STUDYGUIDES

Question 1

Calculate the resonant frequency of a 2.5T system

Answer 1

106.675 MHz/T or just 106.5

Question 2

The strength of the net magnetization vector (NMV) is dependent upon two factors. One is the ambient temperature, name the second

Answer 2

The strength of the static magnetic field

Question 3

Which element is imaged when performing clinical MR studies?

Answer 3

Hydrogen

Question 4

Name the 3 energy fields necessary to create the MR signal

Answer 4

• Main magnetic field (B0)
• Radiofrequency field (B1)
• Gradients

Question 5

Which scientists introduced the use of gradient magnetic fields (time varying magnetic fields) to perform the task of spatial localization of the MR signal?

Answer 5

Paul Lauterbur, Ph.D.

Question 6

What interaction do radiofrequency photons that are transmitted at the resonant frequency undergo with the patient’s tissues?

Answer 6

They are absorbed

Question 7

What interaction do radiofrequency photons that are transmitted at a frequency different from the resonant frequency undergo with the patient’s tissues?

Answer 7

There is no interaction. They are transmitted.

Question 8

What did Orstead discover was the result of moving electrical charges?

Answer 8

A magnetic field

Question 9

Which characteristic displayed by an electrical circuit at room temperature will be absent when a material is cooled below its critical temperature?

Answer 9

Resistance

Question 10

Two things occur when the excitation pulse is transmitted at the Larmor (or resonant) frequency. First the spins begin to precess coherently, or in phase. Name the second.

Answer 10

They get excited and “flip” to precess within the transverse plane

Question 11

What is the name of the effect that causes elevation of the T wave in cardiac gating?

Answer 11

Magneto-hemodynamic effect

Question 12

What velocity does a paper clip achieve when released into a 1.5 T magnetic field?

Answer 12

40 MPH

Question 13

What is the SAR limit in Watts/kilogram for the head in the USA?

Answer 13

3

Question 14

Name three effects time-varying gradient magnetic fields may have on patients being scanned using EPI sequences.

Answer 14

• Peripheral nerve stimulation
• magnetophosphenes
• acoustic noise

Question 15

What is the name of the most up-to-date MRI safety website?

Answer 15

www.mrisafety.com

Question 16

What is the FDA limit for the strength of B0 in clinical MR when scanning an adult patient?

Answer 16

8 Tesla

Question 17

What must everyone who remains in the system room during scanner operation be provided?

Answer 17

Hearing protection

Question 18

What are the transient biologic effects produced by the radiofrequency fields (B1) encountered by patients in the MR environment?

Answer 18

• Tissue heating
• RF antennae effects
• thermal injuries (burns)

Question 19

How much insulation must be placed between the patient and the bore of the scanner or any known conductive materials within the bore to ensure patient safety?

Answer 19

1 cm or 0.25”

Question 20

Within what timeframe must all adverse events, MR safety incidents, or near misses be reported to the MR site medical director should they occur?

Answer 20

24 hours

Question 21

Define Coulomb’s Law

Answer 21

The force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them.

Question 22

What is the distinction between electrification of an object through contact or friction from electrification via induction?

Answer 22

Electrification through induction does not require the objects to touch to become electrified

Question 23

Name the 5 fundamental forces

Answer 23

Electric force, magnetic force, gravitational force, weak force, strong force

Question 24

Which fundamental force is responsible for the formation of molecules?

Answer 24

Weak force

Question 25

Which fundamental force is responsible for locking the protons and neutrons into the nucleus?

Answer 25

Strong force

Question 26

If an object has a curved surface where will the highest concentration of charges be located?

Answer 26

Where the curvature is the greatest

Question 27

What are 3 characteristics are present in a live electrical circuit at ambient temperature?

Answer 27

- Potential difference - current - resistance

Question 28

State the formula to calculate power

Answer 28

P = IV

Question 29

State the unit of measurement of power.

Answer 29

Watts

Question 30

State the units of measurement for current, potential difference, and resistance

Answer 30

Current = Ampere Potential difference = Volt Resistance = Ohm

Question 31

How many kilo-Gauss are in 1 Tesla?

Answer 31

10 kG

Question 32

What is a magnetic moment?

Answer 32

A magnetic moment is a vector that denotes the direction of the north/south axis of a magnet and the amplitude of the magnetic field

Question 33

What is meant by the term thermal equilibrium as it pertains to MRI?

Answer 33

Thermal equilibrium is the condition whereby the net number of transitions of hydrogen nuclei evenly align parallel and anti-parallel to B0

Question 34

What is the term used to describe the magnetic vector produced as a result of the alignment of excess hydrogen nuclei with the external magnetic field?

Answer 34

Net Magnetization Vector

Question 35

Name the three axes of the Cartesian coordinate system.

Answer 35

x, y, z

Question 36

Which axis of the Cartesian coordinate system is commonly called the longitudinal axis?

Answer 36

the z-axis

Question 37

Which axes of the Cartesian coordinate system are commonly referred to as the transverse plane?

Answer 37

x, y

Question 38

In which direction do the magnetic lines of force flow outside of a magnet?

Answer 38

from north to south

Question 39

In which direction do the magnetic lines of force flow within a magnet?

Answer 39

from south to north

Question 40

What are the three components necessary to obey Faraday’s Law of Electromagnetic Induction?

Answer 40

a magnet, a conductor, movement between them

Question 41

A material possesses high permeability and low retentivity. What type of magnetic susceptibility does this describe?

Answer 41

paramagnetic

Question 42

Name the two classifications of scientific theories used to describe the basic principles of MRI.

