MRI is an exciting advancement in Radiology. Since a few decades it occupied a significant place in advanced radiology. High resolution multi plane 3D image Superior contrast resolution.
The principle is based on the that any nuclei with unpaired protons behave like magnet when they spin. When these nuclei are subjected to a strong magnetic field, they release some energy in the form of radio signal. The radio signal is converted in to image
Hydrogen nuclei are particularly suitable, because they have a single proton and neutron in nucleus and also abundant in human body in the form of water 70% of total body weight is water only.
The procedure is that tissue to be imaged is subjected to a strong magnetic field. The instrument is equipped with high power magnets which can produce strong magnetic fields. When the body is subjected to this magnetic field the hydrogen nuclei which are present in the tissues tend to align themselves along the line of force of the filed from their random position because it also has a small magnetic field around it.
To get the image of a particular tissue, the tissue nuclei should be stimulated. To do so, a strong magnetic pulse is applied. The magnetic pulse is the high power magnetic energy released by the instrument. Then the protons present in the tissues absorb the energy and are excited.
When they are excited they increase some energy, that energy is received by the detector in the instrument. After releasing the energy. The protons come back to the normal state when the stimulating pulse is stopped.
The energy released by excited protons is called as radio signals. The image is based on these radio signals by the tissues.
The intensity of radio signal indicates the concentration of the protons in the tissue which is subjected for image. This is the base for the image. The radio signal which is received, will be processed with many calculations by the computer, like how much energy is released and absorbed. After that the final image on film is obtained.
Therefore the image is formed by frequency pulse. which excites the protons with magnetic energy, and same energy is returned from the excited protons in the form of radio signal. Based on the radio signal intensity, the image will show black and white.
- In general, most MRI scans take between 20-60 minutes and patients will experience no discomfort. They will, however, hear a loud knocking or tapping sound when the scanner is actually acquiring information.
Advantages :
- It do not have ionizing radiation, so it is said to be safe It gives high intrinsic contrast.
- In any plane the image can be taken with out changing patients position No known biological hazards.
- It is the investigation of choice to study brain and spinal cord. It is also used for abdominal, musculoskeletal and cardiac imaging and in studying blood flow.
- No radiation is used Multiplanar images can be obtained for further evaluation of organs.
- High soft tissue contrast is seen in the images obtained .
Disadvantages:
- Imaging time is long this is operator dependent Extremely expensive Patient with pacemaker and any other metal implants can not be scanned.
- Claustrophobia Long examination times High cost.
