MRI basics
T1 - how quickly tissue can be magnetied, short TR (<1000ms) and short TE (<30ms)
T2 - how quickly tissue loses magnetization, long TR (>2000ms) and long TE (>60ms)
Proton densitiy (PD) - tissue weighting for density, long TR (>1000ms) and short TE (<30ms)
Time of Repetition (TR) - time between RF pulses
Time of Echo (TE) - time provided for absorbed radio wave energy to be released and detected
Spin Echo (SE) - pulse sequence respnsible for standard T1, T2 and PD
Multiple Spin Echo - aka RARE, FSE, TSE. Reduce image time. can add fat suppression: FLARE and HASTE
Inversion Recovery (IR) - ex: short T1 IR (STIR), tissue with short T1 times are supressed (including fat and gadolinium)
Gradient Recalled Echo (GRE) - short flip angles makes for rapid image sequences, used for MR angiography, can get T1 or T2 weighting, sensitive to field inhogeneity, decay time is termed T2* (star), include FLASH, GRASS, FISP, RAGE
Echo Planar - very fast
In and Out of Phase Imaging - In Phase adds signal from water and fat, Out of Phase subtracts water signal from fat. Good for detecting intracelualr fat. Adipose tissue has little water so no difference on in and out of phase
Diffusion Weighted Imaging (DWI) - reflects diffusion of water through cell membranes. With infarcts, cells swell and NaK pumps fail, causing restricted diffusion which corrspond to a high signal.
Apparent Diffusion Coefficient (ADC) - mapping of tensor vectors
Gadolinium - shortens T1 and T2 relaxation times
