Physics Just the Basics Series #02 - Relaxation and Echoes-Physics Just the Basics

Video Transcription

Video Summary

This webinar, introduced by Mariana Fontana, was part of the SCMR/NCMR “MRI Physics, Just the Basics” series and focused on relaxation and echoes in cardiac MRI. Dr. Anthony Aletras explained how MRI contrast arises from tissue properties and pulse sequence design. He reviewed T1, T2, and T2* relaxation, emphasizing that T2* reflects both intrinsic tissue decay and magnetic field inhomogeneity, while T2 reflects true spin-spin relaxation. He used examples such as myocardial edema and iron overload, noting how T2* mapping can detect iron deposition in thalassemia.<br /><br />The lecture then compared one-pulse, spin echo, and gradient echo sequences. The one-pulse experiment produces an FID and mainly reveals T2*. Spin echo uses a 180° pulse to refocus dephasing caused by field inhomogeneity, allowing true T2 measurement. Gradient echo uses gradient reversals instead of a 180° pulse, so it still reflects T2* and is useful for imaging. Finally, Aletras described T1 relaxation and recovery using saturation recovery and inversion recovery methods, which are important for T1 mapping and contrast-enhanced imaging. The session ended with Q&A on gradient polarity, acquisition timing, electron shielding, and MRI gradients.

Keywords

cardiac MRI

relaxation

T1 mapping

T2 relaxation

T2* mapping

spin echo

gradient echo

iron overload