Imaging and Simulation Laboratory

Worcester Polytechnic Institute

Ultrasound Training Simulator

Ultrasound is a real-time, versatile and lower cost imaging modality. However, in contrast to CT and MRI, it requires substantial training to be utilized competently. The last decade has seen the emergence of smaller, portable, yet capable scanners, often referred to as Point-of-Care (POC) scanners.

While the majority of ultrasound scans are performed by trained sonographers, there is a rapidly expanding group of new ultrasound practitioners, using POC scanners for whom ultrasound training is not always available, affordable or standardized. In response to this challenge, we have developed a simulator for training in ultrasound scanning, with obstetric ultrasound as the demonstration discipline.

The obstetric ultrasound simulator offers freehand, self-paced scan training on an abdomen-sized curved surface and utilizes 3D ultrasound image volumes. The training follows a structured curriculum, provides software-based assessment and feedback, allows continuous scanning (with five degrees of freedom) and uses ultrasound image material acquired directly from pregnant patients.

GUI

The completed prototype provides training for a standard 2nd semester obstetrics exam, which is focused on orientation to obstetric space and fetal biometry, and which is comprised of a set of 8 tasks, formulated by the American Institute of Ultrasound in Medicine (AIUM).

The standard operating mode of the simulator is the asynchronous mode, for self-paced learning, but the simulator can also operate in a synchronous mode (E-learning or group training), which allows multiple training participants at geographically dispersed locations to observe a demonstration by the instructor in real-time or the scan ability of a chosen learner.

Click below to watch a four-minute video demo of the ultrasound training simulator

HARDWARE ASPECTS

The physical components consist of a sham transducer with tracking sensors, a body-sized
curved surface, overlaid with a coded dot pattern (the Anoto pattern). The tracking is performed with 5 Degrees of freedom, using Anoto pen and pattern for position and an Inertial Measurement Unit (IMU) for orientation.

The hardware is low cost, rugged, and provides precise, absolute tracking without an external reference. The IMU is referenced to magnetic north and the gravitational vector. A unique calibration features allows the IMU orientation data to be referenced to the physical scan surface.

scan tracking system

SOFTWARE ASPECTS

The software development platform is MITK, which allows a rendering speed of more than 25 frames (2D images) per second on a typical recent computer. Ot is used for the user interface design.

software flow chart

The simulator software contains several components, or blocks, including the UI, the virtual reality module, the data manager, the sham transducer driver, the 2D image reslicer, the training assessment and the communication module. The simulator UI is responsible for interacting with the user and managing the communication among the software blocks.

GENERATION OF ULTRASOUND TRAINING MATERIAL

The first step is the acquisition of a series of 2D ultrasound images, using freehand scanning with a convex array transducer with a 6 DoF position tracker to the transducer. All 2D images in one sweep were then stored together to generate a sub 3D image volume. Several sweeps had to be performed to capture the necessary anatomical structures inside the abdomen. In the third step, a stitching plane was calculated to remove the overlapped area between two adjacent sub 3D image volumes.

scan protocol

The extended (or mosaicked) 3D image volumes used in the training were acquired from scanning actual pregnant women. To create extended 3D image volumes from several partially overlapping 3D image volumes, a novel Markov Random Field (MRF). This mosaicking process can be divided into five steps, including sub 3D volumes acquisition, rigid registration, calculation of a mosaicking function, group-wise non-rigid registration and finally blending. The group-wise non-rigid registration problem was formulated as a maximum likelihood estimation, where the joint probability density function was comprised of the partially overlapping ultrasound image volumes. Graph based methods were then used for optimization, resulting in a set of transformations that brought the overlapping volumes into alignment.

STRUCTURED TRAINING

The structured training is divided into 3 modules, where Module 1 introduces basic ultrasound concepts, Module 2, provides the learner with practicing skills related to obstetric orientation, and Module 3 instructs the learner how to perform biometric measurements.

training tasks

For a specific training image volume, the tasks in Modules 2 and 3 must be completed in a fixed sequence and with a specified accuracy. Both the accuracy of the biometric measurements and the time on task are monitored by the simulator, which also provide some guidance, in the form of help functions, for learners with difficulty in performing a given task.

TRAINING VIDEOS

To prepare for scan practice, the learner watches a set of separate, pre-recorded demonstration videos, in which a sonographer shows how each individual task is completed. The training videos provide the basic anatomical knowledge and scan skills about how to identify and/or measure a specific anatomical structure as well as the importance of each individual task.

Click here to watch the training videos

The training videos were recorded by a certified sonographer. During the recording, the sonographer explained the importance of a task, how to perform ultrasound scan, and emphasized the key points of that task while she was scanning the physical scan surface. After all tasks were completed, the video clips were edited in the Camtasia to generate eight training videos, each of which corresponds to a training task.

E-TRAINING

While the development of ultrasound scanning skills will only occur with the individual practice, the opportunity to see demos and ask questions in an interactive forum will enhance the learning effectiveness and minimize frustration with the operation of the simulator. This is especially relevant when learners train alone. A set of simulators can be networked and operate in a synchronous mode, creating an E-learning (or group learning) opportunity.

header2

In the synchronous mode, all networked simulators display, on their own screens, the same movement of the virtual transducer on the virtual torso and display the same 2D ultrasound image. In other words, all networked simulators except one work as passive monitors, displaying the 2D ultrasound image, virtual transducer etc., identical to those on the active simulator, on which a user performs ultrasound scan. In our implementation, we only transmit the sham transducer’s position and, so that the data transmission only requires a very low bit rate.