Magnetic resonance imaging (MRI)

Last updated Jun 23, 2022

# Definition

MRI is an imaging modality that uses non-ionizing radiation to create useful diagnostic images.
MRI is used to distinguish pathologic tissue such as a brain tumor or MS lesions from normal tissue.
In simple terms, an MRI scanner consists of a large, powerful magnet in which the patient lies. A radio wave antenna is used to send signals to the body and then a radiofrequency receiver detects the emitted signals. These returning signals are converted into images by a computer attached to the scanner. Imaging of any part of the body can be obtained in any plane.

Source: MRI | Radiology Reference Article | Radiopaedia.org

# Parameter Weighting

Following are some of the main parameter weighting techniques being used in MRI:

# T1-weighted

ONE tissue is bright: fat
provides the most anatomically-relevant images
shape of the brain can be clearly seen, and morphological abnormalities are easy to detect.
fat is depicted in white and water in black.
grey matter is darker than white matter.

# T2-weighted

TWO tissues are bright: fat and water (WW2 – Water is White in T2)
Regular T2 MRI’s are important for tracking long-term disease progression.
White matter is darker than grey
Lesions appear white.
Suitable for lesion evaluation.

# T1Gd

A Gadolinium (gd)-Enhanced T1-Weighted scan reveals only new lesions. These are areas where the disease is currently active.
Before the MRI, an injection of gadolinium (gd) is administered. This will distinguish the active lesions from the normal parts of the brain.
This type of MRI will not show older, inactive lesions.

# FLAIR

Fluid Attenuated Inversion Recovery
FLAIR is similar to T2, but the fluid is darker or suppressed.
In T2, the spinal fluid (water) is white and the lesion is also white, so you have to look for the white in the white, which is difficult to understand. FLAIR can be roughly thought of as T2, in which the water is also black, making it easier to find the lesion.

Magnetic resonance imaging (MRI) is partially defined by the plane or direction of the image that is taken. The most important model coordinate system for medical imaging is the anatomical coordinate system (also called patient coordinate system).

# The Three Basic Anatomical Planes:

This coordinate system consists of three planes to describe the standard anatomical position of a human. The basic orientation terms for an MRI of the body taken: From the side would be a sagittal plane; from the front would be a coronal plane and from the top down would be a transverse or axial plane.

Source: https://users.fmrib.ox.ac.uk/~stuart/thesis/chapter_3/section3_2.html

# Sagittal plane

Also known as median plane.
It is a y-z plane, perpendicular to the ground, which separates left from right.
The mid-sagittal plane is the specific sagittal plane that is exactly in the middle of the body.
A sagittal MRI looks at the brain from the side in a series of images starting at one ear and moving to the other.

# Coronal plane

Also known as frontal plane.
It is an x-z plane, perpendicular to the ground, which (in humans) separates the anterior from the posterior, the front from the back, the ventral from the dorsal.
A coronal MRI looks at the brain from behind in a series of images starting at the back of the head and moving to the face.

# Axial plane

Also known as transverse plane.
It is an x-y-z plane, parallel to the ground, which (in humans) separates the superior from the inferior, or put another way, the head from the feet.
An axial MRI looks at the brain from below in a series of images starting at the chin and moving to the top of the head.

# Sources

Tags: Radiogenomics , Medical Imaging MOC ,
References:
Related: RSNA-MICCAI Brain Tumor Radiogenomic Classification

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