The Larmor frequency of protons at the top of a patient\'s head is 54.30 MHz. Th

Question

The Larmor frequency of protons at the top of a patient's head is 54.30 MHz. The Larmor frequency of protons at the top of the spine 18.0 cm below is 55.15 MHz.

a) what is the magnetic field strength in the MRI apparatus at the top of the head (in T)?

b) what is the magnetic field gradient in the MRI apparatus (in T/m)?

c) The base of the patient's spine is 1.05 m below the top of their head. What will the Larmor frequency at the base of the patients spine be assuming that the magnetic field gradient remains constant across the whole body (in MHz)?

Explanation / Answer

Part a)

Larmor frequency, f = qB/[2*pi*m]

given, f = 54.30 MHz

we know, q = 1.6*10-19 C; mp = 9.1*10-31 kg;

B = [2*pi*m]f/q

B = 1.94*10-3 T

the magnetic field strength in the MRI apparatus at the top of the head is 1.94*10-3T

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