The rotating inside of a medical CT scanner. - Page 1
Forum section: electronics / general

author: BrianHG
author_rank: Super Contributor
timestamp: December 21, 2022, 08:10:46 am
content: How on earth did they balance that?

author: BradC
author_rank: Super Contributor
timestamp: December 21, 2022, 08:50:40 am
content: I’d wager very carefully. Love to know what the rotating mass is.

author: tom66
author_rank: Super Contributor
timestamp: December 21, 2022, 09:20:11 am
content: I'm amazed by how relatively quiet it is at full whack. The bearings on that must be something else, too.

author: BrianHG
author_rank: Super Contributor
timestamp: December 21, 2022, 09:43:51 am
content: This is what I expected to see:

author: Gyro
author_rank: Super Contributor
timestamp: December 21, 2022, 12:02:36 pm
content: I'm just wondering what happens to the rotation speed of all those cooling fans (depending on their direction of rotation).Balancing must be a real work of art - maybe it's dynamically adjusted.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 21, 2022, 12:51:34 pm
content: The speed is not that high, more like slower than the washing machine. Essentially all the ciruit is fixed and balancing the mass only needs to be done once (unless they use leaking capacitors).With the still moderate speed they may get away with a static balance (1 weight to adjust) and may not need an individual dynamic balance (2 weights to adjust).It is not just about noise and external vibrations, but vibrations in the system could also limit the resolution.The fans should see not problem. At least the ones visible in the video have the axis more or less parallel to the axis of rotation and thus no extra forces. A fan at a different angle could see extra forces and may not be such a good idea and complicate the balancing.

author: vidarr
author_rank: Frequent Contributor
timestamp: December 21, 2022, 01:37:42 pm
content: I wonder how many people would opt out of the scan, if it had a glass cover. Or, at least, be very frightened. I think it looks cool.edit: That washing machine video is hilarious.

author: fourtytwo42
author_rank: Super Contributor
timestamp: December 21, 2022, 01:58:49 pm
content: OMG I have been in one of those things several times, if I had seen this first I might have had second thoughts, bit like an inside out meat mincer if things went wrong

author: themadhippy
author_rank: Super Contributor
timestamp: December 21, 2022, 02:15:52 pm
content: Be more fun if the head was stationary and the patient spun

author: tom66
author_rank: Super Contributor
timestamp: December 21, 2022, 02:27:31 pm
content: Quote from: themadhippy on December 21, 2022, 02:15:52 pmWhat's the x-ray transmissibility of vomit?

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 03:03:21 pm
content: Quote from: themadhippy on December 21, 2022, 02:15:52 pmMany industrial computed axial tomography scanners have a stationary x-ray system and rotate the part on a turntable.If the human patient were mounted on a rotisserie (horizontal axis) inside a stationary system, the internal organs would flop around and blur the image.There was limited use of a patient sitting on a bar-stool-like seat with a vertical axis in medical CAT with radiation sources that could not rotate.

author: themadhippy
author_rank: Super Contributor
timestamp: December 21, 2022, 03:10:23 pm
content: QuoteNo idea,but if you like to fund my research,a £100k should get the ball rollingQuoteso spin em faster ,then the centrifugal force should keep everything in place, scream if ya wanna go faster.

author: Gyro
author_rank: Super Contributor
timestamp: December 21, 2022, 03:40:57 pm
content: Quote from: fourtytwo42 on December 21, 2022, 01:58:49 pmYes, I've had quite a few brain ones and it puts you in an ideal position to see it spinning in the slot. The overriding impressionisthat looks like a lot of expensive stuff spinning quite fast!

author: daqq
author_rank: Super Contributor
timestamp: December 21, 2022, 03:52:16 pm
content: Must have quite the brushes, both for data and power.

author: rsjsouza
author_rank: Super Contributor
timestamp: December 21, 2022, 04:07:05 pm
content: And on a similar vein...

