posted
What would be the most sensible way to detect a foreign object inside somebody's head? And can an MRI scan of the head, or a catscan, detect such a thing?
Posts: 2195 | Registered: Aug 2006
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posted
I'm not the best person to describe to you the exact medical useages of CAT vs MRI scans, but if you need someone to describe to you what it's like going thru the process, I can fill you in. I had a CAT scan, PET scan, and MRI done a few months ago.
PET scans work with a radioactive glucose isotope, which is attracted toward high-metabolic cells, such as cancer. Cancer is hungry for sugar, the doctors have told me. The test results show the temperature differences in the body, cancer being a high-metabolic area shows in "hot" colors like orange red and yellow; low metabolic cells showing in blues and greens. My doctor didn't need film, the imaging company sent him my test results on the internet and he could log in and see them without waiting. They do a CAT scan at the same time, and overlay the test results, but I didn't ask questions about the details of what the CAT scan did that the PET scan didn't.
My understanding is that MRIs are less about what is going on inside the organs, as a look at the organ itself. I'm guessing an MRI would pick up a foreign object. I'm not sure exactly how the CAT scan falls into that scenario.
MRIs are loud, and sound like the Emergency Broadcast signal we still hear on American radio stations from time to time. You have to wear a couple of layers of hearing protection (earplugs and earmuffs) to protect your hearing. The tube they put you in is tight, so tight you may only have a fist-width between you and the top of the tube. PET scans, on the other hand, are in a (slightly) larger tube, and while you can hear them, they aren't nearly as abraisively loud as the MRI. By the way, when they did the MRI on me, I could literally feel my intestines jump around when it passed over my stomach area. It was unnerving. If you are claustrophobic, this won't be a fun test. For both tests, you have to lay PERFECTLY still for 45 minutes. No wriggling, moving, or doing anything other than breathing slowly.
posted
If the item is a magnetic metal and is lodged in the head/brain, then they would not use an MRI. The intense magnetic field coudl cause the item to shift, which could cause irreparable damage.
If the item is something intentionally implanted it would more than likely be made of a non-magnetic material. This would definately show up in an MRI. But if there is any suspicion that the item might be magnetic no doctor or hospital would allow the test.
posted
Okay, suspect data...but... On the Art Bell Show one night they had a live broad cast of this surgeon who is interested in "strange" implants that appear in people with no known time they were implanted. Some of these appear to be metallic, iron, even, but are not magnetic. The piece he was trying to remove kept moving around on its own. They had to run several x-rays to relocate it. A few millimeters, not inches, but still...interesting. The piece had small "whiskers" on it. Just thought I'd throw this in the info since you're writing fiction.
Also, on an episode of HOUSE, House shot a bullet into this corpse that had died of cancer, then put the body through an MRI. The bullet fragments came through the skull and wrecked the MRI machine. How true is this? I don't know, but I would think they'd have run the idea by someone who did know.
posted
Hey all. Friendly neighborhood medical physicist here.
An MRI and CT (Probably shouldn't call it a catscan. If you must refer to it colloquially, CAT scan would be better.) are both used in different situations to image different things.
Without knowing what your patient presented with, I would bet a head CT would be ordered in which pretty much any foreign object could be detected, unless that object had a similar electron density to water.
Edit: If you want more information on any of the medical imaging modalities, just let me know and I'll try to help you out.
[This message has been edited by Rahl22 (edited October 11, 2007).]
posted
CT scan: I believe you have to ingest something--barium solution? kind of milky--that is a little radioactive (at least, that's what I think they had me drink when I had a full-trunk CT scan a couple of years ago). Then you wait a little while so that it can move through your system.
The scan took place as I lay on a special table, and, if I remember correctly, they ran the light scanner over me in short bits so that I could hold my breath each time--hold-light on, then breathe, then hold-light on, then breathe. Had plenty of space around me, wasn't claustrophic at all.
I'm not sure how they'd do a head CT scan.
