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 'Short T1 Inversion Recovery' 
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Short T1 Inversion RecoveryInfoSheet: - Sequences - 
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(STIR) Also called Short Tau (t) (inversion time) Inversion Recovery. STIR is a fat suppression technique with an inversion time TI = T1 ln2 where the signal of fat is zero (T1 is the spin lattice relaxation time of the component that should be suppressed). To distinguish two tissue components with this technique, the T1 values must be different. Fluid Attenuation Inversion Recovery (FLAIR) is a similar technique to suppress water.
Inversion recovery doubles the distance spins will recover, allowing more time for T1 differences. A 180 preparation pulse inverts the net magnetization to the negative longitudinal magnetization prior to the 90 excitation pulse. This specialized application of the inversion recovery sequence set the inversion time (TI) of the sequence at 0.69 times the T1 of fat. The T1 of fat at 1.5 Tesla is approximately 250 with a null point of 170 ms while at 0.5 Tesla its 215 with a 148 ms null point. At the moment of excitation, about 120 to 170 ms after the 180 inversion pulse (depending of the magnetic field) the magnetization of the fat signal has just risen to zero from its original, negative, value and no fat signal is available to be flipped into the transverse plane.
When deciding on the optimal T1 time, factors to be considered include not only the main field strength, but also the tissue to be suppressed and the anatomy. In comparison to a conventional spin echo where tissues with a short T1 are bright due to faster recovery, fat signal is reversed or darkened. Because body fluids have both a long T1 and a long T2, it is evident that STIR offers the possibility of extremely sensitive detection of body fluid. This is of course, only true for stationary fluid such as edema, as the MRI signal of flowing fluids is governed by other factors.
See also Fat Suppression and Inversion Recovery Sequence.
 
Images, Movies, Sliders:
 Sagittal Knee MRI Images STIR  Open this link in a new window
      

 
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• Related Searches:
    • Knee MRI
    • Imaging of the Extremities
    • Image Contrast Characteristics
    • Pulse, 180
    • Fat Saturation
 
Further Reading:
  Basics:
Techniques of Fat Suppression(.pdf)
   by cds.ismrm.org    
MRI GLOSSARY
   by fonar.com    
  News & More:
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
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Quadrupole ArtifactInfoSheet: - Artifacts - 
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Quick Overview

Artifact Information
NAME Quadrupole artifact
DESCRIPTION Signal loss, intensity variations
REASON B1 disturbance
HELP STIR

Fat suppression (SPIR or FatSat) is very critical to the magnetic field homogeneity. Eddy currents in the patient results in B1 disturbance from left to right and from anterior to posterior. The artifact is seen as signal intensity variations with SPIR, like a signal intensity loss diagonal in the image. The short T1 inversion recovery (STIR) sequence is due to another type of fat suppression insensitive to this artifact.


Image Guidance
Take short T1 inversion recovery (STIR) instead spectral presaturation inversion recovery (SPIR) for fat suppression.
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Inversion Recovery SequenceForum -
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Inversion Recovery Sequence Timing Diagram (IR) The inversion recovery pulse sequence produces signals, which represent the longitudinal magnetization existing after the application of a 180 radio frequency pulse that rotates the magnetization Mz into the negative plane. After an inversion time (TI - time between the starting 180 pulse and the following 90 pulse), a further 90 RF pulse tilts some or all of the z-magnetization into the xy-plane, where the signal is usually rephased with a 180 pulse as in the spin echo sequence. During the initial time period, various tissues relax with their intrinsic T1 relaxation time.
In the pulse sequence timing diagram, the basic inversion recovery sequence is illustrated. The 180 inversion pulse is attached prior to the 90 excitation pulse of a spin echo acquisition. See also the Pulse Sequence Timing Diagram. There you will find a description of the components.
The inversion recovery sequence has the advantage, that it can provide very strong contrast between tissues having different T1 relaxation times or to suppress tissues like fluid or fat. But the disadvantage is, that the additional inversion radio frequency RF pulse makes this sequence less time efficient than the other pulse sequences.

Contrast values:
PD weighted: TE: 10-20 ms, TR: 2000 ms, TI: 1800 ms
T1 weighted: TE: 10-20 ms, TR: 2000 ms, TI: 400-800 ms
T2 weighted: TE: 70 ms, TR: 2000 ms, TI: 400-800 ms

See also Inversion Recovery, Short T1 Inversion Recovery, Fluid Attenuation Inversion Recovery, and Acronyms for 'Inversion Recovery Sequence' from different manufacturers.
 
Images, Movies, Sliders:
 Brain MRI Inversion Recovery  Open this link in a new window
    
 Knee MRI Sagittal STIR 002  Open this link in a new window
 Brain MRI Coronal FLAIR 001  Open this link in a new window
    
 
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• View the DATABASE results for 'Inversion Recovery Sequence' (8).Open this link in a new window

 
Further Reading:
  Basics:
The equation for a repeated inversion recovery sequence
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
Searchterm 'Short T1 Inversion Recovery' was also found in the following service: 
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Double Inversion Recovery T1 MeasurementInfoSheet: - Sequences - 
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(DIR or DIRT1) Double inversion recovery T1 measurement is a T1 weighted black blood MRA sequence in which the signal from blood is suppressed. The inversion time to suppress blood is described as the duration between the initial inversion pulse and time point that the longitudinal magnetization of blood reaches the zero point. The readout starts at the blood suppression inversion time (BSP TI) and blood in the imaging slice gives no signal. This inversion time is around 650 ms with a 60 beat per minute heart rate at 1.5 T.
The TI can be decreased by using a wider receive bandwidth, shorter echo train length and/or narrow trigger window. Wide bandwidth also decreases the blurring caused by long echo trains at the expense of signal to noise ratio. In case of in plane or slow flow the suppression of the signal from blood may be incomplete. With increased TE or change of the image plane the blood suppression can be improved.
Double inversion recovery is a breath hold technique with one image per acquisition used in cardiovascular imaging. The patient is instructed to hold the breath in expiration (if not possible also inspiration can be taken), so that the end diastolic volume in the cardiac chambers would be the same during entire scanning. DIR provides fine details of the boundary between the lumen and the wall of the cardiac chambers and main vascular and heart structures, pericardium, and mediastinal tissues.
 
Images, Movies, Sliders:
 Normal Dual Inversion Fast Spin-echo  Open this link in a new window
      

Courtesy of  Robert R. Edelman

 
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• View the DATABASE results for 'Double Inversion Recovery T1 Measurement' (2).Open this link in a new window

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Saturation Recovery
 
(SR) Particular type of partial saturation pulse sequence in which the preceding pulses leave the spins in a state of saturation, so that recovery at the time of the next pulse has taken place from an initial condition of no magnetization. A rare used MRI pulse sequence that generates a predominantly proton density dependent signal, basically employing a 90 RF excitation pulse, with a very long repetition time. With this technique T1 times can be measured faster than with inversion recovery pulse sequences.
This saturation recovery sequence consists of multiple 90 radio frequency (RF) pulses with a short repetition time. A spoiler gradient pulse dephases the longitudinal magnetization that remains after the first 90 radio frequency pulse. A repetition time interval after the application of this spoiling gradient turns an additional 90 pulse the new developed longitudinal magnetization into the transverse plane, followed by recording a gradient echo.
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• View the DATABASE results for 'Saturation Recovery' (5).Open this link in a new window

 
Further Reading:
  Basics:
Contrast mechanisms in magnetic resonance imaging
2004   by www.iop.org    
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