TSI feature on your Scan Pad: what it is (and why you don’t need it!)

The Scan Pad is a basic black and white portable ultrasound system, but is equipped with a wide range of functions and the ability to customise its operation for more advanced users. This is vital for researchers, scientists and veterinarians working in highly specialised areas. It can even be important for the serious lay scanner, who may, in time, expand the scope of their work to cover a wide range of species. The ability to customise one’s machine to different species and applications is clearly very important.

For those just starting out with scanning – dog breeders, for example – the number of menu options can feel overwhelming. A glance over the manual can be confusing for the novice: you may feel like you have finally grasped the main controls, and then read about something which sounds so completely alien you start to wonder whether you’ll ever truly master pregnancy scanning at all!

One of the controls people tend to come across after a few months with their Scan Pad is TSI, or Tissue Specific Imaging. When people enquire as to what this does, the short answer is that you will almost certainly never need to use it – and unlike most controls where it’s good to experiment with them, this is one of the few that it would be unhelpful to adjust without knowing what you are doing.

 

So what is TSI?

The TSI setting is what tells the machine what speed to assume that the sound waves are travelling at inside your client/patient. By default, the machine assumes this to be the average speed of sound in soft tissue (1540 metres per second), but there are situations whereby this assumption would be incorrect. Sound travels more slowly than 1540m/s in fatty tissue, and a lot more quickly than 1540m/s through a dense medium like bone. For this reason, some technicians may choose to adjust the machine’s assumed speed of sound based on what they are scanning, but this is only useful in cases where the composition of the subject is well known – an unlikely scenario when scanning animals.

Realistically, the miscalculation that may result from a particularly fatty patient is likely to be negligible. Its only real impact would be when performing measurements, and the more fat one scans through, the more inaccurate the subsequent measurement will become.

This does have potential implications for specialist applications like ultrasound meat grading in sheep or cattle, where accurate measurement of fat depth and muscle thickness is very important. If the speed of sound is assumed to be traveling at 1540m/s, but is in fact traveling at 1430m/s through fat, a hypothetical 10cm fat thickness would be overestimated by 0.77cm. If you’re interested in the numbers behind this, click here (requires full or partial AUA membership to view).

Understanding this is important in interpreting artifacts that arise due to incorrect assumptions made by the ultrasound machine about the speed of sound.

In Summary

TSI may be useful to adjust for scientists scanning specific materials or phantoms with a different speed of sound to 1540m/s, or for certain specialist applications, but for the general user, it is not helpful to adjust this setting.

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