MRI basics Flashcards
(19 cards)
T1 weighting
Short TR and short TE
T2 weighting
Long TR and long TE
Proton density weighting
long TR AND SHORT TE
What is signal to noise ratio
Measures how much true signal (actual anatomy) vs random noise an image has
What is a spin echo sequence
What are fast spin echo and turbo spin echo sequences
What are the diffs between fast spine echo and spin echo?
- Fat is brighter
- Susceptibility artifact is decreased
- Time is saved but more echoes with erroneous weighting is introduced
What is a HASTE SEQ?
What is CSF very bright on HASTE
What is inversion recovery pulse
Includes an additional 180 degree RF prep pulse that occurs at a time T1 prior to traditional 90/180 pulses
Tend to be T1 weighted - STIR OR FLAIR
What is STIR
T1 is short - matching null time for fat
Cannot be used with contrast bc T1 enhancing tissue is shortened and closer to that of fat- leasing to suppression of signal from enhancing tissue on STIR SO IF YOU NEED FAT SUPPRESSION POST CONTRAST THEN WILL NEED FAT SAT TECHNIQUES
What is a FLAIR SEQ
T1 is calculated so that signal from fluid is nulled
Pure fluids like CSF have long T1 relaxation
Can have T1 and T2 FLAIR images
T2 preferred bc water rich lesions will be bright
What are the characteristics of a gradient echo pulse sequence
What are the clinical applications of gradient echo pulse sequences?
What is DWI
How does dwi work
When is a fat sat technique used
When contrast has been given
What is chemical fat saturation?
Exploits diff between frequencies of fat and water protons (chemical shift)
What does a fat sat sequence do?
Uses narrow bandwidth RF pulse tuned to center of lipid resonance
Excited fat protons that flip in transverse plane so null any transverse magnetization due to fat protons. Fat protons are saturated and do not generate a signal
