The MRI Scanner; historical facts, Understanding Nuclear Magnetic Resonance, The Scanner componenets, Radiofrequency coils, the casing, types of MRI magnets, understanding the principle of superconductivity. MRI applications

1. MRI SCANNER HARDWARE
Lecture 1: MRI Scanner System Components
and Functions
Nchanji NKEH Keneth
kennchanji@yahoo.com/excellence660@gmail.com
671459765/662695118
HPD/B.TECH– MDIRT
Radiology Dept.
St. Louis UNIHEBS, Mile 3 Nkwen Bamenda, NWR, Cameroon
2016/2017 Academic Year

2. Introduction
Magnetic resonance imaging (MRI) is an imaging technique
used primarily in medical settings to produce high quality
images of the soft tissues of the human body.
It is based on the principles of nuclear magnetic resonance
(NMR), a spectroscopic technique to obtain microscopic
chemical and physical information about molecules
MRI has advanced beyond a tomographic imaging technique to
a volume imaging technique

3. Historical Aspects of MRI

11. History of MRI
NMR = nuclear magnetic resonance
nuclear: properties of nuclei of atoms
magnetic: magnetic field required
resonance: magnetic field x radio frequency
1946: Block and Purcell
atomic nuclei absorb and re-emit radio frequency energy
1992: Ogawa and colleagues
first functional images using BOLD signal
Bloch Purcell
NMR  MRI: Why the name change?
most likely explanation:
nuclear has bad connotations
Ogawa less likely explanation:
NMR means Nouveau Mouvement Religieux

18. Timeline of MR Imaging
1920 1930 1940 1950 1960 1970 1980 1990 2000
1924 - Pauli suggests
that nuclear particles
may have angular
momentum (spin).
1937 – Rabi measures
magnetic moment of
nucleus. Coins
“magnetic resonance”.
1946 – Purcell shows
that matter absorbs
energy at a resonant
frequency.
1946 – Bloch demonstrates
that nuclear precession can be
measured in detector coils.
1972 – Damadian
patents idea for large
NMR scanner to
detect malignant
tissue.
1959 – Singer
measures blood flow
using NMR (in
mice).
1973 – Lauterbur
publishes method for
generating images
using NMR gradients.
1973 – Mansfield
independently
publishes gradient
approach to MR.
1975 – Ernst
develops 2D-Fourier
transform for MR.
NMR renamed MRI
MRI scanners
become clinically
prevalent.
1990 – Ogawa and
colleagues create
functional images
using endogenous,
blood-oxygenation
contrast.
1985 – Insurance
reimbursements for
MRI exams begin.

20. Nobel Prizes for Magnetic Resonance
 1944: Rabi
Physics (Measured magnetic moment of nucleus)
 1952: Felix Bloch and Edward Mills Purcell
Physics (Basic science of NMR phenomenon)
 1991: Richard Ernst
Chemistry (High-resolution pulsed FT-NMR)
 2002: Kurt Wüthrich
Chemistry (3D molecular structure in solution by NMR)
 2003: Paul Lauterbur & Peter Mansfield
Physiology or Medicine (MRI technology)

21. MRI main components

23. Main Components of a Scanner
 Static Magnetic Field Coils
 Gradient Magnetic Field Coils
 Magnetic shim coils
 Radiofrequency Coil
 Subsystem control computer
 Data transfer and storage computers
 Physiological monitoring, stimulus display, and
behavioral recording hardware

24. A schematic representation of the major
systems on a magnetic resonance imager
Return

25. The Magnet
 The most expensive component of the
imaging system.
 Most magnets are of the
superconducting type. This is a
picture of a 1.5 Tesla
 A superconducting magnet is an
electromagnet made of
superconducting wire.
 Superconducting wire has a
resistance close to zero when it is
cooled to a zero temperature (-
273.15o C or 0 K, by emersion in
liquid helium).
 Once current flows in the coil, it will
continue to flow as long as the coil is
kept at liquid helium temperatures.
Return

26. Equipment
Magnet Gradient Coil RF Coil
RF Coil
4T magnet
gradient coil
(inside)
B0

27. LET US PROBE INSIDE THE MAGNET

31. Permanent magnets

35. Resistive magnets

37. Superconducting magnets

38. Open Superconducting Magnet
• In 1997 Toshiba introduced the worlds
first open superconducting magnet.
•The system uses a special metal alloy,
which conducts the low temperature
needed for superconductivity.•Does not need any helium refills,
which dramatically reduces running costs.
•The open design reduces anxiety and
claustrophobia.

