MRI Sequences: What's the difference b/w them?

What are the differences b/w a T1, T2, and susceptibility weighted MRI? Which, in general, offers the highest resolution and contrast? Let's say we were to compare three MRIs taken on a 4T machine of a patient w/ a hypersensitivity pneumonitis --I know you're supposed to use HRCT for this, but just play along--, using all three sequences. What would the differences in the image be? What about co-registering T1 and T2?

And what tends to be the most expensive; I'm betting SWI.

Could you find a image of a T1 and T2 MRI, of the same slice of the same patient for me to look at; google images isn't bringing much up.

Thanks!!!

Docxter said:

Ok, assuming you are not a troll, and you're just some kid interested in things he doesn't understand, in simple MR terms:

T1 image (or more correctly T1-weighted image) is one with a short TE and TR.

T2 image (or more correctly T2-weighted image) is one with a long TE and TR.

Susceptibility weighted imaging (SWI), assuming you are not confusing it with the plain susceptibility imaging (like probably 99.9% of neurologists and even most radiologists) is when you use the phase maps of a sequence, unwrap it, pass it through a high-pass filter, and apply the resulting mask a few times to the amplitude image, in order to really bring out the susceptibility contrast of the structure of interest (almost always the brain).

What about co-registering T1 and T2? If you're asking if it's doable, yes, you can technically register anything to anything. I don't know why you would want to, but hey its up to you.

Adding SWI software capability to a standard commercial MRI machine (Siemens) will cost you.

SWI of the lungs would show a big black hole.

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Yes, I'm a kid; 16yrs old and starting community college in May; my Dr friend is going to have me shadowing a radiologist and pathologist in the fall, and I'm trying to get some prelim knowledge before I start.

hans19 said:

http://www.mri.tju.edu/lect.htm

Knock yourself out. I could give you the short answer, but it wouldn't help you understand why. I don't have the patience or the time to explain all the nitty gritty detail, and I probably couldn't do it any where near as well as these guys.



Absolutely hypersensitivity pneumonitis is better seen on HRCT. First of all the spatial resolution isn't as good on MRI as it is for CT. Another thing-MRI is imaging of protons. In general the body = ~60% water and ~20% fat = lots of protons. Air = 70% nitrogen, 1 or 2% h20. (Not so many protons)
But - the Lung = 99% air. Air= black and fuzzy on all MRI sequences. QED= you cant see sh-t in the lungs on MRI unless you have lot of fluid in lots of alveoli (ie pulmonary edema or consolidation.)

Let me ask you a question along the same lines. I know a fly swatter would work best but just play along--which type of baseball bat is best for swatting flies-- aluminum or pine? Answer- fine, one might be slightly better than the other, but neither comes close to the fly swatter. Capisce?

Another thing contrast depends on degree of T1 and T2 weighting as well as the inherent T1 and T2 properties of the tissues you are imaging. Fat water soft tissues, etc...

Just check out this website first.

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So, what's plain susceptibility imaging Docxter was referring to? What else is SWI good for? The reason is was talking about co-registering the T1-weighted and T2-weighted images was that certain things should show up on a T1-weighted image that don't show up on a T2-weighted image, and vice versa. Know of any place that that had been done?

colbgw02 said:

I'd consider this beyond preliminary knowledge. Many board-certified non-radiologist physicians don't know and can't tell the difference between T1 and T2.

At your level, if you know the difference between radiographs, CT, MR, and US, then I'd say you're doing pretty well for yourself.

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I am? Really/ Wow, thanks!!! I thought this was common knowledge for physicians; doesn't the physician writing the imaging order has to write something like "Susceptibility-weighted MRI of left femoro-tibial joint, sagittal plane; films to be reviewed by a musculoskeletal radiologist", or "Multislice CT of abdomen, axial and sagittal plane, iodine radiocontrast to be administered; films to be reviewed by a hepatobiliary radiologist"? And how can anyone *not* see the diff b/w a T1-weighted and a T2-weighted MRI; they look *totally* different! Does the ordering physician ever review the films w/ you guys; When I become a Dr, whenever I order imaging or biopsies, I'll make sure I review the films or slides w/ the radiologist or pathologist; that'll be so cool!

Thanks!

Amxcvbcv said:

Your naivete is refreshing. Usually people that come here have a lower than appropriate opinion of physicians.

Judging from the material in the radiology section of my step 2 books, I'd say loads of doctors outside of radiology don't have a good handle on the indications for the various studies available.

Outside of academics or a large tertiary care facility, the ordering clinician will just receive the typed report from the radiologist; they rarely see the images.

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My naviete is refreshing? How so? And, give some examples of the guys who have a "lower than appropiate opinion of physicians".

Has a clinician ever ordered an susceptibility-weighted MRI w/ gadolinium contrast of the brain? Isn't that kinda redundant, since SWI shows blood vessels, and gadolinium contrast shows blood vessels?

