How to Scan a Routine Brain MRI Protocol

Intro to Brain MRIs

How to Perform a Routine Brain MRI

This hardware setup is widely used in clinical practice. It balances acquisition time, image quality, and patient comfort.

3. Capture the Initial Localizer Images

Before we can perform any MRI protocol, we must always capture initial localizer images of the patient. These images act as a guide for planning the detailed scans we will perform next.

We should always capture localizers in three planes:

1. Axial
2. Sagittal
3. Coronal

Once acquired, upload the initial localizer images into the three viewports.

Then, scroll through each of the image stacks to locate a central slice that clearly shows the anatomy of the brain.

✅ Correct Setup of Localizer Images for Routine Brain MRI:

Part 2: Plan and Acquire the Protocol Sequences

When all preparations are ready, we can start planning and acquiring the protocol sequences.

Let’s go through the pulse sequences that a standard brain MRI protocol includes, why we perform them, and how to set them up.

The 6 Sequences of a Standard Brain MRI Protocol

1. Axial T2 TSE
2. Axial T2 FLAIR
3. Axial T1 TSE
4. Sagittal T1 TSE
5. Coronal T1 TSE
6. Diffusion-Weighted Imaging (DWI)

We mainly use fast or turbo spin echo sequences for this study. These sequences provide fast, high-quality images with excellent contrast and minimal artifacts, making them ideal for routine clinical diagnosis.

Turbo Spin Echo also let us create multiple types of contrasts, including T2, T1, and inversion recovery for fat suppression.

This helps us assess the brain's structure, detect abnormalities, and identify common pathologies like tumors, strokes, and demyelination.

In the sections below, we go through how to plan and set up each sequence.

1. Axial T2 TSE

✅ Correct Planning:

Planning Instructions:

• Use the corpus callosum as the anatomical reference.
• Align the slices as follows:
  • Sagittal Localizer: Parallel to the anterior commissure-posterior commissure (AC-PC) line. This can also be aligned using the genu (front) and splenium (back) of the corpus callosum.
  • Coronal Localizer: Perpendicular to the mid-sagittal line, which runs from the sagittal sinus through the third ventricle to the base of the skull.
• Add enough slices to cover from the vertex (top of the head) to the base of the skull.
• Center the slices and adjust the slice thickness and gap for optimal spatial resolution.

Parameters for Axial T2 TSE:

2. Axial T2 FLAIR

✅ Correct Planning:

Planning Instructions:

• Copy the slice geometry and planning from the axial T2 sequence.
• Keep the same slice angulation, coverage, and positioning to ensure images of different contrasts can be clearly compared.

Parameters for Axial T2 FLAIR:

3. Axial T1 TSE

✅ Correct Planning:

Planning Instructions:

• Copy the slice geometry and planning from the axial T2 sequence.
• Keep the same slice angulation, coverage, and positioning to ensure images of different contrasts can be clearly compared.

Parameters for Axial T1 TSE:

4. Sagittal T1 TSE

✅ Correct Planning:

Planning Instructions:

• Use the mid-sagittal line as the anatomical reference.
• Align the slices as follows:
  • Axial Localizer: Position slices parallel to the mid-sagittal line.
  • Coronal Localizer: Position slices parallel to the mid-sagittal line running from the sagittal sinus through the third ventricle to the base of the skull.
• Add enough slices to cover the brain from side to side.
• Set the fold-over direction to anterior-posterior.

Parameters for Sagittal T1 TSE:

5. Coronal T1 TSE

✅ Correct Planning:

Planning Instructions:

• Use the mid-sagittal line and AC-PC line as anatomical references.
• Align the slices as follows:
  • Axial Localizer: Position slices perpendicular to the mid-sagittal line.
  • Sagittal Localizer: Position slices perpendicular to the AC-PC line.
• Add enough slices to cover the brain from anterior to posterior.
• Set the fold-over direction to right-left.

Parameters for Coronal T1 TSE:

6. Axial Diffusion-Weighted Imaging (DWI)

✅ Correct Planning:

Planning Instructions:

• Copy the slice geometry and planning from the axial sequences.
• Adjust the slices as follows:
  • Sagittal Localizer: Adjust the coverage – and position the slice package slightly upward and rotate it clockwise – to avoid the paranasal sinuses and mouth areas. Including these areas can cause susceptibility artifacts.
  • Coronal Localizer: Ensure the scan remains perpendicular to the mid-sagittal line.

Parameters for Axial DWI:

How to Avoid Artifacts When Planning the Sequences

The table below lists the 6 common brain artifacts, and what techniques you can use to avoid them:

Part 3: Review the Images

Finally, we will review the images to ensure all the anatomical information we need is clear.

These key structures must be clearly visible in a brain MRI:

1. Gray and white matter
2. Ventricles and cerebrospinal fluid spaces
3. Basal ganglia
4. Brain stem and cerebellum
5. Corpus callosum
6. Major vascular structures

Below, we will go through all the different image contrasts and explain their specific role in imaging the brain.

T2-Weighted Images – Highlight Fluid-Related Tissues and Conditions

T2-weighted imaging makes fluids appear bright. This contrast is ideal for detecting tissues and abnormalities associated with high water content.

In brain MRI, T2 sequences are excellent for evaluating hydrocephalus, cysts, and edema. They clearly show the ventricles and cerebrospinal fluid spaces, making them useful for assessing size and configuration of these structures.

