0
$\begingroup$

In MRI, the T1 relaxation constant for a tissue type is defined as the time taken for the longitudinal relaxation to recover approximately to 63% of its initial value.

Is there any modification of the T1 time due to application of gradients. Suppose, after application of the RF pulse, the magnetization is tipped completely in the transverse place. If one waits, then 63% of the longitudinal magnetization (z-direction) will recover after T1 seconds. Now, say at the same time I apply a gradient along the x or y direction. Would this have any affect on the longitudinal relaxation time?

Improve this question
$\endgroup$
2
  • $\begingroup$ is this a signal processing question? Sounds like physics to me... maybe EE... $\endgroup$
    – Marcus Müller
    Jun 20, 2016 at 10:08
  • $\begingroup$ hmmmmmm...not sure. I have posted MRI questions here before but please feel free to move it if you think it is best served somewhere else. $\endgroup$
    – Luca
    Jun 20, 2016 at 10:46

1 Answer 1

Reset to default
1
$\begingroup$

It does not have any practical effect on the $T_1$ relaxation, if there is a gradient present or not.

Sure, from an academic point of view, there is an effect: Typically, in biomedical applications $T_1$ gets longer at higher field strengths. This is the reason why imaging sequences have to be adapted to the field strength of the machine, if $T_1$-dependent signal behavior is exploited (see Fluid Attenuation, or magnetization prearation in MPRAGE as an example). So, since you increase the magnetic field in $z$ diretion by a few mT, this would also influence $T_1$. However, I have never seen a practical application where this was a concern.

Improve this answer
$\endgroup$
2
  • $\begingroup$ Thank you. The reason I asked was precisely that because T1/T2 values depend on field strength and whether they have to be taken into account during the acquisition as well. $\endgroup$
    – Luca
    Jun 20, 2016 at 16:20
  • $\begingroup$ This would be a major drawback, if it was true. Just imagine the phase encoding gradient that is different between consecutive measurements - in each case $M_z$ would be different - this would create severe image artifacts. $\endgroup$
    – M529
    Jun 20, 2016 at 17:54

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.