MRI Flashcards
T1 image
Water dark (hypointense)
Fat bright (hyperintense)
Bone dark
FDSB
T2 image
Fluids bright (hyperintense)
- vitreous, CSF
Bone/fat dark
FBSD
What is T2 FLAIR
Fluid signal is suppressed on T2WI allowing visualisation of signal abnormalities associated with change in white matter - e.g. MS
WHite matter vs gray matter
Gray matter hypointense compared to white matter on both T1 and T2
What is Gaolinium contrast used for?
IV
Enhance T1
For inflammatory and neoplastic lesions
What is DWI for?
Most senstive for acute ischaemic change
Can detect changes within minutes
Diffusion coefficient can be used to characterise oedema as cytotoxic vs vasogenic
Ctotxic bright DWI
Vasogenic dark DWI
MRI shows a non-calcified fusiform enlargement of the optic nerve with kinking in the orbit
Optic nerve glioma
Tubular enlargement of the optic nerve sheath, which appears calcified, causing a tram-track sign (parallel thickening and enhancement around the optic nerve).
Optic nerve meningioma
What modality to monitor thyroid eye disease
MRI with STIR sequence
Air and blood on MRI
No signal
Hypointense
T1
T2
FLAIR
STIR
FAT > WHITE MATTER > GRAY MATTER > CSF
T2:
CSF> GRAY MATTER > WHITE MATTER > FAT
FLAIR:
FAT >GRAY MATTER > WHITE MATTER > CSF
STIR:
CSF=GRAY MATTER > WHITE MATTER > FAT
Contraindication to MRI
Cohclear implants
Cardiac pacemakers
Shrapnel
Metallinc FB
(titanium ocular implants compatible)
Substances with short T1 time appear
Bright on T1 images
How does MRI work
Nuclear dipoles aligned with eachother by strong magetic field
Relaxation times required for return of dipole alignment with external magnetic field determine the scan’s appearance
Direction of nuclear dipole alignment is acutely altered by radiofrequency pole
Which MRI sequence for TED
STIR
short tau inversion recovery
(suppresses orbital fat)
- correlates with active orbital ifnlammation
CSF = GRAY, WHITE, FAT
