MRI Quiz Flashcards
The amount of diffusion weighting is determined by:
- Strength of the diffusion gradients
- Duration of the gradients
- Time between gradient pulses
Common problems in DWI
- Sensitivity to magnetic susceptibility when using echo planar readout
- Bulk patient motion
- Low SNR
Contrast in Diffusion Weighted Imaging (DWI) depends on:
- Degree to which molecular mobility is impaired (water restriction)
- Sensitivity of the sequence to Brownian motion (rate of water diffusion, more sensitive than T1 or T2)
- Direction of water diffusion.
Chiari Malformation CSF Flow Study - flow during systole
Bright white
Chiari Malformation CSF Flow Study - flow during diastole
Black
Acoustic Neuroma Scans
- 3mm Axial/Coronal T1 pre and post
- T2 3D volume
- Center at level of EAM
Chiari Malformation Scans
- Sagittal
- Thin, 3mm or less
- T2 for CSF
Pituitary Adenoma Scans
- Thin Sagittal and Coronal (3mm or less)
- DCE or basic T1 perfusion thin Coronal
- Small FOV T2 Coronal useful for CSF superior to pit
- Scan rapidly after contrast (tumors appear as low signal compared to enhanced pituitary gland)
Diplopia Scans
Thin cuts through orbits, usually 3mm Axial/Coronal and including FS pre and post contrast
Bell’s Palsy
A form of facial paralysis resulting from a dysfunction of the cranial nerve VII (the facial nerve) that results in the inability to control facial muscles on the affected side
MS Scans
- Thin slice FLAIR high res Axial/Sagittal
- Delayed post contrast T1
Vertebral arteries
- Originate for subclavian arteries
- Passes through transverse foramen of C6 to C1
- Joins to form basilar artery at the base of medulla oblongata
Increasing the VENC (velocity encodings) value will:
Allow more arterial vessels to be visualized
The insulae play a role in:
Usually linked to emotion or the regulation of the body’s homeostasis:
- Perception
- Motor control
- Self awareness
- Cognitive functioning
- Interpersonal experience
Inverted V sign (T2 hyperintense)
Subacute Combined Degeneration
Level of Conus Medullaris
T12-L1
What images are mandatory in cervical spine imaging for evaluation of cord anatomy (H sign), investigating extramedullary disease, and/or the discrimination of osteophytes vs. disc herniation?
Axial gradient echo T2*
Mandatory sequence in Abdominal MRI protocol
- T1 In/Out Phase
- Evaluate for fatty liver, adrenal adenoma, and other conditions with increased lipid content
Hemosiderin, hemochromatosis best visualized:
MR imaging of the liver with T2* GE (iron deposit, hypointense on T2* and T2)
MR enterography
-Sequences embedded with acceleration factors are essential in this exam, such as high resolution LAVA/THRIVE/VIBE
sequences in the Coronal and Axial planes
-IV gadolinium differentiates chronic from active disease
Standard in Prostate MRI protocol
Small FOV, high resolution T2 in all three planes
Silicone Only
All tissues suppressed EXCEPT silicone using fat and water suppression simultaneously
Silicone Suppression
A T1 Isotropic Voxel technique (THRIVE) with an Inversion Delay time long enough to suppress the signal from silicone
The branches of the abdominal aorta, from proximal (superior) to distal are:
Celiac, superior mesenteric, renal, and inferior mesenteric arteries
The common iliac veins join together to form:
IVC
Disease that is characterized by narrowing of the aorta:
Aortic coarctation (occasionally abbreviated CoA: Coarctation of Aorta)
Most optimal planes for TOF subclavian arteries
Axial/Sagittal
The anterior tibial artery leads into the:
Dorsalis pedis artery
The first major branch of the abdominal aorta is the celiac trunk, which branches into the ________ arteries
Gastric, hepatic and splenic
The _________ transports deoxygenated blood from the posterior walls of the thorax and abdomen into the superior vena cava vein
Azygos vein
The hepatic portal vein is a vessel in the abdominal cavity that drains blood:
From the gastrointestinal tract and spleen to capillary beds in the liver
The hepatic portal vein is formed by the:
Confluence of the superior mesenteric and splenic veins and also receives blood from the inferior mesenteric, gastric, and cystic veins
The four muscles that form the rotator cuff are:
Supraspinatus, infraspinatus, teres minor, and subscapularis (SITS)
Best plane for median nerve:
Axial
Median nerve branches:
- Off the brachial plexus down to wrist
- Only nerve passing through the carpal tunnel
Optimal imaging plane to demonstrate the carpal bones and the interosseous ligaments:
Coronal
Kienbock’s disease
Condition of osteomalacia in the lunate bone of the wrist, an avascular necrosis (death and fracture of bone tissue due to interruption of blood supply) with fragmentation and collapse of the lunate
Triangular Fibro-Cartilage Complex optimal imaging plane
Coronal
Supraspinatus
- Originates above the spine of the scapula and inserts on the greater tuberosity of the humerus
- Abducts, or elevates, the shoulder joint
Infraspinatus
- Originates below the spine of the scapula, in the infraspinatus fossa, and inserts on the posterior aspect of the greater tuberosity of the humerus
- Externally rotates the shoulder joint
Teres Minor
- Originates on the lateral scapula border and inserts on the inferior aspect of the greater tuberosity of the humerus
- Externally rotates the shoulder joint
Subscapularis
- Originates on the anterior surface of the scapula, sitting directly over the ribs, and inserts on the lesser tuberosity of the humerus
- Works to depress the head of the humerus allowing it to move freely in the glenohumeral joint during elevation of the arm
How to apply metal artifact reduction
- Use TSE/FSE instead of GE
- Use STIR instead of FS
- Wider rBW
- No PI or image uniformity correction (they rely on GE based reference scan)
- Thin slices/small pixel/large matrix
- High TSE factor/ETL (multiple 180° RF pulses further compensate for metal artifacts)
- Add NEX/NSA to buy back signal
Knee collateral ligament imaging plane
Coronal
ACL tear positioning
15 deg external rotation
Knee cruciate ligament imaging place
Sagittal
Shoulder MRI landmark
Coracoid process
A useful sequence for the evaluation of bone contusions or fractures is:
STIR
Carpal tunnel imaging plane
Axial
TOF MRA uses:
T1 gradient echoes with TR and FA (flip angle) selections to suppress signal from stationary tissues, visualizing flowing blood by flow-related enhancement
PC MRA uses:
T2 gradient echoes that rely on velocity-induced phase shifts for vascular signal
Laminar flow
Blood flow that is at different but consistent velocities across a vessel
Spiral flow
Blood flow where the direction of flow is spiral
Vortex flow
Blood flow that is initially laminar, then intersects a vessel stenosis or stricture, becoming high velocity central flow and spiral near the walls of the vessel
Turbulent flow
Blood flow within a vessel that is characterized by different velocities that fluctuate randomly
In TOF MRA, to minimize signal from background tissues, TE should be selected that enable the signals from:
Fat and water to be out-of-phase
3D TOF (time of flight) MRA is typically used to visualize smaller vessels, and utilizes thinner slices, but yields:
Less suppression of background tissues than 2D TOF
Two factors that increases intravoxel dephasing and reduces signal in TOF MRA
- Longer TE
- Larger voxel
Phase Contrast MRA
- Relies on velocity induced phase shifts to distinguish between moving protons and stationary protons
- Produces the most background tissue suppression
- Usually has the longest imaging times (compared to 2D TOF and 3D TOF)
- Provides both directional and velocity information from flowing blood
- The most useful technique to evaluate slow flow within a vessel
- The velocity or speed of the vessel(s) of interest determines the signal intensities in phase contrast MR angiography (PCA)
Increasing the VENC (velocity encodings) value will allow:
More arterial vessels to be visualized
Vertebral arteries originate from the:
Right and left subclavian arteries
A Contrast Enhanced MRA Runoff of the Lower Extremities would require coverage to include:
Iliac bifurcation down to and including the dorsalis pedis artery
The optimal technique to visualize the Circle of Willis would be:
3D TOF
The __________ of blood is responsible for the bright blood signal in time of flight MR angiography
Flow
In order to obtain a time of flight MRA of the IVC a presaturation band would be placed:
Superior
The degree of stenosis ___________ with time-of-flight MRA
May be overestimated
Gradient amplitude
Strength of the gradient
Gradient rise time
Time it takes for the gradient to reach its full amplitude (microseconds)
Gradient slew rate
- Speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative (amplitude divided by rise time, mT/m/msec or T/m/sec)
- The strength of the gradient over a specific distance
To convert vendor spatial gradient map into manufacturer conditions chart:
1 Tesla/meter = 100 Gauss / cm
Duty cycle
Time the gradients are on during a TR period, “gradient working time”
Parameter changes affecting the pulse duty cycle include:
- Increased # slices
- Fat suppression pulses (SPAIR requires increased TR compared to SPIR)
- Presaturation slabs/bands
- Increased ETL
180° RF pulse is ____ times the power of the initial 90° RF pulse
Four
Doubling field strength results in ____fold increase in SAR potential
Four
(SAR is proportional to the power of 2 for the resonant frequency)
Managing SAR
- Avoid shortest TR
- Minimize use of presaturation slabs/FS pulses, use least # of slices within TR period
- Shortest ETL possible
- Use PI techniques
- Use longer and lower amplitude transmit RF pulses (increases scan time)
- Consider Transmit/Receive coil (significant increase in scan time)
Utilization of surface coils (linear coils) yields:
-More localized, smaller FOV (field of view) capability, with increased SNR
SNR penetration depth for surface coil
1/2 coil diameter
When going from a linear coil to a quadrature (CP) coil, SNR is increased by:
40%
Doubling the magnetic field strength will:
Double SNR
In a superconducting magnet, the magnetic field strength is increased by:
Increasing the turns of wire, current in the wires, or by reducing the spacing between the wires
System Performance Testing (SPT), or PIQT (Periodic Image Quality Test)
Inherent manufacturer quality mechanism by which a technologist, physicist or field service engineer might evaluate the performance of an MRI system
Center Frequency
To ensure integrity of MR system operating frequency, at which all system coils will be tuned to
Transmit gain is a quality measure evaluating for?
Accuracy of flip angles
Field strength at magnet isocenter is measured in units of:
Tesla
The local RF coil used to image a human brain is typically located/kept in the __________
Magnet room
High field scanners typically have field strengths greater than or equal to
1.5 Tesla
What is the daily/weekly QA/QC indicator testing for the accuracy of the magnetic field in determining coil tuning and consistent magnetic field strength?
Center frequency
Precessional Frequency
Defined as the resonant frequency, and is equal to the product of the magnetic field and the gyromagnetic ratio
Larmor equation for precessional frequency:
42.57 MHz per Tesla
1 Newton per ampere-meter =
1 Tesla [T]
1 Coulomb =
6.24 X 10 18e-
1 Coulomb/second =
1 ampere
The difference in chemical shift is approximately 3.5 parts-per-million (ppm) which at 1 Tesla corresponds to a frequency difference between that of fat and water of approximately:
147 Hz
Faraday’s law of induction states that a changing magnetic field will induce:
A voltage
Ferromagnetic
- Iron and iron-like substances that can generate a relatively strong magnetic field
- Stainless steel, iron, nickel, etc.
Paramagnetic
- Very weak magnetic field
- Gadolinium is used as a contrast
Diamagnetic
No magnetic field
Magnetic susceptibility
Extent to which a material or tissue becomes magnetized in an external magnetic field
Magnetic permeability
How well a material attracts the imaginary lines of the magnetic field
T1 relaxation
- Nuclei give up their energy to surrounding tissues
- SPIN-LATTICE RELAXATION
T2 relaxation
-SPIN-SPIN RELAXATION
When thermal equilibrium is reached
There are more hydrogen protons in the low energy state
____________ states that a changing magnetic field will induce a voltage
Faraday’s law of induction
What is defined as the excess number of hydrogen protons aligned with the static magnetic field direction (B0)?
Longitudinal magnetization
The difference in chemical shift is approximately ______ parts-per-million
3.5 ppm
Immediately following the application of the 90° RF pulse, the transverse magnetization is:
Non-zero
Tort
- In common law jurisdictions, is a wrong that involves a breach of a civil duty (other than a contractual duty) owed to someone else
- May be defined as a personal injury; or as “a civil action other than a breach of contract”
Civil law
Law that pertains to private legal rights and matters
To establish a claim of malpractice, four conditions must be proved true:
- The defendant had a duty to provide reasonable care to the patient
- The patient has sustained some type of loss or injury
- The defendant is the party responsible for the loss
- The loss is attributable to negligence or improper practice
Tau
The time between the pulses (btwn 90ºRF - 180ºRF and 180ºRF - echo) in spin echo (also known as 1/2 TE)
_________ gradient – magnetic field gradient applied during the moment when the echo is formed
Readout
_______________ is defined as the range or spectrum of frequencies (minimum to maximum processed frequency) of a pulse sequence acquired by an RF system
Bandwidth
________ is defined as the ratio of the magnetic moment (field strength) of a rotating charged particle, such as an electron, to its angular momentum (frequency)
Gyromagnetic ratio
The linear increased or decreased change in the magnetic field of a certain orientation is defined as a _________
Gradient
________ is comprised of the components of the magnetization in the imaging object after excitation, sampled from the receiver coil signal and stored as a function of time during the data acquisition of an MR imaging sequence
Raw data
DSC
Dynamic Susceptibility Contrast, or better known as T2* gradient Perfusion imaging
Patients in need of MRI IV gadolinium contrast should first have their glomerular filtration rate (GFR) checked if they:
- Are over the age of 60
- Have a history of hypertension
- Have a history of diabetes
- Have a history of renal disease
Sedated patient must always be monitored with a:
Pulse oximeter
A pediatric patient undergoing an MRI with conscious sedation should be given:
NPO for 4 hours before sedation
Tachycardia / Bradycardia
>100 BPM / <60 BPM
Normal pulse rate
About 60-100 BPM
Normal oxygen saturation levels
Approximately 95-100%
Patient develops severe bronchospasms after the injection of contrast
Epinephrine
Febrile
Pertaining to or marked by fever; feverish
The effects of time varying magnetic fields can include all of the following EXCEPT:
Warmth and/or increase in body temperature
When moving blood enters a magnetic field, an effect on the ECG seen as a “T wave swelling” or spike occurs, also known as:
Magnetohydrodynamic effect
Contrast reactions are very rare in MRI injections, at a rate of:
~1% or less than 1%
FDA limits for whole body SAR
4 W/kg over 15 min
FDA limits for head SAR
3 W/kg over 10 minutes
As the flip angle is doubled, the RF absorption (deposition) increases by:
Factor of 4
FDA guidelines dictate a level of concern when RF energy absorption produces an increase in body temperature of:
1° Celsius
Risk factors of MR exposure with regards to SAR include all of the following:
- Obesity
- Hypertension
- Cardiovascular disease
- Elderly
- Sedatives/Diuretics
- Diabetes
RF energy is:
Low energy, non-ionizing radiation
The FDA limit on time varying magnetic fields is:
Once the patient experiences peripheral nerve stimulation
SE T1 Parameter
TR: 350-700 ms
TE: 10-30 ms
SE PD Parameter
TR: 1500-3000 ms
TE: 10-30 ms
SE T2 Parameter
TR: 2000-6000 ms
TE: 70-120 ms
TR is directly proportional to:
Scan time
When increasing NEX/NSA, SNR (signal-to-noise ratio) increases by:
Square root (√) of the % increase
Reducing the FOV by a factor of 2 will reduce the voxel volume by:
Factor of 4
Spin Echo / Gradient Echo (2D) Scan Time Formula
TR x Phase Matrix x NEX
Fast Spin Echo Scan Time Formula
TR x Phase Matrix x NEX / ETL
Gradient Echo Scan Time Formula
TR x Phase Matrix x NEX x # of Slices
Pixel Size Formula
Field of View / Matrix
Pixel Area Formula
Phase Pixel Size x Freq Pixel Size (answer squared)
Voxel Volume Formula
Pixel Area x Slice Thickness (answer cubic)
T1 weighted ETL
Approx 2-7
PD weighted ETL
Approx 3-12
T2 weighted ETL
Approx 10-40
Increasing ETL will:
Reduces number of slices
Echo Spacing
Time between successive 180º echoes in a fast
spin echo pulse sequence (a typical FSE sequence can have an echo
spacing of 5 ms to 20 ms, approximately)
Number of rows of k-space filled per TR period in a SE sequence
1
Number of rows filled per TR period in a FSE
Same as ETL or TSE factor
Collecting the low frequency (high amplitude signal) data points in k-space at the
start of the scan (in a spiral fashion)
Elliptic Centric K-space Filling
During dynamic enhanced imaging for vasculature or visceral structures, contrast
is administered and k-space is filled with:
Centric K-space Filling (to ensure that the contrast enhancement is well visualized)
For the 180º pulse immediately
prior to the echo chosen as the effective TE, the phase encoding is at its:
Lowest
Acquiring a bit more than half the phase dimension k-space samples, then
interpolating the data with zeroes for the remaining half:
Half Fourier, Partial Fourier, Halfscan, or Zero Fill (made possible due to the symmetry in k-space data)
Only half the views of k-space are filled in the
frequency axis, an acceleration technique used to shorten TR and TE:
Partial or Fractional Echo (advantageous in rapid and EPI imaging, in addition
to CE MRA and faster T1 images)
Time increase for NSA/NEX
Directly proportional
Halving FOV cuts SNR to:
25% of the original value, due to the pixel size reduction by a factor of
4 (phase and frequency dimensions)
Doubling FOV increases SNR to:
400% of the original value, due to the pixel size increase by a
factor of 4 (phase and frequency dimensions)
K-space is typically filled:
One line at a time
If the repetition time (TR) is doubled, the scan time will:
Double
Each line of k-space is defined by the:
Phase encoding gradient
The timing of the RF pulses in an MRI pulse sequence controls:
Image contrast
Reducing the number of lines filled in k-space will produce an image:
Reducing the number of lines filled in k-space reduces the number of phase encoding steps, resulting in shorter scan time, an increase in overall SNR, but a decrease in spatial resolution
The smallest object that can be resolved in an image
FOV / Matrix (Pixel size formula)
With a recFOV that is twice as tall as it is wide, and the phase direction oriented along the smaller “width” dimension of the FOV, which of the following relationships between the frequency and phase steps yields square pixels?
Phase steps must be half the number of frequency steps
A method of reducing MRI scan time by not filling as many lines of k-space in the phase direction, while maintaining spatial resolution, is known as:
Rectangular FOV
Total number of excess protons aligned with the magnetic field
Net Magnetization Vector (NMV)
The signal produced immediately following an RF pulse:
Free Induction Decay (FID)
2D acquisitions usually require an:
Interslice gap
3D sequence provide:
- Greater SNR
- Elimination of crosstalk
The option to reconstruct multiple planes from a single data set is advantageous in a 3D pulse sequence due to:
Thin slices used in 3D sequences and the absence of an interslice gap
TSE (ETL) increased by factor of 2, then the scan time:
Will be 2 times faster
In a Fast Spin Echo sequence, the effective TE are:
Echoes that are encoded with a low amplitude phase encoding gradient (occurs at the line that is closest to the center of k-space)
A wide receiver bandwidth:
- Generates lower signal-to-noise ratio images
- Should be applied in anatomical regions that contain high fat and water interfaces
- Is utilized with a high readout gradient amplitude
Decreasing bandwidth by factor of 2 increases SNR by:
√2 (approximately 40%)
Transmit Bandwidth
- Refers to the RF excitation pulse required for slice selection
- Slice thickness is proportional to the bandwidth of RF pulses
- During transmission, RF pulses contain a range of frequencies (bandwidth) to excite a specific slice thickness or volume
The time the RF pulse is on reflects the type of sequence selected:
- Low SAR: ±3.5ms
- Normal mode: ±2.5ms
- Fast mode: ±1.2ms
Low SAR mode:
- Longer RF pulse with good slice profile
- Reduced SAR values (lower amplitude)
- LESS CROSSTALK between slice, narrower gaps allowed
- Longer minimum TE’s and TR’s
Fast RF mode:
- Shorter RF pulse, with a compromised slice profile
- Higher SAR compared to the other modes (higher amplitude)
- Shorter echo spacing (ES)
- Opportunity for shorter TE’s and TR’s
- FEWER SUSCEPTIBILITY artifacts
Receive Bandwidth
- Adjustable parameter at the console: receiver bandwidth (rBW), defined simply as the range of frequencies accepted by the receiver to sample the MR signal
- Describes which frequency range from our analyzed echo signal is transferred into pixels
- AKA acquisition bandwidth, has a direct relationship to SNR: decreasing bandwidth by factor of 2 increases SNR by √2 (approximately 40%)
The slice selection gradient is the determinant of:
- Scan plane (position and orientation)
- Slice thickness
A thin slice thickness is achieved through the utilization of a:
Steep, high amplitude slice select gradient, and a narrow transmit bandwidth (tBW)
Slice select gradient must be turned on:
During RF energy application
Frequency encoding (readout) gradient is on during
- Sampling or readout of the peak echo
- Production of echo
- Frequency encoding
Sampling time
- Time to sample the entire K-space line
- Controlled by FREQUENCY Gradient
Sampling Time Formula
Frequency matrix (# of samples) / rBW
Sampling Rate
- Signal sampling frequency
- According to Nyquist theory, our sampling rate must be twice that of our sampling frequency in order to avoid aliasing in our image (therefore, we sample twice per cycle-reason why no aliasing in frequency direction)
Sampling rate is proportional to:
rBW
Gradient moment nulling (flow compensation) is used to compensate for:
- First order motion (protons moving with constant velocity)
- Slow flowing vessels
Optimal flip angle that yields the maximum signal for a particular spin in the least amount of time
Ernst Angle
Gradient echo sequences use flip angles to control:
Saturation effects
Which factors affect the flip angle?