Has any clinician ever ordered a susceptibility-weighted MRI of the abdomen, to look for cirrhosis of the liver, fatty infiltration of the pancreas, or choleocystitis? I'm guessing that would be superior to a 64-slice MDCT, but I may be wrong. How many slices can MRI machines manage, 256?

And is HRCT used only for thoracic imaging, or does it have other applications? On the same lines, is SWI used only for neuroimaging?

Thanks!

Docxter said:

Listen, you sounded curious to know stuff at the beginning of the thread, despite the suspicion you may be a forum troll. A friendly advice, again assuming you're being sincere: don't just throw out scientific sounding terms you have superficially heard here and there but have no clue about, especially in company of people who do know. Otherwise, you'll look pretty stupid. Get the most basic understanding of a subject first, then take it from there. You'll be much better off and well-received if you don't sound like a total fake.

And your logic above is laughable. For example, you say "an susceptibility-weighted MRI w/ gadolinium contrast of the brain? Isn't that kinda redundant, since SWI shows blood vessels, and gadolinium contrast shows blood vessels?" Not the best analogy, but it's like you asking "you can hear someone coming into the room with your ears, but you can also see them with your eyes too, so isn't having eyes redundant?" SWI and Gad show different things differently, but they have some overlap.

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Ah, thank you very much for clearing me up on both my personality and my knowledge; I had a suspiscion that was the case, that SWI and gadolinium do different, overlapping things; otherwise, one would've made the other obsolete.

And I do know what most medical terms mean and how to use them; I've been reading my Mom's and my other Dr friend's medical-surgical textbooks for many years during my downtime. I would've asked my Dr friend about this stuff, and I do plan on it this Sunday --he goes to my church--, but I kind of wanted a semi-quick answer. So, forgive me for sounding trollish every once in a while. Thanks.

hans19 said:

Did you check out the website? Until you grasp the fundamentals of MRI physics, its like trying to teach Differential equations to someone who doesn't even know simple arithmetic.

Do you mentioned hypersensitivity pneumonitis, do you even know what that is? Aside from cutting and pasting something from google, do you know why it matters to a clinician? Until you understand what disease processes do to your body and what we look for with the imaging and the implications of those disease process, you really are wasting your time.

Its great that you are curious about such things, but a kid your age should be out socializing, making friends, and worrying about school work. Are you interested in medicine? Fantastic!

You have to think about getting into medical school first. Before you even do that, think about getting into a good undergrad. And before you do that think about that upcoming test in your highschool class and the SAT.

If you want to jump the hurdles with the big boys, you gotta know how to run first. Learn to walk before you run. Learn to stand on your own two feet before you do any of that.

Reading medical textbooks during your 'down time' isn't even the half of a medical education. You won't succeed in impressing any of us (I hope that isn't why you came on here) by trying to talk the talk, especially if your mouth is full of --it.

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Thanks for the excellent advice!!!

I'm homeschooled, and I've got mostly a circle of six friends; Jeff and Joey, who are my age, Jon, who's Joey's older brother and a mathematics sr at Biola, Dr Mark, an internist friend from church, and Dr Sleiman, a Lebanese urologist who leads my weekly Bible study, who's the guy who's setting me up on shadowing an radiologist and pathologist in the fall. I tend to see each once a week; my studies are on hiatus until May, b/c I've completed my HS. And there's not much to do where I live, so this is how I pass my time.

And the hypersensitivity pneumonitides are a group of disorders characterized by chronic inflammation of the lungs caused by exposure to an irritant like bird feces, fungi, coal dust, talc, etc. Symptoms are a chronic dry cough, progressively worsening diffculty breathing on exertion, and a fibrous appearence of the lungs on an HRCT, and a few other things which I don't remember. Treatment is corticosteroids like prednisone and avoiding the irritant. It can be Dx'ed by a thoracic HRCT, or a bronchoscopy, but the latter is rarer, and usually done if an HRCT is positive and an ID is suspected, like if it's fungal or bacterial. If so, treatment w/ appropriate antifungals, like voriconazole, or the approprate antibiotics, in addition to the above treatments of prednisone and removing the irritant. This type can be caused by that black mold that grows on water damaged walls.

And, yes, I wrote that in my own words, recalling from memory my reads in my Mom's textbooks.

Thanks!

hans19 said:

Good for you, but it still sounds like your are regurgitating words, like reciting the Preamble in 4th grade, or like singing the words to an Italian operetta without actually knowing meaning of the words. 'Fibrous' appearance, isn't a discriptor for HRCT. Fibrotic changes on HRCT probably don't mean much to you at this point.

