• three basic varieties–conventional (GRASS, FAST)–spoiled (spoiled grass, RF-FAST)–“T2” enhanced (SSFP, CE-FAST)

Pulse Sequencesgradient echo

• TR has little effect on image contrastTR has little effect on image contrast• TE behavior similar to conventional SE imagingTE behavior similar to conventional SE imaging

– 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 and

606000

Pulse Sequencesgradient echo - general principles

TE=9TE=9 TE=30TE=30

• Desired contrast–T1: spoiled gradient echo

»TE ~10»flip angle 450 to 900

–PD: gradient echo»TE ~ 10-15»flip angle 450 to 600

Pulse Sequencesgradient echo - general principles

• Desired contrast–T2: gradient echo

»TE ~ 15-25»flip angle 100 to 300

Pulse Sequencesgradient echo - general principles

• artifacts–magnetic susceptibility

»black bones»blooming effect

• air in bowel• metal clips• suture material

»artifact reduced with shorter TE

Pulse Sequencesgradient echo - general principles

• 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 Sequencesgradient echo - general principles

Fat and Watergradient echo - phase cancellation

TR 450TE 13.42=45°

TR 450TE 15.7=45°

FESUMin-phase

FEDIFopposed-phase

Fat and Watergradient echo - phase artifacts

»avoid 0.5, 0.75 NEX or PCS acquisition

• 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 Sequencesgradient echo - USE

• “magic” cartilage sequence (MPGR, FE)–TR 600, TE 22, 150

»bright fluid, dark bones, gray cartilage

•patellofemoral joint» lower signal to noise

Pulse Sequencesgradient echo - USE

• tumor imaging–conventional gradient echo (MPGR, FE)–delineates relationship of vessels to tumor–demonstrates bony cortex

Pulse Sequencesgradient echo - USE

• 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 Sequencesgradient echo - USE

• 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 Sequencesgradient echo - USE

• 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 Sequencesgradient echo - USE

• MT gradient echo (3D)–multiplanar capability

Pulse Sequencesgradient echo - USE

• 3D spoiled gradient echo–TR 35, TE 13.4, 500, 124 slices, 128

phase encodings, 0.9-1 mm slice thickness

–multiplanar joint and tendon visualization

Pulse Sequencesgradient echo - USE

CORONALCORONAL OBLIQUEOBLIQUE AXIALAXIAL

Pulse Sequences3D spoiled gradient echo - USE

• DO NOT substitute gradient echo for T2 weighted–CANNOT see bone marrow edema–may miss significant pathologic findings

Pulse Sequencesgradient echo - USE

Pulse Sequencesgradient 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)

Pulse Sequences3D gradient echo - USE

Shoulder Volumeradial labral images

Shoulder Volumeradial labral images