50. RF Coils
 RF coils are needed to transmit and receive
radio-frequency waves used in MRI
scanners.
 volume coils and surface coils:

51. Surface coils

52.  Quadrature Coils:they contain at least two
loops of wire, which are placed at right angles
to one another.
 Phased array coils consist of multiple surface
coils. Surface coils have the highest SNR but
have a limited sensitive area.

53. Radio Frequency (RF) chain
 A very important part is the Radio Frequency (RF)
chain, which produces the RF signal transmitted
into the patient, and receives the RF signal from the
patient.
 The frequency range used in MRI is the same as
used for radio transmissions. That’s why MRI
scanners are placed in a Faraday cage to prevent
radio waves to enter the scanner room, which may
cause artifacts on the MRI image. Someone once
said: “MRI is like watching television with a radio”.

56. RF Coils

57. R F Coils contd…
 RF coils create the B1 field which rotates the net
magnetization in a pulse sequence.
 RF coils can be divided into three general categories
1) transmit and receive coils
2) receive only coils
3) transmit only coils
Return

58. Safety
A third degree RF burn
The patient's arm was against the wall of a
body coil being operated in a transmit
mode with a surface coil as the receiver.
The burn first appeared as a simple blister
and progressed to a charring that had to be
surgically removed.
Return

59. Transmit Receive
rf
coil
rf
coil
main
magnet
main
magnet
gradientShimming
Control
Computer

60. Gradient Coils Principles
 These are room temperature coils
 A gradient in Bo in the Z direction is achieved with an
antihelmholtz type of coil.
 Current in the two coils flow in opposite directions
creating a magnetic field gradient between the two coils.
 The B field at one coil adds to the Bo field while the B field
at the center of the other coil subtracts from the Bo field
 The X and Y gradients in the Bo field are created by a
pair of figure-8 coils. The X axis figure-8 coils create a
gradient in Bo in the X direction due to the direction of
the current through the coils.
 The Y axis figure-8 coils provides a similar gradient in Bo
along the Y axis. Return

62. Gradient Coils
There are 3 sets of wires. Each set can create a
magnetic field in a specific direction: Z, X or Y.

63. See details in MRI physics

64. Gradient Coils

65. Gradient Coils Priciples
 These are room temperature coils
 A gradient in Bo in the Z direction is achieved with an antihelmholtz
type of coil.
 Current in the two coils flow in opposite directions creating a
magnetic field gradient between the two coils.
 The B field at one coil adds to the Bo field while the B field at the
center of the other coil subtracts from the Bo field
 The X and Y gradients in the Bo field are created by a pair of figure-8
coils. The X axis figure-8 coils create a gradient in Bo in the X
direction due to the direction of the current through the coils.
 The Y axis figure-8 coils provides a similar gradient in Bo along the Y
axis.
Return

66. RF Coils

67. R F Coils contd…
 RF coils create the B1 field which rotates the net
magnetization in a pulse sequence.
 RF coils can be divided into three general categories
1) transmit and receive coils
2) receive only coils
3) transmit only coils
Return

68. Safety
A third degree RF burn
The patient's arm was against the wall of a
body coil being operated in a transmit
mode with a surface coil as the receiver.
The burn first appeared as a simple blister
and progressed to a charring that had to be
surgically removed.
Return

69. Knee
Coronal Sagittal
Return

70. Spine in Sagittal Plane
Return

71. Brain MRI
Return

72. REFERENCES
Lecture delivered with help of resources
from Simply Physics, Parth Partel-
MRI Simplified, MRI Introduction by
Mohammed Ali, Fundamentals of
Magnetic Resonance by James D.
Christensen, MRI Principles by Yves
De Deene and MRI and MRS by
Victor R. Lasar

73. Lecture 2
Next lecture will be on MRI Safety Training
QUESTIONS ?