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| __NOTOC__
| | A set of diagnostic criteria were proposed by Del Brutto et al based on the laboratory and imaging tests. The criteria were modified in 2001 to be: |
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| {{CMG}};{{AE}}{{AY}}
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| ==Overview==
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| *MRI is basically a huge magnet that emits energy (Radio Frequency pulse) into the body.
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| *Radiofrequency pulse causes the protons in H+ atoms to spin in different directions from which it used to spin.
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| *When the pulse stops .. the protons go back to spinning in the normal direction .. it releases energy.
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| *As tissues vary in a number of protons in it .. the energy emitted differ from tissue to tissue.
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| *Interpreting this energy using certain techniques enables us to represent every tissue in a unique density.
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| We are going to discuss some of the most commonly used sequences and when to use each one of them.
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| This video simplifies the concept of T1 and T2 relaxation times and their application in MRI.
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| {{#ev:youtube|Z2xpY_hkSBY}}
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| ==MRI Sequences==
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| *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.
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| *Each sequence gives different tissues different intensities and best used in assessing certain pathology.
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| ===T1 weighted imaging:===
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| {| style="float: right; width: 350px;"
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| | [[Image:T1_N2.jpg|right|250px|Case courtesy of Dr Bruno Di Muzio, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/39310">rID: 39310</a>]]
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| |}
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| Tissue densities reflex T1 which is the longitudinal relaxation time of the Net Magnetic Vector (NMV).<ref name="urlT1 weighted image | Radiology Reference Article | Radiopaedia.org">{{cite web |url=https://radiopaedia.org/articles/t1-weighted-image |title=T1 weighted image | Radiology Reference Article | Radiopaedia.org |format= |work= |accessdate=}}</ref>
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| When using T1 weighted imaging .. the tissues give the following densities:
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| *Fat: bright
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| *Muscle: gray
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| *Fluid: dark
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| *Moving blood: dark
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| *Bone: dark
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| *Air: dark
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| *Brain:
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| :*Gray matter: gray
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| :*White matter: bright
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| T1 is best used in assessing the anatomy as the image resembles the tissue macroscopically.
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| ====T1+Contrast (gadolinium)====
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| {| style="float: right; width: 200px;"
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| | [[Image:T1_c_acoustic-schwannoma-14.jpg|right|200px|Case courtesy of Dr Matt Skalski, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/44105">rID: 44105</a>]]
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| |}
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| *Injecting contrast material (gadolinium) increases T1 signal from moving blood .. thus allows detection of highly vascular lesions.
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| *Tissues have the same densities as in T1 except that moving blood is bright.
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| *Useful in assessing hypervascular lesions (e.g. hemangiomas, lymphangiomas)
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| ===T2 weighted imaging:===
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| {| style="float: right; width: 200px;"
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| | [[Image:T2_N.jpg|right|200px|Case courtesy of Dr Bruno Di Muzio, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/39311">rID: 39311</a>]]
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| |}
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| Tissue densities reflex T2 which is the transverse relaxation time of the Net Magnetic Vector (NMV).<ref name="urlT2 weighted image | Radiology Reference Article | Radiopaedia.org">{{cite web |url=https://radiopaedia.org/articles/t2-weighted-image |title=T2 weighted image | Radiology Reference Article | Radiopaedia.org |format= |work= |accessdate=}}</ref>
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| When using T2 weighted imaging .. the tissues give the following densities:
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| *Fat: bright
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| *Muscle: gray
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| *Fluid: dark
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| *Moving blood: dark
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| *Bone: dark
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| *Air: dark
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| *Brain:
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| :*Gray matter: gray
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| :*White matter: bright
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| Most pathologies have increased fluid content of the tissue as a part of the inflammatory process. Thus, lesions appear brighter.
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| Used as in T1 weighted imaging in assessing the anatomy & most lesions in the body.
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| ====Important note:====
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| *T2 weighted imaging is not the best sequence for assessing lesions close to brain ventricles both will look bright.
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| ===Diffusion weighted imaging (DWI):===
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| {| style="float: right; width: 350px;"
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| | [[Image:DWI_N.jpg|right|300px|Case courtesy of Dr Bruno Di Muzio, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/39311">rID: 39311</a>]]
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| |}
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| DWI specifically detects the motion of protons in water molecules.
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| When using DWI weighted imaging .. the tissues give the following densities:
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| *Fat: low signal
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| *Muscle: gray
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| *Fluid: dark
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| *Brain:
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| :*Gray matter: gray
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| :*White matter: hypodense compared to gray matter
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| Fluid restricted areas appear bright. So, it’s most useful in assessing ischemia (e.g. stroke)
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| ===Fluid Attenuation Inversion Recovery (FLAIR):===
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| {| style="float: right; width: 350px;"
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| | [[Image:FLAIR_N.jpg|right|300px|Case courtesy of Dr Bruno Di Muzio, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/39311">rID: 39311</a>]]
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| |}
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| This sequence attenuates signals from fluids (e.g CSf) and thus is helpful in detecting lesions normally covered by CSF (in brain and spinal cord)
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| Tissues acquire the same densities as T2 weighted imaging except for that fluid appears dark.
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| *Fat: bright
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| *Muscle: gray
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| *Fluid: dark
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| *Bone: dark
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| *Air: dark
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| *Brain:
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| :*Gray matter: gray
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| :*White matter: darker than gray matter
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| Best used in assessing lesions near ventricles the lesion can be easily discriminated from CSF.
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| ===Proton density weighted imaging:===
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| {| style="float: right; width: 350px;"
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| | [[Image:PD_N.jpg|right|300px|Case courtesy of Dr Andrew Dixon, <a href="https://radiopaedia.org/">Radiopaedia.org</a>. From the case <a href="https://radiopaedia.org/cases/42982">rID: 42982</a>]]
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| It relies primarily on the density of the protons. So, Tissues with higher density give brighter signals.
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| When using PD-weighted imaging .. the tissues give the following densities:
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| *Fat: bright
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| *Muscle: gray
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| *Fluid: bright
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| *Bone: dark
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| *Air: dark
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| *Hyaline cartilage: gray
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| *Fibrocartilage: dark
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| Excellent in assessing joints as they can discriminate between fluid, hyaline cartilage & fibrocartilage.
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| ===Short Tau Inversion Recovery (STIR)===
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| Similar to FLAIR sequence, STIR suppresses signals from fat tissue.<ref name="urlShort tau inversion recovery | Radiology Reference Article | Radiopaedia.org">{{cite web |url=https://radiopaedia.org/articles/short-tau-inversion-recovery |title=Short tau inversion recovery | Radiology Reference Article | Radiopaedia.org |format= |work= |accessdate=}}</ref>
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| STIR can not be used post gadolinium injection as gadolinium has T1 in the same range of fat & eventually signals from it will be attenuated.
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| When using STIR imaging .. the tissues give the following densities:
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| *Fat: dark
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| *Muscle: darker than fat
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| *Fluid: very bright
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| *Bone: dark
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| *Air: dark
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| *Brain:
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| :*Gray matter: gray
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| :*White matter: darker than gray matter
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| Most useful in assessing fluid filled spaces.
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| This video summerizes some important aspects and uses of common MRI sequences.
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| {{#ev:youtube|mOt2FeGHjaY}}
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A set of diagnostic criteria were proposed by Del Brutto et al based on the laboratory and imaging tests. The criteria were modified in 2001 to be: