INVERSION RECOVERY SEQUENCE VIPIN KUMAR PG MEDICAL IMAGING MCOAHS MANIPAL UNIVERSITY
Jun 20, 2015
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
`nbbgggfffddddddddddddddddddddddddddddd
Thank you