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Flashcards in MRI Physics 1 Deck (99)
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0

Hydrogen makes up approximately what percentage of all atoms in the human body?
A. 20
B. 40
C. 80
D. 100

C. 80%

1

If a voltage V drives a current I through a resistance R, then the value of the current is given by Ohm's Law:
A. I= VxR
B. I = R/V
C. I = V/R
D. None of the above

C. I = V/R

2

If the static magnetic field is .3T, what is the larmor precession frequency of the hydrogen proton spins?
A. 12.8 MHz
B. 42.6 MHz
C. 63.9 MHz
D. 63.9 Hz

A. 12.8 MHz

3

Hydrogen nuclei have a magnetic moment because they have which properties?
I. Spin
II. Charge
III. Relaxation time

A. I only
B. II only
C. I and II only
D. I II and III

C. I and II only

4

About how many times stronger is the static magnetic field from a 1.0T MRI scanner than the earths magnetic field at the surface of the planet?
A. 2 times
B. 20 times
C. 200 times
D. 20,000 times

D. 20,000 times

5

Net magnetization is a vector. Vectors have both:
A. Spin and charge
B. mass and charge
C. Magnitude and direction
D. Mass and direction

C. Magnitude and direction

6

By MRI convention the equilibrium magnetization is represented by:
A. B0
B. B1
C. M0
D. Mz

C. M0

7

The t1 relaxation time is defined as when
A. 37% of the longitudinal magnetization has recovered
B. 63% of the longitudinal magnetization has recovered
C. 63% of the transverse magnetization has recovered
D. 37% of the transverse magnetization has recovered

B. 63% of the longitudinal magnetization has recovered

8

The rate of decay of an FID is given by
A. T1
B. T1*
C. T2
D. T2*

D. T2*

9

A long TR
A. Increases T1 weighting
B. decreases T1 weighting
C. Increases T2 weighting
D. Decreases T2 weighting

B. decreases T1 weighting

10

Which of the following are active MR nuclei?
I. C12
II. C13
III. Na22
IV. Na23

A. I and III
B. II and IV
C. III and IV
D. I II III and IV

B. II and IV

11

For spin echo imaging what type of contrast will TR 2500ms and TE 150ms produce?
A. T1
B. T2
C. T2*
D. PD

B. T2

12

Spins aligned in the anti parallel direction are in a
A. Low energy state
B. high energy state
C. Resonant state
D. Flux state

B. high energy state

13

The cause of transverse magnetization Mxy dephasing is?
A. Spin lattice interaction
B. spin spin interaction
C. Magnetic inhomogeneities
D. B and C

D. B and C

14

Spin density is another term for
A. Nuclear density
B. hydrogen density
C. Proton density
D. B and C

D. B and C

15

For resonance, the B1 field oscillates at what frequency?
A. ω0 = γΒ0
Β. ω1 = γΒ1
C. ω = γ(Β+\-ΔΒ)
D. None of the above

A. ω=γΒ0

16

T2* is a result of dephasing due to a tissues T2 time and
A. T1
B. magnetic inhomogeneities
C. Molecular weight
D. A and B

B. magnetic inhomogeneities

17

Suppose the longitudinal magnetization Mz = M0 is flipped into the transverse plane. Then the initial value for the transverse magnetization is Mxy = M0. Thus during the RF pulse, the spins system is said to have what property?
A. T1
B. T2
C. Coherence
D. Incoherence

C. Coherence

18

The MRI process leading to a voltage or electric current being induced in the receiver coil can be explained by
A. Faradays law
B. Coulomb's law
C. Ohms law
D. Newtons law

A. Faradays law

19

What is the time between two successive RF excitation pulses called
A. Tau
B. TE
C. TR
D. T1

C. TR

20

Radio waved travel at what speed?
A. Speed of sound
B. speed of light
C. 3x10^8 m/s
D. B and C

D. B and C

21

The law for the force F between two electric stationary charges q and Q separated by a distance d is
F = kqQ/d^2

Where k is a constant. This force law is also called?
A. Faraday's law
B. ohms law
C. Coulomb's law
D. Newtons law

C. Coulomb's law

22

At what flip angle is maximum transverse magnetization obtained?
A. 45°
B. 90°
C. 180°
D. Depends on the imaging sequence

B. 90°

23

Images acquired using a long TE time may result in which of the following image quality results?
I. Lower SNR
II. higher image graininess
III. Lower T2 contrast

A. I only
B. II Only
C. I and II only
D. I II and III

C. I and II

24

To calculate the precession frequency, the strength of the magnetic field is multiplied by a constant known as
A. The resonance factor
B. The gyro magnetic ratio
C. The linear attenuation coefficient
D. Planck's constant

B. the gyro magnetic ratio

25

The MR signal is produced by magnetization
A. In the longitudinal direction
B. in the transverse plane
C. Out of phase
D. A and B

B. in the transverse plane

26

Magnetic susceptibility effects are seen most prominent in which pulse sequences below
A. IR
B. CSE
C. GRE
D. FSE

C. GRE

27

Following a 90° RF pulse, the MRI signal that is created is called
A. Spin echo
B. FRE
C. Free induction decay
D. B and C

C. Free induction decay

28

On a t2 weighted image, what is the typical range for allowed TR?
A. 200-700ms
B. 500-700ms
C. 2000 ms or greater
D. Any TR value is allowed

C. 2000 ms or greater

29

On a spin echo pulse sequence, what does the tau time equal?
A. τ=TR
B. τ=TR/2
C. τ=TE
D. τ= TE/2

D. τ= TE/2