Physics Main clinical distinctions Example Spin echo T1 weighted T1 Measuring spin–lattice relaxation by using a short repetition time (TR) and echo time (TE). Lower signal for more water content,[4] as in edema, tumor, infarction, inflammation, infection, hyperacute or chronic hemorrhage.[5] High signal for fat[4][5] High signal for paramagnetic substances, such as MRI contrast agents[5] Standard foundation and comparison for other sequences T2 weighted T2 Measuring spin–spin relaxation by using long TR and TE times Higher signal for more water content[4] Low signal for fat[4] Low signal for paramagnetic substances[5] Standard foundation and comparison for other sequences Proton density weighted PD Long TR (to reduce T1) and short TE (to minimize T2).[6] Joint disease and injury.[7] High signal from meniscus tears.[8] (pictured) Gradient echo (GRE) Steady-state free precession SSFP Maintenance of a steady, residual transverse magnetisation over successive cycles.[9] Creation of cardiac MRI videos (pictured).[9] Effective T2 or "T2-star" T2* Postexcitation refocused GRE with small flip angle.[10] Low signal from hemosiderin deposits (pictured) and hemorrhages.[10] Inversion recovery Short tau inversion recovery STIR Fat suppression by setting an inversion time where the signal of fat is zero.[11] High signal in edema, such as in more severe stress fracture.[12] Shin splints pictured: Fluid-attenuated inversion recovery FLAIR Fluid suppression by setting an inversion time that nulls fluids High signal in lacunar infarction, multiple sclerosis (MS) plaques, subarachnoid haemorrhage and meningitis (pictured).[13] Double inversion recovery DIR Simultaneous suppression of cerebrospinal fluid and white matter by two inversion times.[14] High signal of multiple sclerosis plaques (pictured).[14] Diffusion weighted (DWI) Conventional DWI Measure of Brownian motion of water molecules.[15] High signal within minutes of cerebral infarction (pictured).[16] Apparent diffusion coefficient ADC Reduced T2 weighting by taking multiple conventional DWI images with different DWI weighting, and the change corresponds to diffusion.[17] Low signal minutes after cerebral infarction (pictured).[18] Diffusion tensor DTI Mainly tractography (pictured) by an overall greater Brownian motion of water molecules in the directions of nerve fibers.[19] Evaluating white matter deformation by tumors[19] Reduced fractional anisotropy may indicate dementia.[20] Perfusion weighted (PWI) Dynamic susceptibility contrast DSC Gadolinium contrast is injected, and rapid repeated imaging (generally gradient-echo echo-planar T2 weighted) quantifies susceptibility-induced signal loss.[21] In cerebral infarction, the infarcted core and the penumbra have decreased perfusion (pictured).[22] Dynamic contrast enhanced DCE Measuring shortening of the spin–lattice relaxation (T1) induced by a gadolinium contrast bolus.[23] Arterial spin labelling ASL Magnetic labeling of arterial blood below the imaging slab, which subsequently enters the region of interest.[24] It does not need gadolinium contrast.[25] Functional MRI (fMRI) Blood-oxygen-level dependent imaging BOLD Changes in oxygen saturation-dependent magnetism of hemoglobin reflects tissue activity.[26] Localizing highly active brain areas before surgery, also used in research of cognition.[27] Magnetic resonance angiography (MRA) and venography Time-of-flight TOF Blood entering the imaged area is not yet magnetically saturated, giving it a much higher signal when using short echo time and flow compensation. Detection of aneurysm, stenosis, or dissection[28] Phase-contrast magnetic resonance imaging PC-MRA Two gradients with equal magnitude, but opposite direction, are used to encode a phase shift, which is proportional to the velocity of spins.[29] Detection of aneurysm, stenosis, or dissection (pictured).[28] (VIPR) Susceptibility-weighted SWI Sensitive for blood and calcium, by a fully flow compensated, long echo, gradient recalled echo (GRE) pulse sequence to exploit magnetic susceptibility differences between tissues Detecting small amounts of hemorrhage (diffuse axonal injury pictured) or calcium.[30]