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 04:34:11 pm
content: Quote from: daqq on December 21, 2022, 03:52:16 pmBefore about 1980, the rotating platform did not rotate continuously (before brushes) but went maybe 1-1/2 turns before stopping and rotating back.Flexible cables were used that had a cable-handling system next to the wheel.As I remember it, Varian had the first continuously-rotating CT system, using a small diameter oil-filled slipring at a closed end of the assembly.I worked on the first open-end continuous-rotation CT scanner (Toshiba TCT900) using large-diameter sliprings, with the high-voltage rings enclosed in SF6insulating gas.Modern scanners have the high-voltage supplies on the rotating platform, fed through low-voltage sliprings, with different high-speed data communication paths (optical or electrical).To simplify the discussion of computed axial tomography, one needs to look through every point in the object from every angle to get the data required to "reconstruct" what was there at each point to form the image.

author: tooki
author_rank: Super Contributor
timestamp: December 21, 2022, 07:24:21 pm
content: Can you elaborate more on the data communication?

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 09:11:38 pm
content: I've been out of that field for a while, so I can't comment on current practice.On the continuously-rotating TCT-900, the detector ring did not rotate (that configuration is now essentially obsolete), so the data communication was straightforward.On other scanners, with rotating detector rings, I am aware of complex optical configurations (mirrors without smoke) and slip-ring-like structures with capacitive coupling between rotating and non-rotating platforms.A German company, Schleifring (with a branch in Elgin, Illinois) supplied the latter.I believe they have been acquired( since my time) by GE Medical.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2022, 09:59:56 pm
content: I doubt the balancing is much different than balancing something small, it's just scaled up. In fact I would expect it's easier than balancing something that has to spin at tens of thousands of RPM. In this case you have a handful of components that have to go in specific locations, then you can see where you are and start putting the other components where their mass is most needed. Once you have that as well optimized as possible add ballast weight where needed to get it dialed in. Much of the process could probably be calculated.

author: BrianHG
author_rank: Super Contributor
timestamp: December 21, 2022, 10:06:48 pm
content: Quote from: james_s on December 21, 2022, 09:59:56 pmThat's just it. Calculating a balanced design is one thing. But after that, when it comes to all those wire harnesses, slight different weights of copper and plastic, hand tying and mounting. To balance, where do you know right position to add some weight?It's not like a car wheel where you have a specific machine to measure the wobble and tell you where to place some correction weight.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2022, 10:12:28 pm
content: Quote from: BrianHG on December 21, 2022, 10:06:48 pmMotor armatures are balanced by drilling away material. Flywheels of various types are sometimes balanced by the same method. It's not outside the realm of possibility that they have a special machine to balance the rotating assemblies, or perhaps they attach transducers to the frame of the machine and balance each one in place. The transducers might even be integral in order to detect if it ever goes out of balance. Likely only someone that has seen the manufacturing process knows exactly how it's done in practice. 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.

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 10:15:01 pm
content: Even back in the early 1980s, Hewlett-Packard made dynamic analyzers that could find the oscillation modes of the structure and look for harmonic vibrations from the rotation.The rotating masses are dominated by the lead-packaged x-ray tube, the detector ring with electronics, the lead beam stop behind the detectors, the oil-to-air heat exchanger, and the power supplies.Like anything else at this scale, this must be done carefully, which is why mechanical engineering is still important.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 21, 2022, 10:55:44 pm
content: Quote from: rsjsouza on December 21, 2022, 04:07:05 pmYeah, that's why patients must absolutely say whether they have anything implanted before this kind of exam. It can end up pretty badly.

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 11:07:30 pm
content: I once set a sharp-pointed tweezers on the patient couch of an MRI scanner: luckily it didn't stab anyone on its way into the bore.The field engineers knew that they had to expect paper clips clinging to the magnet, disrupting the high field homogeneity required for good performance.An anecdote I heard from the very early days of MRI involved an installation where a technician was pinned to the machine by a steel oxygen tank.Unfortunately, the first responders were police officers nearby, who carried sidearms.Another anecdote involved "aneurysm clips", a surgical appliance, that were pulled from their location.(These were from the early days, before the dangers were widely appreciated.)I attended an MRI conference back then, where I heard the desk clerks at the conference hotel wondering why so many American Express cards presented at check-in had "wiped" magnetic stripes.

author: amyk
author_rank: Super Contributor
timestamp: December 21, 2022, 11:11:41 pm
content: Quote from: james_s on December 21, 2022, 10:12:28 pmProbably 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 ofveryunbalanced parts being spun in a lathe for comparison.

author: tom66
author_rank: Super Contributor
timestamp: December 21, 2022, 11:18:03 pm
content: Quote from: amyk on December 21, 2022, 11:11:41 pmSurely 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.

