MR Physics & Clinical MRI

Question 1

5 things to make ideal clinical MRI sequence

Answer 1

1. Acceptable to the patient (time, noise)
2. Good contrast
3. Good anatomical resolution
4. Information on structure, blood supply, function
5. Reproducible (different scanner, different occasion)

BEST INFORMATION TO MAKE A DIAGNOSIS.

Question 2

Typical T2 weighted SE of brain

TE

TR

Describe how fluids and solids look in image?

What clinical thing might you be looking for with T2 brain scan?

Answer 2

TR = 3000ms (long)

TE = 100ms (long)

Fluids have a long T2, and so they look bright.

Solids have short T2 and looks darker.

These scans are good at looking for oedema, the fluid will show up bright.

Question 3

Typical T1 weighted SE of brain

TE

TR

Describe how fluids and solids look in image?

What clinical thing might you be looking for with T2 brain scan?

Answer 3

TE = 450 ms (short)

TR = 10ms (short)

Fluids look dark in T1. You would do a t2 scan and a t1 scan so that you can see if the suspected oedema was actually fluid, or if it was solid (cancer). T1 scans also have good contrast between grey and white matter.

Question 4

Summary - [TR TE] ms

T1

T2

PD

Answer 4

T1 - [500 10] short short

T2 - [3000 100] long long

PD - [3000 10] long short

Question 5

Why might you see a dark patch in a T2* weighted image, and not in a T2weighted image

Answer 5

Iron in heamorrage distorts Bo and dephases spins more rapidly. It will only be visible on gradient echo t2* image, int he t2 weighted spin echo image the dephasing will have been reversed.

Question 6

How does fat appear on T1 scan?

How would you know that it is fat?

Where in the body is this partiualrly useful?

Answer 6

Fat is bright on T1

Do a FATSAT with the 180 prepulse to eliminate signal from fat. Or you could do in-phase and out-of phase images. Allowo TE to progress until signals get out of phase and subtract. Dropout of signal on the out-of-phase image lets you know there was fat there.

Useful for knees, but mainly livers.

Question 7

Contrast agents

How does Gadolinium work?

Clinical use in brain?

Answer 7

Gadoliinium us paragagnetic, and reduces the T1 of water that it comes into contact with.

In brain this would allow you to assess the blood brain barrier, look at tumours, assess vessel wall integrity.

Question 8

MR Angiography

How does MRA work?

What do you use it for?

Answer 8

Weight the scan so it’s sensitive only to moving water.

Use it for venography and assessing regions of flow.