Magnetic Resonance Imaging (MRI)
Dr Jeremy Jones et al. http://radiopaedia.org/articles/mri-introduction
MRI (an abbreviation of magnetic resonance imaging) is an imaging modality that uses non-ionizing radiation to create diagnostic useful images. MRI was initially called Nuclear Magnetic Resonance Imaging after its early use for chemical analysis. The "Nuclear" was dropped off about 25 years ago because of fears that people would think there was something radioactive involved, which there is not.
NMR was discovered simultaneously by two physicists, Felix Bloch and Edward Mills Purcell, just after the end of World War II. Bloch trained in quantum mechanics and was involved with atomic energy and then radar counter-measures. At the end of the war he returned to his earlier work in the magnetic moment of neutron. Purcell was involved with development of microwave radar during the War then pursued radio waves for evaluation of molecular and nuclear properties. They received the Nobel Prize in Physics in 1952 for this discovery.
MRI, the use of NMR to produce 2D images was accomplished by Paul Lauterbur, imaging water and Sir Peter Mansfield who imaged fingers of a research student, Dr Andrew Maudsley in 1976. Maudsley continues to make a significant contribution to MRI R&D. Raymond Damadian obtained human images a year later in 1977. Lauterbur and Mansfield received the Nobel Prize in Physiology or Medicine in 2003 for their development of MRI.
An MRI scanner consists of a large and very strong magnet in which the patient lies. A radio wave antenna is used to send signals to the body and then receive signals back. These returning signals are converted into images by a computer attached to the scanner. Imaging of almost any part of your body can be obtained in any plane.
Why use MRI
The advantages of MRI include:
1. the ability to image without the use of ionizing radiation (x-ray) unlike CT scanning
2. images may be acquired in multiple planes (Axial, Sagittal, Coronal, or Oblique) without repositioning the patient. CT images have only relatively recently been able to be recontructed in multiple planes with the same spatial resolution
3. MRI images demonstrate superior soft tissue contrast than CT scans and plain films making it the ideal examination of the brain, spine, joints and other soft tissue body parts
4. some angiographic images can be obtained without the use of contrast material, unlike CT or conventional angiography
5. advanced techniques such as diffusion, spectroscopy and perfusion allow for specific tissue characterisation rather than merely 'macroscopic' imaging
6. functional MRI allows visualisation of both active parts of the brain during certain activities and understanding of the underlying networks.
There are a number of disadvantages and challenges to implementing MRI scanning.
MRI scans are more expensive than CT scans and take longer to acquire so patient comfort is sometimes an issue. Additionally images are subject to unique artifacts that must be recognized and abated (see MRI artifacts).
MRI scanning is not safe for patients with some metal implants and foreign bodies. Careful attention to safety measures is necessary avoid serious injury to patients and staff and this requires special MRI compatible equipment and stringent adherence to safety protocols (see MRI safety)
MRI in HUSM.....
Currently, we are running on Philip Achieva 3.0T TX MRI Machine that kick-started her operation on 2011. The Achieva 3.0T TX is equipped with MultiTransmit technology and intelligent RF management, that addresses 3.0T Mri challenges at the source, since parallel RF transmit eliminates dielectric shading effects by automatically adjusting to each patient's unique anatomy. More, the Achieva 3.0T Tx is also equipped with advance shimming techniques to further improve the imaging capabilities in the breast, body and cardiac area. In addition on the 3.0T system it is mandatory to use ear plugs or headphone foe additional noise reduction due to the acoustic noise increases with respect to higher field strengths.
MRI Exam Preparation
This information is for the purpose of educating public as to the basics of the MRI examination.
Firstly, patient will not be allowed to wear anything metallic during the MRI examination, so it would be best to leave watches, jewelry or anything made from metal at home. Anyhow, there is a safe place provided to lock up valuables if you can’t leave them at home.
In order to prevent metallic objects from being attracted by the powerful magnet of the MR system, patient will be given hospital gown to change into prior to the examination. Items that need to be removed by patients before entering the MR system room include:
· Purse, wallet, money clip, credit cards, cards with magnetic strips.
· Electronic devices such as beepers, MP3 player or cell phones.
· Hearing aids.
· Metal jewelry, necklaces, rings, earrings, watches.
· Pens, paper clips, keys, coins.
· Hair barrettes, hairpins, spectacle or eyeglasses.
· Any article of clothing that has a metal zipper, buttons, snaps, hooks, underwire, or metal threads.
· Shoes, belt buckles, safety pins.
Before the MRI procedure, patient will be asked to fill out a screening form or checklist, asking about anything that might create a health risk or interfere with imaging including allergy reaction and asthma.
Examples of items or things that may create a health hazard or other problem during an MRI exam include:
· Implantable cardioverter defibrillator (ICD).
· Aneurysm clip.
· Metal implant.
· Implanted drug infusion device.
· Foreign metal objects, especially if in or near the eye.
· Shrapnel or bullet wounds.
· Permanent cosmetics or tattoos.
· Dentures/teeth with magnetic keepers.
· Other implants that involve magnets.
Kindly check with the MRI staff if there is any questions or concerns about any implanted object or health condition that could impact the MRI procedure. This is particularly important if patient have undergone surgery involving the brain, ear, eye, heart, or blood vessels.
· Kindly inform us if you are claustrophobia or cannot handle shallow space.
· If you are pregnant or think that you could be pregnant, please notify physician and the radiographer prior to the MRI procedure.