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Original poster

Help! CT scan vs MRI scan?

9 replies

Relativity4 · 05/04/2023 20:30

Following on from a similar post on here.

does anyone understand the difference between a CT and MRI scan? I understand the latter uses magnets rather than radiation, but I suppose what I’m wondering is when is one better than the other?

For context- someone I know had a brain CT scan which was thankfully normal. Would this mean an MRI would likely be normal too? One doctor was considering ordering an MRI as well but then another said there’s no point as the CT would rule out any major abnormalities (eg, brain tumours)

I am not doubting the opinions of either doctor as obviously they know more than myself or the person I know, but I was just curious if anyone knew and was able to explain it in simple terms that could be understood by my non scientific mind!

OP posts:
Jack80 · 05/04/2023 20:32

CT scans take a fast series of X-ray pictures, which are put together to create images of the area that was scanned. An MRI uses strong magnetic fields to take pictures of the inside of the body. CT scans are usually the first choice for imaging. MRIs are useful for certain diseases that a CT scan cannot detect.

Tinysoxx · 05/04/2023 20:40

Get a MRI if they can. In our case, the MRI was looked at by an expert whilst the CT scan didn’t need/warrant/have such a thorough look and seemed the first port of call. MRI picked up damage (in brain) that was not seen by the CT scan.

SonnySideDown · 05/04/2023 20:42

In simple terms MRI is better than CT at looking at soft tissue structures and changes within them. A CT is better for the rest really. However the Doctor is right in that a CT will pick up most abnormalities and is the frontline test as it is much quicker and cheaper, even though is a decent dose of radiation.

In the brain, MRI is used to detect minor changes that a CT can't, for example something like multiple sclerosis. Unfortunately an MRI takes around 45 mins to perform (CT like 2 mins) and not all people can tolerate it or have one eg. if there is a metal implant in the body.

I'm sure someone will come along and give a more detailed explanation but Doctors know which test is the "gold standard" for the conditions they are trying to find and there are protocols to follow for requesting all imaging. If its not justified you won't get it, and if they are looking for a brain tumour they won't perform a different test if they have already ruled it out.

Mummyme87 · 05/04/2023 20:47

My friend had a massive stroke a month back, he had three normal CTs and it was picked up on MRI

Original poster
Relativity4 · 05/04/2023 20:59

apologies- meant to include in the OP, does anyone know about the different types of MRI scan? The person I know said they heard something about an MRA brain scan and an MRV brain scan, we tried to google the difference and I as far as I can tell one is for veins and the other for arteries but that’s the extent of my understanding of it!

OP posts:
Original poster
Relativity4 · 05/04/2023 20:59

Mummyme87 · 05/04/2023 20:47

My friend had a massive stroke a month back, he had three normal CTs and it was picked up on MRI

Sorry to hear that. Hope your friend is doing OK now 💐

OP posts:
malificent7 · 05/04/2023 21:35

Radiographer here but I do not specialise in MRI or CT. The radiographer will select the appropriate protocol on the MRI machine according to the suspected pathology. So they might need to look at the vessels in the brain or the grey/ white matter itself. The scan can also be weighted to look for fat (important as it covers nerves) or water ( important so they can look as CSF.

CT scans are more commonly done for suspected strokes as they are sufficiently sensitive and specific white being much quicker and readily available.They can generally differentiate between a eschemic stroke. ( meaning a blocked vessel leading to lack of blood to brain killing tissue and showing up dark) and a haemorrhagic stroke...bleed on the brain showing up white. This is due to the iron in the blood which blocks the xrays showing white.

Differentiating between these two strokes is imperative as it will dictate treatment. For a haemorrhagic stroke you need blood coagulants whereas for an exchemic stroke you need blood thinners. Getting the treatment wrong can be disastrous!

I'm sure someone more knowledgeable about mri will tell you more or correct me but I do know that the MRI scans are far more detailed than CT. . they are insane! But CT is often the 1st port of call.

malificent7 · 05/04/2023 21:37

Sorry about your friend. Very odd that it didn't show up on CT.

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