DEVELOPMENT OF MRI PREPARED BY ZAINAL AHMAD KEU 97020 SAKINAH HASHIM KEU 97015.
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Transcript of DEVELOPMENT OF MRI PREPARED BY ZAINAL AHMAD KEU 97020 SAKINAH HASHIM KEU 97015.
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DEVELOPMENT OF MRIPREPARED BY
ZAINAL AHMAD KEU 97020
SAKINAH HASHIM KEU 97015
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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?
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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.
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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
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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.
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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.
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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”.
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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.
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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.
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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.
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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?
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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
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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
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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.
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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
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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
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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
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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
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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
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Commercial Model Of MRI
Brain scans are acquired from a Magnetic Resonance Imaging scanner like this.
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Commercial Model Of MRI
Airis II ‘Open’ MRI Scanner
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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)
MRI Application
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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.
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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.
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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
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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
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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.
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Thank you…