Pulse sequences in MRI
Pulse sequence: RFPulse sequence: RF
Bloch Bloch equationequation
Pulse sequence: RFPulse sequence: RF
Lab reference frameLab reference frameRotating reference frameRotating reference frame
Pulse sequence: RFPulse sequence: RF
Gradients onGradients on
Pulse sequence: RFPulse sequence: RF
Slice selective pulsesSlice selective pulses TruncationTruncation
Sin
c p
uls
eS
inc
pu
lse
FT
FT
Pulse sequence: RFPulse sequence: RF
Spectral pulses (chemical shift)Spectral pulses (chemical shift)
Fat suppressionFat suppression
Pulse sequence: RF pulse designPulse sequence: RF pulse design
Pulse sequence: Spin EchoPulse sequence: Spin Echo
Spin echo - “working horse of MR”Spin echo - “working horse of MR”
Pulse sequence: Spin EchoPulse sequence: Spin Echo
contrastscontrasts
Pulse sequence: sequence diagramPulse sequence: sequence diagram
RRFF
Slice Slice selectiveselective
Phase Phase encodingencoding
Frequency Frequency encodingencoding
MR signalMR signal
TETE
TTRR
90
180
90
Pulse sequence: contrastsPulse sequence: contrasts
Returning to equilibrium – T1 Returning to equilibrium – T1
TimeTime
Mag
neti
zati
on
Mag
neti
zati
on
Pulse sequence: contrastsPulse sequence: contrasts
Spin dephasing - T2Spin dephasing - T2
TimeTime
Mag
neti
zati
on
Mag
neti
zati
on
Pulse sequence: Turbo spin echoPulse sequence: Turbo spin echo
Pulse sequence: Turbo spin echoPulse sequence: Turbo spin echo
T2 relaxation time of fat is longer due to suppressedT2 relaxation time of fat is longer due to suppressedJ-coupling by turbo spin echo (refocusing 180 pulses)J-coupling by turbo spin echo (refocusing 180 pulses)
Pulse sequence: SE EPIPulse sequence: SE EPI
Pulse sequence: SE EPIPulse sequence: SE EPI
The sequence is very sensitive to susceptibilityThe sequence is very sensitive to susceptibilityartefacts, to gradient imperfection.artefacts, to gradient imperfection.Very fast acquisition.Very fast acquisition.
Pulse sequence: GEPulse sequence: GE
Pulse sequence: GEPulse sequence: GE
Allows shot TE/TR; easy adopt to 3D;Allows shot TE/TR; easy adopt to 3D;Modification for high resolution structural image:Modification for high resolution structural image:Magnetisation prepared rapid acquisition by gradientMagnetisation prepared rapid acquisition by gradientecho (MP-RAGE) echo (MP-RAGE)
Pulse sequence: Inversion recoveryPulse sequence: Inversion recovery
Spectral selective RF pulseSpectral selective RF pulseIs ineffective in the case of B0Is ineffective in the case of B0inhomogeneityinhomogeneity
Sequence with IR allows one to solve itSequence with IR allows one to solve it
Pulse sequence: Inversion recoveryPulse sequence: Inversion recovery
Fat suppressionFat suppression
Pulse sequence: AngiographyPulse sequence: Angiography
Gradient echo: time-of-flight (ToF)Gradient echo: time-of-flight (ToF)
Spin echo: time-of-flight (ToF)Spin echo: time-of-flight (ToF)
Pulse sequence: AngiographyPulse sequence: Angiography
Pulse sequence: MR SpectroscopyPulse sequence: MR Spectroscopy
PRESS: Point resolved spectroscopyPRESS: Point resolved spectroscopy
Pulse sequence: DiffusionPulse sequence: Diffusion
Spatial encoding of Brownian motion in Spatial encoding of Brownian motion in a given directiona given direction
Pulse sequence: DiffusionPulse sequence: Diffusion
Literature
● Berstein, King, Zhou, Handbook of MRI pulse sequences.
● McRobbie, Moore, Graves, Prince, MRI: from picture to proton.
Problems
● How to estimate a flipping angle knowing the strength of applied B1 and duration of the pulse?
● What is sinc pulse and why it is applied often in imaging?● Show FT for differently cut sinc pulse. What is difference?● Why do we need a gap in slice excitation?● Write the Bloch equation with relaxation times T1 and T2. What is
a solution of the Bloch equation?● What is a spoiler gradient?● You have to learn the basic acronyms of pulse sequences: SE,
GE, TSE, EPI, FLASH, MPRAGE etc.
Next topic is Next topic is image artefactsimage artefacts