Question

This is MRI.

If a sample is put in a magnetic field with B0=1.5T (the most common clinical field strength), and a z gradient with strength Gz=3 Gauss/cm is applied (note conversion 10,000 Gauss/Tesla), what is the Larmor frequency for the protons on the z=0 plane? If you want to image a slice with thickness of 5mm centered at z=0, what is the range of frequencies in the slice?

Answer 1

Lamar frequency is given by f₀ = y B₀

where f₀ = lamar frequency y= gyrometric ratio ( strenghth/angular momentum frequency)

B₀ = strength of external field

GIVEN :     B₀ = 1.5T Gz= 3 gauss/cm

y =

f₀ =       =

B) If you want to slice the image slice has a different center frequency Fc determined by its position (z) along the slice-select gradient (Gss), given by

Fc = ?(Bo + z•Gss) = fo + ?•z•Gss

slice has a finite width (?z) and so it contains a range of frequencies (?F) centered around Fc. These quantities are related by the equation

?F = ? • Gss • ?z    GIVEN : Gss = 3 gauss/cm z =5mm = 0.5 cm

?F =       = 4.5/2pie