Introduction
Hydrolocation is used during out-of-plane approaches and in-plane approaches to deep nerves. Elastography visualises strain or relative displacement . Elastography exhibits patterns not seen on B-Mode imaging such as: inadvertent distal spread, split or bifid spread and a rebound phenomenon whereby fluid is reflected from tissue walls and visualised twice. Our objective was to determine how often
trainees identified the three aforementioned strain patterns omn B-mode compared to elastography.
Methods
We conducted 24 interscalene block and 24 femoral blocks on both sides of two soft embalmed cadavers using 0.25ml. 0.5ml and 1ml volumes. Twenty trainees assessed 20 videos of B-Mode and matched elastography blocks. We compared trainee results to that of two experts. Trainees recorded whether they identified one or two patterns on B-Mode and matched elastography videos. We measured tissue displacement on B-Mode and elastography images using ImageJ.
Results
Experts identified 13 (54%) additional strain patterns with femoral block (6 bifid, 6 rebound, 1 distal) and 14 (58%) additional strain patterns with interscalene block (13 rebound, 1 distal). For femoral block, trainees identified 539 tissue changes using B-Mode and 687 using elastography (27% more). For interscalene block, trainees identified 531 tissue changes using B-Mode and 624 tissue changes
using elastography (18% more). Experts identified between 23% and 26% more changes on elastography compared to B-Mode ultrasound.
Discussion
We have shown that trainees identify tissue change more often using elastography compared to B-mode ultrasound
Conclusion
Our results indicate that trainees and experts identify more tissue changes using elastography compared to B-Mode ultrasound.
Fuison Elastography mode is more sensitive than B-mode in detecting tissue displacement from using test dose 0.25ml-1ml.

How low can you go? A study comparing the accuracy of B-Mode ultrasound and strain elastography in the recognition of femoral and interscalene test doses in the soft embalmed Thiel cadaver model by anaesthesia trainees