Mri
  • Imaging in MRI depends on the electromagnetic properties of the nuclei
    • These properties vary depending on
      • the bonding of the nuclei to other atoms
      • local electromagnetic environment

Usually Hydrogen nuclei is used…

A high field strength magnet ==> introduction of radiofquency energy

  • As time passes —> this energy is lost
  • Patient atoms/nuclei emit radiofrequency signal now
  • this is detected by coil.

All about T1 and T2:

T stands for "time"

That is the time of relaxatioin of the nuclei when radiofrequency fades. This is after they are excited by a radiofrequency pulse.

So there are two " time"s that are important:

  • TE : time to echo
  • TR: repitition time

In T1 —> short TR and long TE
In T2 —> long TR and long TE

In general:

T1

  • more fine anatomic details.
  • water/fluid is black, low in signal
  • gray matter darker than white matter

Example:

  • Intrahepatic Cholangiocarcinoma is hypointense in T1
  • Hyperintense in T2

T2

  • more contrast beween pathology and normal anatomy
  • water/fluid is white, high in signal
  • white matter darker than gray matter

Objects move in and out such as blood flow —> are always low in signal in both T1 or T2

FLAIR

  • This is T2 FLAIR.
  • Suprress free fluid —> edema in brain will be white(high in signal) but CSF dark like T1.