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Flashcards in Magnetism in MR Deck (50)
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1

What type of magnet is used with most MRI systems currently manufactured?

Superconducting

2

What element in the body is the principal nucleus utilized in clinical MR imaging

Hydrogen

3

The precessional frequency of hydrogen, according to the Larmor equation, at 3Tesla is:

127.71 MHz

4

A system operating at 30,000 Gauss has a field strength of:

3 Tesla

5

The protons that align themselves with the direction of the static magnetic field (B0) exist in a ___________energy state than those anti-parallel to the magnetic field.

: Lower

6

___________ substances have strong magnetic properties and can be pulled into the magnetic field

Ferromagnetic

 

7

All of the following are ferromagnetic substances EXCEPT

A. Stainless Steel
 B. Gold
 C. Iron
 D. Nickel

Gold

8

The first documented human MR image was obtained on a 15 MHz RF system, what field strength did it operate at?

0.352 Tesla

9

All of the following are TRUE except:

A. Excitation is the process of moving the net magnetization away from the Z axis
 B. Magnetic field gradients are static
 C. The RF field oscillates at the Faraday frequency
 D. The resonance frequency in a 1.5 Tesla magnet is 63.86 Mhz
 

The RF field oscillates at the Faraday frequency

10

What is defined as the excess number of hydrogen protons aligned with the static magnetic field direction (B0)?

Longitudinal magnetization

11

The energy used to form MRI images is ____________ the patient's tissues

Emitted from

12

All of the following are non-ferrous substances EXCEPT

A. Plastic
 B. Titanium
 C. Iron
 D. Copper

iron

13

The extent to which a material or tissue becomes magnetized in an external magnetic field is called

Magnetic susceptibility

 

14

: If the RF energy transmitted is __ MHz, the slice through the patient would be in a magnetic field of .995T.

42.36

15

_________ magnets can be “shut off” the quickest in case of an emergency.

Resistive

16

The _________ is defined as the resonant frequency, and is equal to the product of the magnetic field and the gyromagnetic ratio

Precessional frequency

17

All of the following are true regarding RF EXCEPT

A. The RF pulse stimulates the protons into parallel or anti-parallel alignment
 B. Relaxation begins after the RF is turned off
 C. RF stimulates the protons to be in phase
 D. RF converts FID into an echo

RF converts FID into an echo

18

The force that an object can be attracted to the magnetic field is reliant upon

A. The field strength (Tesla) of the MR system
 B. The mass of the projectile
 C. The specific ferromagnetic nature/properties of the material
 D. All of the above

All of the above

19

: ______________ is the term used to describe the degree of magnetization of an object

Susceptibility

20

Force on an object in an magnetic environment depends on:
I. Mass of the object
II. Strength of the magnetic field
III. Strength of the RF field
IV. Ferromagnetic properties of the object

I, II, and IV

21

A magnetic vector possesses attributes of both __________ and _____________.

Magnitude; direction

22

Hydrogen is used in MR imaging because

Of its abundance in the body

23

: Calculate the Larmor frequency for H at 0.5Tesla

21.28 Mhz

24

Hydrogen protons in the anti-parallel state are referred to as:

A. Spin down
 B. Low energy spins
 C. High energy spins
 D. Both A and B
 E. Both A and C

Both A and C

25

Immediately following the application of the 90° RF pulse, the precessing protons:

A. Begin to precess in phase
 B. Tip into the transverse plane
 C. All move into a high energy state
 D. Both A and B
 

Both A and B

26

: Immediately following the application of the 90° RF pulse, the transverse magnetization is:

Non-zero

27

In one T2 relaxation time:

63% of the transverse magnetization has decayed

28

In one T1 relaxation time:

63% of the longitudinal magnetization has recovered

29

A Free Induction Decay (FID) is produced from a:

RF pulse

30

When thermal equilibrium is reached

There are more hydrogen protons in the low energy state