This was a single site, prospective, pre-test-post-test, randomized study conducted after Institutional Review Board (IRB) approval. Thirty subjects, including medical students, practicing anaesthesiologists and anaesthesia residents in training at the Penn State Hershey Medical Center, were recruited by formal email invitation to participate. Written consent was obtained from each participant before their inclusion in the study and each participant completed a pre-study form. Once enrolled in the study, participants were given 10 minutes to familiarize themselves with both the ultrasound equipment (SonoSite, MTurbo, Bothell, WA, USA) and the phantom model (MiniSim™ Upper Extremity Series, Life tech Inc., Stafford, Texas, USA). They also viewed a pre-recorded video demonstrating the task they were to perform. As a pre-test, participants performed the required Needle Insertion Accuracy (NIA) task 3 consecutive times and were assessed using a scoring form adapted from the Mayo Clinic. After completing the pre-test, participants were randomly divided into two groups, experimental and control, by a computer-generated randomization list (SAS Institute, Cary, NC). Participants were blinded to their group assignment.

Previously, we have reported details of the new learning tool. Briefly, all spatial movements occur in three dimensions which can be labeled the x-axis, the y-axis and the z-axis. A video camera records movement in two axes. By placing a second video camera at 90 degrees to the first camera, the third axis can be recorded as well as one axis in common with the first camera. Video recordings are stored electronically on a hard-drive and can be reviewed individually or in combination, at normal speed, or slowed if necessary. Still images can also be obtained.

The experimental group was allowed to practice the same pre-test task using the same ultrasound machine and phantom model. On a single computer screen, they were able to visualize their hand and needle movements along with the position of the ultrasound probe. The control group was allowed to practice the same pre-test task using the same ultrasound machine and phantom model but without the added visual aid. Both groups were allowed to practice their pre-test tasks for a maximum of 30 minutes, and recorded their self-assessment as proficient or not proficient at that time. Both groups then performed the post-test, which was the same task used for the pre-test, and each trainee was evaluated using the same scoring tool. To avoid subjective variations and inter-rater variability, all evaluations were recorded by a single blinded investigator.

Statistical analysis Pre- and post-test mean scores (ranging from 5 to15) were analyzed using statistical methods to determine whether this new learning tool improved NIA skills required with USRA. Pre-test and post-test scores (ranging from 5 to 15) were obtained in triplicate and averaged to produce a representative assessment for each participant. The primary endpoint was change in NIA score from baseline, i.e., the score difference obtained by subtracting the mean pre-test score from the mean post-test score. A sample size of 15 subjects per group (experimental and control) provides 80% power to detect an effect size of 1, based on a two-sided t-test with a 5% error probability (calculated using G\*Power version 3.1). Analysis of the primary endpoint utilized a two-sided, two-sample t-test at the 5% level of significance. Secondary analyses evaluated the intervention effect on novice trainees, and trainees with prior USRA experience. Score differences for individual NIA skills (movement, alignment, approach, target, location) were also analyzed.