MIDTERM- PT. 3 Flashcards
_____ WORKS TOGETHER WITH COILS
RADIOFREQUENCY
THESE ARE USED FOR THE PX
COILS
THE ELECTROMAGNETIC COMPONENTS OF THE RF SYSTEM; ATTACHED TO THE RF COILS
RF SYSTEM
ARE MADE WITH VARYING DESIGNS
RF COILS
ACTS AS AN ANTENNA
COILS
WHAT ARE THE 2 TYPES OF COILS:
- SHIM COILS
- RECEIVER COILS
MAKES THE MAGNETIC FIELD HOMOGENOUS
SHIM COILS
DETECTING THE RETURNING RADIO SIGNALS
RECEIVER COIL
ARE THE ANTENNA OF MRI SYSTEM
ACTS AS A TRANSMITTER/ RECEIVER
RF COILS
TYPES OF RF BODY COILS ARE:
- SURFACE COILS
- PAIRED SADDLE COIL
- HELMHORTZ PAIR COIL
- BIRD CAGE COIL
COIL: ARE SIMPLY LOOPS OF WIRE
-CIRCULAR/ RECTANGULAR
-USED FOR SMALL BODY PARTS (E.G. EYES)
-COMMONLY USED IN SPINES, SHOULDERS, TMJ’S
SURFACE COILS
COIL:
-COMMONLY USED FOR IMAGING OF THE KNEE
-PROVIDE BETTER HOMOGENEITY OF THE RF IN THE ARE OF INTEREST AND ARE USED AS VOLUME COILS UNLIKE SURFACE COILS
-ALSO USED OF THE X & Y GRADIENT COILS
PAIRED SADDLE COIL
COIL:
-USED FOR PELVIS AND SPINE & BODY STRUCTURES (HEAVY TO PENETRATE)
- CONSIST OF 2 CIRCULAR COILS PARALLEL TO EACH OTHER
-USED AS GRADIENT COILS IN MRI SCANNERS
HELMHORTZ PAIR COIL
COIL:
-MOST FREQUENTLY USED IN MRI
-COMMONLY USED IN THE HEAD
-ACTS AS A TRANSCEIVER COIL
-PROVIDES THE BEST RF HOMOGENEITY OF ALL THE RF COILS
-HAS THE APPEARANCE OF A BIRDCAGE
- THIS TYPE OF COIL IS ALSO USED OCCASIONALLY FOR IMAGING OF THE EXTREMITIES SUCH AS THE KNEES
BIRD CAGE COIL
POWER SUPPLY OF MRI:
____Kw
____VOLTAGE RIPPLE
2.4
5%
POWER SUPPLY THAT IS COMMONLY USED
1.5 TESLA
-PROVIDES RADIO FREQUENCY SHIELDING
-USES ALUMINUM OR ON CERTAIN CONDITIONS GALVANIZED STEEL TO FORM THE SHIELDED FARADAY CAGE
-SHIELDING FROM OUTSIDE INTERFERENCE
FARADAY CAGE
TO FUNCTION PROPERLY, AN MRI SCANNER NEEDS TO SIT IN A SPECIALIZED ROOM OR CHAMBER SHIELDED AGAINST A RADIO FREQUENCY (RF) INTERFACE. WITHOUT SUCH PROTECTION THE VERY WEAK RF SIGNALS THAT EMANATE FROM THE PATIENT WHEN SCANNED WOULD BE OVERWHELMED
FARADAY CAGE
USED IN MRI TO DESCRIBE RELATIVE CONTRIBUTIONS TO DETECT SIGNAL OF THE TRUE SIGNAL AND RANDOM SUPERIMPOSED SIGNALS
SIGNAL-TO-NOISE RATIO
ALSO KNOWN AS BACKGROUND NOISE
SUPERIMPOSED SIGNALS
FORMULA FOR SNR
MEAN SIGNAL / STANDARD DEVIATION OF BACKGROUND NOISE
IF THE SNR INCREASE: ___ INCREASES (7)
-Bo
-T2
-TR
-NEX
-PIXEL SIZE
-SLICE THICKNESS
-FOV
IF THE SNR INCREASE: ___ DECREASES (4)
-T1
-TE
-MATRIX SIZE
-BANDWIDTH
COMES FROM THE SURROUNDING TISSUES
NOISE
ALL PARAMETERS ARE ____
CONSTANT
RF COIL: SMALLER SENSITIVE VOLUME OF COIL,
THE ____ THE NOISE FROM THE ADJACENT STRUCTURES OF THE SELECTED SLICE PLANE WHICH IT CAN DETECT, AND THE ____ THE SIGNAL-TO-NOISE RATION WILL BE
LOWER
BETER
HAS A HIGHER SIGNAL-TO-NOISE RATIO THAN A BODY COIL
LOCAL COIL / SURFACE COIL
“MUSCLE”
PSOAS
BANDWIDTH= ____Hz
50,000
REFERS TO THE FREQUENCIES ASSOCIATED WITHER WITH RF-EXCITATION (TRANSMITTER BANDWIDTH,tBW) OR SIGNAL RECEPTION (RECEIVER BANDWIDTH, rBW) OR THE HIGHEST OR LOWEST SIGNAL
RF BANDWIDTH
SIGNAL RECEPTION
TRANSMITTER BANDWIDTH,tBW
THE HIGHEST OR LOWEST SIGNAL
RECEIVER BANDWIDTH, rBW
IS THE RANGE OF FREQUENCIES ACCEPTED BY THE RECEIVER TO SAMPLE THE MR SIGNAL.
