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Author Topic: What is the difference between a CT Scan and an MRI scan?  (Read 245414 times)

neilep

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Hello,

I'm Neil...and ewe are ?

Yesterday I had a CT scan.....trying to get to the bottom of my ear related woes......what's the difference between a CT scan & a MRI scan ?
I gather a MRI is far more intense but how do these scan things work ?

Also, I was the only one out of 6 people whop was having a CT scan.......WHY did all the others have to drink a whole jug of water before their MRI scan ?

It would be scantastic for me if ewe revealed the answer and developed my knowledge base further....
« Last Edit: 27/06/2009 20:02:50 by chris »

another_someone

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #1 on: 19/07/2007 16:43:14 »
CT is the same as CAT or Computerised (Axial) Tomography -this is basically a sophisticated X-ray, in 3D.

MRI is Magnetic Resonance Imagining, previously known Nuclear Magnetic Resonance, until people started thinking one should not have the word Nuclear in anything.  MRI immerses you in a massive magnetic field, and then flood you with radio waves, and try and work out what strength of magnetic field will cause the nuclei to resonate at which radio frequencies, and so judge which chemicals exist within a locality of the body.

http://en.wikipedia.org/wiki/Magnetic_resonance_imaging
Quote
MRI vs CT

A computed tomography (CT) scanner uses X-rays, a type of ionizing radiation, to acquire its images, making it a good tool for examining tissue composed of elements of a relatively higher atomic number than the tissue surrounding them, such as bone and calcifications (calcium based) within the body (carbon based flesh), or of structures (vessels, bowel). MRI, on the other hand, uses non-ionizing radio frequency (RF) signals to acquire its images and is best suited for non-calcified tissue.

CT may be enhanced by use of contrast agents containing elements of a higher atomic number than the surrounding flesh (iodine, barium). Contrast agents for MRI are those which have paramagnetic properties. One example is gadolinium.

Both CT and MRI scanners can generate multiple two-dimensional cross-sections (slices) of tissue and three-dimensional reconstructions. Unlike CT, which uses only X-ray attenuation to generate image contrast, MRI has a long list of properties that may be used to generate image contrast. By variation of scanning parameters, tissue contrast can be altered and enhanced in various ways to detect different features. (See Application below.)

MRI can generate cross-sectional images in any plane (including oblique planes). CT was limited to acquiring images in the axial (or near axial) plane in the past. The scans used to be called Computed Axial Tomography scans (CAT scans). However, the development of multi-detector CT scanners with near-isotropic resolution, allows the CT scanner to produce data that can be retrospectively reconstructed in any plane with minimal loss of image quality.

For purposes of tumor detection and identification, MRI is generally superior. However, CT usually is more widely available, faster, much less expensive, and may be less likely to require the person to be sedated or anesthetized.

Contrast enhancement

Both T1-weighted and T2-weighted images are acquired for most medical examinations; However they do not always adequately show the anatomy or pathology. The first option is to use a more sophisticated image acquisition technique such as fat suppression or chemical-shift imaging.[7] The other is to administer a contrast agent to delineate areas of interest.

A contrast agent may be as simple as water, taken orally, for imaging the stomach and small bowel although substances with specific magnetic properties may be used. Most commonly, a paramagnetic contrast agent (usually a gadolinium compound8[9]) is given. Gadolinium-enhanced tissues and fluids appear extremely bright on T1-weighted images. This provides high sensitivity for detection of vascular tissues (e.g. tumors) and permits assessment of brain perfusion (e.g. in stroke). There have been concerns raised recently regarding the toxicity of gadolinium-based contrast agents and their impact on persons with impaired kidney function. Special actions may be taken, such as hemodialysis following a contrast MRI scan for renally-impaired patients.

More recently, superparamagnetic contrast agents (e.g. iron oxide nanoparticles[10][11]) have become available. These agents appear very dark on T2*-weighted images and may be used for liver imaging - normal liver tissue retains the agent, but abnormal areas (e.g. scars, tumors) do not. They can also be taken orally, to improve visualisation of the gastrointestinal tract, and to prevent water in the gastrointestinal tract from obscuring other organs (e.g. pancreas).

Diamagnetic agents such as barium sulfate have been studied for potential use in the gastrointestinal tract, but are less frequently used.

