MIDTERM-PT. 1 Flashcards
WHAT ARE THE 3 PRINCIPAL TYPES OF MAGNETS:
- NATURAL
- PERMANENT
- ELECTROMAGNETS
MAGNET: EARTH
NATURAL
MAGNET: ARTIFICIALLY PRODUCED
PERMANENT
MAGNET: CONSIST OF WIRES
ELECTROMAGNETS
WHAT ARE THE INTERACTION WITH MATTER: (3)
- DIAMAGNETIC
- FERROMAGNETIC
- PARAMAGNETIC
MATERIALS THAT ARE UNAFFECTED WHEN BROUGHT INTO A MAGNETIC FIELD
DIAMAGENETIC
STRONGLY ATTRACTED BY A MAGNET; ALNICO
FERROMAGNETIC
AN ALLOY OF ALUMINUM, NICKEL AND COBALT (MOST USEFUL MAGNETS PRODUCED BY FERRIMAGNETIC MATERIAL)
ALNICO
MATERIALS THAT ARE BETWEEN THE CLASSIFICATION OF DIAMAGNETIC AND FERROMAGNETIC
PARAMAGENTIC
SLIGHTLY ATTRACTED TO A MAGNET AND LOOSELY INFLUENCED BY AN EXTERNAL MAGNETIC FIELD
PARAMAGNETIC
CONTRAST AGENTS USED IN MRI ARE _____
PARAMAGNETIC
THE SI UNIT OF MAGNETIC FIELD STRENGTH
TESLA
OLDER UNIT FOR MAGNETIC FIELD STRENGTH
GAUSS
1 TESLA= ______ GAUSS
10,000
THE EARTH’S MAGNETIC FIELD AT THE EQUATOR IS ____ uT
50
the EARTH’S MAGNETIC FIELD AT THE POLES IS ____ uT
100
LOWER TESLA = ___ QUALITY
LOWER
TYPICALLY COILS OF WIRE THROUGH WHICH A MAGNETIC FIELD IS INDUCED
RESISTIVE MAGNETS
ADVANTAGES: (MAGNET)
1. THEY ARE LIGHTER IN WEIGHT THAN PERMANENT MAGNETS
2. CAPITAL COSTS ARE LOW
3. DOES NOT REQUIRE CRYOGENS
RESISTIVE MAGNETS
A LIQUID HELIUM INSULATOR; MAINTAINS NORMAL TEMPERATURE
CRYOGENS
DISADVANTAGES: (MAGNET)
1. HIGH COSTS
2. LARGE QUANTITIES OF POWER REQUIRED TO MAINTAIN THE MAGNETIC
THE MAXIMUM FIELD STRENGTH IN A SYSTEM OF THIS TYPE IS LESS THAN 0.3T DUE TO ITS EXCESSIVE POWER REQUIREMENTS
3. SCAN TIMES ARE LONGER
4. RESISTIVE SYSTEM IS SAFE; CAN BE EASILY TURNED OFF INSTANTANEOUSLY
3. CREATE SIGNIFICANT STRAY FRINGE MAGNETIC FIELDS
RESISTIVE MAGNETS
MAGNET: FIELD STRENGTH IS LESS THAN 0.3T
RESISTIVE MAGNETS
THE MOST COMMONLY USED MAGNET
PERMANENT MAGNENT
_____ IS USED TO MAKE PERMANENT MAGNETS
ALNICO ALLOY
ADVANTAGES: (MAGNET)
1. THEY HAVE AN OPEN DESIGN; (CHILDREN, OBESE, AND CLAUSTROPHOBIC PATIENTS ARE SCANNED WITH EASE)
3. INTERVENTIONAL AND DYNAMIC PROCEDURES ARE POSSIBLE
4. THEY REQUIRE NO POWER SUPPLY
5. LOW IN OPERATING COSTS
PERMANENT MAGNETS
DISADVANTAGES: (MAGNET)
