3D Objects, Engineering

X-Ray Tomography (Part D)

When all the images were finally scanned (seriously, I may have used the CT scanner more than Ph. D. candidates in a few weeks), there is only one process remaining: Analysis (and visualization, and interpretation, and inference, and the write up, and the dataset organization and many more).

The scanned images can be easily saved in popular formats such as png and tiff. This makes them easy to view in commonly available image viewing software which, we all know is Microsoft’s Photo viewer, because Google decided to discontinue Picassa (which is a shame, in my opinion)…

Skyscan comes with its own analysis software called CTAn, which can not only be used to analyze individual images, but also measure tiny flaws if found! Perhaps the most amazing feature is to analyze multiple images at the same time.

When the region of interest is set for an upper limit and lower limit of an image sequence. Threshold can be set for binary images for each image or the entire data sequence to see the histograms. With this, density can be found (i.e. the density of the poly lactic acid that is used to fill in the specimen in this particular case). In the end it is possible to find the mean total value of voxels (simply put, 3 dimensional pixels) and save the calculations if necessary, and it is, because we’re analyzing. Then, use them to calibrate the attenuation and compare results. The same process is repeated for each individual scanned specimen. Quite mind-numbing, but necessary for what I was doing. Below is an example of a high infill colored cone (20%, pink).

A Marked Region of Interest and Histogram of the Dataset of a Colored Cone

Another important feature of CTAn is to show Density Profiles of each slice of image. but the most underrated and less frequently used feature is to perform dimensional measurements, which was the primary focus of the Optimization of 3D Prints project. Dimensions such as layer thickness, empty space areas inside the object, position of each layer, alignment of layers, angle between two subsequent layers, thickness of the shell etc. could be calculated, which was a tedious task to perform (the things we do to seek the truth, am I right?). With this it was possible to do additional statistical analyses.

Example of Dimensional Measurement of a Hollow Colored Cone showing Angle between 2 Layers

Then there is another software called CTVox, which is used to construct a 3 dimensional view (also called volume rendering in this case) of the internal and external morphological features of each specimen. I may upload videos of them in the future, but right now, there is only a picture as each of them can be a whopping 10 giga bytes (and they look beautiful)! Below is an example image of a volume render of a cylinder.

Volume Rendering of a High Infill Cone

It is also possible to create moving Heat Maps in CTAn, if you know what you’re doing, like I showed in this particular post. Heat Maps are very cool (and so are oxymorons)!

With this, I conclude this (slightly comical) mini-series of showing how X-ray Tomography can be done, and how it was used for my project. Sorry, but there is no party (I meant Part-E).

Starting from the next time, we’ll return to Optimization of 3D Prints and finally see how the project ended.

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