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*Each sequence gives different tissues different intensities and best used in assessing certain pathology. | *Each sequence gives different tissues different intensities and best used in assessing certain pathology. | ||
===T1 weighted imaging:=== | ===T1 weighted imaging:===https://radiopaedia.org/articles/t1-weighted-image | ||
When using T1 weighted imaging .. the tissues take the following densities: | When using T1 weighted imaging .. the tissues take the following densities: | ||
| Line 32: | Line 32: | ||
*Useful in assessing hypervascular lesions (e.g. hemangiomas, lymphangiomas) | *Useful in assessing hypervascular lesions (e.g. hemangiomas, lymphangiomas) | ||
===T2 weighted imaging:=== | ===T2 weighted imaging:===https://radiopaedia.org/articles/t2-weighted-image | ||
When using T1 weighted imaging .. the tissues take the following densities: | When using T1 weighted imaging .. the tissues take the following densities: | ||
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Most pathologies have increased fluid content of the tissue as a part of the inflammatory process. Thus, tissues become brighter. | Most pathologies have increased fluid content of the tissue as a part of the inflammatory process. Thus, tissues become brighter. | ||
Used as in T1 in assessing the anatomy & most lesions in the body. | Used as in T1 weighted imaging in assessing the anatomy & most lesions in the body. | ||
====Important note:==== | ====Important note:==== | ||
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Fluid restricted areas appear bright. So, it’s most useful in assessing ischemia (e.g. stroke) | Fluid restricted areas appear bright. So, it’s most useful in assessing ischemia (e.g. stroke) | ||
===Fluid | ===Fluid Attenuation Inversion Recovery (FLAIR):=== | ||
Tissues acquire the same densities as T2 weighted imaging except for that fluid appears dark. | Tissues acquire the same densities as T2 weighted imaging except for that fluid appears dark. | ||
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Excellent in assessing joints as they can discriminate between fluid, hyaline cartilage & fibrocartilage. | Excellent in assessing joints as they can discriminate between fluid, hyaline cartilage & fibrocartilage. | ||
===Short Tau Inversion Recovery (STIR)=== | ===Short Tau Inversion Recovery (STIR)===https://radiopaedia.org/articles/short-tau-inversion-recovery | ||
*Fat: dark | *Fat: dark | ||
Revision as of 15:56, 11 April 2017
Overview
- MRI is basically a huge magnet that emits energy (Radio Frequency pulse) into the body.
- Radiofrequency pulse causes the protons in H+ atoms to spin in different directions from which it used to spin.
- When the pulse stops .. the protons go back to spinning in the normal direction .. it releases energy.
- As tissues vary in a number of protons in it .. the energy emitted differ from tissue to tissue.
- Interpreting this energy using certain techniques enables us to represent every tissue in a unique density.
We are going to discuss some of the most commonly used sequences and when to use each one of them.
MRI Sequence
- An MRI sequence is a number of radio-frequency pulses (from the machine) and gradients that result (from protons in the body) in a set of images with a particular appearance.
- Each sequence gives different tissues different intensities and best used in assessing certain pathology.
===T1 weighted imaging:===https://radiopaedia.org/articles/t1-weighted-image When using T1 weighted imaging .. the tissues take the following densities:
- Fat: bright
- Muscle: gray
- Fluid: dark
- Moving blood: dark
- Bone: dark
- Air: dark
- Brain:
- Gray matter: gray
- White matter: bright
T1 is best used in assessing the anatomy as the picture resembles the tissue macroscopically.
T1+Contrast (gadolinium)
- Tissues have the same densities as in T1 except that moving blood is bright.
- Useful in assessing hypervascular lesions (e.g. hemangiomas, lymphangiomas)
===T2 weighted imaging:===https://radiopaedia.org/articles/t2-weighted-image When using T1 weighted imaging .. the tissues take the following densities:
- Fat: bright
- Muscle: gray
- Fluid: dark
- Moving blood: dark
- Bone: dark
- Air: dark
- Brain:
- Gray matter: gray
- White matter: bright
Most pathologies have increased fluid content of the tissue as a part of the inflammatory process. Thus, tissues become brighter. Used as in T1 weighted imaging in assessing the anatomy & most lesions in the body.
Important note:
- T2 weighted imaging is not the best sequence for assessing lesions close to brain ventricles both will appear bright.
Diffusion weighted imaging (DWI):
DWI specifically detects the motion of protons in water molecules.
When using T1 weighted imaging .. the tissues take the following densities:
- Fat: low signal
- Muscle: gray
- Fluid: dark
- Brain:
- Gray matter: gray
- White matter: hypodense compared to gray matter
Fluid restricted areas appear bright. So, it’s most useful in assessing ischemia (e.g. stroke)
Fluid Attenuation Inversion Recovery (FLAIR):
Tissues acquire the same densities as T2 weighted imaging except for that fluid appears dark.
- Fat: bright
- Muscle: gray
- Fluid: dark
- Bone: dark
- Air: dark
- Brain:
- Gray matter: gray
- White matter: darker than gray matter
Best used in assessing lesions near ventricles the lesion can be easily discriminated from CSF.
Proton density weighted sequences:
- Fat: bright
- Muscle: gray
- Fluid: bright
- Bone: dark
- Air: dark
- Hyaline cartilage: gray
- Fibrocartilage: dark
Excellent in assessing joints as they can discriminate between fluid, hyaline cartilage & fibrocartilage.
===Short Tau Inversion Recovery (STIR)===https://radiopaedia.org/articles/short-tau-inversion-recovery
- Fat: dark
- Muscle: darker than fat
- Fluid: very bright
- Bone: dark
- Air: dark
- Brain:
- Gray matter: gray
- White matter: darker than gray matter
Most useful in assessing fluid filled spaces.