OT sort of: Son's MRI homework

[supermum_ms]

The MRI

The purpose of a MRI or magnetic resonance imaging machine, is to harmlessly work out what internally is physically wrong with you, without involving exploratory surgery. MRIs have 3 types: conventional, open bore and fully open. In an conventional MRI, a long toroidal (Doughnut-shaped) electromagnet supplies the electromagnetic force, and the subject is put through a long 'tunnel', where a full-body scan is supplied. A open-bore MRI is quite similar, but the hole is larger and less tunnel-like, meaning that larger (Obese) people, and the claustrophobic can use it. However, there is less of an area that can be scanned without moving the person, so this form is better for brain and pelvic scans. The third type, the fully open kind, does not involve a tunnel, so the patient can be scanned while certain joints are bent. However, in all cases MRI s use supercooled superconducting magnets, so great care has to be taken around one.

In an MRI, powerful electromagnets  make certain molecules spin. A radio signal it then fired towards the molecules, and if the molecules are vibrating at a certain frequency, they deviate from the original orientation, and fire a signal back, returning back to it's original position. This is repeated several times, resulting in a 2-D image being built up over time, governed by the response of the atoms. These magnets vary depending on the type of MRI, but the idea behind it is the same.

In some cases, the powerful magnets can cause problems, and can even be fatal. In one case in may 2002, an off-duty American police officer's gun got caught in the magnetic field of a MRI machine, hit the bore, and discharged, bypassing a active safety and two other passive safetys. The gun being brought into the room was the result of a misunderstanding between the officer and trained personnel, but it really is no reason to be not very careful around these things. (By the way, the bullet did not harm anyone, and it only did minor cosmetic damage to the machine. More information at http://www.ajronline.org/content/178/5/1092.full#sec-1 )

As a result, precautions have been made to make sure incidents like this do not happen. For example, certain medical items which are deemed 'MRI unsafe' like ferromagnetic scissors intended for surgery, or metal items like industrial floor polishers (So keep your buckyballs away) are not allowed in the MRI area. Also, MRI safe and 'MRI Conditional' items are tested usually at magnetic static field tests of 1.5 Tesla, and have specific guidelines in how they can be used in the case of the latter (MRI safe things are usually made of non-metals and things like plastic). In most cases, patients are only allowed in the clothes they came in if there is nothing ferromagnetic (Attracted to magnets), in or on their clothes (So no zips); in all other cases the patient may have to wear a gown.

To clarify, MRI conditional means that in certain conditions, these items are ok to expose to the MRI's force. Some MRI conditional items however, are actually slightly 'ferromagnetic' and are only considered not unsafe because the other forces exerted on it in daily use are stronger. If anyone has gone and had an MRI, they may remember the loud noises coming from the machine as it scanned them. The thing is, these pops and bangs are actually caused by the different coils moving as they are activated and deactivated. Also on the topic of experiences, some people may have overheated while undergoing an MRI, and there is a possible reason for this: MRIs' work by polarising and spinning particles, then vibrating them with a radio signal which is then sent back and recorded. This might result in water molecules constantly bumping into each-other, which produces friction and heat similar to the way a microwave cooks a chicken, or other thing with water in it. As a result, large amounts of heat could be produced, and the patient may overheat. However, some doctors will dismiss this as psychosomatic (All in the head) and not an actual phenomenon.

MRI s can be a useful tool for doctors, and can diagnose many illnesses (MS being one of them, as they can scan the brain). But if they are so good, why do hospitals only have one or two of them? The main reason is that they are VERY expensive. MRI equipment varies in cost, depending on the strength of the scanner. Scanners with more strength produce more detailed images so these scanners usually cost more. Firstly, there is the cost of the MRI itself, then there is the specialised MRI 'suites' that are built especially for it, and then there is the cryogenic fluid that is required if the electromagnet undergoes a 'quench', where there is a coolant leak that is caused by near explosive heating of this coolant (Usually liquid helium, hydrogen or nitrogen), and is not able to be recovered resulting in a large downtime before it gets back to fuul strength. As a result, an MRI examination can cost several thousands of dollars, as it includes a charge for using the MRI machine to perform the scan, as well as a professional charge for a radiologist to view the images.

In the end, the MRI machine is a miracle, as long as you don't have a pacemaker, metal hip replacement or metal ANYTHING replacement, and you can afford it.

References
information was gained from all of the following MRI-related sites.
http://www.ccmr.cornell.edu/education/ask/index.html?quid=41
http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/MRI_scan
http://www.fonar.com/patient/mri_faqs.htm#faq2
http://mediluxhealthcare.com.au/open_mri.html
http://www.medicinenet.com/mri_scan/article.htm
http://www.cis.rit.edu/htbooks/mri/inside.htm
http://www.ajronline.org/content/178/5/1092.full#sec-1
http://www.mrisafety.com/list.asp
http://www.ehow.com/about_4731161_much-do-mri-machines-cost.html

Did you know?
Most of the MRI machines used on animals are actually stronger than the MRIs used on people!

[HVAC]

Cool. Many animals who get MRIs are much bigger than people such as livestock, race horses, and zoo animals. Using an MRI purely in a small animal practice would not work because of the cost would be to high. Mostly Vet Schools have them. Plus larger animals are harder to do exploratory surgery on because they can't lie down for long or the weight crushes organs and they can't be under anesthesia for as long either with out risk of death. Also animals move more in MRIs so you need sharper images taken faster.

Alex

[SarahL2491]

also you can now have an MRI with a pacemaker.  I had one done in Febuary.  The pacemaker representative has to be there to turn off the pacemaker (to keep the settings from being messed up) and a cardiologist usually is there in case he might be needed.  Then afterwards, they turn the pacemaker back on and recheck the settings.  Very good write up though!