Lea Alhilali, MD Profile picture
May 1, 2023 22 tweets 10 min read Read on X
1/Do radiologists sound like they are speaking a different language when they talk about MRI? T1 shortening what? T2 prolongation who?

Here’s a translation w/a #tweetorial introduction to MRI.

#medtwitter #FOAMed #FOAMrad #medstudent #neurorad #radres #ASNR23 #neurosurgery Image
2/When it comes to bread and butter neuroimaging—MRI is definitely the butter. Butter makes everything taste better and packs a lot of calories. MRI can add so much information to a case Image
3/In fact, if CT is a looking glass into the brain—MRI is a microscope. It can tell us so much more about the brain and pathology that affects the brain.

So let’s talk about the basic sequences that make up an MRI and what they can show us. Image
4/Let’s start w/T1—it is #1 after all! T1 is for anatomy. Since it’s anatomic, brain structures will reflect the same color as real life. So gray matter is gray on T1 & white matter is white on T1. So if you see an image where gray is gray & white is white—you know it’s a T1. Image
5/T1 is also for contrast. Contrast material helps us to see masses. Contrast can’t get into normal brain & spine bc of the blood brain barrier—but masses don’t have a blood brain barrier, so when you give contrast, masses will take it up & light up, making them easier to see. Image
6/So to review, T1 is for anatomy and contrast. I remember this bc anatomy is the number 1 thing a radiologist needs to know and a mass is the number 1 thing a radiologist doesn’t want to miss. Image
7/Now to T2! T2 sequences are water sensitive sequences. What is pathologic water in the brain? Edema! My attending once said, “Everything bad in this world is trying to turn you back into what you came from—water."

So T2 shows you edema—but this edema can be from many things Image
8/To review—T1 is for anatomy and contrast, T2 (and FLAIR, which is a type of T2) is for water—which is bright on T2. I remember this bc H20 has a 2 in it—T2 is for H20. Image
9/Next to diffusion or DWI. Diffusion is primarily to detect stroke. Acute strokes are bright on diffusion. But just as all that glitters is not gold, not all that is bright on DWI is an acute stroke. Image
10/This is bc all diffusion imaging does is detect how difficult it is for water to move. Anything that makes the space around water crowded and difficult to move will be bright on diffusion imaging Image
11/So classically, it’s from a stroke. When cells run out of ATP, the Na/K pump stops working & immediately water rushes in from osmotic pressure & the cells swell. These swollen cells fill the interstitium & restrict the movement of water. This is why strokes are bright on DWI! Image
12/But other things can make it crowded and difficult for water to move

For example, tightly packed cells in aggressive tumors will also fill the spaces & make it difficult for water to move—it's trapped between the tumor cells! So highly cellular tumors are often bright on DWI Image
13/Here is an example. Here is a mass that is as bright as stroke on diffusion bc of its densely packed cells. On contrast images, we see it avidly enhance, as we would expect for a mass. On CT, the tumor is very dense bc of the densely packed cells. Image
14/Hematomas are also bright on DWI. In normal blood, water flows happy & free—but once the clotting cascade starts & fibrin & thrombin & whatever stuff I don’t remember as a radiologist clumps everything together, things get tight—water is trapped in the clot interstices! Image
15/Here is an example. The hemorrhage is bright on CT bc it is clotted, and thus more dense than the brain and CSF, which are closer in density to water. For this same reason, the hemorrhage is bright on diffusion—bc the dense clot traps the water. Image
16/Pus is also bright on diffusion. As a radiologist I don’t often see pus, but as a mom, I sure do. It is thick and gooey and you can just imagine how difficult it is for water to travel through that gelantinous blob of pus. Image
17/Here’s an example. There is a ring enhancing lesion w/a lot of edema on T2. Centrally, there is restricted diffusion, meaning that there is something gooey or thick or dense centrally. Bc this central stuff doesn’t enhance, we know it’s not a mass. This is pus in an abscess! Image
18/So to review--while not everything that is bright on diffusion is a stroke, the most important use is for strokes. I remember his bc it's called DWI--which I jokingly say stands for Diagnose With Infarct Image
19/Last but not least is gradient imaging. Gradient imaging is sensitive to metals. And what’s the most important metal in body? Iron—bc iron is in blood. So gradient is our blood sensitive sequence Image
20/Blood is black on gradient. I remember this bc gradient is for metal—and when I think of metal, I think of blacksmiths forging metal products. So BLACKsmith=metal is BLACK on gradient. Image
21/But other metals will be black too. Notably, calcium, which is in our bones and in many other lesions. So remember, just all that glitters is not gold, not all that is black on gradient is blood—other metals are black too Image
22/So now you know the basic MRI sequences and what they are used for.

