Part III Flashcards by Queenie Francisco

3 Parts of MRI Suites

Gantry
Control Console
Computer Network/System

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Operating console is composed of :

-imaging acquisition
-image processing

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Operating console [added]

Start-up
Image acquisition
Prescan Calibrators
Image Scanning
Image Processing/Display/Manipulation

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MRI computers is composed of:

Multitasking operating system
Control Computer
Acquisition Control System
Image Reconstruction
Processing Computer

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MRI system electronics

Frequency Synthesizer
RF Amplifier
Gradient Coil Power Supply
Sequencing System
Digital Signal Acquisition System
Digital Image Processing System

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Ancillary Equipment

Power Injectors
Infusion Pumps
Pads and Pillows
Cryogenic Filling Equipment

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CM used in MRI

Gd DPTA -contrast (paramagnetic)
Diethylenetriamine Penta-acetic acid

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[ancillary equip.] Facilitate introduction of CM, Nonmagnetic

Power injectors

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[ancillary equip.] Used for introduction of saline/fluid, automatic set rate/amount

Infusion Pumps

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[ancillary equip.] used for pt comfort, headphones, pillows, blankets

Pads and pillows

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[ancillary equip.] cooling system used to ensure magnetic property

Cryogenic filling equipment

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[operating console-start- up] energizes the system

Power On/Off

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[operating console-start- up] should be used if the pt is in danger (in case of adverse fx, claustrophobic)

Emergency Off

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[operating console-start- up] installed with TV system for communication

Intercom - speaker and Tv monitor to ensure pt is not moving

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[operating console-start- up] selection of pulse sequence, pulse delay timings, other parameters

Scan Control Module

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[operating console-start- up] SLICES (no of gaps); scout images

Image-Guided Graphical Prescription

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[operating console-start- up] review the image (display windowing), parametric imaging processing

Image Display System

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[operating console] involves stimulation of H and receiving of signal

Image Acquisition

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[operating console-image acquisition] often automatic, accommodate the body part/FOV

Tuning Control

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[operating console-image acquisition] RT can modify, 90-90deg..90-180deg/..

Pulse Sequence Selection

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[operating console-image acquisition] selection of repetion time [TR] and echo time [TE]

Timing selection

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[operating console-image acquisition] optimize image contrast and SNR (reduce artifacts)
X and y axis to get FID

RF pulse flip angle selection

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[operating console-image acquisition] Matrix Size

256x256; larger matrix size = better image, longer imaging time

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[operating console-image acquisition] FOV

reduced FOV = better spatial resolution (requires more signal acquisition)

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[operating console-image acquisition] amount of FID needed

Number of Signal Acquisitions (NSA) Number of Excitations (NEX) Number of Averages (NA)

[operating console-image acquisition] Slice Thickness

Reduced slice thickness improves spatial resolution Thicker slice = < detail

[operating console-image acquisition] affects the SNR and chemical shift artifact Range of frequency/signals

Receiver Bandwidth (BW)

[operating console-image acquisition] pre saturation pulses to eliminate signals from certain samples (fats and water)

Magnetization Preparation Schemes

[operating console-image acquisition] 2D and 3D images, usually for advanced imaging system - possible in MRI arteriogram

Reconstruction Strategies

[operating console-image acquisition] number. Of slices, gaps b/w slices, orientations - sagittal , coronal, axial

Slice Positioning and Orientation

[operating console] role of computer system

Prescan Calibrators

[operating console-prescan calibrators] accommodate the patient’s size - adjust RF coil to match patient habitus

Transmit/Receive Coil Tuning

[operating console-prescan calibrators] establishes the slice position and resonance frequency of fats and water photons (automatic)

Center Frequency Tuning

[operating console-prescan calibrators] sets the duration that radio frequency is on and the amount of power to generate the radio frequency (if short-blurry)

Pulse Amplitude Calibration

[operating console-prescan calibrators] ensures that signal is not too low (noisy image) or too high (image distortion)

Receiver Gain Control

[operating console-prescan calibrators] makes the MF homogenous

Autoshimming

Importance of Magnetic Shimming

-maintain homogenousfield -minimize fringe field-stray field that can interfere with electronic devices

Magnet ensure safety within [..]

