MRI-MEDICAL RESONANCE IMAGING

1. MAGNETIC
RESONANCE
IMAGINING

2. The machine
• The strength of the magnet varies from
0.5 – 4 tesla
• Average cost between 1-2.5 million

3. 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.

4. MRI is a very close relative of NMR, which allows
clinicians to obtain chemical and physical
information about certain molecules. In the 1970’s
the name was changed from NMRI to MRI due to the
negative connotations associated with the word
“nuclear”. Many patients thought that the exam
would expose them to radiation.

5. In 1952 Felix Bloch and Edward
Purcell were awarded the Nobel
Prize when they discovered the
concepts surrounding NMR/MRI.
During the time between 1950-
1970, the idea was used for
chemical and physical analysis of
molecules.

6. • In 1971, Raymond Damadian
discovered that NMR could be
used in the detection of diseases.
• In 1974, Damadian received a
patent for the design of his MRI
machine.
• In 1977, Damadian did his first
scan on a human, his assistant,
Larry Minkoff. He couldn’t go in
himself due to his enormous size.

7. Damadian’s first prototype
was called “Indomitable”, due
to criticism and the seven
years that it took to complete.
In 1978, Damadian
established a new corporation
called FONAR, which
introduced the first
commercial MRI scanner in
1980.

8. MRI machines look like a large block with a tube
running through the middle of the machine, called
the bore of the magnet.
The bore is where the patient is located for the
duration of the scan.

9. The MRI machine picks points
in the patients body, decides
what type of tissue the points
define, then compiles the
points into 2 dimensional and
3 dimensional images.
Once the 3 dimensional image is created, the MRI
machine creates a model of the tissue. This allows
the clinician to diagnose without the use of
invasive surgery.

10. The largest and most important components of
the MRI machine are the magnets.
The magnet strength is measured in units of
Tesla or Gauss (1 Tesla = 10,000 Gauss).
Today’s MRI machines have magnets with
strengths from 5000 to 20,000 Gauss.
To give perspective on the
strength of these magnets,
the earth’s magnetic field is
about .5 Gauss, making the
MRI machine 10,000 to
30,000 times stronger.

11. Background Information
• Our bodies are made up of roughly 63%
water
• MRI machines use hydrogen atoms
• The hydrogen atoms act like little
magnets, which have a north and south
pole
• The atoms inside our body are
aligned in all different directions

12. • An MRI consists of:
– a primary magnet: creates the magnetic field
by coiling electrical wire and running a
current through the wire
– gradient magnets: allow for the magnetic
field to be altered precisely and allow image
slices of the body to be created.
– a coil: emits the radiofrequency pulse
allowing for the alignment of the protons.

13. • The signals are then ran through a
computer and go through a Fourier
equation to produce an image.
• Tissues can be distinguished from each
other based on their densities.

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

15. Different types of MRI
• Interventional MRI
– Used to guide in some noninvasive
procedures
• Real Time MRI
– Continuous filming/ monitoring of objects in
real time
• Functional MRI
– Measures signal changes in the brain due
to changing neural activity

16. MRI and Radio Frequencies
• The RF coil produces a radio frequency
simultaneously to the magnetic field
• This radio frequency vibrates at the perfect
frequency (resonance frequency) which helps
align the atoms in the same direction
• the radio frequency coil sent out a signal that
resonates with the protons. The radio waves are
then shut off. The protons continue to vibrate
sending signals back to the radio frequency coils
that receive these signals.