So hopefully now, the radiologist won’t sound like they are speaking a different language when they talk to you—they will just be nerdy and socially awkward when they do! Image

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Lea Alhilali, MD

Lea Alhilali, MD Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @teachplaygrub

Sep 15
1/Time is brain!

So you don’t have time to struggle w/that stroke alert head CT.

Here’s a thread to help you with the CT findings in acute stroke! Image
2/CT in acute stroke has 2 main purposes

(1) exclude hemorrhage (a contraindication to thrombolysis)

(2) exclude other pathologies mimicking acute stroke. But you can also see other findings to help diagnosis a stroke. Image
3/Infarct appearance depends on timing.

In first 12 hrs, the most common imaging finding is…a normal head CT

However, you may see a hyperdense artery or basal ganglia obscuration. Later, you see loss of gray white differentiation & sulcal effacement Image
Read 13 tweets
Sep 12
1/Do you feel there’s a back-log of findings in a spine MRI report?

Everyone talks about discs & facets, but not everyone talks about the endplates

Do you?

Do you need to talk about degenerative changes (Modic changes) of the endplates?

Here’s thread w/all you need to know! Image
2/Over 30 years ago, Modic et al. found there were 3 types of degenerative endplate changes:

(1) T2 bright changes (indicating edema, Modic 1)
(2) T1 bright changes (indicating fat, Modic 2)
(3) T1 & T2 dark changes (indicating sclerosis, Modic 3)

But what do they mean? Image
3/Let’s start w/Modic 1.

These are bright on T2, indicating edema

On pathology, it’s what you’d expect w/edema: inflammation, vascular granulation tissue, & high cellular turnover

Vascular granulation tissue means these can enhance on post contrast images—mimicking discitis! Image
Read 18 tweets
Sep 10
1/Are you FISHING for a way to better evaluate subarachnoid hemorrhage?

Are you hungry for a way to classify these patients?

Donut you worry!

Here’s a short thread to help you remember the modified Fisher scale for classifying subarachnoid hemorrhage. Image
2/Just think of the brain as a donut. Like a donut, it’s a bunch of stuff around a hole in the middle.

Ventricles are the hole in the middle of the brain just like there’s a hole in the middle of the dough in a donut.

Just don’t quote me to your neuroanatomy professor…. Image
3/Subarachnoid hemorrhage (SAH) added to the brain makes it less healthy, the same way adding toppings to a donut makes it less healthy.

Increasing severity of SAH is like increasingly unhealthy donut toppings. Fisher scale quantifies the vasospasm risk for increasing SAH Image
Read 8 tweets
Sep 8
1/Talk about twisting your back!

Do spine vascular lesions make your brain feel as tangled as the dilated vessels you see?

Want some more information on malformations?

Here’s a thread on spine vascular anatomy to give you durable knowledge on dural arteriovenous fistulas (dAVF)Image
2/To understand spinal dural AVFs, you need to understand basic spinal vascular anatomy.

The spine is LONG—to get blood from the top to the bottom is like going through the length of a marathon course Image
3/So we will need to tackle it like you tackle running a marathon.

When you run a marathon, you replenish yourself at aid/water stations along the way so you can make it all the way through.

Same w/spinal arterial vasculature—it needs to be replenished on the way down. Image
Read 19 tweets
Sep 3
1/Does the work up for dizziness make your head spin?

Wondering what to look for on an MR for dizziness

This month’s @theAJNR SCANtastic will tell you all you need about imaging Meniere’s disease!

ajnr.org/content/46/8/1…Image
@TheAJNR 2/The etiology for dizziness can have very diverse causes—each with very different treatments.

So it is important to try to differentiate

Meniere’s is a common cause & we can help diagnose it w/imaging! Image
@TheAJNR 3/To understand Meniere’s disease, you must know labyrinth anatomy

It has layers, like Russian nesting dolls. Outer doll is the bony labyrinth, holding perilymph & a second doll—membranous labyrinth.

Inside the membranous labyrinth is endolymph Image
Read 13 tweets
Aug 1
1/They say form follows function!

Brain MRI anatomy is best understood in terms of both form & function.

Here’s a short thread to help you to remember important functional brain anatomy--so you truly can clinically correlate! Image
2/Let’s start at the top. At the vertex is the superior frontal gyrus. This is easy to remember, bc it’s at the top—and being at the top is superior. It’s like the superior king at the top of the vertex. Image
3/It is also easy to recognize on imaging. It looks like a big thumb pointing straight up out of the brain. I always look for that thumbs up when I am looking for the superior frontal gyrus (SFG) Image
Read 12 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(