The rotating inside of a medical CT scanner.

[EPAIII]

Actually, if that thing starts to come apart, the patient is in the safest place in the room. All the pieces will be flung outwards to the walls, ceiling, and floor. But he/she will definitely need a change of underwear.

[BrianHG]

Actually, if that thing starts to come apart, the patient is in the safest place in the room. All the pieces will be flung outwards to the walls, ceiling, and floor. But he/she will definitely need a change of underwear.

Anything flung toward the 'ceiling' will succumb to gravity and end up impaling or crushing the patient.

[TimFox]

Here is a time-lapse upgrade of a Magnetom Prisma 3T MRI machine: (Maybe 3T means it's coil is 3 Tesla strong.)

Yes, 3T means 3 Tesla = 30 kgauss.
For years, 1.5 T was the standard DC field strength in MRI.

[Gyro]

Here is one of the MRI views from my flattened Lumbar Disc which I got during an accident:



Though, I did get the full 'DICOM' folder and with a proper 3D viewer, I can go inside and view around my spine, discs and nerves in 3D to a degree, but since this was scanned on older low res MRI hardware and no tracer dyes were injected, the view is merky at best.

Also, sadly, currently there is nothing I can do about my lower back as any surgery can possibly mean loosing the use of my legs or worse future debilitating pain, so no one is willing to take the chance.

I'll see your spine and raise you a brain - well most of it anyway!

A very nice, careful man took chunks out of it while we chatted.

[WatchfulEye]

Here is a time-lapse upgrade of a Magnetom Prisma 3T MRI machine: (Maybe 3T means it's coil is 3 Tesla strong.)

3T means 3 Tesla - which is a the standard high-end field strength.
1.5T is the more common standard.

As superconducting magnets are expensive, and have a long service life, there is an increasing market for field-upgrades, where the magnet is retained and the electronics and support equipment are upgraded. Not shown in this video is some of the support equipment, which might be of interest.

Here's an example of some of the support equipment for a typical MRI scanner (Bottom left: PDU and power conditioning, Top left: PSUs for gradient magnet drivers, Top right: RF synthesizer and power amplifiers, Bottom right: Gradient magnet driver power amps.)
Not shown are the cryogenics and computers, or RF receive chain (typically integrated into the scanner unit to minimize RF losses in cabling, or integrated into the coil (antenna) assembly on some models)

[james_s]

Actually, if that thing starts to come apart, the patient is in the safest place in the room. All the pieces will be flung outwards to the walls, ceiling, and floor. But he/she will definitely need a change of underwear.

I think that's extremely unlikely. The rotating assembly is a massive metal casting and it's sitting within an even more massive metal casting. I haven't tried to calculate it but I'm betting the forces are nowhere even close to where anything would start to come apart.

[Gyro]

Hey, if we all club together we can come up with a thread to rival the Thermal Imaging Gallery!    https://www.eevblog.com/forum/thermal-imaging/thermal-imaging-gallery-ii/

[amyk]

I don't know that small variations in wiring harnesses and such would be enough to throw off the balance. The rotating assembly weighs hundreds of pounds, especially the older ones that had iron core transformers for the xray generator.

Probably even a few pounds out of balance wouldn't be a problem, as long as the base is massive enough, and the machine is firmly secured to the floor; look at the various machining videos on YouTube of very unbalanced parts being spun in a lathe for comparison.

Surely being out of balance would create issues for the image, because it would lead to the x-ray sensor and generator moving away from the ideal circular shape for the CT scan.  Additionally, being significantly out of balance will wear the bearings more quickly and create more noise.

You're still able to machine perfectly round areas on unbalanced parts with a lathe specifically because the amount of mass that's out of balance is tiny relative to the total mass of the machine. Balance is important but this isn't anywhere near the tolerances of something like a gas turbine.

[BrianHG]

Here is how the rotating CT scan is decoded:

[grumpydoc]

Interesting - not seen the inside of one, though I've looked at "one or two" of the scans that come out.

That style of CT scanner is a "spiral scan" device - as has been mentioned the earliest machines rotated a single x-ray source with a rotating detector to collect the data for a "slice", the patient bed was stationary for each slice and then moved for the next one.

Current devices move the patient and the x-ray sources simultaneously - producing a "spiral" of data which has to be de-convolved in 3 dimensions, but they are *much* faster to do a scan, and produce vastly better resolutions (1mm or even 0.5mm "slices" compared with 5 or 10mm for early devices).

We've just had the 50th anniversary of the CT scanner, the 1st patient scan on the EMI prototype was 1971.

[thm_w]

Also, sadly, currently there is nothing I can do about my lower back as any surgery can possibly mean loosing the use of my legs or worse future debilitating pain, so no one is willing to take the chance.

