Monday, November 5, 2007

Introduction to Mimics

Why Mimics?
Placement of new prosthesis on a patient requires measuring the exact dimension of a patients body. Such measurement involves multiple dimensions and hence a precise method is required. Artistic rendering using manual measurements involves considerable time, effort and expense and are also prone to error. Hence conversion of precisely obtained Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) data to 3D models provides a better alternative to the artistic rendering. These 3D models can then be analyzed using Finite Element Methods (FEM) or can be converted in to physical 3D model by using Rapid Prototyping (RP) for 3D printing or prosthesis creation.

There are various softwares available to perform each of these operations independently but Mimics (Materialise NV, Belgium) provides a one step interface for performing all these operations. It provides a seamless workflow platform and hence conversion from CT and MR data in to 3D models can be performed in less time. It also converts these 3D models in to FEM models and export them to different FEM softwares.

Steps in creation of 3D models
The various steps involved in the conversion of CT and MRI data in to 3D model are
1. Segment the data to obtain only the object of interest
2. Convert the segmented data in to 3D model and
3. Export the model in to various formats as required for FEM or RP.

Mimics modules
Mimics has various modules like Mimics base, STL+, FEM, Simulation, ... In this article, we will evaluate the first three modules.

Mimics base
The Mimics base module allows user to read CT and MRI data in DICOM format. The first step in the 3D model creation process is segmentation. Mimics provides standard segmentation threshold range for various parts like bone, soft tissue, ... and hence the user need not select range for most common parts. Mimics refers to each of these segmented images as “Mask”. In addition, Mimics also provides user the ability to change the threshold range. To obtain only pixels belonging to a particular part, use region growing based thresholding . A 3D model can then be generated for this particular mask.

Editing mask
To edit the mask, Mimics provides mask editors that work in both 2D slices or 3D volumes. The masking involves adding pixels that have not been included in the segmentation process or removing excess pixels which the user judges as not belonging to the part. The masking operation works by painting over pixels that need to be selected and for precise selection, a threshold range can also be set. Similarly, the 3D masking operation performs a 3D erase along a cylindrical axis.

The edited mask can then be converted in to STL format, which can then be read using other CAD packages or can be used for 3D printing using RP or can be FEM meshed using FEM module

The FEM module converts the 3D mask in to a mesh. The mesh can then be refined both globally and locally by controlling individual mesh elements. The edited mesh can then be stored in different FEM file formats that includes most commonly used FEM formats for packages like Ansys, Abaqus, Patran etc.

Please leave your comments at the bottom and if many users request, I can work on a more detailed tutorial on Mimics and post it in the future.

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