Re: [CAD_CAM_EDM_DRO] help putting together a complete system

Yes they do use the same basic X-Ray generator system

The key difference is that no images (pictures) are produced by the imaging
system during the X-Ray exposure. Only measurements of the amount of
radiation that passed through the object are recorded (many many thousandsof
these measurements) and the angle that the beam was at at the time of the
measurement.

The images that the doc's all look at are reconstructions based on the
radiation measurements and the angle of the beam through the object.

Is why it is called Computed Axial Tomography Scan CAT scan for short now
shortened to CT Scan. .

How close can you tie CAT Scans to CAD-CAM-DRO read on my friends.

The origional work was was done in England. First was the developement of
the math to reconstruct the image from a set of radiation measurements.
These measurements actualy represent the density of the object in a narrow
beam through. The math was developed to do crude reconstructions and then
they needed to see if they could do a head reconstruction from real data and
the machine to get the data had not yet been developed or built.

Well take one below freezing big cooler, one bridgeport with rotary table
mounted to the base floating just above the table, one X-Ray tube on one end
of the table and a radiation measuring probe on the other end and now fix by
one cadaver head by freezzing the neck to the rotary table. We can't have
the guy move his head during this several day process.

Now start with head at zero angle on the rotary table and slowly move the
main table in Y so that a thin round beam transverses the head from front to
back, make many stops (1000) to measure the radiation on the opsite side
thereby getting a measurement of the density in the beam. Now rotrate the
rotary table a degree and make the Y scan again. When you have made 360
steps on the rotary table you are done measuring.

Now enter all the data into a computer file and start testing your program
for reconstruction. It works so design a CAT scanner that does the rotrate
and translate measurements with the patient keeping his head still and the
X-Ray tube and measuring instraument rotate about you head. Was called step
and translate CAT Scanning

Now days they use fan beams and many radiation sensors, no translate
movement.

Also it is now called CT Scanning because you can just run the patient
through the ring without it rotating, no axial movement of the X-Ray system.

First Nobel Prize in Medican in Radiology. EMI built the first commercial
systems.

Probably more than you wanted to know but that is just part of the story as
they say.

Radiation exposure is quite low now, always remember its a tradeoff in
finding and curing something that can kill you in the near future in
exchange for some radiation exposure that MAY cause something 10 -40 years
from now.

Hugh
by now you should have figured out that I have been involved to some extent
in the field of medical imaging.

----- Original Message -----
From: <info.host@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, June 05, 2001 4:51 PM
Subject: Re: [CAD_CAM_EDM_DRO] help putting together a complete system


> > Jeff:
> >
> > Very good, and quite workable too. Since I have access to a cat
scanner,
> I
> > do the same thing sorta, but mine requires radiation. (I pretty much
glow
> in
> > the dark these days).
> >
> > And you can eat the bread afterwards.....hmmm the marvels of technology.
>
> Do cat scanners use exactly the same wavelength as a normal x-ray tube in
a
> hospital? Because I've seen them take tens and tens of pictures to slice
up
> someone's head, photographically of coarse, isn't that like having many,
> many x-rays in one go or is each shot a lower energy?
>
> John
>
>
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