MRI Flashcards
T1 shortening and prolongation
T2 shortening and prolongation
T1: Hyperintense and hypointense
T2: Hypointense and hyperintense
Spin-echo conventional
T1 and T2
T1 shortening causes
Gad, fat, protein
- Paramagnetic blood stage (intra/extra methemglobin)
- Melanin
- Mineralization
- SLOW flowing blood
- Calcium, when not in bone
T2 shortening
Paramagnetic blood stage (except hyper acute and extracellar methemoglobin
-Calcification
-Fibrous
-High cellularity (lymph, Medulloblastoma)
Vascular flow void
Mucin (dessicated sinus mucin is hypointense and muscinous lesions which are hydrated are hyper)
FLAIR
Water suppressed T2
White/grey on T1
T1: White matter BRIGHT DUE TO FAT
Diffusion MRI
DWI and ADC. Principle that with ncrease Brownian motion, signal is lost. Pathology reduces diffusion and hence less signal loss
-DWI is a T2 weighted sequence and reduced diffusion is HYPER, and hypo on ADC.
T2 shine through
Anything bright on T2 is bright on DWI hence look at ADC to confirm for restricted diffusion
B value
Higher the b value, the higher the contrast provided for determining reduced diffisivity.
Downside to increasing the B value
Decrease in signal to noise ratio meaning scan time should be proportionally increased
How to calculate ADC
Need at least two different B value images
Restricted diffusion differential
Acute stroke Bacterial abscess Lymphoma, mdulloblastoma epidermoid cyst herpes encephalitis Creutzfieldt-Jakob
GRE
T2* signal. Omits 180 degree rephasing pulse. Susceptible to signal loss
Causes of dark spots on GRE
Hemosiderin and calcium
Differential for dark spots on GRE
- Hypertensive microbleedss
- Cerebral amyloid angiopathy
- Familial cerebral cavernous malformation
- Axonal shear injury
- Multiple hemorrhagic mets
Difference b/w hypertensive microbleeds and cerebral amyloid angiopathy
Location!
- Cerebral amyloid spots= subcortical white matter (parietal and occipital lobes)
- Hypertensive= Basal ganglia thalami, cerebellum, pons
Blood products components over time (hyperacute, acute, early and late subacute, chronic)
Hyperacute: Intracellular oxy-Hb Acute: intracellular deoxy-hb Early subacute: Intracellular methe-Hb Late subacute: Extracellular methe-Hb Chronic: Extracellular hemosiderin/ferritin
T1/T2 for the following:
Hyperacute: Intracellular oxy-Hb Acute: intracellular deoxy-hb Early subacute: Intracellular methe-Hb Late subacute: Extracellular methe-Hb Chronic: Extracellular hemosiderin/ferritin
Hyperacute: Iso to low/High Acute: Iso to low/Low Early subacute: High/Low Late subacute: High/High Chronic: Low/Low
