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Objective:
Ultrasound (US) guided biopsy requires visual-spatial understanding of the 3D anatomy with respect to the 2D US image, and hand-eye coordination for accurate localization of the target lesion and positioning of the biopsy needle. Patient safety and biopsy success heavily depends on the operator's expertise. Simulation can help achieve clinical proficiency sooner while in a safe controlled environment. Unfortunately, most mannequin based simulators often have an unfavorable trade-off between anatomic realism and cost. We sought to develop a low-cost high-fidelity alternative making use of a smartphone and personal computer.

Materials and Methods:
Virtual phantoms including a torso, tumor and liver were created to simulate US-guided liver biopsy. A virtual biopsy needle and US transducer were created using 3D computer aided design software [3ds Max, Autodesk]. These virtual objects were imported into a game engine [Unity, Unity Technologies] which ran the simulation on the user’s computer. The trainees would interact with the simulation using their smartphone. A smartphone application [Unity 5 Remote, Unity Technologies] was used to capture the inertial measurement unit (IMU) data from the device. Motion of the phone would control the motion of either the biopsy needle or the US transducer. The interface initially starts up with a tutorial. Users can practice gaining familiarity with controlling the virtual instruments before attempting a biopsy. Additionally, a transparency slider is available for the user to fade out the virtual anatomy to accentuate the underlying tumor. This helps the user to develop their visual-spatial instincts as they try to map their 3D understanding of the anatomy to the 2D US display. Upon beginning a biopsy attempt, the trainee would first scan with the virtual US transducer to localize the target lesion. Then the user would advance the needle making small sliding or sweeping motions parallel to the US scanning plane until the needle was well visualized and located at the desired position within the target lesion. The user would then deploy the needle and a post-fire path was simulated through the lesion confirming a successful tissue sample.

Results:
User evaluation and feedback sessions are currently undergoing. Initially, trainees (n = 5) were given a demo of our simulator and afterwards completed a brief survey based on a Likert scale (1: strongly disagree, 5: strongly agree). Participants believed that they had a better appreciation of the anatomy involved in the procedure, and that the simulation experience was a valuable use of their time (4.6/5 and 4.4/5 respectively).

Conclusion:
We present a prototype simulation platform that has the potential to provide high fidelity simulation experiences at a low cost. Our implementation on a virtual phantom and end-user operation with laptops and smartphones may be expanded to simulate training of additional US-guided procedures.