MRI INSTRUMENTATION

Question 1

It is the second most powerful fundamental force of nature

Answer 1

Magnetism

Question 2

o A force created by a magnetic field which behaves similarly to that of an electric field.

Answer 2

Magnetic force

Question 3

Gravitational force is given by

Answer 3

Newton’s law

Question 4

Electric force is given by

Answer 4

Coulombs’s Law

Question 5

Magnetics force is given by

Answer 5

Gaus’s Law

Question 6

refers to the relative ease with which a material can be made magnetic.

Answer 6

Magnetic susceptibility

Question 7

Easily magnetized

Answer 7

Ferromagnetic

Question 8

Very weakly magnetized

Answer 8

Paramagnetism

Question 9

Unaffected by magnetic field

Answer 9

Diamagnetic

Question 10

• this occurs when a nuclei has spin directions that are not equal and opposite.
• Also known as “Net Spin”
• Observed in nuclei with odd number of protons, odd number of neutrons or an odd number of proton and neutrons

Answer 10

Angular Momentum

Question 11

• Refers to the rotational motion of the angular momentum vector of a particle around an external axis or field

Answer 11

Precession

Question 12

• Precessional frequency of a particle

Answer 12

Larmor Frequency

Question 13

• Electromagnetic radiation with frequencies of approximately 10 to 200 MHz.

Answer 13

Radiofrequency

Question 14

refers to the position of the magnetic moments on the precessional path at any moment in time.

Answer 14

Phase

Question 15

▪ Magnetic moments are on different places on the precessional path at a
moment in time

Answer 15

Out of Phase (In Coherent)

Question 16

▪ Magnetic moments are on the same place on the precessional path at a
moment in time

Answer 16

In Phase (Coherent)

Question 17

• Refers to the natural precessional motion of nuclear magnetic moments after an RF pulse
has been applied and subsequently turned off.

Answer 17

Free Precession

Question 18

Time required for an excited particle (hydrogen), after being applied with an RF pulse and subsequently turned off, to lose its energy.

Answer 18

Relaxation Time

Question 19

• Also known as Proton Density
• Refers to the number of hydrogen nuclei (protons) per unit volume of tissue that can be magnetized and contribute to MRI signal

Answer 19

Spin Density

Question 20

• Most popular MRI system and features a tunnel-shaped magnet bore.

Answer 20

Closed Bore

Question 21

• Longitudinal table movement in these system allows the patient to be positioned with the Region of Interest (ROI) lying at the center of the magnet bore.

Answer 21

Closed Bore

Question 22

• This system encloses the patient from the front, back and side but still allows limited access.

Answer 22

Closed Bore

Question 23

• The design also facilitates easy side access to the patient when undertaking
interventional procedures (biopsies).

Answer 23

Open Systems

Question 24

These scanners permit a degree of sideways table movement

Answer 24

Open Systems

Question 25

Uses large Permanent Magnets and superconducting solenoids to generate the main magnetic field.

Answer 25

Open Systems

Question 26

• Are designed to scan limbs and are smaller in size.

Answer 26

Extremity Systems

Question 27

• Typical design is approx. the size and shape of a washing machine with an aperture in the center large enough to accommodate an arm or a leg.

Answer 27

Extremity Systems

Question 28

describes the number of flux lines passing through a given area.

Answer 28

FLUX DENSITY

Question 29

magnetic field strength is measured in

Answer 29

Amperes per meter

Question 30

Flux density (field strength) is measure in

Answer 30

Tesla

Question 31

• The law quantifies and states that when an electric current flows through a conductor, it generates a magnetic field around the conductor.

Answer 31

Ampere’s Law:

Question 32

• This system is equipped with large discs of ferromagnetic alloy.

Answer 32

Permanent Magnets

Question 33

• Employs copper-wound solenoids that operate just below room temperature.

Answer 33

Resistive Electromagnets

Question 34

• Introduced to address resistivity issues of Resistive electromagnets.

Answer 34

Superconducting Electromagnets

Question 35

Also known as coolants; and are used to reduce the temperature of the windings to within 4 degrees of absolute zero (4 Kelvin).

Answer 35

Cyrogen System

Question 36

• Derived from Greek word meaning “Cold” and “Stable”

Answer 36

CRYOSTAT

Question 37

• This is the area inside the cylinder of the cryostat.

Answer 37

WARM BORE

Question 38

reroutes the fringe field away from the outside environment and back toward the scanner

Answer 38

Passive shielding

Question 39

• which requires the scanner to be surrounded by large steel plates

Answer 39

Passive Shielding

Question 40

• which uses additional solenoid magnets.

Answer 40

Active Shielding

Question 41

uses shims to adjust for large changes in magnetic field homogeneity

Answer 41

Passive shimming

Question 42

• use electromagnets and is used addition to passive shimming types:

Answer 42

Active Shimming

Question 43

- can be manipulated at anytime by adjusting the current flow through windings

Answer 43

resistive

Question 44

- no electrical power is needed.

Answer 44

superconducting

Question 45

• create linear slopes along the B0. • apply a current to the gradient coils that offsets any minor inhomogeneity in the main magnetic field

Answer 45

Gradient Offset (Dynamic) Shimming

Question 46

o LEFT AND RIGHT o SAGITTAL CUTS o PAIR OF COILS POSITIONED ON EITHER SIDE OF THE CYLINDER o POSITIONED SO THAT THE GRADIENT MAGNETIC FIELD IS ACROSS THE PX LATERALLY o PROVIDES SPATIAL LOCALIZATION ALONG THE X-AXIS, PHASE- ENCODING OR FREQUENCY ENCODING

Answer 46

X Gradient Coils

Question 47

o ANTERIOR/ POSTERIOR o CORONAL CUTS o POSITIONED SO THAT THE GRADIENT MAGENTIC FIELD IS ACROSS THE PX VERTICALLY o PROVIDES SPATIAL LOCALIZATION ALONG THE Y- AXIS, PHASE - ENCODING OR FREQUENCY ENCODING

Answer 47

Y Gradient Coils

Question 48

o PAIR OF CIRCULAR COILS EACH OF WHICH IS WOUND ON THE CYLINDER AND OPPOSITE ENDS o MAXWELL COILS OR HELMWOTHS COILS o ALLOWS SLICE SELECTION ALONG THE AXIS OF THE GRADIENT o FOR AXIAL AND TRANSVERSE CUTS

Answer 48

Z Gradient Coils

Question 49

are the receivers, and sometimes also the transmitters, of radiofrequency (RF) signals in equipment used in magnetic resonance imaging

Answer 49

Radiofrequency coils (RF coils)

Question 50

are designed to provide a homogeneous RF excitation across a large volume. Most clinical MRI scanners include a built in volume coil to perform whole-body imaging, and smaller volume coils have been constructed for the head and other extremities.

Answer 50

Volume Coils

Question 51

are designed to provide a very high RF sensitivity over a small region of interest. These coils are often single or multi-turn loops which are placed directly over the anatomy of interest. The size of these coils can be optimized for the specific region of interest.

Answer 51

Surface coils