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 11:21:16 pm
content: Being way out of balance would cause the machine to vibrate, which is not good.The rotating platform itself is a quite rigid casting, with a large bore to clear the patient and couch, and the runout of the orbit (deviation from circular) of the tube and detectors is controlled by an expensive bearing between the rotating and non-rotating platform.Balance is such an obvious consideration that it is considered from the very beginning of the mechanical design of these expensive machines.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: December 21, 2022, 11:25:19 pm
content: Quote from: TimFox on December 21, 2022, 09:11:38 pmSchleifringis still around, they along withSpinnerandMoogare well known suppliers of high-speed slip ring assemblies, often used for radar systems. Moog has asectionon CT-specific units, with pictures. For high data rates, one way they do this is with optical rotary joints, though for such large bores, they could do all the processing on the gantry and send the data over wifi.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 21, 2022, 11:25:32 pm
content: I'm pretty sure there are angular sensors to get accurate positioning, so a good balance is essentially for limiting vibrations as far as I can tell.

author: BrianHG
author_rank: Super Contributor
timestamp: December 21, 2022, 11:42:45 pm
content: Looking at the CT scanner's cover opened to the top of the video at 30 seconds in, you can see it begins to vibrate until the machine begins to rotate really fast. Maybe this machine was being serviced and needed re-balancing...

author: TimFox
author_rank: Super Contributor
timestamp: December 21, 2022, 11:47:41 pm
content: Sometimes when the continuous rotation is ramping up to full speed, you go through the frequency of a resonant mode of the entire structure, or maybe a gyroscopic interaction between the main rotation and the rotating anode inside the x-ray tube.In normal operation, the desin speed of both the structure rotation and anode rotation are fixed, so the transient vibration state is not critical.

author: jmelson
author_rank: Super Contributor
timestamp: December 21, 2022, 11:57:53 pm
content: Quote from: TimFox on December 21, 2022, 04:34:11 pmActually, Artronix, a tiny manufacturer of medical systems, based in St. Louis, MO, had a head CAT system using continuous rotation and slip rings in 1976 or so. They shipped 3-phase mains power to the head, and control and data was serial digital. They had a VERY inno vative detector that they managed to keep a trade secret for a number of years. Finally, GE figured out who fabricated the detector assembly for them and paid somebody to slip them the details and the game was up. The HV tank was on the rotating head, very close to the X-ray tube. The detector was in a stainless steel tank filled with Krypton at about 3000 PSI. A friend of mine was a field service tech for them before they went broke. He then did MRI service for GE.Jon

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2022, 01:08:13 am
content: Quote from: TimFox on December 21, 2022, 11:47:41 pmSeems like I recall that being a thing with helicopters too, a range of main rotor speed that you want to get through as quickly as possible while spooling up before something shakes itself to pieces.Years ago I had a vibration in my car, it would come on at about 50 mph and go away around 70. I figured a balancing weight had come off, then after a few weeks I finally got under it and realized there was a big bulge on the inner sidewall. That was a bit too close for comfort.

author: BrianHG
author_rank: Super Contributor
timestamp: December 22, 2022, 06:53:30 am
content: Quote from: bigfoot22 on December 22, 2022, 06:34:30 amMRI machines do not rotate. They are purely magnetic & their magnetic fields are controlled via software.3D CT scan machines are X-Ray based and to generate a 3D X-Ray. The X-Ray source and CCD exposure plate on the other side of the body either needs to be rotated around the object being scanned, or, the object itself needs to rotate as it slowly gets pushed through the focal point.

author: BrianHG
author_rank: Super Contributor
timestamp: December 22, 2022, 12:01:43 pm
content: @40 seconds in, take a look at how fast this CT scanner goes when it hist second gear...

author: tom66
author_rank: Super Contributor
timestamp: December 22, 2022, 12:42:01 pm
content: That's incredible. I wonder how much power it requires to accelerate a mass like that up to speed. Is the motor in the fixed part of the machine?

