Week 2 Flashcards
Basic principles
According to Faraday’s law of induction, the amount of current produced in a loop of wire moving through a magnetic field is proportional to the:
a. Strength of the magnetic field
b. Resonance frequency of protons in the wire
c. Spin density of the wire
d. Length of the wire
a. Strength of the magnetic field
In the Larmor Equation, B0 stands for:
b. Static magnetic field
A condition whereby there are MORE spins “in line” with the magnetic field than “opposed” is known as:
a. Thermal equilibrium
b. High energy
c. Low energy
d. Excitation
a. Thermal equilibrium
During thermal equilibrium, the vector that represents the “spin excess” is known as the:
Net magnetization vector (NMV)
The RF pulse is applied to achieve a condition known as:
b. Excitation
T1 relaxation time is defined as when:
a. 63% of the longitudinal magnetization has regrown
b. 76% of the longitudinal magnetization has regrown
c. 63% of the transverse magnetization has regrown
d. 37% of the tissue’s longitudinal magnetization has regrown
a. 63% of the longitudinal magnetization has regrown
T2 relaxation time is defined as when:
a. 76% of the longitudinal magnetization has decayed
b. 37% of the tissues longitudinal magnetization has decayed
c. 63% of the longitudinal magnetization has decayed
d. 63% of the transverse magnetization has decayed
d. 63% of the transverse magnetization has decayed
Images acquired with SHORT TR and TE values yield images known as?
T1 weighted images
Images acquired with LONG TR and TE values yield images known as?
T2 weighted images
Images acquired with LONG TR and SHORT TE values yield images known as?
Proton density images
Which of the following is an extrinsic parameter?
a. T2 decay
b. Echo time
c. Proton density
d. Spin-Spin relaxation
b. Echo time
Which of the following is an intrinsic parameter?
a. T2 decay
b. Echo time
c. External magnetic field
d. TR
a. T2 decay
What is repetition time? (TR)
The duration of time between each RF pulse
What is echo time? (TE)
The time interval between a RF pulse and the peak of the ensuring signal
What are the modifiable, extrinsic parameters involved in image contrast?
Relaxation time (TR) and Echo time (TE)
What are the intrinsic parameters involved in image contrast?
T1 relaxation, T2 decay and proton density
T1 relaxation (spin-lattice/ longitudinal relaxation) involves the recovery of the ______ as excited protons release energy and return to the ______ of the ____
- thermal equilibrium
- longitudinal orientation
- B0/ external field
T2 Decay involves the ___ of ___ as interactions between protons lead to the ___ of spins
- loss
- transverse magnetism
- dephasing
Proton density is:
the number of protons per unit volume of a substance
What is Faraday’s law?
B0 = kl
l= current flowing through a wire (motion) k= proportionality constant (quantity of charge) B0= strength of magnetic field
There are more protons aligned with the magnetic field . Alignment with the field produces a lower energy state.
Is the net magnetisation vector (NMV) aligned or against the external field?
the NMV is aligned/ in the direction of the external field.
what is the Larmor Equation?
The frequency of the precession is directly proportional to the strength of the magnetic field and is defined by the Larmor Equation.
wø = γBø
wø (omega zerio) is known as either the precessional, Larmor or resonance frequency.
Gamma (γ) is the gyromagnetic ratio and is a constant unique to every atom.
what is excitation?
the application of an electromagnetic radio frequency (RF) pulse to increase the energy state of a proton if the pulse is applied at the resonance frequency.
The receiver bandwidth is related to the slope of the:
a. Frequency-encoding gradient
b. Transmitting gradient
c. Phase-encoding gradient
d. Slice-selecting gradient
a. Frequency-encoding gradient
Gradient magnetic fields are used to:
Spatially encode the data
Slice thickness is controlled by
the slope of the gradient
The gradient that is on during the sampling of the echo is the:
frequency encoding gradient
The predominant biologic effect of RF fields is:
Tissue heating
The term used to describe RF absorption is:
a. Specific absorption rate (SAR)
b. Summated absorption region (SAR)
c. Susceptibility attack region (SAR)
d. Sensitive acquisition range (SAR)
a. Specific absorption rate (SAR)
Areas of the body that are most sensitive to the heat (from SAR) are:
a. Vertebral bodies
b. Globes of the eyes and testicles
c. Pancreas and liver
d. Brain and spinal cord
b. Globes of the eyes and testicles
Imaging centres should be separated into “Zones” including all of the following EXCEPT:
Select one:
a. Zone 1 – freely accessible to any “Level” of MR personnel
b. Zone 0 – the parking lot
c. Zone 3 – the “warm” Zone, generally the console area and the last stop before the scan room
d. Zone 4 – The “hot” Zone, the scan room itself
e. Zone 2 – the interface between Zone 1 and Zone 3
b. Zone 0 – the parking lot
