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MRI Brain
- 1. Dr. Rabail Akbar Qazi
- 3. • Best for ‘anatomical’ imaging of the brain • White matter is of a higher signal intensity than the grey matter • Fat appears bright • Fluid appears dark • T1-weighted sequences provide the best contrast for paramagnetic contrast agents
- 4. BLACK: • Air • Calcium • Bone DARK: • CSF • Edema • Most lesions GREY: • White matter and grey matter WHITE: • Blood • Fat • Melanin • Protein rich fluid • Slow flowing blood • Paramagnetic substances
- 5. • Opposite to that of T1 • Grey matter appears white and white matter appears dark • Fat is dark • Fluid is bright • Vessels: Black (Flow void)
- 6. BLACK: • Air • Dense bone • Calcium • Flow DARK: • Grey matter • White matter WHITE: • CSF • Blood • Edema • Most lesions
- 8. Usually gadolinium is used as a contrast agent Sensitive to the presence of intravascular as well as extravascular gadolinium Useful for visualization of: Normal vessels Vascularity Disruption of the blood brain barrier
- 11. Same as T2 except that free CSF is suppressed i.e hypointense. Important in delineating lesions close to CSF containing spaces Contrast enhanced FLAIR useful for leptomeningeal involvement.
- 15. The concentration of mobile Hydrogen atoms within a sample of tissue The higher the number of protons in a given unit of tissue, the brighter the signal on the proton density image. Excellent signal distinction between fluid, hyaline cartilage and fibrocartilage.
- 16. FLUID: Hyperintense Fat: Hyperintense
- 22. THANKYOU
Editor's Notes
- The clinical benefits of gadolinium-based contrast agents when used for brain MR imaging are significant, and they include the ability to see more lesions and improve lesion characterization most commonly used for enhancement of vessels in MR angiography or for brain tumor enhancement associated with the degradation of the blood–brain barrier. Gd(III) chelates do not pass the intact blood–brain barrier because they are hydrophilic. Thus, these are useful in enhancing lesions and tumors where blood-brain barrier is compromised and the Gd(III) leaks out.
- The fluid-attenuated inversion recovery (FLAIR) is a special inversion recovery sequence using a long repetition time that effectively suppresses signals from free water in cerebrospinal fluid (CSF), thus allowing to highlight hyperintense lesions adjacent to CSF containing spaces
- Proton density images were extensively used for brain imaging, however they have largely been replaced by FLAIR