Brain MRI: Difference between revisions
No edit summary |
|||
| Line 9: | Line 9: | ||
==Ordering Studies== | ==Ordering Studies== | ||
===Ordering for Rule-Out [[CVA]] or [[TIA]]=== | ===Ordering for Rule-Out [[CVA]] or [[TIA]]=== | ||
*[[MRI Brain]] DWI and | *[[MRI Brain]] with DWI (without contrast) '''and''' | ||
*Cervical vascular imaging (to predict short-term risk):<ref name="ACEP">ACEP Clinical Policy: Suspected Transient Ischemic Attack[https://www.acep.org/Physician-Resources/Policies/Clinical-policies/Clinical-Policy-Suspected-Transient-Ischemic-Attack/ full text]</ref> | |||
**MRI with DWI/MRA in patients with high short-term risk for stroke (ACEP Level B) | **MRI with DWI/MRA in patients with high short-term risk for stroke (ACEP Level B) | ||
**Carotid US/CTA/MRA in patients with high short-term risk for stroke (ACEP Level B) | **Carotid US/CTA/MRA in patients with high short-term risk for stroke (ACEP Level B) | ||
***Carotid US is slightly less sensitive than MRA, but useful for carotid stenosis eval<ref>Nederkoorn PJ, Mali WP, Eikelboom BC, et al. Preoperative diagnosis of carotid artery stenosis. Accuracy of noninvasive testing. Stroke. 2002;33:2003-2008.</ref> (ACEP Level C) | ***Carotid US is slightly less sensitive than MRA, but useful for carotid stenosis eval<ref>Nederkoorn PJ, Mali WP, Eikelboom BC, et al. Preoperative diagnosis of carotid artery stenosis. Accuracy of noninvasive testing. Stroke. 2002;33:2003-2008.</ref> (ACEP Level C) | ||
==MRI Modalities== | ==MRI Modalities== | ||
Revision as of 17:50, 18 February 2017
Background
- MRI uses magnetic fields and radiowaves to develop high definition imaging of the brain and excellent tissue contrast
- No radiation associated with imaging
- Ideal for looking at brain parenchyma and midbrain
- Contrast is commented on by signal intensity
- Dark areas are hypointense
- Bright areas are hyperintense
Ordering Studies
Ordering for Rule-Out CVA or TIA
- MRI Brain with DWI (without contrast) and
- Cervical vascular imaging (to predict short-term risk):[1]
- MRI with DWI/MRA in patients with high short-term risk for stroke (ACEP Level B)
- Carotid US/CTA/MRA in patients with high short-term risk for stroke (ACEP Level B)
- Carotid US is slightly less sensitive than MRA, but useful for carotid stenosis eval[2] (ACEP Level C)
MRI Modalities
T1 Weighted Imaging
- Ideal for brain parenchyma
- With the addition of contrast, this can differentiate causes of inflammation
- Fluid is hypointense (similar to CT imaging)
- Methemoglobin, fat, and protein are hyperintense
T2 Weighted Imaging
- Highlights CSF
- Good for identifying tissue edema around pathologic areas
- Fluid is hyperintense (reverse of T1)
- Tissue tends to be more hypointense
Fluid Attenuation Inversion Recovery (FLAIR)
- Appears as T2 images with hypointense CSF
- Ideal for identifying tumors/GBS
- Also used to identify leptomeningeal enhancement in meningitis
Diffusion Weighted Imaging (DWI)
- A method of measuring the Brownian motion of water molecules
- Diffusion within the intracellular fluid, diffusion within extracellular fluid, and between these areas will differ depending on pathology
- Ideal for cellular swelling especially in acute ischemic stroke which will be hyperintense
Blood
| Age of Blood | T1 Imaging | T2 Imaging |
|---|---|---|
| Hyperacute | Iso | Bright |
| Acute | Iso/Dark | Dark |
| 1-3 Days | Bright | Dark |
| 1-2 Wks | Bright | Bright |
| 2-3 Wks | Iso/Dark | Dark |