17. MAGNETIC RESONANCE
IMAGING
Magnet Gradient Coil RF Coil
RF Coil
4T magnet
gradient coil
(inside)
B0

18. Magnetic Resonance Imaging
• Magnetic nuclei are abundant in the human body (H,C,Na,P,K) and spin randomly
• Since most of the body is H2O, the Hydrogen nucleus is especially prevalent
• Patient is placed in a static magnetic field
• Magnetized protons (spinning H nuclei) in the patient align in this field like compass needles
• Radio frequency (RF) pulses then bombard the magnitized nuclei causing them to flip around
• The nuclei absorb the RF energy and enter an excited state
• When the magnet is turned off, excited nuclei return to normal state & give off RF energy
• The energy given off reflect the number of protons in a “slice” of tissue
• Different tissues absorb & give off different amounts of RF energy (different resonances)
• The RF energy given off is picked up by the receiver coil & transformed into images
• MRI offers the greatest “contrast” in tissue imaging technology (knee, ankle diagnosis)
• cost: about $1450 - $2000
• time: 30 minutes - 2 hours, depending on the type of study being done
Open MRIClosed (traditional) MRI scanner

19. MRI machines have come a long way since
Indomitable. Previously, it took up to five hours
to get an image, whereas today, it takes minutes.
In 1992, functional magnetic resonance imaging
(fMRI) was discovered, which allowed clinicians to
see various regions of the brain, their functions, and
their specific locations.
Slide shows which
area of the brain is
responsible for touch.

20. X- Rays
• X-rays are generated from the interaction of accelerated e-
’s & a target metal (tungsten)
• Patient is placed between X-ray tube and silver halide film
• X-rays passed through the body are absorbed in direct proportion to tissue density
• X-rays penetrating the body strike the silver halide film and turn it dark
• The more x-rays that penetrate, the darker the area inscribed on the film
• Bones & metal absorb or reflect X-rays r inscribed film is “lighter” or “more white”
• Soft tissues allow more X-rays to penetrate r inscribed film is “darker”
• Visualizing tissues of similar density can be enhanced using “contrast agents”
• Contrast agents: dense fluids containing elements of high atomic number (barium, iodine)
• Contrast agents absorbs more photons than the surrounding tissue r cavity appears lighter
• These contrast agents can be injected, swallowed, or given by enema
electron beam generator
tungsten target metal
resultant X-ray beam
silver halide film

21. Magnetic Resonance Techniques
Nuclear Spin Phenomenon:
• NMR (Nuclear Magnetic Resonance)
• MRI (Magnetic Resonance Imaging)
• EPI (Echo-Planar Imaging)
• fMRI (Functional MRI)
• MRS (Magnetic Resonance Spectroscopy)
• MRSI (MR Spectroscopic Imaging)
Electron Spin Phenomenon (not covered in this course):
• ESR (Electron Spin Resonance)
or EPR (Electron Paramagnetic Resonance)
• ELDOR (Electron-electron double resonance)
• ENDOR (Electron-nuclear double resonance)

22. There are three types of
magnets:
1.Resistive Magnets
2.Permanent Magnets
3.Superconducting Magnets

23. The resistive magnet has many coils of wire that
wrap around the bore, through which electrical
currents are passed, creating a magnetic field. This
particular magnet requires a large amount of
electricity to run, but are quite cheap to produce.
The permanent magnet is one that delivers a
magnetic field, which is always on at full strength
and therefore, does not require electricity. The cost
to run the machine is low due to the constant
magnetic force. However, the major drawback of
these magnets is the weight in relation to the
magnetic field they produce.

24. The superconducting magnets are very similar to
the design of the resistive magnets, in that they too
have coils through which electricity is passed
creating a magnetic field. However, the major
difference between the resistive magnet and the
superconducting magnet is the fact that the coils
are constantly bathed in liquid helium at -452.4ºC.
This cold temperature causes the resistance of the
wire to be near zero, therefore reducing the
electrical requirement of the system. All of these
factors allow for the machine to remain a
manageable size, have the ability to create high
quality images, and still operate at a reasonable
cost.

25. The superconducting magnet is the most commonly
used in machines today, giving the highest quality
images of all three magnet types.

26. There is
another type of
magnet that is
found in all MRI
machines,
called gradient
magnets
These magnets
are responsible
for altering the
magnetic field in
the area to be
scanned and can
magnetically
“slice” the tissue
to be examined
from every angle.

