Equipment Magnetic resonance imaging (MRI) scan requires_MRI

The patient is placed within the magnetic field by lying on a table which is placed through the center of the opening of the magnet, similar to lying on a road running through a tunnel.
the front of the patient.

Sagittal: Imagine the patient is standing sideways and is sliced across from front to back.
• You are viewing
from the side of the patient.
Equipment

Magnetic resonance imaging (MRI) scan requires the use of a very strong magnetic field.
• Unlike other devices used in radiology, MR •
imaging uses no radiation. The magnet is contained in the housing of the scanner and this creates a magnetic field oriented down the center of the magnet.

T1 weighted images emphasize the difference in T1 relaxation times between different tissues.
• In these images, water containing structures are
dark. • Since most pathologic processes (such as tumors, injuries, CVA's, etc.) involve edema (or water), T1 weighted images do not show good contrast between normal and abnormal tissues. • However, pathologic processes do demonstrate excellent anatomic detail.
gauss. • The strongest magnetic field permitted in MRI scanning of humans is 1.5 Tesla (1.5T).

Three types of magnets are available for use in MRI.
• Most MRI scanners in use today are •

T2 weighted images emphasize the difference in T2 relaxation times between different tissues.
• Since water is bright on these images, T2
weighted images provide excellent contrast between normal and abnormal tissues, although the anatomic detail is less then that of T1 weighted images.

A radiofrequency electromagnetic pulse is then applied, which deflects the protons off their axis along the magnetic field.
• As the protons realign themselves with the
• Permanent magnets are madБайду номын сангаас of solid
magnetic material, similar to bar magnets, and create the weakest magnetic fields.
• However, they can be arranged in a configuration

The picture shows the actual magnet (the outer container resembles a thermos and contains the superconducting wire surrounded by liquid helium).
Creating an Image
•
You are viewing from the patient's feet.

Coronal: Imagine the patient is standing in front of you and is sliced across from right to left.
• You are viewing from
• However, three standard views are usually
used:

Transverse (axial): Imagine the patient is lying on their back and is sliced across from right to left.
•
magnetic field, a signal is produced. This signal is detected by an antenna, and with the help of computer analysis, is converted into an image.

The process by which the protons realign themselves with the magnetic field is referred to as relaxation.

The strength of the magnetic field is measured in units called gauss or Tesla:
• 10,000 gauss equals 1 Tesla.
• The earth's magnetic field is approximately 0.6

Intravenous contrast is often used to improve the sensitivity of MR imaging,
• especially in the brain and spine.

MR contrast agents contain gadolinium, which increases T1 relaxation and causes certain abnormalities to "light up" on T1 weighted images.


The physics of MRI are extremely complex. When a patient is placed within and MR scanner, the protons in the patients tissues (primarily protons contained in water molecules) align themselves along the direction of the magnetic field.
that doesn't require the patient to be surrounded by the magnet and are used in Open MR scanners.

The strongest is a superconducting magnet.
• This is a type of electromagnet in which current
superconductng magnets. Resistive magnets are electromagnets, similar to superconducting magnets, but they are air cooled therefore have greater resistance to current and create weaker magnetic fields.
• These agents contain no iodine, and allergic
reactions are extremely rare.
Image Orientation

MRI images can be obtained in any imaging plane without moving the patient.
The protons undergo 2 types of relaxtion:

• T1 (or longitudinal) relaxation and • T2 (or transverse relaxation) relaxation.

Different tissues undergo different rates of relaxation, and these differences create the contrast between different structures, and the contrast between normal and abnormal tissue, seen on MRI scans.