Clinical Scans

Question 1

For neurological imaging, what do T2WI show and how are they produced? (3 marks)

Answer 1

Long TR (3 s) and TE (100 ms).

They show edema (swelling) due to the increased water content. Water appears bright on these images. Sometimes referred to as pathology scans.

Question 2

For neurological imaging, what do T1WI show and how are they produced? (3 marks)

Answer 2

Short TR (less than 750 ms) and TE (10 ms).

Used to show structure due to the quicker scan time. Water is dark on these images due to the slow Mz relaxation.

Question 3

What effect would a haemorrage have on a T2WI? (2 marks)

Answer 3

It would cause the surrounding tissues to appear darker due to the more rapid dephasing of the M_xy signal, from the presence of iron in the blood, which is ferromagnetic.

Question 4

How does IOOP gradient echo work? (2 marks)

Answer 4

It is a GRE sequence which utilises the differences in the precessional frequencies of fat and water.

The echo time is varied so that the water and fat signals are acquired in-phase and out-of phase. Allowing the differences in intensity in the images to indicate the % of fat in the tissue or organ, such as in liver imaging. The technique was originally described by Dixon and was termed ‘Dixon’ imaging.

Question 5

What contrast agents are used in neuro imaging, how do they work and what are the clinical applications? (3 marks)

Answer 5

Chleated Gadolinium, used as it is ferromagnetic and therefore causes more rapid dephasing of the spins, areas where it is close to appear dark.

Used to show areas of damage to the blood-brain barrier.

Question 6

What are the characteristics of the ideal MRI sequence? (5 marks)

Answer 6

• Reproducible.
• Quiet, quick.
• Sufficient contrast and resolution to see pathology of interest.