anyone know about CT scanner

smiles · Apr 3, 2007

if yes, help me about it, I just wonder by which way the gantry with its X-ray tube and detector system rotate around patient, I know there is a motor but don't know about the mechanism of motion propagation that make the gantry rotating ?
thanks !!!

CaseyK · Apr 4, 2007

I can't help but think that there is a micro PLC or an embedded (sort of PLC) controller involved!

Rick Densing · Apr 4, 2007

Sorry Casey- no PLC. I worked in college at GE Medical's CT plant.
Unfortunately, I don't remember how they turned the gantries.
I left in '93, but then all the controls were GE proprietary designed and built.

It is a motor, and I would expect it is a servo motor.

smiles · Apr 5, 2007

it is a big motor, I have just ask the one who familiar with CT repairing, he said that this motor connect with gantry via chain, like bicycle chain !!!
but could you tell me a little about servo motor, dont sure what its function ?
thanks!!!

Rick Densing · Apr 5, 2007

I thought it was a chain, but my memory was too hazy for me to post a guess.

A Servo motor has feedback, so it can position precisely. Since it is a chain, it may not be a servo, but certainly a motor that they can vary the speed. There will be a position sensor on the gantry position so the computer can do the CT calculations.

kamenges · Apr 5, 2007

That chain thing really surprises me. I would think the velocity ripple caused by the chord length change as the chain engages would not be a welcome thing. I would have thought a toothed belt or a low backlash gearset.

Keith

Hugh Jack · Apr 5, 2007

A CT scanner works by moving an X-ray tube around the patient. It will stop (?) at regular intervals (angles) to take a 1-D picture. To do this there is a brief X-ray exposure. On the other side there is a linear diode array (sort of like one line from a digital camera) that captures the X-rays. The scans from all angles are then combined (hence the name computed tomography) to get a body slice. You may then move the patient forward or back to get more slices.

kamenges · Apr 5, 2007

Shows what I know about CT scanning. I thought they took the shots on the fly.

Keith

Hugh Jack · Apr 5, 2007

It it possible to take the images while moving if they can be captured quickly, or the motion blur can be filtered out. My knowledge is based on a unit I built in the 1980s.

Rick Densing · Apr 5, 2007

kamenges said:
Shows what I know about CT scanning. I thought they took the shots on the fly.

Keith

They do. Hugh is a little out of date.

I haven't worked in the field since '93 and they did then. They had just developed slip-rings so the gantry did not have to unwind after every slice. Time is alwasy money.
Back then the xray dectection was done by an array of scintilating material, that in turn excited photo-detectors. The material was (is) a trade secret.

http://en.wikipedia.org/wiki/CT_scanner

smiles · Apr 6, 2007

kamenges said:
...I would have thought a toothed belt ...
Keith

toothed belt, I means that, sorry my bad definition

CaseyK · Apr 6, 2007

Rick Densing said:
Sorry Casey- no PLC. I worked in college at GE Medical's CT plant. Unfortunately, I don't remember how they turned the gantries. I left in '93, but then all the controls were GE proprietary designed and built. It is a motor, and I would expect it is a servo motor.

I was with GE ED&C 94-96, and we did a lot of white cabinets for GE Med, but all that was inside was motorstartes and pilot devices. I would have thought they would have modernized by now!

But then, I am realy surprised that they are not still marketting the GE "Smart Relay"!

anyone know about CT scanner

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