RECEIVER (OR ACQUISITION) BANDWIDTH
rBW HAS A _____ RELATIONSHIP TO THE SIGNAL TO NOISE RATIO (SNR)
DIRECT RELATIONSHIP
SNR= _____
1/SQUAREFOOT (rBW)
HIGHER THE BANDWIDTHE= _____ IMAGE QUALITY
HIGHER
HIGHER THE MAGNETIC FIELD STRENGTH= _____ IMAGE QUALITY
HIGHER
BANDWIDTH FORMULA IS:
^W= FOVf / Nf
REFERS TO THE RF EXCITATION PULSE REQUIRED FOR SLICE SELECTION IN A PULSE SEQUENCE.
TRANSMIT BANDWIDTH
THE SLICE THICKNESS IS _____ TO THE BANDWIDTH OF THE RF PULSE, AND ____ TO THE APPLIED GRADIENT STRENGTH
PROPORTIONAL
INVERSELY PROPORTIONAL
LOW PULSE BANDWIDTH= ___ SLICE THICKNESS
REDUCED
SLICE THICKNESS IN MRI IS DETERMINED:
- THE BANDWIDTH OF THE RF (LONGER BW, LOWER SLICE THICKNESS)
- STEEPNESS OF THE SLOPE OF THE GRADIENT COIL (STRENGTH)
MRI USES TECHNIQUES CALLED ______ TO ACQUIRE IMAGES WITH DIFFERENT TISSUE CONTRAST MECHANISMS.
PULSE SEQUENCE
ARE SET OF PARAMETERS THAT ENABLE US TO IDENTIFY THE ANATOMY
PULSE SEQUENCES
ARE A SET OF SPECIFIC INSTRUCTIONS PROGRAMMED INTO THE COMPUTER WITH AN EXPECTATION AS TO HOW THE IMAGES SHOULD APPEAR
PULSE SEQUENCES
DWI; ALSO KNOWN AS __
DIFFUSION WEIGHTED IMAGING
____ MOVEMENT OF _____ DUE TO RANDOM MOTION
DIFFUSION
MOLECULES
USED FOR CVA (STROKE) & CNS (CENTRAL NERVOUS SYSTEM)
DIFFUSION WEIGHTED IMAGING
THE COMBINATION OF ACTUAL DIFFUSION VALUES AND ___T2 SIGNAL
T2
DIFFUSION WEIGHTED IMAGING
DWI: IF AN INCIDENT OCCURS LESS THAN ____ HOURS PRIOR TO THE SCAN, SWELLING DUE TO EDEMA OCCURS
72
MRI: COLOR/ IMAGE
BLEEDING APPEARS _____
RUGGAE IS ____ IN THE IMAGE
BRIGHT
VISIBLE
IS MOST APPLICABLE WHEN THE TISSUE OF INTEREST IS DOMINATED BY ISOTROPIC WATER MOVEMENT (E.G. GREY MATTER IN THE CEREBRAL CORTEX AND MAJOR BRAIN NUCLEI, OR IN THE BODY
DWI
DWI REMAINS SENSITIVE TO ____ AND _____
T1 RELAXATION
T2 RELAXATION
TO ENTANGLE DIFFUSION AND RELATION EFFECTS ON THE IMAGE CONTRAST, ONE MAY OBTAIN ______ IMAGES OF THE DIFFUSION COEFFICIENT, OR MORE EXACTLY THE APPARENT DIFFUSION COEFFICIENT (ADC)
QUANTITATIVE
WAS INTRODUCED TO TAKE INTO ACCOUNT THE FACT THAT THE DIFFUSION PROCESS IS COMPLEX IN BIOLOGICAL TISSUES AND REFLECTS SEVERAL DIFFERENT MECHANISMS
ADC (APPARENT DIFFUSION COEFFICIENT) CONCEPT
IS THE INVERTED GREY SCALE DWI IMAGES
ADC (APPARENT DIFFUSION COEFFICIENT)
ARE IMAGES REPRESENTING THE ACTUAL DIFFUSION VALUES OF THE TISSUE WITHOUT T2 EFFECTS
ADC MAPS
ADC: THEY ARE THEREFORE MUCH MIRE USEFUL, AND OBJECTIVE MEASURES OF _____ CAN BE OBTAINED, HOWEVER THE ARE ______
DIFFUSION VALUES
MUCH LESS PRETTY TO LOOK AT
MOST WIDELY USED. STARTS WITH 90 DEGREES PULSE AND ENDS WITH 180 DEGREES PULSE
SPIN ECHO
A GRADIENT TO REFOCUS THE SPINS.
-ARE MORE SUSCEPTIBLE TO BLOOD FLOW. THEY UTILIZE FLIP ANGLE LESSER THAT _____ DEGREES IN ADDITION TO TR AND TE
GRADIENT ECHO
90 DEGREES
AKA REVERSE POLARITY OF GRADIENT
GRADIENT ECHO SEQUENCES (GRE)
GRE: FLIP ANGLES IS
LESS THAN 90 DEGREES
