LOCATION OF COILS FROM INSIDE OUT
-RF>GRADIENT>SHIM>MAIN MAGNET
GRADIENT AMPLITUDE
-THE STRENGTH OF THE GRADIENT.
GRADIENT RISE TIME
-THE TIME IT TAKES FOR THE GRADIENT TO REACH ITS FULL AMPLITUDE.
-mT/m or G/Cm
-The shorter the rise time, the faster the
gradients and therefore echo spacing. Gradients with a shorter echo spacing will have a better resolution and more available slices p
GRADIENT SLEW RATE
-THE SPEED RATE OF ASCENT OR DESCENT OF A GRADIENT FROM ZERO TO ITS MAXIMUM AMPLITUDE, EITHER POSITIVE OR NEGATIVE.
-mT/m/ms or T/m/s
-THE STRENGTH OF A GRADIENT OVER A SPECIFIC DISTANCE.
-PEAK GRADIENT STRENGTH/RISE TIME.
DUTY CYCLE
-THE TIME THE GRADIENTS ARE ON DURING A TR PERIOD.
-THE GRADIENT WORKING TIME.
NOISE IN MR ROOM
-THE RAPID, SUCCESSIVE SWITCHING OF THE GRADIENT COILS.
SLICES/PLANES
-SAGITTAL: X
-CORONAL: Y
-AXIAL: Z
-APPLYING 2 GRADIENTS SIMULTANEOUSLY DURING SLICE SELECTION WILL PRODUCE AN OBLIQUE SLICE.
RF COILS
-TWO MAJOR PARTS OF THE RF SYSTEM IN THE MRI HARDWARE.
-CLOSEST TO THE PATIENT, THEREFORE UTILIZATION OF MULTIPLE, POWERFUL RF PULSES (FAST SPIN ECHO SEQUENCES) CAN LEAD TO INCREASED SAR INDUCTION IN A PATIENT.
-THE 180 DEGREE RF PULSE IS 4X THE POWER OF
MEASUREMENT OF RF ABSORPTION
-W/KG
-LOW ENERGY, NON-IONIZING RADIATION.
PRIMARY BIOLOGICAL EFFECT OF RF FIELDS
-TISSUE HEATING
ENERGY TRANSFER BETWEEN TRANSMITTER AND RECEIVER
-THE TWO MUST BE AT THE SAME FREQUENCY.
UTILIZATION OF SURFACE COILS (LINEAR COILS)
-YIELDS A MORE LOCALIZED, SMALLER FOV CAPABILITY, WITH INCREASED SNR, THUS PROVIDING OPPORTUNITY FOR IMPROVED IMAGE QUALITY ON MOST SYSTEMS.
SNR PENETRATION DEPTH
-HALF COIL DIAMETER.
AVOID RF BURNS IN PATIENT
-CABLES FROM LOCAL RF COILS AND GATING LEADS SHOULD BE BRAIDED AND POSITIONED STRAIGHT IN THE BORE, NEVER IN DIRECT CONTACT WITH THE PATIENTS SKIN.
-THE CABLES SHOULD NEVER BE COILED OR LOOPED, AS THIS CAN LEAD TO RF BURNS IN THE PATIENT.
CP COIL
-CIRCULARLY POLARIZED TRANSMISSION OR RECEIVER COIL WITH TWO ORTHOGONAL TRANSMISSION AND/OR RECEIVER CHANNELS, ALSO KNOWN AS A QUADRATURE COIL. THIS YIELDS BETTER SIGNAL-TO-NOISE THAN A LINEAR COIL.
SNR IS INCREASED BY 40%
-WHEN GOING FROM A LINEAR COIL TO A QUADRATURE COIL.
PHASED ARRAY COIL
-COMPRISED OF MULTIPLE COIL ELEMENTS COMBINED WITH MULTIPLE RECEIVER CHANNELS.
A RECENT DEVELOPMENT IN MRI
-SOPHISTICATED MULTI-ELEMENT PHASED ARRAY COILS WHICH ARE CAPABLE OF ACQUIRING MULTIPLE CHANNELS OF DATA IN PARALLEL. THIS 'PARALLEL IMAGING' TECHNIQUE USES UNIQUE ACQUISITION SCHEMES THAT ALLOW FOR ACCELERATED IMAGING.
COILS USED BY PERMANENT MAGNETS WITH A VERTICAL MAGNETIC FIELD.
-USE SURFACE COILS THAT ARE SOLENOIDS BECAUSE THE SECONDARY MAGNETIC FIELD (B1) CREATED BY THE RF COIL MUST BE PERPENDICULAR TO THE ORIENTATION OF B0.
OPERATOR CONSOLE IN THE SCAN CONTROL ROOM
-PATIENT IMAGE DISPLAY WITH SEQUENCE PARAMETER VISUALIZATION.