Application

In clinical practice, MRI is used to distinguish pathologic tissue (such as a brain tumor) from normal tissue. One advantage of an MRI scan is that it is harmless to the patient. It uses strong magnetic fields and non-ionizing radiation in the radio frequency range. Compare this to CT scans and traditional X-rays which involve doses of ionizing radiation and may increase the risk of malignancy, especially in a fetus.

While CT provides good spatial resolution (the ability to distinguish two structures an arbitrarily small distance from each other as separate), MRI provides comparable resolution with far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not identical tissues). The basis of this ability is the complex library of pulse sequences that the modern medical MRI scanner includes, each of which is optimized to provide image contrast based on the chemical sensitivity of MRI.

For example, with particular values of the echo time (TE) and the repetition time (TR), which are basic parameters of image acquisition, a sequence will take on the property of T2-weighting. On a T2-weighted scan, fat-, water- and fluid-containing tissues are bright (most modern T2 sequences are actually fast T2 sequences). Damaged tissue tends to develop edema, which makes a T2-weighted sequence sensitive for pathology, and generally able to distinguish pathologic tissue from normal tissue. With the addition of an additional radio frequency pulse and additional manipulation of the magnetic gradients, a T2-weighted sequence can be converted to a FLAIR sequence, in which free water is now dark, but edematous tissues remain bright. This sequence in particular is currently the most sensitive way to evaluate the brain for demyelinating diseases, such as multiple sclerosis.

The typical MRI examination consists of 5-20 sequences, each of which are chosen to provide a particular type of information about the subject tissues. This information is then synthesized by the interpreting physician.


neilep

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #3 on: 19/07/2007 22:09:04 »
GEORGE..THANK YOU VERY MUCH.......wonderful information.




IKO !!...DOH !!!

Post by Karen W. click to view.

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #4 on: 20/07/2007 01:33:17 »
Shrunk
LOL LOL HOMER!!!!!!!!!!!!!! LOL LOL LOL LOL!!!!!!

Simulated

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #5 on: 20/07/2007 02:20:32 »
Yepp! That's funny! LoL. I hate MRI's. I sat in one for over an hour. Not moving at all. It stunk!. I've had lots of X-Ray's and no CT scans. Thanks for posting this I've always wannted to know!

neilep

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #6 on: 20/07/2007 12:17:31 »
My CT Scan only lasted a couple of minutes...it was quite fun...I wanted to go again !!

I like the spinny turny thing !!

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #7 on: 20/07/2007 13:01:07 »
My cat scan took about ten minutes and my MRI Took all total AROUND 25 TO 30 MINUTES.. It was like having a jack hammer pounding above my head with the ear plugs and the headphones it was still loud.. he forgot to turn the music on until about half way through the procedure...LOL  Then I could barely here that over the pounding and the ear phones..

Simulated

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #8 on: 20/07/2007 13:04:55 »
HAHA Karen! I was sitting in there for an hour with those things moving and I don't think I had ear plugs in. lol. And I wish I would have had a CT scan.

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #9 on: 20/07/2007 13:17:03 »
Cat scan was relatively quiet in comparison!

Simulated

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #10 on: 20/07/2007 13:27:38 »
Plus the spinny thing. Done Deal! LoL. Why is there a gap between some of the replies? Am I the only that has it?

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #11 on: 20/07/2007 14:40:08 »
You have to open it up. Use your shrink button to your right some comments are shrunk if they are "pointless comments " Just chit chat!

neilep

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #12 on: 20/07/2007 15:54:29 »
Did ewe guys and gals have to drink lots of water for your MRI scans ! ?





