Objectives

In Work Package 8 the input from the model, the preplanning data from the surgeon and the imaging data will be combined to a specific navigation module that guides the surgeon through the surgery as he/she has pre-planned.

Progress

Registration of MRI patient data

The basis for the musculoskeletal model is MRI data of the patient, having the benefit of allowing to visualize the muscles, tendons and bones without applying radiation to the patient. To make it possible for the surgeon to see where the tools are relative to the MRI during surgery, the data has to be registered to the patient. "Registration" in medical navigation is the process of indicating to the computer what the relationship between the images and the patient is. As a result the computer is able to show the surgeon in real time where the instruments are relative to the patient data.

Figure 1 - Simultaneous visualization of CT and MRI data for a patient. The green instrument is used by the surgeon to indicate positions in the patient. Top row shows CT data, bottom row MRI.

In most cases, registration is based on matching points acquired on the patient to the datasets. These methods rely on bone surface information and are not easily applicable to MRI data where the bone surface is not readily apparent. In case of tumor patients, the point acquisition introduces an additional risk to the patient. The tool to acquire the points has a sharp tip and may inadvertently break through the bone and release cancer cells.

To make it as easy as possible for the surgeon and reduce the risk for tumor patients, the registration of the patient will be improved in the TLEMsafe project by implementing it as an automatic process using pre-calibrated CT scanners and 3D c-arm data. The intra-operative scan show the situation exactly as it is during surgery and the calibration information allows to use the data for navigation without an additional registration step.

The surgeon can concentrate on performing the surgery and spend less time preparing the navigation system for use.

Figure 2 - Example 3D c-arm image showing the femoral head in the acetabulum. Top left shows a digitally reconstructed radiograph based on the data. There is no information about muscles visible, this has to be provided by the MRI.

Intra-operative data is either CT or 3D c-arm data. To be able to overlay the pre-planning data in the MRI onto the CT or 3D c-arm, the MRI data is image fused to the intra-operative data. The main benefit of this procedure is there is no need to provide access to bone to acquire landmarks making surgical procedures less invasive and in the case of tumor surgeries less risky for the patient. The MRI data provides the additional information about muscles and tendons missing in the intra-operative scan.

Integration between planning and navigation software

The planning is performed in the software module developed in work package 4 before the surgical procedure. To be able to use the data in the navigation software, a data exchange layer has been implemented linking the output of the planning software to a prototype version of the navigation software.

Figure 3 - The pre-operative planning software provides the information about the surgical procedure to the navigation

Intra-op review and update

Even though the planning is performed pre-operatively, it may be necessary to update the plan during surgery to be able to react to unexpected circumstances. The navigation software prototype provides a touch optimized user interface allowing the surgeon to check the plan and update it if necessary.

Figure 4 - Intra-operative updates of the planned surgery showing the cutting planes in relation to the bone surfaces.

Helping the surgeon perform his task

During implementation of the pre-operative plan, the surgeon is guided to his pre-planned cuts in the navigation software. The software helps the surgeon by providing him real-time information about the position and orientation of his tool relative to the plane.

Figure 5 - When aligning his tool to the plane, the surgeon needs to optimize three parameters. The software shows each of them separately making it easy to cut perfectly.

By giving constant feedback, the surgeon can perform his pre-planned surgery accurately and with confidence.