🔍 What is an MRI?
MRI (Magnetic Resonance Imaging) uses powerful magnets and radio waves to create detailed pictures of your brain. Unlike CT scans, MRIs don't use radiation and provide much better detail of soft tissue like brain tumors.
During your GBM journey, you'll have many MRIs. Understanding the basics helps you participate more actively in your care and reduces anxiety about what the images mean.
📊 Types of MRI Sequences
A brain MRI includes several different "sequences" - think of these as different camera filters that highlight different things. Here are the main ones:
T1-Weighted Most Common
What it shows: Basic brain anatomy. Good for seeing structure.
How it looks: Gray matter is gray, white matter is white, fluid (CSF) is dark/black.
Used for: Baseline anatomy, planning surgery.
T1 with Gadolinium (Contrast) Critical for GBM
What it shows: Areas where the blood-brain barrier is broken - typically where active tumor is growing.
How it looks: Active tumor appears bright white (enhanced).
Used for: Measuring tumor size, tracking response to treatment, detecting recurrence.
Key point: The "enhancing" portion is what doctors measure to track your tumor.
T2-Weighted
What it shows: Fluid and swelling (edema).
How it looks: Fluid appears bright white.
Used for: Seeing the total area affected, including swelling around the tumor.
FLAIR (Fluid-Attenuated Inversion Recovery) Important
What it shows: Like T2, but suppresses normal fluid - making abnormalities stand out more.
How it looks: Normal brain fluid is dark, but tumor and swelling appear bright.
Used for: Detecting tumor infiltration that doesn't enhance, seeing the full extent of disease.
Key point: FLAIR abnormality is often larger than the enhancing tumor because GBM cells infiltrate surrounding tissue.
DWI (Diffusion-Weighted Imaging)
What it shows: How easily water moves through tissue. Restricted diffusion can indicate high cellularity (lots of cells packed together).
Used for: Differentiating tumor from other abnormalities, detecting stroke.
Perfusion MRI
What it shows: Blood flow through the brain. Tumors often have increased blood flow.
Used for: Distinguishing true progression from pseudoprogression (treatment effect).
💉 What is Gadolinium?
Gadolinium is a contrast agent (dye) injected into your vein during the MRI. Here's what you need to know:
How It Works
In a healthy brain, the blood-brain barrier keeps gadolinium out. But where there's active tumor (or other damage), the barrier is broken, and gadolinium leaks in. This makes the tumor "light up" (enhance) on T1 images.
Is It Safe?
Gadolinium is generally safe for most people. However:
- People with kidney problems may not be able to receive it
- Some newer research suggests gadolinium can deposit in the brain over time, though the clinical significance is unclear
- Allergic reactions are rare but possible
📏 What Doctors Measure
Enhancing Tumor
The bright area on T1 with contrast. This is measured in two or three dimensions and used to calculate tumor volume. Changes in this measurement indicate whether the tumor is responding to treatment, stable, or growing.
FLAIR/T2 Abnormality
The larger area of brightness on FLAIR images. This includes edema (swelling) and infiltrating tumor cells. It's usually larger than the enhancing portion.
Mass Effect
Whether the tumor is pushing on or shifting brain structures. Significant mass effect may require steroids or surgery.
Midline Shift
Whether the center of the brain has been pushed to one side. Measured in millimeters. Significant shift can be dangerous.
🔄 Understanding Changes Over Time
| What You Hear | What It Means |
|---|---|
| Stable disease | No significant change in tumor size - this is good news during treatment! |
| Partial response | Tumor has shrunk by at least 50% |
| Complete response | No visible enhancing tumor (rare in GBM, but possible) |
| Progression | Tumor has grown by 25% or more, or new tumors appeared |
| Pseudoprogression | Looks like growth but is actually treatment effect (swelling/inflammation). Common 1-3 months after radiation. |
| Pseudoresponse | Tumor appears smaller because certain drugs (like bevacizumab) reduce enhancement without killing tumor |
❓ Questions to Ask About Your MRI
- What is the size of the enhancing tumor now versus last scan?
- Is there new enhancement or new areas of concern?
- Has the FLAIR abnormality changed?
- Is there mass effect or midline shift?
- Could this be pseudoprogression?
- When should my next scan be?
💪 Tips for MRI Day
Brain MRIs typically take 45-60 minutes
No metal - you'll likely change into a gown
Many centers let you listen to music during the scan
If claustrophobic, your doctor can prescribe something
⚠️ Medical Disclaimer
This guide is for educational purposes only. MRI interpretation requires years of specialized training. Always rely on your radiologist and neuro-oncologist to interpret your scans. This information helps you understand discussions but does not replace professional medical advice.