1 / 12

Chapter 6 Lecture Spin Echo Imaging Methods Mark D. Herbst, MD, PhD

Chapter 6 Lecture Spin Echo Imaging Methods Mark D. Herbst, MD, PhD. Two Main Types of MR methods Spin Echo –uses RF pulse to get an echo Gradient Echo –uses gradient pulse to get an echo. The spin echo process.

phuc
Télécharger la présentation

Chapter 6 Lecture Spin Echo Imaging Methods Mark D. Herbst, MD, PhD

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 6 LectureSpin Echo Imaging MethodsMark D. Herbst, MD, PhD • Two Main Types of MR methods • Spin Echo –uses RF pulse to get an echo • Gradient Echo –uses gradient pulse to get an echo

  2. The spin echo process • Net magnetization vector starts at equilibrium, pointing up along the +z direction. • 90 degree RF pulse M now in xy plane • Spins in xy plane begin dephasing, and when totally dephased, M=0. • 180 degree refocusing RF pulse is applied • Spins in xy plane begin to rephase, and echo forms. This echo is captured and stored in k-space.

  3. The Spin Echo Process

  4. Three basic spin echo methods • PD-weighted (proton density) – long TR, short TE • T2-weighted – long TR, long TE • T1-weighted – short TR, short TE

  5. Causes of Spin Dephasing • Spin-spin interactions – energy exchange among the spinning nuclei causes relaxation (dephasing) • Magnetic field inhomogeneity – cases spins to dephase, reversed by 180 degree RF refocusing pulse

  6. Multiple Spin Echo • Done by using more than one 180 degree RF refocusing pulse • Commonly used to get both PDW and T2W images at the same time • Used in FSE (fast spin echo, turbo spin echo) to get images faster by filling k-space faster than conventional spin echo (CSE)

  7. Inversion Recovery • Gives high level of T1 contrast • Used to suppress either water or fat (STIR suppresses fat, FLAIR suppresses water) • Starts with a 180 degree RF inversion pulse, placing M in the –z direction • Then, wait TI (inversion time) before applying the 90 degree RF pulse that puts M in the xy plane • Finally, apply the 180 degree RF refocusing pulse to form the echo for data collection, put it in k-space.

  8. TI: inversion time • The time of inversion • The time that M is allowed to stay inverted (-z) • The time between the initial 180 degree inversion pulse and the 90 degree pulse that puts M in the xy plane.

  9. 180 degree pulse

  10. IR pulse diagram (STIR and FLAIR)

  11. STIR – fat at null point

  12. FLAIR -- water at null point

More Related