PARTS Of An MRI
Magnet: The magnet is responsible for maintaining a strong, uniform magnetic field in the scanner.
One of three types of magnets are used in MRIs.
1) Resistive magnets are made from wire that is coiled around a cylinder, which is the pathway for an electrical current. When the current is turned on, it activates the magnet by causing the coils to generate a magnetic field.
2) A permanent magnet is very heavy and generates a constant but relatively weak magnetic field.
3) Super-conducting magnets
Computer System and Console
One of three types of magnets are used in MRIs.
1) Resistive magnets are made from wire that is coiled around a cylinder, which is the pathway for an electrical current. When the current is turned on, it activates the magnet by causing the coils to generate a magnetic field.
2) A permanent magnet is very heavy and generates a constant but relatively weak magnetic field.
3) Super-conducting magnets
- The most frequently used magnets in an MRI system are superconducting electromagnets.
- the basic design uses a coil of conductive wire, a cooling system, and a power supply.
- The coils are made by wrapping wire, constructed from filaments of a niobium titanium alloy embedded in copper, in a large loop. To create the necessary magnetic field, a number of coils are used. In one type of system eight coils are used, six to create the primary magnetic field and two to compensate for the excess field.
- The coils are immersed in a vessel containing liquid helium. This reduces the temperature to a level that makes the magnet superconductive. To maintain a stable temperature, the vessel is surrounded by two more vessels containing other coolants such as liquid nitrogen. This construction is then suspended with thin rods in a vacuum-sealed container. A power supply is hooked up to the magnetic coils and is used only when the magnet needs to be energized.
- The RF system has different roles within an MRI machine. First, it is responsible for transmitting the RF radiation that induces the atoms to emit a signal. It then receives the emitted signal and amplifies it so it can be manipulated by the computer. RF coils are the primary pieces of hardware in the RF
system. They are constructed to create an oscillating magnetic field. This field induces atoms in a defined area to absorb RF radiation and then emit a signal. In addition to sending the RF signal, the coils can also receive the signal from the patient. Depending on the type of MRI system, either a saddle RF coil or a solenoid RF coil is used. The coil is usually positioned alongside the subject and is designed to fit the patient. To reduce RF interferences, an aluminum sheet is used (HowProductsAreMade 2016).
- provide a method to decode the NMR signal that is received from a sample. Normally, three sets of gradient coils are used to provide data in each of the three dimensions. The gradient coils are made of a conducting loop that creates a magnetic field. In the MRI system, they are wrapped around the cylinder that surrounds the patient.
Computer System and Console
- controls the signals sent and processes and stores the signals received. Before the received signal can be analyzed by the computer, it is translated through an analog-digital convertor. When the computer receives signals, it performs various reconstruction algorithms, creating a matrix of numbers that are suitable for storage and building a visual display using a Fourier transformer (HowProductsAreMade 2016).
Fields Used In An MRI
How Magnetic Fields Are Used
An MRI uses a combination of an electric and magnetic field. In magnetic resonance imaging, a superconducting magnet is used to create a large stable magnetic field of 2.0 T in strength. This magnetic field is important in producing detailed images of soft tissue in the human body.
The human body mass is two thirds composed of water that contain billions of hydrogen atoms. Water molecules are made up of two elements, hydrogen and oxygen. In the centre of an atom, there is a proton. A proton is a particle with a positive charge. It acts as a magnet and is responsive to magnetic fields. MRIs take advantage of this feature by interacting with these hydrogen atoms to produce images that can be later used to diagnose injuries and diseases.
The water molecules in our body are arranged in no particular arrangement. In the presence of an MRI, the first magnet the body encounters causes the molecules to align in the same direction which can be north or south. The number of atoms that align with the external field will almost equal the opposite. However it will never be the exact same. The difference in numbers depends on the type of material the atoms are from such as skin, organ, or bone. Another reason is that it depends if the material is healthy or diseased.
A second magnetic field, radio frequency wave, switches on and off which causes each hydrogen atom to align in the same direction and then relax when off. When the pulse ends, the atoms emit energy they had absorbed. Electricity is passed through gradient coils, producing a magnetic field. This causes the coils to vibrate which produces a knocking sound in the scanner.
Three gradient magnets are turning on and off in a particular pattern. They are smaller than the primary magnet but allow for accurate precision. By altering these gradient magnets, the magnetic field can be focused on one particular spot. Changing the gradient magnets are important because they form a 3D image without moving the patient. The MRI sends signals to a computer which can produce an image.
An MRI uses a combination of an electric and magnetic field. In magnetic resonance imaging, a superconducting magnet is used to create a large stable magnetic field of 2.0 T in strength. This magnetic field is important in producing detailed images of soft tissue in the human body.
The human body mass is two thirds composed of water that contain billions of hydrogen atoms. Water molecules are made up of two elements, hydrogen and oxygen. In the centre of an atom, there is a proton. A proton is a particle with a positive charge. It acts as a magnet and is responsive to magnetic fields. MRIs take advantage of this feature by interacting with these hydrogen atoms to produce images that can be later used to diagnose injuries and diseases.
The water molecules in our body are arranged in no particular arrangement. In the presence of an MRI, the first magnet the body encounters causes the molecules to align in the same direction which can be north or south. The number of atoms that align with the external field will almost equal the opposite. However it will never be the exact same. The difference in numbers depends on the type of material the atoms are from such as skin, organ, or bone. Another reason is that it depends if the material is healthy or diseased.
A second magnetic field, radio frequency wave, switches on and off which causes each hydrogen atom to align in the same direction and then relax when off. When the pulse ends, the atoms emit energy they had absorbed. Electricity is passed through gradient coils, producing a magnetic field. This causes the coils to vibrate which produces a knocking sound in the scanner.
Three gradient magnets are turning on and off in a particular pattern. They are smaller than the primary magnet but allow for accurate precision. By altering these gradient magnets, the magnetic field can be focused on one particular spot. Changing the gradient magnets are important because they form a 3D image without moving the patient. The MRI sends signals to a computer which can produce an image.
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Summary Procedure of MRI |
1. The body is paced in a steady magnetic field causing a steady state of magnetism through out the body.
2. The body is stimulated with radio waves to change the steady orientation of protons 3. MRI machines stops producing radio waves and detects the body's electromagnetism. 4. Transmitted signals are used to form an image of the body. |