✅ Axial T2 of the Brain – Correct Image:

The axial T2 sequence provides a horizontal view of the brain, which lets us:

• Assess the ventricles for size and symmetry.
• Evaluate brain parenchyma for areas of abnormal signal intensity.
• Identify fluid collections such as cysts or edema.
• Visualize the basal ganglia and other deep brain structures.

T2 FLAIR – Best for White Matter Lesions

T2 FLAIR (Fluid Attenuated Inversion Recovery) is a special type of T2-weighted sequence that suppresses the signal from a specific tissue – in this case the cerebrospinal fluid (CSF) – making it appear dark instead of bright. This contrast is ideal for detecting lesions adjacent to CSF spaces.

In brain MRI, FLAIR sequences are crucial for evaluating multiple sclerosis, small vessel disease, and chronic ischemia. They are particularly effective at highlighting white matter lesions near the ventricles.

✅ Axial T2 FLAIR of the Brain – Correct Image:

The axial T2 FLAIR sequence provides a view similar to T2, but with CSF suppression, which lets us:

• Detect periventricular white matter lesions more clearly without interference from bright CSF.
• Evaluate areas of edema which remain bright against the dark CSF background.
• Identify subtle abnormalities that might be overlooked on standard T2 images.

T1-Weighted MRI – Key for Gray-White Matter Contrast and Post-Contrast Scans

T1-weighted imaging makes fat appear bright and fluid dark. This contrast is ideal for anatomical detail and fat-containing structures.

In brain MRI, T1 sequences are essential for evaluating structural anatomy, tumors, metastases, and sub-acute hemorrhage. They provide excellent contrast between gray and white matter, and serve as the baseline for post-contrast studies.

✅ Axial T1 of the Brain – Correct Image:

The axial T1 sequence provides a horizontal view, showing:

• Clear differentiation between gray and white matter.
• Anatomical details of brain structures.
• Fat-containing structures appear bright, helping to identify normal and abnormal fat distribution.

✅ Sagittal T1 of the Brain – Correct Image:

The sagittal T1 sequence provides a side view of the brain, which lets us:

• Evaluate midline structures such as the corpus callosum, brainstem, and cerebellum.
• Assess the pituitary gland and sella turcica.
• Visualize the ventricles from a different perspective.

✅ Coronal T1 of the Brain – Correct Image:

The coronal T1 sequence provides a front-to-back view, useful for:

• Comparing left and right hemispheres side by side to check for symmetry.
• Evaluating the temporal lobes and hippocampus.
• Assessing the ventricular system from an alternative angle.

Diffusion-Weighted Imaging (DWI) – Best for Acute Stroke

Diffusion-weighted imaging is sensitive to the movement of water molecules in tissue. In normal brain tissue, water diffuses freely, but in damaged areas (like in acute stroke), water movement is restricted.

In brain MRI, DWI sequences are critical for evaluating acute stroke and cytotoxic edema. They can detect ischemic changes within minutes of onset, making them invaluable for early stroke diagnosis.

The DWI sequence generates 3 different types of images from a single acquisition, each providing unique diagnostic information:

1. b=0 Image (Susceptibility Image)

The b=0 Image is acquired at the beginning of the diffusion sequence with no diffusion gradients applied. It’s essentially a T2-weighted image that shows baseline tissue contrast before diffusion weighting.

In clinical practice, this image is sometimes informally referred to as a "susceptibility image" because it clearly displays susceptibility artifacts caused by magnetic field inhomogeneities. These artifacts appear as signal distortions near air-tissue interfaces or metal implants.

The b=0 image serves three important purposes:

1. Provides anatomical reference for the diffusion-weighted images.
2. Shows T2 effects that might cause "T2 shine-through" on DWI.
3. Enables correction of susceptibility-induced distortions that affect the entire diffusion dataset.

By comparing the b=0 image with the true diffusion image, radiologists can better distinguish between actual diffusion restrictions and artifacts.

✅ Correct Image Example:

2. True Diffusion Image (b=1000)

The True Diffusion Image (b=1000) shows areas of restricted water diffusion as bright signal intensity. It detects acute ischemic changes where water movement is restricted due to cytotoxic edema.

This is the primary image for identifying acute stroke, showing the infarct core as a hyperintense (bright) region within minutes of symptom onset.

✅ Correct Image Example:

3. ADC Map (Apparent Diffusion Coefficient)

The ADC (Apparent Diffusion Coefficient) Map quantifies the degree of water diffusion, where restricted diffusion appears dark.

The map verifies whether bright areas on the DWI are truly due to restricted water movement (as in acute stroke), or simply because the tissue naturally appears bright on T2-weighted images (called "T2 shine-through"). This distinction is crucial for accurate diagnosis.

Specifically, this map is crucial to differentiate acute ischemia vs sub-acute or chronic ones. Acute stroke appears dark on ADC maps, while chronic lesions typically show normal or increased diffusion.

✅ Correct Image Example:

When these three DWI images are evaluated together, they provide comprehensive information about water diffusion in brain tissue.

This enables accurate diagnosis of acute ischemia, and lets us differentiate it from other pathologies that appear similar on standard sequences.

Final Checks:

When reviewing brain MRI images, always check for:

1. Symmetry – Structures on both sides of the brain should appear and disappear together when scrolling through slices. Asymmetry may indicate pathology or poor positioning.
2. Coverage – Ensure all required anatomy is included, from vertex to base of skull.
3. Image quality – Look for artifacts that might interfere with diagnosis.
4. Signal-to-noise ratio – Images should be clear with good contrast between different tissues.

By following this protocol and carefully reviewing the images, you can ensure an excellent diagnostic evaluation of the brain.