Machine Design

Merging medical imagery with CAD

Authored by:
Jim Voegele, P. E.
Jacob Crabtree, co-op
Ethicon Endo-Surgery
Cincinnati, Ohio
Edited by Leslie Gordon,
[email protected],
Twitter @LeslieGordon

Ethicon Endo-Surgery

Obesity is a problem in the U. S. and even software has joined the battle to eliminate it. For example, a Dicom image-processing program called Slicer lets users import positron-emission tomography-computed tomography (PET-CT) scans into a CAD package for further manipulation of the segmented image. (Dicom, short for “digital imaging and communications in medicine,” is a standard for handling, storing, printing, and transmitting information in medical imaging.) But how is putting medical imagery in CAD useful in the battle against obesity?

It is helpful to note that a tissue known as Brown Adipose Tissue (BAT) plays a large part in burning calories. To study BAT in regulating metabolism and, thus, help reduce obesity, it is helpful to identify BAT’s volume and anatomical variation.

Most medical-imaging technologies can segment tissues for further study, but they do not contain the analytical capability of CAD programs. Slicer, a free and open-source software package for visualization and medical-image computing, can segment BAT from a PET-CT scan and then import it into 3D CAD software.

Here is how using Slicer typically works:

First, technicians send the designer or researcher PET-CT image files on a CD that contains individual PET and CT folders. Each folder holds multiple files comprising the slices captured. Also on the disc is a viewer that lets users see the images. We use a freeware program downloaded from Slicer’s site, selecting Slicer3 3.6.2010- 08-23 for Windows. The download takes just a few minutes.

Next, we open the Slicer program and select the Dicom directory from the browser. A slide-bar adjusts the transparency of the PET and CT scans. The 3D Slicer files (xxx.nrrr) can be saved at this point.

Upon first opening the Editor function, a dialogue box opens that lets users select a color table for selecting tissue colors. Here, users can label the images created. With the PET layer active, one selects the “Threshold” tool and then selects a threshold limit using the Range slider. All tissue with a threshold in the range that was input is now color labeled, for instance, green.

The user identifying the labeled BAT islands uses mouse controls to adjust the sagital, axial, and coronal views to reveal the volume of interest. An “Identity Island” tool can give each island a distinct color.

A “Make Model” tool segments the BAT islands. Users choose the colored label corresponding to the island they want to model. Naming the model and selecting “Apply” displays the 3D view. Users repeat this step for each island they want to use to create models.

Once all the needed islands are made into models in Slicer, users can export the models as .STL files into CAD.

To create a composite of BAT deposits, one must capture anatomical references. The axial, coronal, and sagital views have a slider that lets users see each slice in the volume set giving 3D coordinates. Users now know the special thickness of each slice and the number of slices between anatomy and tissue reference points.

Users can import the segmented image into any CAD package such as SolidWorks 3D that accepts .STL files. When users import the .STL file, a dialog box pops-up asking if they want to run import diagnostics. Clicking “Yes” shows the image of the segmented tissue. Users can assemble the .STL images into a digital human model to illustrate anatomical relationships to other tissue or landmarks.

© 2012 Penton Media, Inc.

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