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MRI vs CTA 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 enhancementBoth 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. 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 compound) 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) 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.ApplicationIn 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.
*I hate the grow/shrink thing It makes me miss posts!*
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!
Ewe may be thinking of a barium meal ...sorry, you cannot view external links. To see them, please
REGISTER or LOGINIt'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 !
Blasting radiation into yourself was never a safe thing. Neither was eating purified radioactive material.Though I don't see how an MRI could do that. If I understand correctly, it functions like an NMR which just works on changing the spin of protons. Come to think of it, are the MRI Machines in hospitals Carbon, Phosphorus or Hydrogen NMRs? I figure it'd be one of these three since these are most abundant.
I don"t know.. but I had so many iodized cat scans and exrays and such that they said I was at the limit.. so I just had another and my doctor was worried because she said She had hoped she did the right test as she doesn't want me having too much yet.. I guess there is some kind of time frame and limit before trouble..I really don't understand..
Does anyone know what Neuro Vascular Digital Subtraction is??
Quote from: Karen W. on 05/02/2009 10:28:57I don"t know.. but I had so many iodized cat scans and exrays and such that they said I was at the limit.. so I just had another and my doctor was worried because she said She had hoped she did the right test as she doesn't want me having too much yet.. I guess there is some kind of time frame and limit before trouble..I really don't understand..Karen, I would look into getting MRI from now on, instead. It's relatively harmless compared to CT. They may be more reluctant to order MRI just because it may cost the medical system a little more than CT. I don't think this is a good reason though, when we're talking about your health.As far as I know, with CT, it's the cumulative radiation (e.g. the number of scans you've had in total) that matters, not the amount of time that elapses between scans. The time concern probably has more to do with iodine. (e.g. to rest your kidneys before giving you more contrast).
Quote from: Counterpoints on 09/06/2009 19:36:45Quote from: Karen W. on 05/02/2009 10:28:57I don"t know.. but I had so many iodized cat scans and exrays and such that they said I was at the limit.. so I just had another and my doctor was worried because she said She had hoped she did the right test as she doesn't want me having too much yet.. I guess there is some kind of time frame and limit before trouble..I really don't understand..Karen, I would look into getting MRI from now on, instead. It's relatively harmless compared to CT. They may be more reluctant to order MRI just because it may cost the medical system a little more than CT. I don't think this is a good reason though, when we're talking about your health.As far as I know, with CT, it's the cumulative radiation (e.g. the number of scans you've had in total) that matters, not the amount of time that elapses between scans. The time concern probably has more to do with iodine. (e.g. to rest your kidneys before giving you more contrast).I am sorry that I missed this post.. thank you for the information . Its been a long while now but as you said with this information and my further talking with the doctor, it was indeed more cat scans and regular exrays they were worried about, I had taken her comments as being about MRI's in particular, when she was telling me about all the exrays cat scans and MRI's. Turns out I had had Far too many exrays ct scans etc.... between all the different Doctors. Thanks....
Do you think there is anything to this..?...sorry, you cannot view external links. To see them, please
REGISTER or LOGIN I just saw the ad here in the forum!
They are ok.. but the noise was awful. Towards the end my arm felt as if the insides were moving around on my left arm.. It was odd! The music they put on was totally inaudible over the pounding of the machine. I go for another Ct Scan in September. At least thats what Stanford has said!
Quote from: Karen W. on 29/06/2009 07:50:23Do you think there is anything to this..?...sorry, you cannot view external links. To see them, please
REGISTER or LOGIN I just saw the ad here in the forum!Gadolinium is the contrast they use in MRI. It isn't always needed though. If there is no gad contrast, MRI (as far as we know) is completely safe, so long as you don't have metal in your body, or a pacemaker, etc.An MRI with gad contrast is also relatively safe. The contrast is considered safer than the iodine used in CT, with a very small percentage (about 0.03%-.1%) having serious allergic reactions. The risk they're talking about is nephrogenic systemic fibrosis, which from what I've read, is extremely rare and has only been associated with people who have severe kidney impairment (for instance, those in need of dialysis). If you do have kidney problems though, it is something to discuss with the doctor before having GAD contrast with an MRI.
I am not sure why.. but when I spoke with the nurse last week she did say it was an CT scan they were setting up. Couldn't hurt to ask I guess. They will be taking measurements and looking at two anuerysms in the Aorta and checking the valves etc.. I have to have them all replaced coming up. The doctor said to me that after the surgery he can give me five years maybe ten...Is that a common time frame for replacement of all that stuff and dealing with the aneurysms? So what kind of a time frame does one have if I were to refuse the surgical replacements/do you know what the statistics are for that?Is it worth 5 years? Will the distress and healing of surgery out weigh the gift it gives..?
THE CARDIOLIGIST/SURGEON.I do not know yet! That is one of the reasons for tests.. more CT scans etc..Sorry I just thought you might know if that was about standard life expectancy after these kinds of surgeries. It's ok.. I cannot find any real sound stats on it although the ones I did find were vague.
I can't find how to start a new topic so I am replying to this topic. I have had a lot of problems and pain this week in my lower stomach (where I suspect my ovaries would be). It started Monday when I had a gush of blood accompanied by pain. The Dr said I had a cyst burst and sent me home with no tests done. The following day I was in so much pain so I went back to emerg and they kept me there all day. The Dr on call was the same Dr whom I seen the first time he ran a X-Ray, Ultra Sound and a Ct scan and found nothing. I'm still in a lot of pain and the pain has spread from my lower stomach to shooting down my right leg and my lower to mid back now. Will a MRI show things these other tests couldn't?