The overall goal of this methodology is to utilize sub-surface laser engraving, or SSLE, on glass crystals to visualize tomographic imaging data with labeled structures. The resulting handheld models can serve as a powerful teaching tool. This method creates robust, handheld models derived from clinical or preclinical x-ray CT datasets that facilitate the education of patient or student populations.
The main advantage of this technique is the text labels are suspended within the glass medium and attached to the associated structure without obstructing the view of the high-resolution anatomical display. Visual demonstration of this method is critical, as the generation of surface maps with text and scale bars is difficult to learn because of the multiple steps and precision required for accurate display of the structures. To begin, convert the CT image slice in a DICOM dataset to the proper file format.
In the image processing software, select the load DICOM command under the view setting. Then, save the dataset in the NIfTI file format. Now, import the NIfTI files into a common medical imaging program that generates surface maps using automated segmentation.
For 3D Slicer, use the add data tool. Then, select the grayscale model maker tool, and toggle the specification, create and rename new model. Next, lower the threshold values to approximately 300 HU, or the segmentation of bone, and save the resultant grayscale models as STL files for further data processing.
Next, import the surface map files into a 3D data preparation software. Using Netfabb Studio Basic, select the repair mode. Then use the select part and delete tools to remove all surfaces that do not represent the structure of interest.
Next, use the add triangle tool to partially cover the holes in the surfaces, and then use the automatic repair script to completely close any remaining gaps. Now from the action menu, select the repair degenerate faces script to resolve the edges lacking surface area, and then use apply repair to exit repair mode and save the modifications. The next step is to use the cut tool to remove unwanted features or reduce the size of the model.
From the cut menu of the context area, designate the location of each cut within the x-y-or z-plane. Then use the execute cut tool and select triangulate cut setting to automatically close all the resulting holes. To delete all the surfaces resulting from the cuts that do not represent the structure of interest, use the select part and delete tools simultaneously.
Lastly, if a scale bar is not going to be used, then modify the dimensions of each surface map using the scale option. The model can thus be modified to fit within an eight centimeter cube, or five centimeter by five centimeter by eight centimeter rectangular prism. Now the data file can be used for the sub-surface layer engraving to make a model without labels or a scale bar.
First produce label data files for the SSLE file. Use CAD software with a metric template. Open a new file and make a 2D sketch in any plane.
Use the text tool to produce typed anatomical labels in a two millimeter Times New Roman font. When finished, select the finish sketch option in the exit menu of the toolbar. To extrude the font using default settings, choose the extrude tool from the create menu, and toggle the 2D text option.
Next, produce one label line for each label. Start with a new file, and choose the center point circle tool under the draw menu. Then make a circle with a center at the origin, and define the diameter of the circle as one millimeter using the dimension tool in the constraint menu.
Extrude the column to a desired length, ranging from 10 to 50 millimeters. Scale bars are made in a similar manner. After making each text label, each label line, and the scale bar, save the data as an STL file.
A unique label line is needed for each text label. Then, into the SSLE model, import all of the text labels, cylindrical label lines, and the scale bar. Use 3D data preparation software capable of saving the assemblage as a single STL file.
Next, use the move part tool to position the text labels near the associated anatomy. In this process, use the rotate part tool to orient labels so they all face the same direction. Then use the same tools to position the label lines so they connect the labels to the associated structure in the model.
As needed, the label lines can be made smaller by going to the repair mode and choosing select triangles and remove selected triangles. Now position the scale bar in a similar manner. If three bars were made, one for each axis, position them accordingly.
After everything has been positioned, select all parts and export the data as a single STL file. Techniques for additional reduction of faces and engraving process are described in the text protocol. Sub-surface laser engraving of glass crystals is a profound means to visualize numerous types of biomedical tomographic imaging data.
Since dimensions are modified prior to engraving, structures of various sizes can be represented through laser engraving. The scale bars can be implemented in two manners. They can span the sides of the structure, which is ideal for dilated structures such as the bone core.
The other option is for three scale bar axes to converge at a corner. This is best suited for to scale or reduced structures. Key feature of sub-surface engraving is the ability to attach text labels as needed to anatomical features.
Here, text was placed on two planes to space the labels out and to maintain a clear view of the anatomy. Bones and other structures that can be clearly viewed from one side can have their labels aligned along just one plane. Following this procedure, virtually any three-dimensional dataset can be converted into a format that may be appropriately labeled for scientific display in a handheld, ultrapure glass crystal medium.
