My question is how to measure very small movements of a needle and syringe when injecting. When doctors inject local anaesthetic, they always aspirate (suck back) first to make sure they are not in a blood vessel. My contention, particularly if the aspiration is done single-handed, is that the change in direction of forces on the needle/syringe combination whilst aspirating causes significant movement of the end of the needle - probably several mm - which negates the purpose of aspiration in the first place.
I want to do an in vitro study, in which I have a needle and syringe combination and inject into a piece of meat or similar - and then get volunteers to aspirate / inject under 3 circumstances:
- stabilise with other hand and inject directly
- stabilise with other hand, aspirate and then inject
- aspirate with one hand and then inject
I have hit a block in terms of finding a method of measuring these movements of the needle tip down to maybe 0.1mm. I thought that an accelerometer might be the way but have not found anything small enough to be mounted on the needle tip.
The only other way I thought of doing it was to use a camera mounted side on to the tip of the needle which would be protruding through some sort of artificial 'skin' and then have a graticule calibrated to measure the distance moved.