Final Flashcards
The most abundant atom in the body is
Hydrogen
Protons
Positive
Neutrons
No Charge
Electrons
Negative
The principles of MRI rely on
The ‘Spinning Motion’ of specific nuclei present in biological tissues
The laws of electromagnetic induction refer to three individual forces
Motion
Charge
Magnetism
At 1.0T the precessional frequency of hydrogen is
42.57 MHz
The ___ is the time from the application of the pulse to peak of the signal induced in the coil
TE - Echo Time
What is the purpose of image weighting in MRI
Highlight Specific Tissues
Which type of weighting is characterized by bright signals for tissues with short T1 relaxation times
T1 Weighting
What parameter is primary adjusted to control T1 weighting
TR - Repetition Time
T2 weighted images are commonly used to visualize
Edema and Pathology
What factor is crucial for achieving optimal contrast in MRI
Pulse Sequence Parameters
Increasing the TE Echo Time in an MRI sequence primarily affects
T2 Weighting
What is T1 Recovery Time in MRI
Time taken for Longitudinal Magnetization to Reach 63%
Increasing the TR Repetition Time in an MRI sequence primarily affects
T1 Recovery Time
What is T2 Decay Time in MRI
Time taken for Transverse Magnetization to Decrease to 37%
What is the primary purpose of a 180 degree pulse in a Spin Echo Sequence
Refocus Magnetization
In a typical Spin Echo Sequence, the Echo is formed by
180 Degree Pulse
The time between the initial 90 degree pulse and the center of the echo is known as
TE - Echo Time
What parameter is adjusted to control the T2 weighting in a Spin Echo sequence
TE - Echo Time
The formation of multiple echoes in a Spin Echo sequence is known as
Fast Spin Echo
Fat remains bright on T2 weighted images due to the multiple RF pulses which reduce the effects of spin spin interactions in fat and known as
J Coupling
Pulse sequences enable us to control the way in which the system applies pulses and gradients. In this way, image ___ and ___ are determined.
Weighting and Quality
Another modification to Single Shot Fast Spin Echo is a reverse flip angle excitation pulse which is applied at the end of the Echo Train
Drive
____ is an extremely important sequence in musculoskeletal imaging
STIR
___ is used in brain and spine imaging to see Periventricular nd Cord Lesions more clearly
FLAIR
What is the primary advantage of Gradient Echo Sequences over Spin Echo Sequences
Shorter Scan TImes
The Flip Angle in a Gradient Echo sequence is typically called a
Variable
Gradients can be used to dephase and rephase the residual magnetization.___ is the opposite of rewinding
Gradient Spoiling
This Gradient Echo was initially developed for imaging of the Heart and Great Vessels but is now used for Spinal Imaging
Balanced
In Gradient Echo sequences what is the role of the dephasing gradient.
Accelerate Signal Decay
What is the primary limitation of Gradient Echo sequences in terms of susceptibility artifacts
The are highly susceptible
There are three types of motion present within an atom
Electrons Spinning
Electrons Orbiting
Nucleus itself Spinning
The ___ of hydrogen produces a significant vector that is used in clinical MRI
NMV - Net Magnetic Vector
At 1.5T the precessional frequency of hydrogen is
63.86 MHz
The Hydrogen Atom is utilized in MRI because
Abundant in the human body
The ___ is the time from the application of one RF pulse to the application of the next pulse for each slice and is measured in milliseconds
TR - Repetition Time
The decay of Transverse Magnetization
T2 Decay
The Recovery of 63% of Longitudinal Magnetization in the tissue
T1 Relaxation Time
The ___ is produced when coherent (in phase) magnetization cuts across the coil
MRI Signal / Echo
The ___ is the time from the application of the pulse to peak of the signal induced in the coil and is also measured in milliseconds (ms)
TE - Echo Time
The influence of Bo produces an additional spin or wobble of the magnetic moments of hydrogen around Bo. This Secondary Spin is called
Precession
The Larmor Frequency of a ___ is proportional to the magnetic field strength it experiences
Hydrogen Nucleus
In a T2 Weighted Image
TE - Echo Time - Controls the amount of T2 weighting so the TE must be long
The factors that affect Image Contrast in diagnostic imaging are usually divided into two categories
Intrinsic and Extrinsic contrast parameters
Sequences that use a 180 degree pulse to regenerate a signal
Spin Echo pulse sequence
___ are generated by coils of wire situated within the bore of the magnet
Magnetic Field Gradient
The time from the 90 degree excitation pulse to the 180 equals the time from the 180 to the signals
TAU
Whether a gradient field adds or subtracts from the main magnetic field depends on the direction of the current passing through the gradient coils
Polarity
