Components inside a CT scanner

Does anyone know, how much processing is needed to take all the density slices, and combine those into a cross section image. The X-ray detector must have some very small antenna to enable what ever the equivalent small area to detect density and calculate. I assume minion of scans are averaged to remove the noise of X-ray scatter and such stuff I know nuttin about.
I know enough for working for Dr. Harold Bale, on his X-ray diffraction machine (60KV, rotating anode target, target a spinning disk 6" diameter 1" thick, and water cooled interior, several different materials were seen on his bench, all with burn marks from the electrons). My part was to integrate the stepper motor driver hardware, with the IBM PC (1983), and some custom made X-ray counter rack mounted, and using a 6502 at 500KHz read the BCD output from that counter, and via the IBM, and a BASIC program, automate data collection. Dr. Bale wanted to find the center of the beam, as part of calibration, and then I think had the stepper do some sort of logarithm step off center, and collect all the data. At the time, the DOE contracted to come up with a model for powerderized coal, as that was going to be the next power plant generation method. I think that all died. But what Dr. Bale was able to show, that a Mandelbrot fractal could model the coal surface for what ever modeling that needed this to simulate the burning. I heard that years later. I was lucky my crude coding skills and hardware digital smarts, got me side jobs working at the U, and paid for my BS degree.
Dr. Bale was adamant, to never expose to any X-rays, unless it's for a health issue, as any is too much. Difference between a physicist that got his PHD working with X-rays, and Medical Dr. that are taught it's a non evasive procedure.
So I lost a front tooth, and now need an implant, had to go to a specialist for that, they took a CT of my head, with just this standing in a small cubical machine did in less then 45 seconds of scanning. By the time I got back to the chair where the technician continued prodding. The computer screen in front of my chair had my skull, colored image to bone and 3D. When this this tech happen?
I hear China has a MRI that does not use helium. Are they able to get the noise down using nitrogen? Soon room temp.

Components inside a CT scanner - GIF