Objectives

To obtain quantitative data of the functional performance of healthy individuals during various activities. Different methods will be used to obtain as much data as possible that is related to functional activity. This data is of utmost importance as they can be used to validate the musculoskeletal model predictions in general and can subsequently be used to quantify the differences (for example in muscle activity) between subjects and can serve as a validation basis for the subject-specific models.

In addition, the marker-free optographical method to measure kinematics is developed, tested and validated so that it can be used for patient measurements in Work Package 5.

Progress

Healthy subject measurements

Work Package 1 is the first step of the TLEMsafe project. Its tasks result in data that forms the basis for the rest of the project. The primary tasks of WP1 lie in the field of human movement analysis. This is a field of science that specializes in tracking human movement with state-of-the-art measurement techniques. These are, for instance, a 3-D infrared camera system, force plates in the floor, and wireless measurement of muscle activation (called ‘electromyography’). These measurement techniques were used to record movement and force generation of the muscles during all kinds of activities of daily living, such as walking, stair negotiation and getting up from a chair. All functional measurements were performed by UMC St Radboud. The figures below illustrate what such a movement analysis looks like.

Figure 1 - Healthy subject standing on two legs (left) or standing on one leg (right). Movement (wireframes) and forces (red arrows) were recorded in this session suring each of the movements.

Figure 2 - Getting up from a chair was recorded using three forceplates: one under each foot and one in the seating area. This allows us to fully capture the movement and forces, so that a thoroug analysys is possible. This data is of utmost importance to validate musculo-skeletal models.

Figure 3 - Electromyography recordings of three muscles of the leg during walking at +30% comfortable walking speed: Tibialis Anterior (top), Gastrocnemius Lateralis (middle) and Gluteus Medius (down).

Oxygen consumption, maximum strength tests and positron-emission tomography were also part of the measurements. In the TLEMsafe project, we use this data as an input for subject-specific model ‘validation’. ‘Validation’ in this case means that when we create subject-specific models of healthy subjects (see Work Package 3), we then compare functional predictions of the model with the corresponding actual outcomes from human movement analysis.

The 4-D scanner prototype

One of the goals of the TLEMsafe project is to improve patients’ comfort during functional measurements performed before and after the surgery. The kinematic measurements are usually conducted using the motion capture (aka. mocap) systems, using retro-reflective markers to track segments’ movement. A number reaching dozens of markers is attached to the skin. Placing them takes a significant amount of time and affects patients’ comfort of movement during the measurement. Within the TLEMsafe project, a marker-less motion-tracking system is being developed for convenience of the patients.

The 4D scanner is being developed at the Warsaw University of Technology. A single-directional measurement head consists of a projector and a camera, and is able to capture 3D surface of the object with 60 frames per second (Figure 4). It uses a structured light projection technique and fringe image analysis methods to reconstruct a 3D shape of the surface from a single captured frame.

Figure 4 - Single-directional measurement using fringe pattern projection.

The surface coverage is extended by utilization of multiple viewpoints (Figure 5). High captured surface coverage allows to track kinematics of measured object. Kinematic description of subject’s lower limbs acquired with the 4-D scanner is going to be able to drive the TLEM mechanical model as well as output data from marker-based systems.

Figure 5 - Two-directional measurement with special spectral separation of measurement heads.

References

Janusz Lenar, Robert Sitnik and Marcin Witkowski, "Multidirectional four-dimensional shape measurement system", Proc. SPIE 8290, 82900W (2012); http://dx.doi.org/10.1117/12.907706