MRI pulse sequence

Timing diagram for a spin echo type of pulse sequence.

An MRI pulse sequence in magnetic resonance imaging (MRI) is a particular setting of pulse sequences and pulsed field gradients, resulting in a particular image appearance.[1]

A multiparametric MRI is a combination of two or more sequences, and/or including other specialized MRI configurations such as spectroscopy.[2][3]

Overview table

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This table does not include uncommon and experimental sequences.

Group Sequence Abbr. 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).

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 in standard Spine Echo (SE),[4] though not with Fast Spin Echo/Turbo Spin Echo (FSE/TSE). FSE/TSE is the standard of care in modern medicine because it is faster. With FSE/TSE, fat has high signal due to disruption of hyperfine J-coupling between adjacent fat protons.[6]
  • 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).[7] Joint disease and injury.[8]
Gradient echo (GRE) Steady-state free precession SSFP Maintenance of a steady, residual transverse magnetisation over successive cycles.[10] Creation of cardiac MRI videos (pictured).[10]
Effective T2
or "T2-star"		 T2* Spoiled gradient recalled echo (GRE) with a long echo time and small flip angle[11] Low signal from hemosiderin deposits (pictured) and hemorrhages.[11]
Susceptibility-weighted SWI Spoiled gradient recalled echo (GRE), fully flow compensated, long echo time, combines phase image with magnitude image[12] Detecting small amounts of hemorrhage (diffuse axonal injury pictured) or calcium.[12]
Inversion recovery Short tau inversion recovery STIR Fat suppression by setting an inversion time where the signal of fat is zero.[13] High signal in edema, such as in more severe stress fracture.[14] 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).[15]
Double inversion recovery DIR Simultaneous suppression of cerebrospinal fluid and white matter by two inversion times.[16] High signal of multiple sclerosis plaques (pictured).[16]
Diffusion weighted (DWI) Conventional DWI Measure of Brownian motion of water molecules.[17] High signal within minutes of cerebral infarction (pictured).[18]
Apparent diffusion coefficient ADC Reduced T2 weighting by taking multiple conventional DWI images with different DWI weighting, and the change corresponds to diffusion.[19] Low signal minutes after cerebral infarction (pictured).[20]
Diffusion tensor DTI Mainly tractography (pictured) by an overall greater Brownian motion of water molecules in the directions of nerve fibers.[21]
Perfusion weighted (PWI) Dynamic susceptibility contrast DSC Measures changes over time in susceptibility-induced signal loss due to gadolinium contrast injection.[23]
  • Provides measurements of blood flow
  • In cerebral infarction, the infarcted core and the penumbra have decreased perfusion and delayed contrast arrival (pictured).[24]
Arterial spin labelling ASL Magnetic labeling of arterial blood below the imaging slab, which subsequently enters the region of interest.[25] It does not need gadolinium contrast.[26]
Dynamic contrast enhanced DCE Measures changes over time in the shortening of the spin–lattice relaxation (T1) induced by a gadolinium contrast bolus.[27] Faster Gd contrast uptake along with other features is suggestive of malignancy (pictured).[28]
Functional MRI (fMRI) Blood-oxygen-level dependent imaging BOLD Changes in oxygen saturation-dependent magnetism of hemoglobin reflects tissue activity.[29] Localizing brain activity from performing an assigned task (e.g. talking, moving fingers) before surgery, also used in research of cognition.[30]
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[31]
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.[32] Detection of aneurysm, stenosis, or dissection (pictured).[31]
(VIPR)
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  3. ^ Tahmassebi A, Wengert GJ, Helbich TH, Bago-Horvath Z, Alaei S, Bartsch R, et al. (February 2019). "Impact of Machine Learning With Multiparametric Magnetic Resonance Imaging of the Breast for Early Prediction of Response to Neoadjuvant Chemotherapy and Survival Outcomes in Breast Cancer Patients". Investigative Radiology. 54 (2): 110–117. doi:10.1097/RLI.0000000000000518. PMC 6310100. PMID 30358693.
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