*side note: not too sure if i like the grow/shrink thing yet*

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #13 on: 20/07/2007 16:11:07 »
*I hate the grow/shrink thing It makes me miss posts!*

I did not as it was for my shoulder and arm.. I think it is different if its a full body scan for some reason.At least on the MRI..! They have these weird little cocktails which I believe allow them to see other things maybe digetion system or something.. I am not sure!

neilep

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #14 on: 20/07/2007 16:15:41 »
Ewe may be thinking of a barium meal http://en.wikipedia.org/wiki/Barium_meal


It's only because all the others who were waiting had to drink this whole jug of water !....they were MRIing..I was CTing!!....I just can't imagine that all 5 had the same condition requiring all that luffley H20 !

paul.fr

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #15 on: 20/07/2007 16:19:56 »
*I hate the grow/shrink thing It makes me miss posts!*


The grow shrink thing is there to cut out the chat in topics, this reduces the necessity to split topics to remove said chat. You can always get them back by having the grow shrink thing, grow as opposed to shrink  ;)

Simulated

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #16 on: 20/07/2007 16:31:38 »
You have to open it up. Use your shrink button to your right some comments are shrunk if they are "pointless comments " Just chit chat!

Thanks Karen and Neil I didn't have any water.

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #17 on: 20/07/2007 16:32:41 »
Ewe may be thinking of a barium meal http://en.wikipedia.org/wiki/Barium_meal


It's only because all the others who were waiting had to drink this whole jug of water !....they were MRIing..I was CTing!!....I just can't imagine that all 5 had the same condition requiring all that luffley H20 !

Well It has been many years ago but they made my mom drink a lot of something.. I don't think it was water though right before her MRI.. Could have been , but I thought it was something else.. LOL who knows..

I do know about the barrium thingy.. That is the chalky tasting thing is it not?

cocojambo

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #18 on: 22/11/2008 22:53:15 »
Here are the differences & similarities between MRI scans and CT scans taken from the Mesothelioma Library

- CT scans allow the radiologist to see detailed views of the lungs & the pleura
- CT scans help determine the location, extent & size of tumor masses residing in the lungs more accurately than x-rays
- CT scans can reveal thickening of the pleura by examining the absorption rates of varying thickness levels of tissues
- CT scans can also indicate lung cancer beyond the pleura within the chest wall or lymph nodes
- CT scans can help evaluate the conditions of the lungs

Magnetic Resonance Imaging (MRI) is a medical imaging technique used to take pictures of the lungs, structures of the body and organs. It can provide detailed visuals of the body in any plane. The advantage of using MRI over Computed Tomography (CT) scans is that MRI scans provide greater contrast between different tissues of the body making it easier to detect malignant cancerous cells & tumors.
Source: http://www.themesotheliomalibrary.com

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #19 on: 23/11/2008 23:50:57 »
Thanks and welcome to the forum cocojambo!

Counterpoints

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #20 on: 28/11/2008 01:48:17 »
Some of the information in this thread is misleading.

- The word "nuclear" wasn't removed simply because people "felt nothing should have the world nuclear in it".  Unlike CT, you are not exposed to any ionizing radiation with an MRI scan.
- CAT is an older version of CT.  "Although historically the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures."
- Generally, MRI is much better at imaging soft tissue (e.g. brain).  Sometimes CT is better at imaging hard structures (bones). 
- You don't always have to drink something before taking an MRI.  Sometimes you will have a contrast agent (magnetic dye) to make the image clearer.  Many times this isn't needed.  Also note there is regular MRI, and functional MRI (fMRI).
« Last Edit: 28/11/2008 01:54:04 by Counterpoints »

demografx

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #21 on: 06/12/2008 01:33:18 »
All I know is that when my cat was alive, she refused to be scanned. or touched in any way ;D

OldDragon

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #22 on: 06/12/2008 20:03:36 »
There is a woman near me - elderly cat owner - who had to have some sort of scan and had to drink a barium meal before. She had me in stitches afterwards when she said that she needed to jump the queue for the ladies loo because they'd made her drink a barbarian meal. Another eldery woman in the queue remarked that they must have liquidised it first.

There Neil, ewe been warned - stay away from the queues for hospital's ladies loos, else face the danger of PYSL... like me!  :D;D

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #23 on: 06/12/2008 22:09:30 »
I've got to go for another CT scan on my lung. I don't remember much about the last 1 as I was pretty ill :(, but I'm sure that was the scan when they injected something into my arm that made me feel as if I'd wet myself. My groin & the top of my legs suddenly went warm. It was a very strange feeling

Karen W.

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Re: What is the difference between a CT Scan and an MRI scan?
« Reply #24 on: 10/12/2008 09:32:14 »
Over the last two years i have had several of both and at one point had to hold off on one as they said... the were making me sick....They were iodized cat scans...

 

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