mri inversion

INVERSION RECOVERY SEQUENCE

VIPIN KUMAR PG MEDICAL IMAGING MCOAHS MANIPAL UNIVERSITY

MRI SEQUENCES

A sequence is a pre selected set of defined RF and gradient pulses usually repeated many times during the scan wherein the time interval between pulses and the amplitude and shape of the gradient wave forms will control NMR signal Reception and effect the characteristics of the MRI image

Spin echo sequencesConventional spin echo..Fast or turbo spin echo..Inversion recovery ..Stir Flair

Gradient echo pulse sequencesConventional gradient The steady state and echo formationCoherent gradient echoSteady state free precessionBalanced gradient echoFast gradientEcho planar imaging

Pulse sequences

INVERSION RECOVERY SEQUENCE

Inversion recovery sequences were initially designed to produce very heavy T1 weighting. However at present they are mainly used in conjunction with a FSE sequence to produce T2 weighted images.

In low field MRI inversion recovery is using in T1 imaging

INVERSION RECOVERY SEQUENCE

mechanism. SPIN ECHO Sequence ,,

Begins with 180 o inverting pulses which invert the NMV in 180 0

TR - time between successive 180 o inverting pulse

Remove the pulse .

NMV begins to relax back to B 0

Then apply 90 o PULSE at an interval Ti

Apply 1800 RF pulse to re phase the spin in transverse plain This produces an echo at time TE

18090

180 180

TR

TI

TE

FIDECHO

INVERSION RECOVERY PULSE SEQUENCE

•TI is the main factor that controls the IR sequences

•If the 90 opulse applied shortly after the NMV pass through the transverse plain which causes heavy T1weightning and saturation .•TIs 300ms to 700 ms result in heavy T1 weighting •The TE controls the amount of T2decay •For T1 weightning TE should be short•For T2 TE should be long •TR must always be long enough to allow full longitudinal recovery of magnetization before each inverting pulse

CONTRAST

ADVANTAGES

•VERY GOODSNR BEC TR IS LONG •EXCELENT T1 CONTRAST

LONG SCAN TINES UNLESS USED IN CONJUNCTION WITH FAST SPIN ECHO

DISADVANTAGES

FAST INVERSION RECOVERY

Combination of Inversion recovery and fast spin echoNMV is flipped through 1800 into full saturation by 1800inverting pulseTR is time between the two successive 180 0 pulse At time t1 90 0 excitation pulse is applied Then multiple 180 0 inverting pulse are applied to produce multiple echoes Multiple lines of k space are filled in each TR so reduces the scan time FAST IR allows much shorter scan time

STIR (short TI inversion recovery)

SHORT TIs 100-180ms .. TIs of this magnitude place the 90 0 excitation pulse at the time that NMV of fat is passing exactly through the transverse plane

This point there will be no longitudinal magnetization in fat (null point)

there for Ft is suppressed in the image

APPLICATION OF STIR

MUSCULOSKELETAL IMAGING ALSO USEFUL IN GENERAL MR IMAGING

PARAMETERS

Short tue .- 150-175 msLong TE – 5O ms Long TR – 4000 ms Long turbo factor 16-20 Average scan time .. 5-15 min

FLAIR (fluid attenuated inversion recovery

Used to supress the csf signal in t2 weighted images Use long TIs -1700- 2200msUse to null CSF/ FLUID signal TI must be long to correspond with null point .

Applications of FLAIR

Use ful in brain imaging To Visualize peri ventricular lesions such as Ms plaques Leasion in cervical and thoracic cord Sub arachanoid hemorrhage and meningits

PARAMETERS

Long TI 1700-2200 ms Long TE 70 ms +Long TR -6000ms+Long turbo Factor 16-20 Average scan time 8-15 mins

ADVANCEMENTS IN APPLICATION INVERSION RECOVERY

NULL BLOOD CARDIAC IMAGING with double IR prep with two 180o pulse TI -800ms

Tripple IR prep with TI 150ms to null fat and blood together Use full in determining fatty in filteration of heart walls

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Thank you