MRI

Question 1

What are the TR and TE values for T1 imaging?

Answer 1

• ** T1 weighted images = short TR and short TE
• Short TR (100-1000 ms) (<1000)***
• Short TE (20-30 ms) (<30)

Question 2

What are the TR and TE values for T2 imaging?

Answer 2

• **T2 weighted images = long TR and long TE
• Long TR (1600-3000 ms) (>2000)
• Long TE (70-100 ms) (>60)***

Question 3

T1

Answer 3

Fat image

• Fat = white, water = black
• Operator manipulates TR and TE to produce images in which contrast between tissues reflects differences in T1 of those tissues
• T1 images produced by a short TR
• Those tissues that return to Bo the fastest (fat) give off the most energy and appear bright (white) on T1 images
• The water (H2 nuclei) in fat is closest to the resonant frequency of the RF pulse, so it gives off the most energy and appears brightest.
• That is why the T1-weighted image is often referred to as the fat image
• Fat has a shorter T1 than does free water
• Free water gives off the least signal on a T1 image and appears black.

Question 4

T2

Answer 4

Water image (T2 or “H20” image)

• Fat = black, water = white
• Operator manipulates TR and TE to produce images in which contrast between tissues reflects differences in T2 of those tissues
• T2 images produced by long TE
• Those tissues that hold their transverse magnetization longest give of the strongest signal and appear bright
• Free water gives off the strongest T2 signal and appears bright (white) on a T2 image
• That is why the T2-weighted image is often referred to as the water image
• Free water has a longer T2 than does fat
• Bound water (protein) moves more slowly as a molecule, and has a less intense signal

Question 5

What is Gadolinium?

Answer 5

IV contrast material that can be used to suppress fat on a T2 image
o This has the same type of effect as STIR imaging (super T2), but IV
Gadolinium does NOT suppress fat uniformly

Question 6

Identifying fluid filled lesions

Answer 6

o PRIMARY USE OF GADOLINIUM IS FLUID-FILLED LESIONS
o You will see a bright “rim” sign surrounding lesion
o MOST COMMON use of IV gadolinium is for identifying soft tissue structures that have fluid in them like a ganglion
o When using gadolinium on a mass, you are checking to see if you are looking at a fluid filled image or not, so the image will be a T1
o Generally speaking, cystic lesions (water-filled lesions) tend to be non-malignant

Question 7

What disease can gadolinum cause?

Answer 7

o An association between gadolinium and the development of nephrogenic systemic fibrosis (NSF) has been recognized in patients with severe renal impairment, but it doesn’t have to be a patient with prior renal failure

Question 8

Magic angle effect

Answer 8

• Common 4th year question at residency sites
• This is an artifact that produces false pathology on a T1
• Occurs whenever the body part is orientated 55 degrees from the plane of the magnetic field (Bo)
• In podiatry, we typically see this in images around the ankle
  o It will occur where ever structures change direction, so it happens to tendons and ligaments around the ankle
  o It occurs in tissues with highly structured collagen fibers (tendon/ligament)
• Normal tendons and ligaments appear dark on T1, so if you see brightness in a tendon or ligament, you would typically think there is some injury/pathology
• What you have to do in order to determine if this is the magic angle artifact or actual pathology is look at the T2 image
• ***If the tendon/ligament is truly torn, there will be bright signal on T2 as well
• ***If the structures look normal on T2, there is no damage and this is the magic angle effect