Artificial disk replacement, its just incredibly expensive: https://orthoinfo.aaos.org/en/treatment/artificial-disk-replacement-in-the-lumbar-spine/
The general complication risk is around 10-15%, losing leg use a lot less than that. Its not that they are not willing to take the chance, its that in their eyes the risk/reward ratio isn't high enough, and there are other patients with arguably more serious issues that could use our limited medical resources (IMO). Of course I could be completely wrong and there is a specific reason they have.

also not nothing you can do, you can make small gains with physio, posture improvement, etc.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4365564/

[Wallace Gasiewicz]

I don't know if someone said this before but EMI, Electornic Music Instruments, was owned by the Beatles when the scan machine came out.

[BrianHG]

Also, sadly, currently there is nothing I can do about my lower back as any surgery can possibly mean loosing the use of my legs or worse future debilitating pain, so no one is willing to take the chance.

Artificial disk replacement, its just incredibly expensive: https://orthoinfo.aaos.org/en/treatment/artificial-disk-replacement-in-the-lumbar-spine/
The general complication risk is around 10-15%, losing leg use a lot less than that. Its not that they are not willing to take the chance, its that in their eyes the risk/reward ratio isn't high enough, and there are other patients with arguably more serious issues that could use our limited medical resources (IMO). Of course I could be completely wrong and there is a specific reason they have.

also not nothing you can do, you can make small gains with physio, posture improvement, etc.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4365564/

Disc replacement for the upper back towards the neck do generate long term success.  However, lumbar discs mechanically wear out because of extreme forces on the mechanical hardware, especially if you want to remain physically active.

Some physio does help, however, my unique circumstance has meant any time I try to sit with proper posture, it actually makes things worse.   I literally have a time limit on how many hours I sit upright per day.  Hunched over, or controlled angle mild exercising can improve this, but it goes against proper posture.  Literally, if I cycle on a road racing bike, so long as it is done regularly and in a greatly controlled manner, it improves my ability to tolerate siting in a normal chair.  (However, this may be due to my long term bike training as a youth.  Precise angle and muscle memory may be whats helping here.)

[tooki]

I don't know if someone said this before but EMI, Electornic Music Instruments,

No, EMI was short for Electric and Musical Industries.

was owned by the Beatles when the scan machine came out.

No it wasn’t.

At best, the Beatles’ success simply gave the company cash flow to work with:
https://www.cnet.com/culture/how-the-beatles-funded-the-ct-scan/

[Wallace Gasiewicz]

Sorry, I thought the Beatles owne a big part of EMI, apparently not.

[thm_w]

Disc replacement for the upper back towards the neck do generate long term success.  However, lumbar discs mechanically wear out because of extreme forces on the mechanical hardware, especially if you want to remain physically active.

Some physio does help, however, my unique circumstance has meant any time I try to sit with proper posture, it actually makes things worse.   I literally have a time limit on how many hours I sit upright per day.  Hunched over, or controlled angle mild exercising can improve this, but it goes against proper posture.  Literally, if I cycle on a road racing bike, so long as it is done regularly and in a greatly controlled manner, it improves my ability to tolerate siting in a normal chair.  (However, this may be due to my long term bike training as a youth.  Precise angle and muscle memory may be whats helping here.)

They wear out, but manufacturers are claiming 40+ years of life based on normal wear testing (titanium + UHMWPE).
Studies show 12 years of use without needing replacement: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5435628/
Although this does highlight some issues: https://www.mdpi.com/2075-4442/3/2/346

Sitting is not great, even with proper posture, limiting sitting hours is a good idea regardless of injuries.
But yeah I see what you mean, cycling/hunch would probably take pressure off of that lower area. Cycling will also increase blood flow which is always good.

[LaserSteve]

I used to work on them.

Tungsten ballast  blocks in strategic places in a cast aluminum pan that rotates around the PT.

5.6 Gb per second free space optical data link using distributed  laser diodes.  480/ 3 phase + safety signal [Canbus + DC current]  on slip rings.

There is a massive 400 Hz Synchro around the PT with interpolation, more accurate then an optical encoder.   If there is jitter in the sync signal from vibration, the unit will shut down.

Newer ones are air bearing using massive porous tungsten blocks as the bearing surface.

Factory balanced.  Repair parts are strictly controlled in tolerance.

Cooling fans have high torque drives, they are unaffected by the rotation. Same for the rotating anode drive, and the pumps for the X-ray oil cooling.  There are heat exchangers spinning around the PT filled with oil.

Spins are sequenced, fans may not be on until the rotor is moving. Testing / alignment is done while spinning. Variable speed drive is programmed to avoid resonance.

Exposure time is limited by the heat storage in the anode.  The anode is massive. Anodes are preheated prior to each PT run. There is a very precise anode temperature calculator, run duration is limited by anode heat.  There is a deflection plate to position the e-beam spot in the tube, so heat is distributed and resolution increased.