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2022, 02:56:53 pm
content: Originally, a large motor in a corner of the fixed platform drove the rotating platform through a belt.I believe some later machines integrated a motor into the circumference of the fixed platform.

author: tooki
author_rank: Super Contributor
timestamp: December 22, 2022, 05:27:39 pm
content: Quote from: BrianHG on December 22, 2022, 12:01:43 pmLooks like about 4 rotations per second, or about 240RPM. A bit of googling says that they spin at 100-300RPM, though from the sounds of it 300RPM isn’t that common. They look a lot faster than they are!

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2022, 06:07:10 pm
content: I was thinking it looked like about 2 revolutions per second but I didn't put a lot of effort into actually measuring it. The rotational RPM is not all that fast, it looks about the same as a ceiling fan, but the size of the thing means the linear velocity of the components around the perimeter is quite high, they must experience several g's. All of this could be calculated of course if one had measurements of the machine. Same with the power required to accelerate the mass, the bearings I'm assuming are quite good so the motor may not be all that powerful, a couple of horsepower perhaps.

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2022, 06:13:40 pm
content: Quote from: bigfoot22 on December 22, 2022, 07:15:14 amA lot of people confuse the two. Also MRI machines were originally called NMRI with the N standing for Nuclear, as in the nucleus of atoms, but so many people hear "nuclear" and think radiation that they dropped the N from the name.A CT scan on the other hand does use radiation and quite a large dose of it, at least with the older machines. IIRC a single CT scan of the head results in a noticeable rise in the statistical risk of developing some form of cancer. I'm surprised sometimes at how freely they are used, personally I would weigh very carefully the medical benefit of getting a CT scan in the particular circumstances and discuss that with my doctor before getting one.

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2022, 06:14:49 pm
content: Over the years, the rotation increased to speed up the data collection.Besides increasing throughput, this is also necessary when cardiac frequency is important (gating data collection to EKG to freeze heart motion).When the speed got faster than 1 rev/sec, breath-hold imaging became much easier for other purposes.I found that abdominal motion with breathing was quite large.Of course, all of this became far easier to engineer when the systems progressed past cable-handling to continuous rotation.

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2022, 06:22:45 pm
content: Quote from: TimFox on December 22, 2022, 06:14:49 pmThat's really clever, it hadn't occurred to me that they would synchronize it with heart motion but it makes sense.

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2022, 06:39:44 pm
content: Quote from: james_s on December 22, 2022, 06:22:45 pmIt's not practicable to synchronize the rotation to heartbeat, but with redundant data collection the data can be re-sorted to use only those collected during relatively non-moving parts of the cardiac cycle.Similar tricks can be used in MRI data collection for this purpose.

author: WatchfulEye
author_rank: Regular Contributor
timestamp: December 22, 2022, 08:26:14 pm
content: Quote from: james_s on December 22, 2022, 06:13:40 pmHistorically, this is definitely true.A whole body CT scan on earlier generation machines was said to carry an approx 1 in 1000 risk of cancer over the next 20-30 years, with a head CT scan approx 1 in 10000.Modern devices are much better - close to an order of magnitude better with a variety of strategies: sophisticated exposure control algorithms, higher sensitivity detectors, better reconstruction techniques and noise reduction algorithms (now using deep learning).There has been a lot of effort to raise awareness of this in the medical community over the last decade or so, with a variety of campaigns with names like "image wisely" and "image gently", aiming to ensure that CT was used only when necessary, and that the minimum examination with the minimum acceptable image quality was used.MRI is definitely preferable in many cases , because it avoids the ionising radiation - the image quality and diagnostic performance is also better in most cases, at the cost of longer examination duration and higher cost. (Edit for clarification - There are certainly cases where CT is clearly preferable, e.g. bone where very high X-ray contrast yields excellent images, and where the lack of mobile water hydrogen nuclei means MRI works less well; similarly much emergency work is CT based, because time is of the essence - a CT examination which can be completed in 10-15 minutes is a huge advantage if an MRI might take 1-2 hours; finally in many cases, the different physical processes used by CT and MRI give different diagnostic information, so for some work, CT and MRI give complementary information and both may be needed for diagnosis).MRI has its own safety issues - such as ferromagnetic objects and magnets and electrical conductors, as well as heating. RF related heating (SAR) can be substantial with MRI - there is a regulatory limit of 4.0 W/kg whole body averaged over 6 minutes, which is actually quite a substantial heat load. Local heating can be higher under certain circumstances - for example, crossing your legs forms a loop antenna, and the current flow across the high impedance skin-to-skin contact patch can result in sufficient heating to cause 2nd or 3rd degree burns.

