Normal Brain MRI - Kenhub

Introduction

MRI is the most sensitive imaging method when it comes to examining the structure of the brain and spinal cord. It works by exciting the tissue hydrogen protons, which in turn emit electromagnetic signals back to the MRI machine. The MRI machine detects their intensity and translates it into a gray-scale MRI image. 

Thus, for describing the MRI appearance of the parts of the brain we use the terms hyperintense and hypointense, with the gray matter being the reference point. This means that everything that is brighter than the grey matter is hyperintense, while everything that is darker is hypointense. For example, in all sequences, the bone is the dimmest structure on the scan since it has the lowest density of the protons. Hence, we say that the bone is hypointense.  

It’s worth noting that MRI can be combined with contrast agents, such as gadolinium. The radiological contrasts increase the visual contrast between the examined structure and the surrounding tissue.

Are you new in the world of MRI? We can help you learn about it with our MRI study guide!

The most frequently used MRI sequences for the brain examination are T1-weighted and T2-weighted, as well as FLAIR. Roughly speaking, T1w sequences are very useful to examine the normal anatomy of the brain, while T2w is mostly used to detect the pathological changes in the neural tissue. This is due to the specific characteristics of these sequences;

• The T1w sequence shows best the structures that are mostly made of fat. So it shows the cerebrospinal fluid (CSF) as black, gray matter as gray, white matter as white, the bones as black, and the adipose tissue as white.
• The T2w best shows the structures with a high amount of water. In this sequence, the CSF is white, gray matter is gray, white matter is darker gray, the bones are black and the adipose tissue is white.

Another important concept is the orientation of the scans. For coronal scans, everything that’s on the left side is actually the patient’s right, and vice versa. For axial scans, imagine as if you are looking at the patient through their feet while facing the opposite directions. Then everything that’s on your left is on the patient’s right, and everything that you anteriorly is on the patient’s posterior side. To recall the principles of the MRI, have a look at our article about the fundamentals of the MRI.

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