X-ray Flux is modulated as the rig spins to reduce dosage.  Software does look ahead and look back to control dosage, as well as real time contrast control.

480 + hot oil + 200 Kv.

The Doppler shift + Amplitude Modulation of the fan noise is memorable with the cover off.  Fans are variable speed.

A technician's worst nightmare is oil on the slip ring brushes.

We moved them around on removable wheels with screw jacks. Fine positioning before bolt down may have involved pry bars and large hammers.

If you disabled the rotor brake and clutch , the rotor would very slowly turn to a position dictated by gravity. Great but not perfect balance.

Any questions?

Steve

[MrMobodies]

3:08 The 3 Tesla magnetic field it generates if 60,000 times the strength of the Earth's magnetic field.

So it I put attractive facing magnet in there would that also increase the strength of the attraction?

[SeanB]

Not likely, as the magnet you bring would probably saturate long before the field addition is going to be noticed.

Been in both last year, got the CD images as well, and it is an older unit, so no pretty rotation just static images, though there is a collection of CT scan images with the needles in my spine as well. Fun losing all sensation in your lower body for a week when the doc found the wrong nerve, and the relief is only temporary. You can feel your body move in the MRI from the field changes, and, even with no contrast injection, you can taste the field changes as you move through the unit, and my fillings definitely got hot going in and out, just from that magnetic field gradient.

[BrianHG]

Not likely, as the magnet you bring would probably saturate long before the field addition is going to be noticed.

Been in both last year, got the CD images as well, and it is an older unit, so no pretty rotation just static images, though there is a collection of CT scan images with the needles in my spine as well. Fun losing all sensation in your lower body for a week when the doc found the wrong nerve, and the relief is only temporary. You can feel your body move in the MRI from the field changes, and, even with no contrast injection, you can taste the field changes as you move through the unit, and my fillings definitely got hot going in and out, just from that magnetic field gradient.

If you got the CD with a folder called 'DICOM', then you have the full 3D voxel image.  What you require is a proper DICOM viewer to get an image you can rotate and zoom in and out of, like exploring a video game level.

Try these guys : https://www.radiantviewer.com/

I used their 1 month free preview viewer on my MRI.  With varying gamma and contrast adjustments, plus a little editing to slice out my spine from some surrounding guts, I was able to achieve a view of my spine and discs as if it were removed from my body.  Rotate it around and see it from any angle.

Since I did not have any tracer contrast dyes injected, the editing took a little work because of poor contrast in the scan, but the results were worth it.

[SeanB]

Used the aeskulap viewer, so probably need to figure it out a bit as to how it really works, but the images are there.

[BrianHG]

Used the aeskulap viewer, so probably need to figure it out a bit as to how it really works, but the images are there.

Are you sure aeskulap viewer is a 3D render-er?  Which 3D library and which 3D accelerators is it compatible with?

This is what RadiAnt does with your DICOM folder: (Please mute the embarrassing music)

[LaserSteve]

Every thing you ever wanted to know on CT mechanics is in the second half of the attached thesis.  At 1700 Kg of rotor mass,  one hopes to never experience an orbital mechanics problem.

The runout measurement on the rotor is impressive.

See attached..

[BrianHG]

H O L Y  S H I T

Take a look at the speed on this one, the second time they run it at 5 RPS / 360 RPM.



And, here are the specs of an MRI scanner, including coil wattage and frequency...

[WatchfulEye]

And, here are the specs of an MRI scanner, including coil wattage and frequency...

That video is complete nonsense. The idea that the RF in the MHz range produces the sound when it is far outside of the audio range is twaddle.

The source of the loud sound is the action of the gradient coils - used to cause spatial modulation of the static field in order to perform spatial localisation. These are modulated in the audio frequency range, and due to the substantial fields generated and huge slew rates, there are huge lorentz forces generated which physically deform the coils themselves. This deformation results in vibrations transmitted to the scanner structure (which may add various resonances). The structural resonances can be problematic and most scanner control software includes provision to prevent the use of protocols which could result in physical damage if an important resonance is excited.

The gradient amplifiers have progressed significantly. Historically modified audio PAs (in the multi kW range) were used. But switching amplifiers have been standard for best part of 20 years. The may the amplifiers are rated tends to be as the product of the peak outout voltage and peak outout current. 1MVA amplifiers have been seen in high end scanners for some time, with new top end now coming with 2 MVA amps (e.g. 1.2 kv and 1.7 kA)

The latest scanner from one vendor achieves it's exceptional slew rate specification by using a pair of 2 MVA amplifiers for each gradient coil - one PA drives each half of the coil, allowing the system to achieve double the slew rate of the predecessors.

Anecodatlly I know of sites which have been caught out by assuming a field upgrade would be relatively straightforward only to find that the increased electrical and chilled water demand required major building facilities upgrade.