Gradients that dephase are called ___
Gradients that rephase are called ___
Spoilers /
Rewinders
The middle of the axis of the gradients remains at field strength of the main magnetic field
Magnetic Isocenter
TE at which the operator wishes to weight the resultant image
Effective TE
What is the purpose of Spatial Encoding in MRI
To assign Spatial Locations to image signals
In MRI what is the function of the magnetic field Gradients during Spatial Encoding
To vary the Resonant Frequency of spins along different directions
Which gradient is responsible for dividing the object into slices along the z axis
Slice Select Gradient
The process of assigning spatial locations to the signals in the phase encode direction
Phase Encoding
What is the role of the readout gradient in spatial encoding
Encodes spatial information in the frequency direction
In MRI the matrix size refers to the number of pixels in
Two-dimensional space
In MRI the readout gradient is applied during which part of the imaging sequence
When signal is received
Once the slice is selected the signal is Located or ___ along both axes of the image
Encoded
The position of a nucleus along a gradient can be identified according to its
Precessional Frequency
X Gradient
Sagittal Slices
Y Gradient
Coronal slices
Z Gradient
Axial Slices
To give each slice thickness a ___ of nuclei must be excited by the excitation pulse
Band
The Frequency encoding gradient is switched on when the signal is received
Readout Gradient
Enough frequencies must occur during readout to achieve sufficient data points. This is determined by the
Receive Bandwidth
These data points are Stored in
K- Space
The ___ of K space is horizontal and is centered in the middle of several horizontal line.
The ____ of k space is vertical and is centered in the middle of k space perpendicular to the frequency axis
Frequency Axis
Phase Axis
The central region of k-space corresponds to
Low Spatial Resolution
In k-space acquisition which part corresponds to the low frequency (low resolution) information in the image
Central Part of K- Space
What is the term for the process of Filling k-space with acquired dat in MRI
K-space Filling
In MRI what effect does Increasing the number of phase encoding steps have on k space
Increases Spatial Resolution
The Outer Portion of K- space contains data that have High Signal Amplitude and Low Resolution
(TRUE or FALSE)
False
What is the primary goal of protocol optimization in MRI
Enhancing Image Quality
Spin Echo pulse sequences generally have ___ that Gradient Echo sequences, as all the longitudinal magnetization is converted into transverse magnetization by the Flip Angle
More Signal
The ___ controls the amount of transverse magnetization that is allowed to Decay before an echo is collected
TE- Echo Time
This is the amount of times data are collected with the same amplitude of phase encoding slope
NEX
The ___ controls the amount of Transverse Magnetization that is created which induces a Signal in the Coil
Flip Angle
____ is a Random as it is in a different position each time data are stored
Noise
In large voxels individual signal intensities are averaged together and are not represented as distinct within the voxel. This results in
Partial Voluming
____ always provide better spatial resolution than ____ as the image is equally resolved along both the frequency and phase axis
Square Pixels
Rectangular Pixels
The dimensions of the FOV in the phase direction is reduced compared to that in the frequency direction and so should be used when
Imaging anatomy that fits into a rectangle
Large Voxels result in ___ as small structures are not resolved so well
Low Spatial Resolution
Of the three main factors that affect Scan Time which one does not fit
TR
TE
NEX
Phase Matrix
TE
With respect to voxel size it is directly affected by all but one
FOV
Flip Angle
Slice Thickness
Number of Pixels or Matrix
Flip Angle
_____ appears as a Dense Line on the image at a specific point which is caused by extraneous RF entering the room interfering with the signal coming from the patient
Zipper Artifact
Anti- Aliasing along the phase axis
Anti- Foldover
An artifact that produces a Banding Artifact at the interfaces of High / Low signal
Truncation
In gradient echo pulse sequences a Moire Pattern, a Black and White banding that encompasses the edge of the FOV, is is caused by a combination of
Wrap and Field Inhomogenity
The use of foam pads or water bags between the coil and the patient will usually take care of what artifact
Shading
The 180 rephasing pulse used in Spin Echo Sequences is very effective at compensating for phase differences between fat and water in magnetic susceptibility, while ___ are very poor at this
Gradient Echo Sequences
When fat and water signals are out of phase their signals cancel each other out
