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You wish to produce an image with a 8 cm FOV and 256 phase encoding gradient steps. The maximum phase encoding gradient you can produce is 1 G/cm. What should the width of the phase encoding gradient be?
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G_{max} dt = N / (2 g FOV)
where

N = number of phase encoding steps

g = gyromagnetic ratio for H = 42.58 MHz/T

FOV = field of view

G_{max} = maximum phase encoding gradient

If we assume a square phase encoding gradient pulse the equation reduces to

t = N / (2 g FOV G_{max})

where t is the duration of the gradient.
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t = 4 ms
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