Sunday, November 04, 2007

Alas, Poor Becky. I Knew Her, Horatio

I have two CD-ROMs from CT scans of my head. The first has 32 slices; the second has 290 slices plus some other images that were reconstructed of my Circle of Willis. These scans were done in August of 2006, just to make sure that my migraine-like headaches weren't caused by some sort of horrible brain problems that show up on a CT scan.

Previously I'd extracted the images from these scans. They're kind of cool but not all that exciting. A series of black and white slices of my head. You can see my skull, my brain, my sinuses, my eyeballs, all in cross-section. Looked something like this.

A random stream of consciousness led me to take another look at those images. The DICOM viewer that came on the CDs is Windows only, so I looked for a Mac one. I found the amazing and awesome OsiriX, which has taken up most of my time this weekend.

In order to be suitably impressed, you have to realize that a CT scan is not magic. In a CT scan a beam of x-rays passes through the plane of the object from different directions. Based on these lines of varying intensities (1-dimensional images!), a reconstruction of each slide (2D image) can be created using fairly clever math. The key here: not magic. Lots of line segments showing varying intensities of x-ray are put together to create 2D axial slices of my head.

OsiriX took 290 axial slices of my head and reconstructed them into a 3D model that I could then slice from front to back or from ear to ear.

Then I was able to take this rendering of my head and do all sorts of awesome stuff with it. I could make a 3D view of my entire head (with skin!) that I could rotate on the screen. It was so accurate that you could not only see the expression on my face but you could also see the mole on my cheek. When I adjusted the tolerance on the image, I could get it to make a grainy image (lots of artifact) that even included my hair. Surface portraiture from an x-ray! It was like something out of CSI!

I could also take the surface rendering of my head and change the opacity of the tissue, so I could fade out the soft tissue of my face, revealing the bones beneath. My skull! Rotating in 3D on my computer! And then, so awesome, it had the option for 3D glasses mode. Now all I need to do is figure out how to take a volume rendering and use a segmentation tool to take away the bone, creating a rotating image of my brain.

Unfortunately, I don't have several more hours to spend obsessed with adjusting my medical images, so I must close OsiriX and get to work writing a midterm and making calculus PowerPoint slides.