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2022, 09:14:43 pm
content: Another important difference is what kind of material is under examination.MRI essentially looks at tissue (including brain and other organs), liquid (blood and blood motion), or lipid (fat), where the protons give a useful signal, but MRI cannot get a useful signal from bone.X-ray CT is usually the choice for bone, or when a fast examination is required.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: December 22, 2022, 09:41:04 pm
content: Quote from: TimFox on December 21, 2022, 11:07:30 pmThey should have called the villain from the second Die Hard movie--the one with the gun made out of porcelain. You know, the one that costs more than you make in a year.

author: TimFox
author_rank: Super Contributor
timestamp: December 22, 2022, 09:43:12 pm
content: Quote from: Sal Ammoniac on December 22, 2022, 09:41:04 pmBronze would work better than porcelain, and be cheaper.

author: BrianHG
author_rank: Super Contributor
timestamp: December 23, 2022, 06:14:37 am
content: Now for the scariest view:

author: BrianHG
author_rank: Super Contributor
timestamp: December 23, 2022, 06:17:34 am
content: Here is a time-lapse upgrade of a Magnetom Prisma 3T MRI machine: (Maybe 3T means it's coil is 3 Tesla strong.)

author: BrianHG
author_rank: Super Contributor
timestamp: December 23, 2022, 06:26:08 am
content: 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.

author: EPAIII
author_rank: Super Contributor
timestamp: December 23, 2022, 08:14:35 am
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: December 23, 2022, 09:13:56 am
content: Quote from: EPAIII on December 23, 2022, 08:14:35 amAnything flung toward the 'ceiling' will succumb to gravity and end up impaling or crushing the patient.

author: TimFox
author_rank: Super Contributor
timestamp: December 23, 2022, 02:40:52 pm
content: Quote from: BrianHG on December 23, 2022, 06:17:34 amYes, 3T means 3 Tesla = 30 kgauss.For years, 1.5 T was the standard DC field strength in MRI.

author: Gyro
author_rank: Super Contributor
timestamp: December 23, 2022, 07:24:59 pm
content: Quote from: BrianHG on December 23, 2022, 06:26:08 amI'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.

author: WatchfulEye
author_rank: Regular Contributor
timestamp: December 23, 2022, 07:41:22 pm
content: Quote from: BrianHG on December 23, 2022, 06:17:34 am3T 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)

author: james_s
author_rank: Super Contributor
timestamp: December 23, 2022, 11:41:02 pm
content: Quote from: EPAIII on December 23, 2022, 08:14:35 amI 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.

author: Gyro
author_rank: Super Contributor
timestamp: December 24, 2022, 09:58:21 am
content: 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/

author: amyk
author_rank: Super Contributor
timestamp: December 24, 2022, 11:32:31 am
content: Quote from: tom66 on December 21, 2022, 11:18:03 pmYou'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.

author: BrianHG
author_rank: Super Contributor
timestamp: January 03, 2023, 07:54:42 am
content: Here is how the rotating CT scan is decoded:

author: grumpydoc
author_rank: Super Contributor
timestamp: January 03, 2023, 09:06:00 am
content: 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.

author: thm_w
author_rank: Super Contributor
timestamp: January 03, 2023, 10:38:37 pm
content: Quote from: BrianHG on December 23, 2022, 06:26:08 amArtificial 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/

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 03, 2023, 11:30:52 pm
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: January 04, 2023, 01:45:37 am
content: Quote from: thm_w on January 03, 2023, 10:38:37 pmDisc 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.)

