Transcript MRI - GEOCITIES.ws

DEVELOPMENT OF MRI
PREPARED BY
ZAINAL AHMAD KEU 97020
SAKINAH HASHIM KEU 97015
Content
What is MRI?
Basic Theory Of MRI
The Development Of MRI
MRI Instrumentation
MRI Safety Consideration
Advantages & Limitation Of MRI
Application Of MRI
How Does MRI Altered The Diagnostic
Method?
What is MRI????
is a scanning method that makes use of the
resonance property found in some of the
nucleus present in the human
body,
especially the hydrogen nucleus (i.e the
proton).
This is of interest due to its large presence
in water and body molecules.
Basic Theory of MRI
To obtain an image, patient is placed in a highly
uniform and static magnetic field
Magnetized proton within the patient align like a
small magnet
A radio frequency(RF) pulses is then utilized to
create oscillating magnetic field perpendicular to
the main field from which the nuclei absorb
energy and move out of the alignment in a state of
excitation
Cont…
As the nuclei return from excitation to equilibrium
state, a signal is induced in the receiver coil.
The signal is then transformed by a series of
algorithms into diagnostic images.
Images based on different tissue characteristics
can then be obtained by varying the number and
sequence of pulsed RF fields in order to take
advantage of magnetic relaxation properties of the
tissues.
The development of MRI The conception of ideas
Before the World War II – Paul Lauterbur’s
conception of ideas.
Initial experiments on existing NMR
machine.
1967 - Raymond Damadian proposed the
idea of detecting cancer using NMR method
which is utilized in the MRI.
The invention process
April 1969 meeting of the Federation of American
Societies in Experimental Biology – Damadian
and Freeman Cope succeeded in conducting an
experiment to detect potassium in bacteria from
the dead sea.
Damadian obtained a grant from the national
Cancer institute that enable him to buy an NMR
spectrometer and develop a research team.
1972 – Damadian filed a patent claim for “an
apparatus and method for detecting cancer in
tissue”.
Cont…
1976- a prototype machine of MRI
July 1977- Damadian accomplished in creating
crude image of the human chest
Damadian set up FONAR corporation to produce
a permanent-magnet MRI machine and introduce
it at the meeting of American Roentgen Ray
Society and later that year at the annual meeting of
the Radiological Society of North America.
The MRI instrumentation
A large, powerful cylindrical magnet with a
bore
A set of electrically conducting gradient
coils
An RF transmitter and receiver
A computer to control the entire process.
A cathode ray tube.
As the technology evolved…
As the technology of MRI emerged, all
researchers in biomedical sciences, clinical
investigators, practicing physicians and
consumers gather to make a scientific
assessment of technologies and to seek
agreement on their safety and effectiveness.
QUESTIONS?????
Are there any
contraindications to or
risks of MRI?
What are the
technological
advantages and
limitations of MRI?
What are the clinical
indications for MRI,
and how does it alter
the diagnostic methods
and its applications
effectiveness?
Answers!!!! 1st question.
Risks related to the static and oscillating magnet
fields used in MRI
Adverse biologic effects at high exposure
Major effect = Projectile effect = forceful
attraction of ferromagnetic objects to the magnet
Endanger the patient with ferromagnetic objects
embedded in their body i.e. shrapnel, pacemaker
wires or aneurysm clips
Cont……..
Biologic effects = ECG changes in T
wave
amplitude and magnetohydrodynamic
flow
effects
Appear to be hazardous at fields
strength above 2 tesla
Electric current induced in
conductive tissues by rapidly changing gradient
fields
Cont……
Heating effects in tissues due to circulating
currents from radio frequency coils
Care to the patient whose heat loss mechanisms
are impaired and with hyperpyrexic individuals
Adjustable pulse sequence = prevent excessive
heat buildup especially in warm and humid
environments.
Cont………….
Caution to the infants, patients requiring
monitoring and life-support systems and
patients who are pregnant
In vitro studies raise the questions of whether
exposure might pose risks to the developing
embryo and fetus
Answers!!!!!2nd question
Advantages:
Capability in characterizing and discriminate
among tissues according to their physical and
biochemical properties
Both physiologic and pathologic can be evaluated
Calcium emits no signal on spin echo images, thus
tissues surrounded by bone can be imaged
Beam hardening artifacts are avoided
Cont……..
Sectional images of equivalent resolution in any
projection without moving the patient
Excellent delineation of anatomic structure
Para- and super paramagnetic contrast agents
relatively nontoxic
Little patient preparation and is noninvasive
Disadvantages
Slow scan acquisition produce an artifacts
due to biological motion i.e. cardiac,
vascular respiratory excursion, etc
Patient experience claustrophobia due to
small bore of the magnet
Strong static magnetic field interferes the
proper function of the usual life-support
equipment
Cont……..
Patients with pacemakers and ferromagnetic
appliances cannot be studied
Limitation of the ability in detecting
pathological calcification in soft tissue and
tumors
Greater technological expertise is required
for MRI utilization
Commercial Model Of MRI
Brain scans
are acquired
from a
Magnetic
Resonance
Imaging
scanner like
this.
Commercial Model Of MRI
Airis II ‘Open’ MRI Scanner
MRI Application
 Flow imaging (MRI Angiography)
 Diffusion Imaging
 Chemical Shift Imaging (Fat Suppression)
 Echo Planar Imaging (Functional MRI)
 Magnetization Transfer Contrast
 Variable Bandwidth Imaging
 Tissue Classification
 Volume imaging (3-D Imaging)
These slices can be rendered into a 3D volume and then viewed from
any plane. From these images the measurement of the brain volume
regions which play a role in the pathophysiology of disease can be done.
Example: hippocampus
The measurement of the volume of a structure by manually tracing it's
outline (using specialised computer software) on all slices in which it
appears. Volumes are calculated by summing across all slices.
How Does MRI Altered The
Diagnostic Method??
Enhanced the diagnosis ability
Enhanced the study on basic
biological
processes in vivo
Widely used in central
nervous system
diagnosing since 1980’s
- high quality spatial resolution
- does not use radiation
- clear from the attenuation spectrum of
human body
Conclusion
After being introduced in 1980’s, MRI has
become the major choice of diagnostic
imaging technique since it is:
Noninvasive
Appears to be relatively innocuous in
clinical application
Involves no exposure to ionizing radiation
Conclusion….cont……
However, the full potential of MRI has not
been reached yet. It requires continuing
refinement of equipment, contrast agents
and software may be anticipated. Further
study of the long-term biologic effects of
magnetic fields is required.
Thank you…