100. MRI: INVERSION RECOVERY SEQUENCE Flashcards
- Define: Inversion Recovery.
- this is a Spin Echo Sequence
- it begins at a 180° inverting pulse
- What happens when the inverting pulse is removed?
- the Net Magnetisation Vector begins to relax
- it will go back to the Longitudinal Direction of the
External Magnetic Field (B₀)
- Define: TI.
- this stands for the Time of Inversion
(Inversion Time) - a 90° pulse is applied at this point
- this happens after the 180° Inverting Pulse
- What happens after the Time of Inversion (90°) pulse has been applied?
- there will be another 180° Radio Frequency Pulse that
will be applied - this will re-phase the spin
- it will re-phase it into the Transverse Plane
- this produces an Echo (TE)
- this is produced after the Excitation Pulse
- What is the main purpose of the TI (Inversion Time)?
- it is the main factor that controls the weighting in
Inversion Recovery Sequences
- What is the main difference between Inversion Recovering Sequences and Conventional Spin Echo Sequences?
INVERSION RECOVERY SEQUENCES:
- begin the sequence with a 180° Inverting Pulse
CONVENTIONAL SPIN ECHO SEQUENCES:
- begin the sequence with a 90° Pulse
- What kind of weighted images does the Inversion Recovery image favour?
- the images are more heavily T1 weighted
- this produces a large contrast difference
- between the fat and the water
- Why is there such a large difference between the contrast in fat and water?
CERTAIN INVERSION TIME (TI) VALUES:
- will result in the suppression of the signal from tissues
- this will enhance the fat and the water signals
- What is the Inversion Time (TI) value that is needed to make the tissue from a signal insignificant?
- the Inversion Time (TI) has to be:
0.69 x T1 Relaxation time of the tissue
- What are Inversion Recovery Sequences divided based on?
- they are divided based on the Inversion Time (TI) value
used
- What are the three different types of Inversion Recovery Sequences we can get?
- SHORT SEQUENCES
- the Inversion Time (TI) is between 80 - 150 ms - MEDIUM SEQUENCES
- the Inversion Time (TI) is between 300 - 1200 ms - LONG SEQUENCES
- the Inversion Time (TI) is between 1500- 2500 ms
- What does Short Inversion Time Recovery (STIR) make use of?
- it uses short Inversion Times
THESE SHORT INVERSION TIMES:
- place a 90° Excitation Pulse at the time of the Net
Magnetisation Vector of Fat
- this happens when the Net Magnetisation Vector of fat
is passing through the Transverse Plane
- In which axis do we find the Transverse Plane?
- the Z-Axis
- What happens after we have applied the 90° Excitation Pulse to the Net Magnetisation Vector of Fat?
- this Excitation Pulse will move the Net Magnetisation
Vector from the Transverse Plane to the Longitudinal
Plane - this is called the Null Point
- What is the result of applying a short Inversion Time to the Net Magnetisation Vector of Fat?
- there will be a 90° Excitation Pulse added to the
Transverse Plane - there will be no Transverse Component in the fat
- no signal will be produced from the Fat
- the signal from the fat will be suppressed in the
images
- What do the Long Inversion Times (TI) used in the FLAIR sequence do?
- they make the signals coming from the
Cerebro-Spinal Fluid (CSF) insignificant
THE PROCESS IS AS FOLLOWS:
- there will be a 90° Excitation Pulse added to
the Transverse Plane
- this places the Net Magnetisation Vector of
the Cerebro-Spinal Fluid in the Longitudional
plane
- there will be no Transverse Component of
the water in the Cerebro-Spinal fluid
- no signal will be produced from the water
- the signal from the water in the Cerebro-
Spinal fluid will be suppressed in the images
- What are Periventricular lesions?
- they are white matter lesions
- they are found around the centre black spaces
EXAMPLE:
- Multiple Sclerosis Plaques