But an MRI does use a powerful magnetic field, so they wouldn't use it if they thought you had anything in you that would react to the field, and be pulled right out of your body.
posted
Kathleen, the barium contrast of which you speak probably wasn't a radiopharmaceutical unless you were undergoing a combined CT/PET scan in which case they'd probably forgo the contrast entirely in exchange for a positron emitter. The barium is merely a heavy metal which shows a high contrast under CT due to the large deviations in physical/electron density from the adjacent soft tissue. CTs of the head are performed in exactly the same way, except the importance of breath-hold techniques becomes insignificant.
Posts: 1621 | Registered: Apr 2002
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Imagine we are going to run a CT scan, I guess, on this patient, and we are trying to detect a foreign object in his head. It is also important that our patient is not conscious for the procedure, is the CT scan still recommended?
[This message has been edited by Zero (edited October 12, 2007).]
Are you sure contrast would be used when evaluating a foreign object in the head? I'm not a physician, but I've never seen that.
The reason why you never see this is because most physicians always assume there is bleeding involved with a foreign body. Hence why I said if no bleeding is suspected.
But I'm assuming he wanted reality for his story and if there are no contraindications (allergies, active bleeding, or increased intracranial pressure) for contrast most doctors would prefer contrast.
posted
If someone had metal in their body (joint replacement, for example), the metal would disrupt the MRI image, making it difficult to see surrounding tissue. Whether or not a foreign object was metal, the test of choice would probably be a CT scan.
BTW, here's an article on which implants/foreign objects are contraindications to using an MRI:
Also, why not do an x-ray first? Lots of foreign objects show up on those, and it's usually done as a preliminary, let's-see-what-we-have-here sort of test.
posted
A catscan (CT) is not really for finding foreign objects. An X-ray will do that just fine. CT's and MRI's are generally for the brain. If you want an order of seriousness, from least to greatest, it would go X-ray, CT, MRI. Also, if you use MRI, you have to realize that the patient has a 2-hour prep time. They have to drink three doses of contrast (basically looks like Mountain Dew, I have no idea how it tastes) an hour apart. So you take one dose immediately (each dose fits in a styrofoam cup), the dose an hour later, and the third an hour after that. An MRI can be used to scan the whole body, while a CT generally scans the brain. Go to wikipedia if you want more detail, though.
Posts: 657 | Registered: Jan 2007
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posted
I don't mean to be a jerk, but lots of the information I've seen in this thread (not all of it, so I'm probably not talking about _you_, so don't get pissed) has seemed to be awfully spurious. I mention this because it makes me wonder about other advice-seeking threads in which I have NO experience whatsoever. Are people giving similar conjecture?
Posts: 1621 | Registered: Apr 2002
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posted
Zero, seems like hteadx has it most concisely and accurately. However, RMatthewWare is also correct in that sometimes simple x-ray films will be taken (generally, go with the CT) in smaller clinics.
Posts: 1621 | Registered: Apr 2002
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posted
The contrast used for the CT scan and the MRI I underwent was injected intraveneously via a needle in my arm. I did not have to drink anything at all either time.
The contrast, by the way, within about hmm... 30 to 45 seconds after being injected, has a strange sensation of a rush of sudden heat in the back of your throat, and then in your urinary tract so it feels like you just wet your pants. The nurse warned me not to panic when I felt it happen. It wasn't uncomfortably hot, but it was still a pretty strong feeling. The heat flush lasts for about a minute or so, then subsides.
Having spent a brief month filling in on housekeeping duty at the local hospital, and having had to mop the MRI/CT room, I can tell you the technicians sometimes spill drops of the contrast on the floor and it's a bear to mop up because it dries like sugar water on the floor... leaving hard to clean spots that are also hard to see if the light isn't right. It's a bit sticky. There's another fact you won't find in a medical text book.
[This message has been edited by Elan (edited October 15, 2007).]
posted
in my underground medical practse if we suspict that someone has something in their head we saw the top of their head off and pockaround until we find something. most of the time the person dose not make it. more to eat for us. Posts: 856 | Registered: Nov 2006
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