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An- Najah National University Faculty of Graduate studies “ Magnatic Resonance Imaging” By Isra Murrar. Outline. Introduction History Alternative Names Uses MRI components How MRI works How to Prepare for the Test How the test will feel Economics of MRI
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Faculty of Graduate studies
“Magnatic Resonance Imaging”
How MRI works
How to Prepare for the Test
How the test will feel
Economics of MRI
Benefits or advantages
Risks or disadvantages
Magnetic resonance imaging (MRI) is done for many reasons. It is used to find problems such as
An MRI scan can be done for the:
Placing many protons in a magnetic field, we find that some align anti-parallel and a slight majority aligns parallel. Protons aligned in the parallel orientation are said to be in a low energy state. Protons in the anti-parallel orientation are said to be in a high-energy state.
With a patient in a MRI machine, and the magnet turned on, the nuclei of the hydrogen atoms tend to spin in one of two directions. These hydrogen atom nuclei can transition their spin orientation, or precess, to the opposite orientation. In order to spin the other direction, the coil emits a radiofrequency (RF) that causes this transition (the frequency of energy required to make this transition is specific, and called the Larmour Frequency).
A) The protons spinning in the nature, without an external strong field. The directions of spins are random and cancel out each other. The net magnetization is nearly 0. B) In the presence of a large external magnetic field Bo the spins align themselves either against (high energy state) or along (low energy state). There is a slight abundance of spins aligned in the low energy state.
The signal that is used in creating MRI images is derived from the energy released by molecules transitioning, or precessing, from their high-energy to their low-energy state. This exchange of energy between spin states is called resonance, and thus the name magnetic resonance imaging.
n = g Bo
The RF system has various roles in an MRI machine. First, it is responsible for transmitting the RF radiation that induces the atoms to emit a signal. Next, it 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.
The final link in the MRI system is a computer, which 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.