1. Basic MRI I Dr. Mark D. Herbst
Chapter 8
Basic MRI I
Dr. Mark D. Herbst

3. Selective Signal Suppression
Reasons;
Increase contrast between tissues
Between normal and abnormal in one tissue
Between two different normal tissues
Usually applied to the whole image
Based on T1 values, resonant frequencies, or molecular binding properties
Reduce artifacts
Usually applied to part of image or outside the image –”specific anatomic regions”

4. Fat and Fluid Suppression
T1 based methods
Fat T1 = about 260 ms
Fluid T1 = about ms
STIR –use TI about ms to catch fat at its null point for T.
FLAIR—use TI about to catch fluid at its null point
SPIR inversion pulse applied at fat frequency only, then 90 degree pulse applied (to fat and water) to start sequence when fat is at its null point. This gives a water-only image.

5. Fat and Fluid Suppression
Frequency based methods
SPIR above is partly based on frequency, see above.
FAT SAT—saturation pulse at fat frequency is applied to whole image so fat gives no signal, only water is seen.
WATER SAT—saturation pulse at water frequency is applied to whole image so water gives no signal, only fat is seen.

6. Fat and Fluid Suppression
More frequency based methods
Water excitation
Fat excitation
MTC = magnetization transfer contrast
Sat pulse applied to the wider peak of the bound water, and it becomes saturated. But the unbound water that exchanges with it also gets saturated. Only the separate water, not exchanging with bound water, escapes the effect of this saturation pulse. That is why this works well in MRA, since water molecules in the blood vessels are separate from the bound and unbound water in the brain tissue.
This sat pulse does not affect fat or separate bulk water.

9. STIR

12. SPIR

13. T SPIR

14. SPIR

15. T SPIR

16. SPIR

19. FLUID SUPPRESSION (FLAIR)

22. REGIONAL SATURATION
(REST)