-THE CPU USED TO PLOT AND ADJUST SLICES IN AN MR SEQUENCE.
MR EQUIPMENT ROOM
-THE ARRAY PROCESSOR, RESPONSIBLE FOR RECONSTRUCTING THE COLLECTED MR IMAGES/DATA USING FOURIER TRANSFORM.
-RF POWER AMPLIFIER
RF SHIELDING
-CAN BE ACHIEVED BY LINING THE SCANNER ROOM WALLS WITH COPPER.
MAGNETIC FIELD INHOMOGENEITY
-EXPRESSED IN PARTS PER MILLION (PPM)
MAGNETIC FIELD SHIELDING
-CAN BE ACCOMPLISHED VIA ACTIVE OR PASSIVE SHIELDING METHODS.
-PASSIVE SHIELDING: LINING THE MR ROOM WITH STEEL/FERROMAGNETIC PLATING, THUS REDUCING THE SCOPE AND DISTANCE OF THE FRINGE FIELD.
-ACTIVE SHIELDING: REQUIRES THE IMPLEMENTATION OF SUPERCONDUCT
FIELD STRENGTH AT MAGNET ISOCENTER
-MEASURED IN UNITS OF TESLA, THE SI DERIVED UNIT OF MAGNETIC FIELD MEASUREMENT.
HIGH FIELD SCANNER STRENGTH
-GREATER THAN OR EQUAL TO 1.5 TESLA.
DOUBLING THE MAGNETIC FIELD STRENGTH
-WILL DOUBLE THE SNR
FRINGE FIELD
-THE MAGNETIC FIELD SURROUNDING THE PERIPHERY OF THE MR SCANNER
-UNIT : GAUSS
-INTENSITY LIMIT FOR A STATIC MAGNETIC FIELD IN CLINICAL USE
-4.0 TESLA FOR ALL PATIENTS
-8.0 TESLA FOR ALL PATIENTS OVER 1 MONTH OF AGE
SUPERCONDUCTING MAGNET
-MOST COMMONLY USED SYSTEM IN MR IMAGING TODAY
-THE MAGNETIC FIELD STRENGTH IS INCREASED BY INCREASING THE TURNS OF THE WIRE, CURRENT IN THE WIRES, OR BY REDUCING THE SPACING BETWEEN THE WIRES
ORIENTATION OF THE MAIN MAGNETIC FIELD IN A HIGH FIELD, SUPERCONDUCTING, SHORT BORE MAGNET
-HORIZONTAL
LIQUID CRYOGENS
-COOLED IN A SUPERCONDUCTING MAGNET AT A TEMPERATURE OF 4 DEGREES KELVIN
-THE LIQUID CRYOGENS MOST OFTEN USED TO MAINTAIN FIELD STRENGTH IN A SUPER CONDUCTING MR SYSTEM ARE HELIUM
THE ADDITIONAL MAGNETIC FIELDS PRODUCED BY SHIMMING..
-ADD TO THE OVERALL MAGNETIC FIELD OF THE SUPERCONDUCTING MAGNET IN SUCH A WAY THAT THE TOTAL B0 FIELD BECOMES MORE HOMOGENEOUS.
FACTORS THAT MAKE PATIENTS LESS VULNERABLE TO THE RF HEATING EFFECTS
-CONSISTENT ROOM TEMPERATURE OF 65-75 DEGREES F, HUMIDITY OF 50-70%, AND SUFFICIENT AIR FLOW IN THE MR SCAN ROOM.
DURING THE QUENCH OF THE MR SYSTEM..
-PATINTS AND EMPLOYEES SHOULD BE EVACUATED FROM THE SCAN ROOM TO AVOID ASPHYXIATION, FROSTBITE, AND/OR DAMAGE TO TYMPANIC MEMBRANES.
MAGNETIC FIELDS ASSOCIATED WITH MR IMAGING
-STATIC MAGNETIC FIELDS
-OSCILLATING MAGNETIC FIELDS (RF): PRIMARY BIOLOGICAL EFFECT IS TISSUE HEATING/DEPOSITION
-TIME VARYING MAGNETIC FIELDS (GRADIENT) : have been documented to cause muscle contractions, cardiac arrhythmias, mild cutaneous sensations
THE BODY COIL
-INTEGRATED PART OF THE MAGNET DESIGN.
-ACTS AS ITS OWN TRANSCEIVER COIL
-LARGE FOV CAPABILITIES
-LACKING THE HIGH SNR OF LOCALIZED COILS
MRI SYSTEM COMPONENT THAT PRODUCES THE MAGNETIZATION OF PROTON SPINS (ALIGNMENT)
-MAIN MAGNET
MRI SYSTEM COMPONENT THAT PROVIDES THE ABILITY TO PERFORM SPATIAL ENCODING
-THE GRADIENT SYSTEM