Question

Explain why CSF shows up dark in a T1 weighted image and dark in a T2 weighted image.

Answer 1

This is described under the MRI interpretation:

As there are he two basic types of MRI images are T1-weighted and T2-weighted images, often referred to as T1 and T2 images.

The timing of radiofrequency pulse sequences used to make T1 images results in images which highlight fat tissue within the body.

The timing of radiofrequency pulse sequences used to make T2 images results in images which highlight fat AND water within the body.

So, this makes things easy to remember.

T1 images – 1 tissue type is bright – FAT

T2 images – 2 tissue types are bright – FAT and WATER

Furthermore regarding T1-weighted image – taking the Anatomy (spine)

• T1 images can as a map of proton energy within fatty tissues of the body
• Fatty tissues include subcutaneous fat (SC fat) & bone marrow of the vertebral bodies
• And Cerebrospinal fluid (CSF) contains no fat – so it appears black on T1-weighted images

Hence it shows black appearance.

Similarlly taking the case of T2-weighted image, considering the Anatomy (spine)

• T2 images are a map of proton energy within fatty AND water-based tissues of the body
• Fatty tissues are distinguished from water-based tissues by comparing with the T1 images – anything that is bright on the T2 images but dark on the T1 images is fluid-based tissue
• For example, the CSF is white on this T2 image and dark on the T1 image above because it is free fluid and contains no fat
• Note: that the bone cortex is black – it gives off no signal on either T1 or T2 images because it contains no free protons
• Hence i thing the concept is sufficient for the query regarding the black color in the imaging in MRI.