Mri

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Always Thinking Ahead.

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MRI ROOM REQUIRMENT

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When performing an MRI scan, a patient is placed inside a cylinder

that contains a strong magnet. Radio waves are then introduced

into the cylinder, which cause the atoms of the body to resonate.

Each type of body tissue emits characteristic signals from the

nuclei of its atoms, and a computer translates these signals into a

two-dimensional picture.

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The Atom

Everything in nature is made up of tiny bits of matter called atoms. An atom is the smallest unique part of a chemical element. Atoms consist of three components:

· protons, which are positively charged; · neutrons, which have no charge; · electrons, which are negative charged.The protons and neutrons form the core or nucleus to the atom,

while the electrons orbit the nucleus like the planets orbit the sun.

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Spin of the Nucleus

One important property of the proton is that of spin or intrinsic angular momentum. The proton rotates about its own axis much like a top or a gyroscope. Since the proton is a positively charged particle and spins, it has a magnetic field associated with it. The hydrogen protons in the body, or spins,behave like tiny magnets called magnetic dipole vectors (two poles - northand south), having both orientation and magnitude

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Nuclei are built up of protons and neutrons. The number of protons in a

nucleus determines the chemical element. Nucleus with the same number of

protons but with an different number of neutrons are called isotopes.

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Hydrogen atom

The simplest atom is Hydrogen. It consists of just one proton and no neutrons.

The advantages of hydrogen for MR are: 1. It is the most common element found in the human body;

primarily in water and fat molecules. 2. It has the highest sensitivity to magnetic resonance of any

element in nature

MR-imaging (MRI) is almost exclusively limited to the study of hydrogen nuclei

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In a homogeneous magnetic field the

spin vectors of the hydrogen nuclei

(protons) align parallel or anti

parallel to the magnetic field.

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The sample to be scanned is placed into the center of the magnet. The RF transmitter is turned on for a short duration. The RF energy from the transmitter is absorbed by the hydrogen nuclei (protons) in the sample. Once the RF transmitter is turned off, the hydrogen protons in the sample give up the energy they received from the transmitter in a process called relaxation. During the relaxation process, the hyrdogen protons emit a signal that is detected by the antenna system and the RF receiver. The data acquisition system (DAS), digitizes the signal so that the host computer can process the data into an image.

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MAGNET TYPES

PERMANENT MAGNET RESISTIVE SUPERCONDUCTIVE

LOW FIELD MAGNETS FOR MAGNETIC FIELDS UP TO APPROX. 0.3 T PERMANENT MAGNETS RESP. RESISTIVE ELECTRO MAGNETS ARE USED. HIGH FIELD MAGNETS MRI SYSTEMS USING FIELD STRENGTH FROM 0.5 T UP TO 2.0 T OR EVEN HIGHER, REQUIRE SUPERCONDUCTIVE ELECTRO MAGNETS.

RF Room Control Room Equipment Room

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