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2023, 03:06:08 am
content: Quote from: Wallace Gasiewicz on January 03, 2023, 11:30:52 pmNo, EMI was short for Electric and Musical Industries.Quote from: Wallace Gasiewicz on January 03, 2023, 11:30:52 pmNo 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/

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: January 04, 2023, 12:53:34 pm
content: Sorry, I thought the Beatles owne a big part of EMI, apparently not.

author: thm_w
author_rank: Super Contributor
timestamp: January 04, 2023, 10:41:23 pm
content: Quote from: BrianHG on January 04, 2023, 01:45:37 amThey 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/2075-4442/3/2/346Sitting 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.

author: LaserSteve
author_rank: Super Contributor
timestamp: January 06, 2023, 10:15:56 am
content: 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

author: MrMobodies
author_rank: Super Contributor
timestamp: January 06, 2023, 10:21:56 am
content: QuoteSo it I put attractive facing magnet in there would that also increase the strength of the attraction?

author: SeanB
author_rank: Super Contributor
timestamp: January 06, 2023, 10:46:57 am
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: January 06, 2023, 12:52:28 pm
content: Quote from: SeanB on January 06, 2023, 10:46:57 amIf 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.

author: SeanB
author_rank: Super Contributor
timestamp: January 06, 2023, 08:40:43 pm
content: Used the aeskulap viewer, so probably need to figure it out a bit as to how it really works, but the images are there.

author: BrianHG
author_rank: Super Contributor
timestamp: January 06, 2023, 11:57:27 pm
content: Quote from: SeanB on January 06, 2023, 08:40:43 pmAre 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)

author: LaserSteve
author_rank: Super Contributor
timestamp: January 07, 2023, 04:43:18 am
content: 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..

author: BrianHG
author_rank: Super Contributor
timestamp: September 12, 2024, 10:04:02 pm
content: H O L Y S H I TTake 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...

author: WatchfulEye
author_rank: Regular Contributor
timestamp: September 14, 2024, 06:48:50 pm
content: Quote from: BrianHG on September 12, 2024, 10:04:02 pmThat 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.

author: coppice
author_rank: Super Contributor
timestamp: September 14, 2024, 07:09:22 pm
content: Quote from: BrianHG on December 22, 2022, 06:53:30 amThey are also so noisy the patient has ear mufflers to dampen the noise. An MRI machine is quite uncomfortable. It feels like they could do a lot more to make is pleasant for the patient, like at least keep the temperature better controlled with better air flow.

author: coppice
author_rank: Super Contributor
timestamp: September 14, 2024, 07:13:09 pm
content: Quote from: vidarr on December 21, 2022, 01:37:42 pmYou do see a strip of the rotating mechanics when you are inside a CT machine. The narrow ring where the x-rays go is exposed. You can't see the sheer bulk of what is spinning around, but you can see its speed, and its clearly not something small and light.

author: SiliconWizard
author_rank: Super Contributor
timestamp: September 14, 2024, 07:49:21 pm
content: Good thing they don't make the patient spin instead.

author: tooki
author_rank: Super Contributor
timestamp: September 15, 2024, 08:29:26 am
content: Quote from: coppice on September 14, 2024, 07:09:22 pmThat was never an issue in the MRIs I’ve had done. That sounds more like a design flaw in a particular model and/or some deficiency in the machine’s setup. (Like how the ambient air is handled.)The machines I was in had earphones (using air hoses to carry the sound, like really old airplanes used to do). I don’t remember whether there were over-ear hearing protection over them or not. (Probably??)

author: tom66
author_rank: Super Contributor
timestamp: September 15, 2024, 10:01:03 am
content: I had a sinus CT a few months ago, and whilst the machine wasn't silent, I wouldn't call it particularly loud. It was about as loud as being in a conversation with a few people.That said it was probably an older generation of machine so perhaps wasn't rotating as fast.

