark lines, in contrast, are a sign of permanent damage to the transducer crystals. However you move your transducer, these black lines will follow you about as ‘dead zones.’ Being able to actually visualise individual vertical scan lines, however, as in the picture below (particularly to the right) taken from the Edan U50’s phased array probe, is a sign that the transducer has a low crystal count:

Scan lines on Edan U50

This is how transducers in the 1980s used to all look. Now, it’s found only in cheap transducers, or in the case of the U50, in an attempt to make what is normally a £3000 phased array probe more affordable to those looking to do entry-level cardiac imaging. All transducers generate scan lines, but they’re normally so fine, we do not notice them.


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