1. THEY ARE EXCESSIVELY HEAVY
2. ONLY LOW FIXED FIELD STRENGTHS (0.2- 0.3 T) CAN BE ACHIEVED
3. LONGER SCAN TIMES ARE NEEDED, DUE TO LOWER FIELD STRENGTHS
4. COST OF THE MAGNET
5. HEAVY SUPPORTING STRUCTURES
PERMANENT MAGNETS
MAGNET: FIELD STRENGTH IS 0.2- 0.3 T
PERMANENT MAGNET
MAGNET: CONSIST OF COIL MADE OF NIOBIUM-TITANIUM (Nb-Ti) ALLOY
SUPERCONDUCTING MAGNETS
ADVANTAGES: (MAGNET)
1. IT GIVES MAGNETIC FIELD STRENGTH (0.5-3T) WITH LOW POWER REQUIREMENTS
2. LOW OPERATING COSTS
3. RESISTANCE IS VIRTUALLY ELIMINATED, THERE IS NO LONGER A MECHANISM TO DISSIPATE CURRENT
4. NO ADDITIONAL POWER INPUT IS REQUIRED TO MAINTAIN THE HIGH MAGNETIC FIELD STRENGTH
5. ADVANCED APPLICATIONS ARE POSSIBLE AND OPTIMUM IMAGE QUALITY IS OBTAINED
SUPERCONDUCTING MAGNETS
MAGNET: FIELD STRENGTH IS 0.5- 3T
SUPERCONDUCTING MAGNETS
____ HAS A SPECIAL COOLING AGENT CALLED ____ ARE USE TO PRODUCE LOW TEMPERATURE (4K)
SUPERCONDUCTOR MAGNETS
LIQUID CRYOGENS
THE ELECTROMAGNETIC COILS ARE PLACED IN AN INSULATED CHAMBER CALLED ____ (CONTAINS HELIUM)
DEWAR/ CRYOSTAT
THE PROCESS OF BRINGING THE SUPERCONDUCTING MAGNETS TO THE NECESSARY TEMPERATURE IS CALLED ____
RAMPING
REFERS TO A MAGNET’S SUDDEN LOSS OF SUPERCONDUCTIVITY WITH SUBSEQUENT BREAKDOWN OF THE MAGNETIC FIELD; SUDDEN LOSS OF ABSOLUTE O TEMPERATURE
QUENCHING
DEWAR: 2 TYPES OF CHAMBER
- OUTER CHAMBER
- INNER CHAMBER
CONTAINS LIQUID NITROGEN
OUTER CHAMBER
CONTAINS LIQUID HELIUM
INNER CHAMBER
THIS RESULTS IN HELIUM ESCAPING FROM THE CRYOGEN BATH EXTREMELY RAPIDLY
QUENCHING
63%; MAGNETIZATION
T1
ANATOMY & SPIN (INTERACTION)
T2
ARE BASED ON THE FACT THAT NUCLEI OF CERTAIN ELEMENTS HAVE A MAGNETIC MOMENT
MRI
THE _____ IN MRI IS DUE TO THE ANGULAR MOMENT
PRECESSION
ROTATION OF AN OBJECT AROUND THE DIRECTION OF A FORCE ACTING ON THAT OBJECT
PRECESSION
USES THE SIGNAL FROM THE NUCLEI OF HYDROGEN ATOMS FOR IMAGE GENERATION
MRI
PERTAINS TO ROTATION (CLOCKWISE/COUNTER CLOCKWISE)
ANGULAR MOMENT
PERTAINS TO THE ALIGNMENT; PARALLEL/ ANTI-PARALLEL
MAGNETIC MOMENT
NORMALLY PROTONS ARE ALIGNED IN RANDOM FASHION ALIGNMENT: (2)
- PARALLEL
- ANTI-PARALLEL
TYPES OF SPIN: (ANGULAR MOMENT)
- CLOCKWISE
- COUNTERCLOCKWISE