author: Halcyon
author_rank: Unknown
timestamp: September 15, 2024, 10:54:45 am
content: MRI's are fascinating machines. Watching the magnet being "quenched" is just as fascinating.The helium expands at such a rate that if allowed to escape into a relatively well sealed room, it can blow out windows/doors and even the joint where the walls meet the ceiling, which it why it's vented outside the building.Pushing that red emergency button results in a very expensive repair.

author: BrianHG
author_rank: Super Contributor
timestamp: September 15, 2024, 12:21:34 pm
content: Quote from: tom66 on September 15, 2024, 10:01:03 amCTs are quiet compared to MRIs.The field RF coils in MRIs are being modulated with RF inside a slower ramp signal, something like a slow 3 dimensional CRT monitor's yoke. This heavy-duty ramp signal, when it deflects from one axis to the next creates those huge different buzzing noises as that scan rate is slow, down in the audible range.

author: WatchfulEye
author_rank: Regular Contributor
timestamp: September 15, 2024, 12:57:41 pm
content: Quote from: BrianHG on September 15, 2024, 12:21:34 pmThis is the same mistake as in the video above.It is spatial modulation of the static magnetic field (e.g. A nominal 1.5 T static field may be modulated to 1.6T at the head and 1.4 T at the feet in order to extract location information in that axis), and not the RF.The sound produced can be substantial. With the exception of some ultra low field portable MRI systems, all current medical MRI can operate at well above 99dB(A) although they may not necessarily do so for all examinations.Higher gradient slew rates facilitate faster scanning and higher spatial resolution. Examinations of small body parts like hands, ankles, knees and inner ear as well as cine images, tend to be louder than most other scans. 120dB(A) can be reached by some scanners running these protocols.

author: TimFox
author_rank: Super Contributor
timestamp: September 15, 2024, 01:53:23 pm
content: Yes: an MRI scanner uses three different coil sets: from the outside in.1. The superconducting solenoid establishes the DC magnetic field, which is uniform in the imaging volume, in the z-direction.2. The gradient coils, which are pulsed, vary the magnetic field in a programmed fashion, as a function of x, y, and z. This coil set is also used to trim the uniformity of the DC magnetic field with appropriate DC bias currents.3. The RF coils (or resonator) excites the nuclear resonance of the protons in the patient, where the resonant frequency is proportional to the local magnetic field value. They are also used to receive the radio-frequency signal (not waves) from the rotating net magnetization of the proton spins. The complicated pulse sequence rotates the net magnetization away from the z-axis, and that magnetization vector then rotates in the x-y plane at the resonant frequency.The system is very flexible and designing the appropriate pulse sequence (for gradients and RF) is an important exercise.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 22, 2024, 11:19:18 am
content: I wonder what method they use to impart the spin motion. The first thought would probably be "electric motors" but they have their own magnetic fields which would have to be shielded from the diagnostic ones. Otherwise the magnetic crosstalk could affect both.

author: tom66
author_rank: Super Contributor
timestamp: September 22, 2024, 12:14:53 pm
content: Quote from: IDEngineer on September 22, 2024, 11:19:18 amHuh? The CT scanner can use electric motors since it is sensing X-rays from the generator.An MRI does not rotate the patient or scanning head, it detects everything via the RF coils. There are probably cooling fans and the like inside the machine that need some care if positioned near sensitive components, and the bed itself and moved in/out using a motor, but I imagine the fields produced by those are quite small.

author: BrianHG
author_rank: Super Contributor
timestamp: September 22, 2024, 05:12:53 pm
content: Quote from: IDEngineer on September 22, 2024, 11:19:18 amYou do realize that a CT scanner is a 3D X-ray machine. It does not see any magnetic fields, just X-rays.And an MRI is a 3D magnetic resonance imaging machine. No moving parts.Right?The 2 are not the same thing.

