MRI - PPT Flashcards
Who discovered the properties of MRI?
1940s
Bloch & Purcell
Who produced 1st MRI image of a human being?
1977
Damadian
Who awarded Nobel Prize in Physiology for discoveries in MRI?
2003
Lauterbur & Mansfield
Who produced 1st MRI image of an object?
1973
Lauterbur
When was 1st MRI equipment became available for
installation?
1980s
MRI depends of
The properties of the nucleus of an atom
Hydrogen is used since
It is the most abundant element in the body
Hydrogen with a single proton in its nucleus is
The strongest nuclear magnet, therefore creating the strongest MRI signal
RF (radiofrequency) coils are
“antenna” of the MRI system that broadcasts the RF signal to the patient and/or receives the return signal
(Received signals & send feedback)
Gradient coils are used to
- Produce deliberatevariations in the main magnetic field (Bo).
- There are usually three sets of gradient coils, one for each direction (x, y, z axes)
Resistive magnets
- Simple, large electromagnets
- Limited field strength (no more than 0.6 T)
Superconductive (cryogenic) magnets
- Electromagnets that use liquid helium for cooling
- Permits higher magnet strengths than resistive magnets
Permanent magnets
- Does not require electricity or cooling
- Heavy, massive
- Smaller fringe field
Clinical MRI uses
Superconductive (cryogenic) magnets
Magnetic field strength is measured in
tesla (T) or gauss (G)
1 T = 10,000 G
Earth’s natural magnetic field is
0.5 G
Low-field magnets range is
0.2 T – 1.0T
High-field magnets range is
1.5T and higher
FDA has approved up to ………………….. magnets for clinical imaging of babies and up to 8T for clinical imaging of adults and children
4T
Outside the U.S., up to ……………. can be used
15T
China 27T
Patient Table is
Hydraulically or mechanically driven
Magnetically safe and contain no metal parts
Patient Table Must allow for
attachment of coils and immobilization devices
Patient Table Weight limits range from
300 – 660 lbs
T1‐weighted image is Used to evaluate
- Anatomy (structure)
• Characterized by bright fat & dark water
T2‐weighted image is Used to evaluate
- Pathology
• Characterized by bright water & dark fat
2 Types of Contrast Media
- Gadolinium compounds
2. Iron oxide mixtures
Gadolinium compounds also called
Paramagnetic substance
T1 agent
Gadolinium compounds is
- Most commonly used
- Lower toxicity and fewer side effects than iodinated IV contrast
- Used in the evaluation of the CNS and for tumor detection
Iron oxide mixtures also called
Superparamagnetic substance
T2 agent
Iron oxide mixtures is used to
Detect and diagnose liver lesions
MRI Safety: 4 Basic Areas of Concern
- Thermal injuries
- Acoustic noise
- Projectiles
- Nephrogenic Systemic Fibrosis
Thermal Injuries
Burns can result when:
• Cables from coils are in contact with the
patient’s skin
• Metals, wires, medication skin patches with
foil, and ferromagnetic inks from tattoos are
present in the scanner
Acoustic Noise
- MRI can produce noise up to 130 dB
- Ear plugs can reduce the noise by 10-30 dB
Projectiles
The missile effect
the force with which projectiles are pulled towards a magnetic field is proportional to:
• the strength of the magnet
• the distance from the magnet
• the mass of the object
• the material that the object is made of
Ferromagnetic metal object can reach a
terminal velocity of ……………….when pulled into a
………………………. magnet
40 mph
1.5T
MRI offers
superior imaging of soft-tissue structures
MRI does NOT use
ionizing radiation
MRI Contrast material is better tolerated compared to
Radiography and CT
Proper patient screening is
utmost importance
the magnet is ALWAYS
ON