Answer 42

classical physics and quantum physics

Question 43

Define the term: atom

Answer 43

the smallest component of an element having the chemical properties of the element, consisting of a nucleus containing combinations of neutrons and protons and one or more electrons bound to thenucleus by electrical attraction

Question 44

Define the term: molecule

Answer 44

any subatomic particle contained within the nucleus

Question 45

Define the term: proton

Answer 45

a subatomic particle with a positive charge that is contained within the nucleus by the strong fundamental force of nature

Question 46

Define the term: neutron

Answer 46

a subatomic particle with a neutral charge and slightly more mass than a proton that is contained within the nucleus

Question 47

Define the term: electron

Answer 47

a subatomic particle with a negative charge that spins about its own axis while orbiting the nucleus of an atom

Question 48

Define the term: isotope

Answer 48

any of two or more forms of a chemical element, having the same number of protons in the nucleus, or the same atomic number, but having different numbers of neutrons in the nucleus, or different atomicweights. There are 275 isotopes of the 81 stable elements, in addition to over 800 radioactive isotopes,and every element has known isotopic forms. Isotopes of a single element possess almost identicalproperties.

Question 49

Define the term: ion

Answer 49

an electrically charged atom or group of atoms formed by the loss or gain of one or more electrons, as a cation (positive ion), which is created by electron loss and is attracted to the cathode in electrolysis, or as an anion (negative ion), which is created by an electron gain and is attracted to the anode. Thevalence of an ion is equal to the number of electrons lost or gained and is indicated by a plus sign forcations and a minus sign for anions, thus: Na+, Cl−, Ca++, S=.

Question 50

What is the mass number and why is it important in MRI?

Answer 50

The mass number is the number of protons and neutrons contained in an atom’s nucleus. It is important because for an element to be MR active it must posses an odd mass number.

Question 51

Which element is imaged when performing clinical magnetic resonance scans?

Answer 51

hydrogen

Question 52

What does the size of a magnetic vector represent? What does the arrowhead of a magnetic vector represent?

Answer 52

The size of the vector represents the magnitude or strength of the magnetic field. The arrowhead represents the direction of the north pole.

Question 53

What conditions are necessary for resonance

Answer 53

The scanner must transmit a radiofrequency pulse that matches the precessional frequency of the nuclei.

Question 54

Describe the two results of resonance.

Answer 54

The spins precess in-phase or coherently, and their magnetic moments flip into the transverse (Mxy) plane.

Question 55

Define T1 recovery

Answer 55

The time it takes for a tissue to recover 63% of its longitudinal magnetization.

Question 56

Define T2 decay.

Answer 56

The time it takes for a tissue to lose 63% of its transverse magnetization.

Question 57

Which pulse sequence timing parameter determines the time interval applied between one radiofrequency excitation pulse to the next?

Answer 57

TR or repetition time

Question 58

Which pulse sequence timing parameter determines the time interval between the excitation pulse and the peak of the echo?

Answer 58

TE or echo time

Question 59

Which set of coils is closest to the patient within the MR system gantry?

Answer 59

the RF probe or coil

Question 60

What is the purpose of the shim coils within the MR system gantry?

Answer 60

to keep the B0 field even or homogenous

Question 61

What alloy is the primary magnet winding composed of?

Answer 61

niobium titanium

Question 62

What are the two types of magnetic shielding?

Answer 62

active and passive

Question 63

What material is used to provide passive shielding to the MR suite?

Answer 63

steel

Question 64

Where are the active shielding electromagnet windings housed within the MR system gantry?

Answer 64

within the cryostat

Question 65

What is the purpose of the Faraday cage that is built into the walls of the MR system room?

Answer 65

to prevent external RF from entering the system room and contaminating the signal transmitted by the system, as well as to protect the signal picked up by the receiver coil

Question 66

What type of material is the Faraday cage composed of?

Answer 66

copper

Question 67

How many sets of gradient coils does a MR system have?

Answer 67

three: x, y, & z

Question 68

What increments must the MR system table have the ability to position patients at?

Answer 68

milimeters

Question 69

Which component of the MR system allows the user to perform image processing and post-processing tasks?

Answer 69

the console or operator interface

Question 70

According to the FDA all patients must be monitored how?

Answer 70

visually & verbally

Question 71

The need for a large storage capacity and the ability to perform multiple calculations per second requires that the MR system operate with what type of computer system?

Answer 71

a minicomputer

Question 72

Which portion of the MR system hardware monitors the specific absorption rate of various pulse sequences?

Answer 72

the pulse control unit

Question 73

What is the primary role of the pulse control unit?

Answer 73

the sequencing of the RF and gradient coils of the MR system

Question 74

What calculation is performed by the MR system computer when sampling data points for temporary storage in the array processor?

Answer 74

the fast Fourier transformation (FFT)

Question 75

How many shades of grey can each pixel in the image display?

Answer 75

one

Question 76

What unit of measurement is used to describe gradient amplitude?

Answer 76

mT/m or G/cm

Question 77

What phenomenon is responsible for producing the acoustic noise made by the gradients during the performance of a pulse sequence?

Answer 77

the Lorentizan force

Question 78

What is the definition of gradient rise time?

Answer 78

the time it takes for the MR system's gradient coils to reach maximum amplitude

Question 79

Which type of coil allows for the high SNR of a small receiver coil and use of a large of FOV of a large receiver coil?

Answer 79

a phased array coil

Question 80

What type of coil is required to perform pulse sequences with parallel imaging?

Answer 80

a multi-channel or multi-element coil

Question 81

FID- It is in the transverse plane and it is the first time they relax back is FID The giving up of the energy or the relaxing back of the NMV Our signal is decaying while it relaxes back to b0

Question 81

FID- It is in the transverse plane and it is the first time they relax back is FID The giving up of the energy or the relaxing back of the NMV Our signal is decaying while it relaxes back to b0