Gradients and Fields 1 Psy 8960, Fall ‘06 S = 10 =-10Hz S = 10 =-15Hz S = 0 S = 0 S = 10 =-10Hz S = 10 =-10Hz S = 10 =-10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =10Hz S = 10 =10Hz S = 10 =15Hz S = 10 =15Hz S = 10 =20Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =-15Hz S = 10 =-20Hz S = 10 =-20Hz S = 0 S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =15Hz S = 10 =20Hz S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =-15Hz S = 10 =-20Hz S = 10 =-10Hz S = 10 =15Hz S = 10 =20Hz S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =-15Hz S = 10 =-20Hz S = 10 =-10Hz S = 10 =15Hz S = 10 =20Hz S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =-15Hz S = 10 =-20Hz S = 10 =-10Hz S = 10 =15Hz S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 10 =-15Hz S = 10 =-10Hz S = 10 =10Hz S = 10 =-5Hz S = 10 =0Hz S = 10 =5Hz S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 S = 0 Gradients and fields • Static magnetic field • Gradients – Effect of simultaneous gradients • Excitation and slice selection
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Psy 8960, Fall ‘06 Gradients and Fields1 Gradients and fields Static magnetic field Gradients –Effect of simultaneous gradients Excitation and slice selection.
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Gradients and Fields 1Psy 8960, Fall ‘06
S = 10=-10Hz
S = 10=-15Hz
S = 0S = 0
S = 10=-10Hz
S = 10=-10Hz
S = 10=-10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=10Hz
S = 10=10Hz
S = 10=15Hz
S = 10=15Hz
S = 10=20Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=-15Hz
S = 10=-20HzS = 10
=-20HzS = 0
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=15Hz
S = 10=20Hz
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=-15Hz
S = 10=-20Hz
S = 10=-10Hz
S = 10=15Hz
S = 10=20Hz
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=-15Hz
S = 10=-20Hz
S = 10=-10Hz
S = 10=15Hz
S = 10=20Hz
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=-15Hz
S = 10=-20Hz
S = 10=-10Hz
S = 10=15Hz
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 10=-15Hz
S = 10=-10Hz
S = 10=10Hz
S = 10=-5Hz
S = 10=0Hz
S = 10=5Hz
S = 0
S = 0
S = 0
S = 0
S = 0S = 0 S = 0
S = 0S = 0 S = 0 S = 0S = 0 S = 0 S = 0S = 0 S = 0 S = 0 S = 0
S = 0 S = 0 S = 0
S = 0 S = 0
S = 0
S = 0
S = 0
S = 0
S = 0 S = 0
S = 0 S = 0 S = 0
S = 0
S = 0 S = 0 S = 0
S = 0S = 0 S = 0 S = 0S = 0 S = 0 S = 0S = 0 S = 0 S = 0 S = 0
Gradients and fields
• Static magnetic field• Gradients
– Effect of simultaneous gradients
• Excitation and slice selection
Gradients and Fields 2Psy 8960, Fall ‘06
Imaging
B
Gradients and Fields 3Psy 8960, Fall ‘06
One field, one resonant frequency
B
RF in RF out
Gradients and Fields 4Psy 8960, Fall ‘06
Field gradient: frequency = localization
RF in RF out
Gz = 3 G/cm
Bz = (3 + 0.0003z) T
Gradients and Fields 5Psy 8960, Fall ‘06
Gradients
• Typical strength – 10 to 40 mT/m (1 to 4 G/cm)
• Always produce fields aligned with B0
• Typical rise time: 300 microseconds• Risks to subjects: