MRI Flashcards
MRI scanners in clinical use have field strengths between 0.2T and 3.0T, with 1.5T being the most common
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Magnetic field homogeneity refers to the uniformity of the magnetic field throughout the magnet.
T
Superconducting magnets operate at room temperature
F (They are cooled using liquid helium and surrounded by liquid nitrogen for thermal insulation.)
Superconducting magnets consume large amounts of liquid helium in modern scanners
F (Modern scanners are designed to consume little liquid helium, making them more efficient.)
The long narrow bore of superconducting magnets improves magnetic homogeneity
T
Permanent MRI magnets are used widely in clinical practice
F
Resistive MRI magnets require large amounts of electricity to generate a high magnetic field.
F. (Resistive magnets consume large amounts of electricity but produce only low-strength magnetic fields)
The RF system transmits RF energy at the Larmor frequency and detects echoes emitted by the patient.
T
As the field strength increases, the requirement for RF power decreases.
F. (RF power requirements increase with higher field strengths)
Receive coils can be separate from transmit coils in MRI systems
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The amplitude of the echo detected by the RF coil does not require amplification
F. (Echo signals are very small and must be amplified before processing)
The gradient system alters the magnetic field to provide spatial information about the patient
T
Gradient coils alter the main
𝐵0 magnetic field strength.
T
The loud noise in an MRI scanner is caused by the switching on and off of gradient coils.
T
In the absence of an external magnetic field, hydrogen protons are randomly oriented
T
Hydrogen protons align parallel or antiparallel to 𝐵0, creating equal energy levels.
F. (Protons align in two different energy states)
The Larmor frequency is the resonant frequency of the tissue at a given magnetic field strength.
T
The Larmor equation determines the frequency at which protons resonate
T
T1 relaxation involves the transfer of energy to surrounding tissues (the lattice).
T
Water has long T1 relaxation times
T
Water has long T1 relaxation times and appears white on T1-weighted images
F. (Water has long T1 times but appears black on T1-weighted images)
T2 relaxation involves the loss of phase coherence
T
T2 relaxation always involves energy transfer
F. (T2 weighting may or may not involve energy transfer)
T1 relaxation always involves energy transfer
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T1 relaxation times are dependent on B0
True
T1 relaxation times are independent of B0
F. (T1 relaxation times are dependent on B0)
In a Spin Echo sequence, T1 weighting requires a short repetition time (Tr) and echo time (Te)
T
Inversion Recovery sequences start with a 90-degree pulse followed by a 180-degree pulse.
F. (They start with a 180-degree pulse, followed by a 90-degree pulse.)
STIR is a fat suppression sequence, and FLAIR is a CSF suppression sequence.
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Gradient Echo sequences produce low signal-to-noise ratio (SNR) images.
T
GE sequences are faster and have improved SNR compare to SE sequences
F. (GE sequences are faster but have reduced SNR compared to Spin Echo sequences)
Image acquisition time is proportional to the number of frequency encoding steps.
F. (It is proportional to the number of phase encoding steps)
Wrap-around artefact can be mitigated by increasing the field of view (FOV).
T
The projectile effect depends on the rate of change of the magnetic field
T
Cryogens used in MRI systems can pose hazards such as frostbite or asphyxiation
T
AR measures the RF power absorbed per kilogram of tissue during an MRI scan
T
Superconducting magnets are the most commonly used type in clinical MRI.
T
Superconducting magnets have poor homogeneity
F. (They have excellent homogeneity)
Permanent magnets are very stable and unaffected by external disruptions
F. (Permanent magnets are sensitive to external disturbances and temperature changes, which can destabilize the magnetic field.)
Resistive magnets are energy-efficient and produce high field strengths.
F. (Resistive magnets consume large amounts of electricity and produce low field strengths.)
Superconducting magnets are always on, regardless of whether a scan is in progress.
T
The strength of 𝐵0 is unaffected by gradient coils
F
The loud noise during MRI scans is caused by RF coil vibrations
F. (It is caused by the rapid switching of gradient coils.)
The spatial resolution of an image depends on the central lines of k-space
F. (Spatial resolution is determined by the peripheral lines of k-space, while contrast is influenced by the central lines)
Slice Thickness depends on the RF pulse bandwidth and the amplitude of the slice selection gradient
T
A narrower RF bandwidth and lower gradient amplitude produce thicker slices.
F. (A narrower RF bandwidth and lower gradient amplitude produce thinner slices.)
Energy transfer in T1 relaxation occurs via dipole-dipole interactions
T
In T1-weighted images, fat appears bright and water appears dark.
T
T1 is typically shorter than T2 for liquids
F. (T1 and T2 are similar for liquids)
Gradient Echo (GE) sequences are faster than Spin Echo sequences but have lower SNR.
T
The echo is the signal emitted by rephased spins and contains image information
T
FID is used to form images
F. (FID does not contain image information and is ignored)
The Fourier Transform is used to extract frequency and spatial information from MR signals.
T
Frequency encoding is applied along the Y-axis, while phase encoding is applied along the X-axis.
F. (Frequency encoding is along the X-axis, and phase encoding is along the Y-axis.)
The number of phase encoding steps determines the image acquisition time
T
The projectile effect depends only on the strength of the magnetic field
F. (It also depends on the rate of change of the field and the properties of ferromagnetic materials)
Chemical shift artefacts of the first kind can occur in both Spin Echo and Gradient Echo sequences.
T
Superconductive magnets are attractive as they offer little to no resistance
T
B0 is altered by gradient coils
T
Anti-parallel protons are of lower energy than parallel ‘with field’ protons
F. (Antiparallel ‘against field’ protons have higher energy)
T2 relaxation time is known as longitudinal relaxation time
F. (T1 Spin-Lattice relaxation time is known as longitudinal relaxation time)
Contrast shows up better on a T1 weighted image
T
Technetium is the most common contrast agent used in MRI
F. (Gadolinium)
The rate limiting factor to produce an image is the number of phase encoding steps
T