(TRUE or FALSE)
TRUE
The number one problem to look for when you see zipper artifact on your images and before you call for service is burned out light bulbs
(TRUE or FALSE)
TRUE
Chemical shift can be limited by scanning at lower field strengths and by keeping the FOV to a minimum
(TRUE or FALSE)
TRUE
At what temperature does an alloy of niobium and titanium become superconductive
4 Kelvin
Permanent Magnets
Magnets that retain their magnetism
Passive Shimming
Uses metal discs/ plates at installation to adjust for large changes in field homogeneity
Superconductive Electromagnets
Solenoid electromagnet that uses super cooled coils of wire so that there is no inherent resistance in the system through which the current flows and therefore the magnetism is generated without a driving voltage
Duty Cycle
Is a percentage of time during the TR period that the gradient is permitted to be at maximum amplitude or ‘Work’ during n imaging sequence
Passive Shielding
Shielding accomplished by surrounding the magnet with steel plates
Shimming
Process whereby the evenness of magnetic field is optimized
Gradient Amplifier
Supplies power to the gradient coils
Active Shimming
Additional solenoid magnets to adjust field homogeneity
Para magnetism
Substance with a small but positive magnetic susceptibility
Active Shielding
Uses additional superconducting coils located at each end of the main magnet inside the cryostat to shield the system
Patient and ____ is the most effective way to avoid potential safety hazards to patients
Safety Education
Although ___does not seem to be a safety issue it is a condition that commonly affects patients and MR operators should appreciate
Claustrophobia
What is the primary safety concern related to ferromagnetic objects in the MRI environment
Projectile Effect
The four zones concept in MRI safety refers to
Different areas in the hospital or imaging center
IN MRI safety ‘Acoustic Noise’ refers to
The noise produced by the gradient coils
To minimize the risk of burns during an MRI scan it is essential to
Limit the scan time and power deposition
The MR Conditional designation for medical devices means that they are
Safe under certain conditions specified by the manufacturer
In MRI safety the static field in the MRI suite is measured in
T- Tesla
Cryogen Venting in MRI safety refers to the controlled release of
Cryogenic Gases
What safety precaution is essential when using contrast agents containing gadolinium
Monitor the patient for nephrotoxic effects
what is the primary concern regarding metallic implants or devices in the MRI environment
Induction of electric currents/ Heating
The 5 Gauss Line is a safety guideline related to
Magnetic field strength
In MRI safety, Quenching refers to
The release of cryogenic gases in case of an emergency
In MRI safety what does SAR stand for
Specific Absorption Rate
What is the purpose of an MRI compatible patient monitoring system during scanning
To monitor vital signs and patient conditions
The technologist can leave a patient who is getting out of a wheelchair
(TRUE or FALSE)
FALSE
A patient explains to the technologist what type of pain is being experienced
Subjective Data
When transporting a patient back to the hospital room, some safety measures to be used are
Place the side rails up, the bed in the low position, and call bell at hand
Inform the nursing staff that the patient has been returned to the room
Patient transfers from gurney to imaging table and back to gurney should be performed
By two or more technologist to ensure patient and technologist safety
Pain control is not within the technologists scope of practice and should not be a concern
(TRUE or FALSE)
FALSE
The leasing cause of work related injuries in the field of health care is
Abuse of the spine when moving and lifting patients
The most effective means of reducing friction when moving a patient is by
Placing the patients arm across the chest and using a pull sheet
The ___ controls the amount of transverse magnetization that is created which induces a signal in the coil
Flip Angle
The ___ is the ratio of amplitude of the signal received to the average amplitude of the noise
SNR
This is the number of times data are collected with the same amplitude of phase encoding slope
NEX
The ___ controls the amount of transverse magnetization that is allowed to decay before an echo is collected
TE - Echo Time
The ___ determines the number of data points we must collect during readout
Frequency Matrix
Enough frequencies must occur during readout to achieve sufficient data points. This is determined by the
Receive Bandwidth
The position of a nucleus along a gradient can be identified according to its
Precessional Frequency
What is the role of the readout gradient in spatial encoding
Encodes spatial information in the frequency direction