Strength and duration of the RF field
Decreasing the slice selection gradient strength will ________ of the resulting slice
Change the slice thickness
The presaturation pulses typically are found:
Prior to the excitation pulse
Decreasing the receiver bandwidth (utilizing a narrow BW)
- Decreases the number of slices available
- Decreasing the receiver bandwidth (utilizing a narrow BW) decreases the number of slices available (Decreasing the bandwidth increases the sampling time and lengthens the sequence timing, creating longer minimum TR and TE values)
The time during which the frequency encoding gradient is on:
Increases with a reduction in receiver bandwidth
_________ is a file on the computer where the collected echoes are stored prior to being processed into an image by the Fourier Transform
Raw data
Gradient echo sequences can yield either:
T1 or T2* characteristics, with influences caused by susceptibility, chemical shift, and inhomogeneities
The condition of steady state occurs when the TR in a gradient echo is:
less than the T2 (or T2*), resulting in residual transverse magnetization at the time of the next excitation pulse
Gradient echo sequences requiring high signal from fluid are known as:
T2* gradient echo, steady-state gradient echo or coherent gradient echo
Incoherent gradient echo (or spoiled gradient echo) sequences yield:
- T1 contrast due to the removal of residual transverse magnetization before the next excitation and short TE (to reduce T2 effects)
- RF spoiling occurs when additional RF pulses are used to “spoil away” the steady state effect (residual transverse magnetization) before the next excitation
BTFE (Balanced Turbo Field Echo) Sequences
- Variations of high T2 signal, balanced steady state sequences
- Equipped with slice, phase, and frequency rewinder pulses
- Yields images with mixed contrast T2/T1
- Results in an image of high SNR with bright fluids, useful in evaluation of cranial nerves
In a spin echo sequence, the time between the 90° RF pulse and the 180° RF pulse is known as:
1/2 TE time (TAU)
Dual Spin Echo
- Generates 2 images for every slice with varying TE’s but same TR
- Typically acquired as a short TE (proton density weighted) and a long TE (T2 weighted) combination
- Second echo image has more T2 contrast but lower signal-to-noise ratio (SNR) than the first echo image
In a Fast Spin Echo sequence, the effective TE are:
Echoes that are encoded with a low amplitude phase encoding gradient. This would occur at the line that is closest to the center of k-space (k0)
In a Fast Spin Echo sequence, the number of shots (non-redundant RF excitations) is calculated by:
Phase encodings / ETL
TI (Inversion Time)
Time interval between the 180° Inverting RF pulse and the 90° RF excitation pulse
Different types of inversion recovery sequences
- STIR (short TI inversion recovery)
- FLAIR (fluid attenuated inversion recovery)
- 3D-IR (T1 weighted inversion recovery)
If the desire is to null the signal from a specific tissue using an inversion recovery sequence, the inversion time (TI) selected should be:
69% of the T1 relaxation time of that tissue
STIR sequences are typically used for the evaluation of
- Compression fracture
- Lesions within retro-orbital fat
- Musculoskeletal contusions -Fat suppression
T2 weighted FLAIR (fluid attenuated inversion recovery) sequences are typically used for evaluation of:
Periventricular white matter
Reducing the flip angle yields images with:
Less T1 information
As the TE is increased, the available number of slices is:
Decreased (longer TE means fewer slices can fit into the TR period)
In a spin echo pulse sequence, an echo is produced from:
A combination of two or more RF pulses
In a Fast Spin Echo sequence, the effective TE are the echoes that are encoded:
With a low amplitude phase encoding gradient
What specifically is a SPGR sequence spoiling?
Transverse magnetization
The timing of RF pulses in an MRI pulse sequence controls:
Image contrast
In order to produce an echo in a gradient echo pulse sequence, ________ are used
Gradient field and an RF pulse are used
In a STIR sequence, the null point of fat in a 1.5 Tesla magnet is approximately:
140-160 milliseconds
To null the signal from fluid in a FLAIR sequence (CSF, for example) at 1.5 Tesla, an Inversion Time (TI) of approximately ____ would be used
2000 milliseconds
_____ would yield a T1* weighted gradient echo
45 TR; 90° flip angle combination
T1 weighting/contrast properties:
- Spin lattice
- Short TR (350-700 ms), short TE (10-30 ms)
- Recovery of 63% longitudinal magnetization
- Contrast is controlled by TR
- “Anatomy” standard weighting
A Proton Density weighted image has:
A TR that is long to minimize T1 contrast, and a TE that is short to minimize T2 contrast, yielding an image that is neither T1 nor T2
T2 weighting/contrast properties:
- Spin spin
- Long TR, Long TE
- 63% decay of transverse magnetization
- Contrast is controlled by TE
- “Pathology” standard weighting (edema bright)
In an inversion recovery sequence, image contrast is controlled by:
- TR (repetition time)
- TE (echo time)
- TI (inversion time)
Enabling Driven Equilibrium (DRIVE: Philips) will enable the operator to:
Reduce TR and preserve contrast
Intrinsic Parameters
- ADC
- T1/T2 time
- Specific proton density
- Flow
Extrinsic Parameters
- Flip Angle
- TR
- TE
- TI (Inversion time)
- TSE Factor/ETL
Structures that will always appear black on an MR image
- Air
- Tendons
- Ligaments
- Metallic susceptibility
- Cortical bone
Which sequence would be best suited for evaluation of demyelinating disease?
