MRI ch 21

Question 1

Most scanners today have a magnetic field strength between ___ and ___ Tesla.

Answer 1

0.5 and 3T

Question 2

The coils withing the magnet are responsible for____

Answer 2

either transmitting radiofrequency (RF ) pulses = trasnmitter coils

or recieving the signa / or echo given off by these excited protons = reciever coils

Question 3

What is T1?

Answer 3

T1 = relaxation or recovery is the time it takes for the tissue to recover to its longitudinal state (parallel to the magnetic field); i.e. the time before the radiofrequency pulser was administered

Question 4

What is T2?

Answer 4

T2 relaxation (or decay) is the time it takes for the tissue to regain its transverse orientation (perpendicular to the magnetic field) before the radiofrequency pulse was administered.

Question 5

The two main pulse sequences are ___ and ___.

Answer 5

spin echo and gradient recalled echo

Question 6

What is pulse sequence?

Answer 6

Pulse sequence consist of a set of imaging parameters determined in advance by protocols for specific diseases and body parts,

Question 7

Pulse sequence can last between

Answer 7

20s to 15 min

Question 8

What is TR?

Answer 8

TRis the repetition time between two RF pulses, and it indlueces the amount of T1 weighting.

Question 9

What is TE?

Answer 9

TE is th echo time between pulse and its resultant echo and it influences the amount of T2 weighting.

Question 10

Tissues that have a short T1 will be ____

Answer 10

bright

Question 11

Tissues with a long T2 will be ___

Answer 11

bright

Question 12

Water will be ____ on T1 images and ____ on T2 images.

Answer 12

dark on T1 and bright on T2

Question 13

Certain tissues and structures are typically bright on T1-weighted images. Those are:

Answer 13

fat,
hemorrhage (depends on the age of hemorrhage), proteinaceous fluid (in renal/hepatic cysts) – but water cyst will be dark,
melanin
gadolinium and other paramagnetic substances

Question 14

Certain tissues and structures are typicallybright on T2-weighted images. Those are:

Answer 14

fat,
water, edema, inglammation, infection, cysts
hemorrhage (depends on age of hemorrhage)

Question 15

What 2 structures are bright on both T1 and T2 imaging

Answer 15

fat and hemorrhage

Question 16

____ is the most common IV agent used in clinical MRI imaging

Answer 16

Gadolinium

Question 17

What is gadolinium’s effect?

Answer 17

its effect is to shorten the T1 relaxation times of hydrogen nuceli (and to a lesser extent also shorten T2)

T1 shortening will cause a brighter signal on T1-weighted images than the same images without gadolinium and it is for this reason that images obtained after gadolinium administration are usually T1 weighted to take advantage of this eeftc.

Question 18

Structures that become BRIGHT on postgadolinium images are typically ___ or are ____ tissues, and are described as ____.

Answer 18

Structures that become BRIGHT on postgadolinium images are typically vascular (e.g. tumor) or are inflamed tissues, and are described as enhancing.

Question 19

What is an absolute contraindication for MRI exam

Answer 19

ferromagnetic objescts inserted ina location where motion of the object may be harmful to the patient

e.g. cerebral aneurysm repair clips, vascular clips, surgical staples

Question 20

In general what are contraindications and considerations for MRI exam?

Answer 20

1. claustriphobic patients
2. those who have ferromagnetic objects (staples, foreign bodies - bullet, metal in the eyes)
3. mechanical or electrical devices - pacemakers, pain stimulator implants, insulin pumps, implantable drug infusion pumps, cochlear implants
4. pregnant patients (we cannot administer gadolinium here)
5. nephrogenic systemic fibrosis