author: TimFox
author_rank: Super Contributor
timestamp: September 22, 2024, 05:25:36 pm
content: Yes, like any other expensive device, careful engineering is required to minimize unwanted noise in the signals.For x-ray computed axial tomography (CAT), normal motors are required to rotate the gantry around the patient, and an oil pump with cooling fans on the rotating platform to run a heat-exchange loop on the x-ray tube's anode.A motor built into the x-ray tube rotates a large anode disc to allow high-power anode dissipation for short times, since typical scans are done while the patient holds his breath; if the tube's anode is out of balance, this will degrade the image.Modern CAT scanners have a high-voltage supply on the rotating platform for the x-ray tube, and it must be shielded and filtered appropriately.Most CAT scanners have the detector array (now two-dimensional) rotating on the same platform with the tube, with fancy data communication from the detector electronics to the stationary platform.As posted above, MRI machines do not require motion (except for the patient couch), but the pulsed gradient currents could interfere with electronic signals; the basic signals from the patient go through a resonant "receive" coil, tuned to a much higher frequency.Sometimes, motors are required to operate vacuum-variable capacitors to tune the high-power RF coils: these motors are an engineering problem to avoid loss of homogeneity in the DC field due to ferrous components near the main magnet.Again, as mentioned above, the clearly-audible noise results from interactions between the gradient fields, the DC field, and the coil structure. Also audible is a mechanical refrigerator that often accompanies the magnet to minimize loss of liquid helium.

author: coppice
author_rank: Super Contributor
timestamp: September 22, 2024, 07:36:22 pm
content: Quote from: tom66 on September 22, 2024, 12:14:53 pmThe only motors in the heart of the machine are ultrasonic motors used to move the patient. Other types of motor are useless in such a powerful magnetic field. For cooling I believe they duct all the air, and the motors are well away from the magnetic field. Early MRI machines, before ultrasonic motors were commercially available, used electromagnetic motors to move the patient, but had to site them remotely, and used non-ferrous gears and long rods.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 22, 2024, 07:39:46 pm
content: Quote from: coppice on September 22, 2024, 07:36:22 pmInteresting. I thought perhaps they used hydraulic or pneumatic motors/cylinders, with the pump remotely located for sound/cleanliness. Those can be made quite powerful yet with minimal crosstalk to magnetic fields. You can hold a 10HP hydraulic motor in the palm of your hand.

author: coppice
author_rank: Super Contributor
timestamp: September 22, 2024, 07:44:21 pm
content: Quote from: IDEngineer on September 22, 2024, 07:39:46 pmCan you make good high lifetime hydraulic motors without using ferrous metals?

author: WatchfulEye
author_rank: Regular Contributor
timestamp: September 22, 2024, 08:15:01 pm
content: Quote from: coppice on September 22, 2024, 07:36:22 pmWhen I happened to see an MRI system with the covers off, I was so surprised to see the fans bolted to the magnet, that I had to snap a picture!

author: TimFox
author_rank: Super Contributor
timestamp: September 22, 2024, 08:38:12 pm
content: The warning about the magnetic part is extremely important!I once set down a tweezers on the patient couch during a repair and it went flying point-first into the bore.Field engineers were always finding paper clips stuck to the magnet (not good for homogeneity) despite the availability of plastic clips at office-supply stores.

author: IDEngineer
author_rank: Super Contributor
timestamp: September 22, 2024, 09:44:49 pm
content: Quote from: coppice on September 22, 2024, 07:44:21 pmThe seals aren't metal so no problem there. Pump bodies are already available in aluminum. The big question is the shafts and (if a gear motor) the meshing gears. If it's a vane pump design the vanes are not metal and I suspect the shafts and carriers wouldn't need to be either.I'm not a pump expert nor a metallurgist, but we had Danfoss (huge hydraulics manufacturer) quote a pump that would be submerged and operated in seawater indefinitely and they had no problem with it. I'm pretty certain it didn't have any ferrous metal content since that doesn't mix well with seawater (well, actually, it mixes a bittoowell).

author: tom66
author_rank: Super Contributor
timestamp: September 22, 2024, 09:46:04 pm
content: For MRIs there is a whole industry of 'MRI-safe' equipment.The interesting ones are devices like headphones and televisions. For headphones the answer is usually simple - typically the sound unit is placed far away from the MRI and air hoses conduct the sound. It's not particularly good but it does work. For analysing the brain's response to visual stimuli, a monitor is needed. This usually relies on mirrors from an external monitor, though there's aheadset availablewhich does this in VR. With sufficient shielding and minimising ferrous components the device can be made sufficiently safe for MR environments.