2. • TR has little effect on image contrastTR has little effect on image contrast
• TE behavior similar to conventional SETE behavior similar to conventional SE
imagingimaging
–more T2* effect with increased TEmore T2* effect with increased TE
• less T1 weighting with shorter flip anglesless T1 weighting with shorter flip angles
–maximum signal to noise between 30maximum signal to noise between 3000
and 60and 6000
Pulse Sequences
gradient echo - general principles
TE=9TE=9 TE=30TE=30
5. • artifacts
–magnetic susceptibility
»black bones
»blooming effect
•air in bowel
•metal clips
•suture material
»artifact reduced with shorter TE
Pulse Sequences
gradient echo - general principles
6. • artifacts
–phase cancellation of water and fat
» alternates every ~2.2 msec at 1.5 T
–additional phase artifacts due to
absence of 1800
refocussing pulse
»avoid 0.5, 0.75 NEX or PCS
acquisition
Pulse Sequences
gradient echo - general principles
7. Fat and Water
gradient echo - phase cancellation
TR 450
TE 13.42
α=45°
TR 450
TE 15.7
α=45°
FESUM
in-phase
FEDIF
opposed-
phase
ν
9. • conventional gradient echo (MPGR, FE)
–usually a multislice 2D acquisition
–cartilage and joint visualization (e.g.
shoulder labrum)
»TR 450 +, TE 10-15, 450
•difficult to distinguish fluid from
cartilage, but signal to noise is good
Pulse Sequences
gradient echo - USE
10. • “magic” cartilage sequence (MPGR, FE)
–TR 600, TE 22, 150
»bright fluid, dark bones, gray
cartilage
•patellofemoral joint
»lower signal to noise
Pulse Sequences
gradient echo - USE
11. • tumor imaging
–conventional gradient echo (MPGR, FE)
–delineates relationship of vessels to tumor
–demonstrates bony cortex
Pulse Sequences
gradient echo - USE
12. • fast gradient echo (GRASS, SER FAST)
–usually a single slice 2D acquisition
–kinematic motion studies (shoulder)
»TR 50, TE 10, 450
• ≈ 20 second scan
Pulse Sequences
gradient echo - USE
13. • fast spoiled gradient echo (SPGR, RF-fast spoiled gradient echo (SPGR, RF-
FAST)FAST)
–usually a single slice 2D acquisitionusually a single slice 2D acquisition
–extremity MRA (2D time of flight)extremity MRA (2D time of flight)
»30-60 slices, 5-10 sec / slice30-60 slices, 5-10 sec / slice
Pulse Sequences
gradient echo - USE
14. • MT gradient echo (2D)MT gradient echo (2D)
–excellent joint visualizationexcellent joint visualization
–MTC contrast for muscle and fatMTC contrast for muscle and fat
–bright fluidbright fluid
–routine axial kneeroutine axial knee
Pulse Sequences
gradient echo - USE
18. • DO NOT substitute gradient echo for T2
weighted
–CANNOT see bone marrow edema
–may miss significant pathologic findings
Pulse Sequences
gradient echo - USE
19. Pulse Sequences
gradient echo - USE
• DO NOT use gradient echo imaging for
primary diagnosis of rotator cuff disease or
meniscal tears
–CANNOT reliably distinguish a tear from
normal bright signal seen within
fibrocartilage on most gradient echo
sequences
• DO NOT use T2 enhanced sequences
(SSFP, CE-FAST)