Unlike a smart kid finding work as a web designer or network administrator, if you want to practice medicine, you have to jump through very regulated hoops, and pay some hefty dues. You could read about this stuff until you are blue in the face, but until you go to medical school and do a residency, you won't be able to practice medicine. Until you see and treat patients first hand, you can never really 'know' medicine.

Back to the main issue -it seems your grasp of MRI is superficial at best and your questions are all over the place. If you really have so much free time on your hands and you REALLY wish to have a cogent discussion about MRI, take the time to browse the link I posted. Do your homework, go to the website and learn about MRI. Once you've demonstrated that you have a grasp of the basics we can talk. Until then, I don't think many people will take you seriously-- hence some of the 'troll' comments.

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I know, I know...

Here's my current state of knowledge of MRI: A 4 telsa magnet causes the hydrogen atoms in a patient to orient themselves in a particular way. A RF pulse is then emitted by the machine, which causes the hydrogen atoms to go out of alignment; when they do, they emit an RF pulse, which is detected by the machine, which uses complex algorithms to reconstruct an image. The purpose of the gradient magnets is to constrain the RF pulse emitted by the machine, so you can look at a very thin slice of the patient.

And I do plan on going to medical school, doing a residency in IM, and doing a fellowship in heme/onc. I *do not* think I know everything about medicine, or even a great deal; a lowly MS2 probably knows more than me. That's why I hang around Drs, and these fora to learn more about my chosen career.

And, in my knowledge, fibrotic changes are where collagen encapsulates foreign bodies that get into the alevoli, walling them off so they can't do damage to the lung tissue, but this tends to do more damage by using up valuable gas exchange space. It happens in the hypersensitivity pneumonitides, pulmonary TB, etc.

Thanks

hans19 said:

Thats a decent start! But what you are missing are the steps between the immunogenic stimulus and the final collagen deposition. Hint - 'hypersensitivity'

You understand the first basic principle of MRI now for the next level - Do you know the difference between T1 and T2 properties? In practice we only use 1.5 T and 3 T magnets. The 3 T magnets cause more severe artifacts so for many applications 1.5T is just fine. There isn't much added benefit to a 4T, let alone I don't know of any 4Ts that are approved for use outside of research.

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I know that the irritant causes an allergic response; how exactly this causes the collagen encasement, I still need to research.

And T1 is measuring the recovery of longitudnal magnetization, while T2 is the loss of transverse phase coherence. What the practical applications --as in, when will T1 be superior over T2, or vice versa-- of this is, I need to research.

Thanks

hans19 said:

Great start! In general (there are many exceptions) T2 is good for looking at water, pathologic processes involve derangements in fluid. T1 shows fat and water is dark, hence so it ends up as a good way to evaluate anatomic structures and morphology. By putting together T1 and T2 characteristics you can elucidate whats abnormal and what it might be, IE water, fat from a lipoma, hemorrhage, a tumor.

Throw into the mix T1 with IV Gadolinium contrast (tumors recruit blood vessels and tend to enhance) gradient echos (iron and calcium and other metals are paramagnetic) and cause a huge artifact that actually makes detection of subtle calcium or hemorrhage easier.

I'm glad you have this curiousity, and you are discovering where to get the resources to learn on your own. This is a valuable lesson if you want to be a doctor, because you will be a life-long learner. Once you finish your residency, you have to keep learning on your own to keep abreast of technological developments. Nobody is going to spoon feed you the information.

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Yeah, I've always been interested in research...I hate being spoon-fed info and never being asked to analyze or synthesize said info...I felt like a computer when I was in public school for 4th grade, even though I got a Teacher's Choice award for being "the whiz kid" --I hated that title, and the cheap honor along with it--. Coupled w/ the fact that the classes were too easy, but they wouldn't let me into the advanced track, b/c I was special needs; "it'd be too fast for me and I wouldn't keep up", my aide and Mom, plus me, flagrantly denied this. And my teacher threw my desk at me once, for no reason, in view of my Mom. I've been homeschooled ever since.

And I now believe, according to my research, that the fibrotic changes in the hypersensitivity pneumonitides occur due to, since the inflammation brought on by the allergic reaction damages the alevoli, and since repeated exposure to the irritant worsens the inflammatory reaction, thus causing more damage, metaplasia sets in the lung parenchyma, forming scar tissue composed of collagen, which reduces the area for gas exchange. Please correct me if I'm wrong. And could you please direct me to some more resources for furthering my knowledge of medicine.

And, I still can't figure this out, but why can CT show soft tissue, while plain films can't? Because a CT reads the level of X-ray attenuation as a density, while plain films simply show a superimposition of X-ray data? Harder X-rays? Am I on the right track in trying to figure this out?

So, if MRI is better at resolving soft tissue detail, why do they use CT pulmonary angiograms to evaluate whether you have a pulmonary emboli, instead of a magnetic resonance pulmonary angiography?

Thanks!