Which of the following statement is false about magnetic res

Which of the following statement is false about magnetic resonance imaging?

1)The MRI signal represents a time- and position-dependent magnetization function, where position dependency is based on the addition of magnetic field gradients and phase differences to the basic magnetic field B₀.

2)T₁, or spin-lattice relaxation, describes the recovery of a spin to its equilibrium magnetization along the z-axis, while T₂, or spin-spin relaxation, describes the gradual dephasing of any component of the magnetization in the xy-plane, towards random phase that equates with a null transverse component.

3)The Spin-Echo pulse sequence is based on a 90-degree flip angle soon followed by a 180- degree flip angle that reverses the effect of magnetic inhomogeneity and causes the portion in the xy-plane of the magnetization to briefly rephase.

4)Frequency encoding has no effect on the Larmor frequency of spins.

5)None of these statements is false.

Please explain why

Solution

Ans: 1)True;The MRI signal is time & space dependant, the space dependance is coming due to the gradiant of the field and the time dependancy(or phase) due to the the constant field B0.

2)True:The strength of the MRI signal depends on the difference between the no of up spin & the no. of down spin.And this spin flipping highly depends on T1 & T2.

3)True: Using spin Echo technique the responce time of the spins can be made faster by reducing the effect of transverse magnatization.

4)False:If we do not want to excite the whole volume of a particular portion but only a single slice of the object we have to tailor the RF-pulse accordingly.After a slice has been chosen there is still no information available about the origin of the signal. For this purpose an additional gradient (Gx) along the x-axis(if we take xy as the transverse direction), generally denoted as the readout or frequency encoding direction, is applied, leading to an altered magnetic field.This changes the Larmor frequency of the spins in dependence of their position along the readout direction.Therefore the measured signal contains a spectrum of known frequencies which can be used to decode the exact position in one dimension by means of a Fourier transform.

5)False