Protect the magnet from outside things that can affect the homogenous MF

Shimming

Protect public and environment

Fringe field

Two types of magnetic shielding

Passive - walls of MRI gantry (s), MRI suite (f) Active - magnet in gantry

[operating console-Imaging Scanning] Patient Positioning

Uses: surface coils/phased array coils Laser positioning system

Surface coil purpose:

Added on POI, receive only Shorten distance -enhance contrast

[operating console-Imaging Scanning] Patient Monitoring

Uses TV and intercom

[operating console-Imaging Scanning]inspect date for quality and positioning of data

Image Quality Inspection

[operating console] Imaging Scanning

Pt Positioning Pt Monitoring Image Quality Inspection

[operating console-Image Processing/Display/Manipulation] set the contrast and shades of gray. Wider range in MRI

Window Width Level

[operating console-Imaging processing/ display/ manipulation] pointer

Cursor On/Off

[operating console-Imaging Processing] calculation of area of measure and average and standard deviation of pixel values

Region of Interest (ROI)

[operating console-Imaging processing] magnify the image. Some may produce fixed magnification. Reconstructive [..] is not possible in MRI

Zoom

[operating console-Image Processing] selects pixel values within a given range for special attention

Highlight

[operating console-Imaging Scanning] simultaneous display of multiple images or portions of an image on one wide screen

Display Matrix Format

[operating console-image processing/display manipulation] plotting of pixel values along the identified axis in a line graph

Profile/ Histogram

[operating console-image processing/display manipulation] selects pixel values within a given range for special attention

Highlight

[operating console-image processing/display manipulation] simultaneous display of multiple images or portions of an image on one wide screen

Display Matrix Format

types of computer system

-control computer -acquisition control computers -image processing computer

control computer provides an interface with the operator for:

control and display functions data archiving and network communications

[computer system] computer that control the gantry, receive instructions from control computers -converts instructions to specific pulses, timing delays and amplifier gain

acquisition control computers

location of acquisition control computer

equipment room

[computer system] for image reconstruction

image processing computer

[computer system] should have high capacity to store data for manipulation; fast to handle the high rate of data acquisition; can accommodate enormous no. of calculations

image processing computer

image processing time: [..]

1 sec - to entertain more frames

additional subsystems to assist in the functioning of computers

MRI System Electronics

[MRI System Electronics] produce RF pulse, generates the fundamental resonance frequency used to excite the magnetic nuclear spins

Frequency Synthesizer

[MRI System Electronics] produces low-level sinusoidal wave signal from a fixed time base oscillator [high intensity = low RF frequencu

Frequency Synthesizer

types of RF Synthesizer

direct digital synthesizer (DDS) dividing time

[RF Synthesizer] creates arbitrary waveforms using frequency and pulse-tunable output signals

direct digital synthesizer (DDS)

[RF Synthesizer] fixed frequency precision clock source referenced to DDS

MRI System Clock

[MRI System Electronics] the DDS scales the frequency clock using a programmable binary tuning word that is typically [...] long

Dividing Time 24-48 bits

[MRI System Electronics] increase signal out put from the frequency synthesizer; should be immune to load changes

Radiofrequency Amplifier

RF energy is [..] to RF frequncy

directly proportional

T/F MRI amplifiers must have an increasing power ratings when used with higher field magnets

RF AMPLIFIER : 1.5 T maximum outputs

18 kW -25 kW

RF AMPLIFIER : 3 T maximum outputs

30 kW - 40 kW

[MRI System Electronics] operates in a current-driven mode; installed with cooling system to ensure stability of temperature

Gradient Coil Power Supply

Gradient Coil Power Supply : peak output current can range up to [..] and peak voltages up to [..]

1 kA 500 V

high powered GPS for the whole body categories

-Linear GPS - Switching GPS System and Resonant System -Pre-emphasis circuitry module

[GPS] deliver power directly to the coils

linear GPS

[GPS] uses energy storage strategies to reduce power dissipation [backup power]

Switching GPS System and Resonant System

[GPS] modifies the gradient pulse waveform to minimize EDDY CURRENT

Pre-emphasis circuitry module

result of current opposing the cause that produced them, produced in any conducting material subjected to changing MFs

EDDY CURRENT

[MRI System Electronics] inorder to accept current, magnetic coils must have resistance

Magnetic Power Supply

[MPS]

persistent switch magnetic power supply stabilized Bo Field

[MPS} superconducting heat switch may be used - help in giving current

Persistent Switch

programmed to slowly inject current until the specific MF had been attained

Magnet power supply

[MPS] the current to the switch is turned off

Stabilized Bo field

[MRI System Electronics] traffic cop of MRI Scanner that takes instruction from the computer and setting up proper parameters; controls the RF transmitter and gradient amplifiers to cause an MR image

Sequence System (Pulse Programmer)

[MRI System Electronics] sets parameters such as bandwidth for the subsystem receiver

Sequence System (Pulse Programmer)

[MRI System Electronics] signals (from H atoms) -receiver - preamplifiers

Digital Signal Acquisition System

increase the amplitude of MRI signal from tens to hundreds of mV to several Volts

Pre Amplifiers

[MRI System Electronics] Digital Image Processing System includes:

GENERAL PURPOSE MICROPROCESSOR FIELD PROGRAMMABLE GATE ARRAYS (FDGAS) Digital Signal Controllers Stream Processor

Part III Flashcards

(91 cards)