27. MRI’s of the heart can be done to look at many
different areas including: vessels, chambers, and
valves.
The MRI can detect problems
associated with different heart
diseases including plaque
build up and other blockages
in blood vessels due to
coronary artery disease or
heart attacks.

28. MRI’s of the brain can
evaluate how the brain is
working, whether normal or
abnormal.
Brain MRI’s can show damage resulting from
different problems such as: damage due to stroke,
abnormalities associated with dementia and/or
Alzheimer’s, seizures, and tumors.
fMRI are done prior to brain surgery,
to give a map of the brain, and help
plan the procedure.

29. MRI’s can be done on the knee to
evaluate damage to the
meniscus, ligaments, and
tendons.
Tears in the ligaments are given
a grade 1-3 depending on their
severity:
1-fluid around the ligament
2-fluid around the ligament with partial disruption
of the ligament fibers
3-complete disruption of the ligament fibers

30. Often prior to a MRI scan, a patient would need to
have a contrast dye, either injected or taken orally,
usually gadolinium as seen here.

31. The Procedure…

32. Once the contrast dye has been injected, the patient
enters the bore of the MRI machine on their back
lying on a special table.
The patient will enter the machine head first or feet
first, depending on the area to be scanned.
Once the target is centered,
the scan can begin.

33. •The scan can last anywhere from 20-30 minutes.
•The patient has a coil that is placed in the target
area, to be scanned.
•A radio frequency is passed through the coils that
excites the hydrogen protons in the target area.
•The gradient magnets are then activated in the
main magnet and alter the magnetic field in the
area that is being scanned.

34. The patient must hold completely still in
order to get a high quality image. (This is
hard for patients with claustrophobia, and
often times a sedative will be given, if
appropriate.)
The radio frequency is then turned-off and the
hydrogen protons slowly begin to return to their
natural state.

35. The magnetic field runs down the center of
the patient, causing the slowing hydrogen
protons to line-up.
The protons either align themselves pointed
towards the head or the feet of the patient,
and most cancel each other out.
The protons that are not cancelled create a
signal and are the ones responsible for the
image.

36. The contrast dye is what makes the target
area stand out and show any
irregularities that are present.
The dye blocks the X-Ray photons from
reaching the film, showing different
densities in the tissue.
The tissue is classified as normal or
abnormal based on its response to the
magnetic field.

37. The tissues with the help of the magnetic
field send a signal to the computer.
The different signals are sent and modified
into images that the clinician can evaluate,
and label as normal or abnormal.
If the tissue is considered abnormal, the
clinician can often detect the abnormality,
and monitor progress and treatment of the
abnormality.

38. Uses for an MRI
Used to image a large variety of tissues and
substances.
• Brain imaging: to define anatomy, identify
bleeding, swelling, tumors, or the presence of
a stroke
• To locate glands, organs, joint structures,
muscles and bone
Some diseases manifest themselves in having
an increase in water content
The MRI can detect inflammation (tumors) in
many tissues
Helpful in diagnosing problems with eyes, ears,

39. MRI Results
• Creates a 2D and sometimes 3D image
that comes from the information of the
radio waves of the protons
• Example heart scan
• https://www.youtube.com/watch?v=G4dFVeP

40. MRI treatment is a wonderful option for most
patients, but there are some people who are not
candidates.
Those include:
1) Patients with pacemakers cannot have the scan
done as the magnet from the MRI interferes with
the signal sent from the pacemaker, and
deactivates it.
2) Patients who are too tall, or too obese
3) Patients who have orthopedic hardware can get
distortion in the image, and the scan quality is
not as high.

41. THE FUTURE OF MRI:
•The possibility of having very small machines
that scan specific parts of the body.
• The continuing improvements on seeing the
venous and arterial systems.
• Brain mapping while the patient does specific
tasks, allowing clinician’s to see what part of the
brain is responsible for that task/activity.
• Improvements on the ability to do MRI’s of the
lungs.
• ETC.

42. THANK YOU
Garima Kotnala
Mtech (NST)-1st
Sem
Enroll.
No:01440801014