DEVELOPMENT OF MRI PREPARED BY ZAINAL AHMAD KEU 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 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 – Damadian filed a patent claim for “an apparatus and method for detecting cancer in tissue”.

Cont… a prototype machine of MRI July 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!!!! 1 st 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!!!!!2 nd 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

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

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.

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