A T2 FLAIR sequence is best utilized for evaluation of white matter lesions / demyelinating disease
To produce an image based on differences in T1, the time interval between 90° excitation pulses should be:
Short
Presaturation pulses typically occur:
Prior to the excitation pulse
Chemical or spectral fat suppression techniques suppress fat signal based on the:
Precessional frequency of fat
Most clinically used MRI contrast agents work through:
Shortening the T1 relaxation time of protons located nearby - due an increase in rate of stimulated emission from high energy states (spin anti-aligned with the main field) to low energy states (spin aligned)
Gadolinium (PARAMAGNETIC)
- Shorten the T1 (brightens) and T2 (darkens) times of tissue, dependent upon concentration
- T1 weighting increases with gadolinium contrast, while T2 weighting is suppressed
MRI contrast agents delivered through the blood stream
Chelated metals
Routine weight based contrast administration is typically:
0.1 mmol/kg (0.2mL/kg)
Nephrogenic systemic fibrosis (NSF)
- Causes fibrosis in various tissues and organs in the body
- Patients with poor renal function are considered to be more at risk
Patients with _____ or _______ are more likely to have a potentially serious reaction following the injection of contrast
Asthma, allergic respiratory disorders
Safest Gad compound:
Cyclical ionic Gad compounds (least likely to release the Gad ion)
Two types Iron Oxide (SUPERPARAMAGNETIC) contrast agents:
- Superparamagnetic Iron Oxide (SPIO)
- Ultrasmall Superparamagnetic Iron Oxide (USPIO)
Iron Oxide (SUPERPARAMAGNETIC) contrast agents
- Reduce T2 signals of absorbing tissue (darkens)
- Liver tumor enhancement
Manganese (PARAMAGNETIC)
-Used for detection of liver lesions (normal liver cells enhance)
Oral contrast for T1 enhancement:
- Gadolinium and manganese chelates
- Iron salts
- Natural - blueberry and green tea (high manganese concentration)
Oral contrast to lower T2 signal:
- SPIO
- Barium sulfate
- Air
- Clay
______ has been used as a GI MRI contrast for pediatric imaging, works by reducing the amount of protons (as hydrogen) in a body cavity, causing it to appear dark
Perflubron (type of perflorocarbon)
VoLumen timing
- Typical adult 1-1.5 L over 45-90 min
- Child 1 L one hour prior to exam
- Filling of TI (terminal ileum) occurs in kids at 20-25 minutes, adults 1 hour
Biphasic agents
- Water, polyethylene glycol, dilute barium with sorbitol
- Low signal intensity on T1 and high signal intensity of T2
- Predominant oral contrast agents used for bowel MRI
- Typically include nonabsorbable high osmolarity additives
VoLumen charactertistics
- Dilates bowel
- T1 Dark
- T2 Bright
Following the administration of IV gadolinium contrast, it is recommended to:
Follow the injection with a flush of 5 mL saline
Gadolinium has:
7 unpaired electrons in its 4f orbitals giving it a very large magnetic moment
Contraindications for IV gadolinium contrast use are:
There are no known contraindications to IV gadolinium contrast usage
Digital magnetic resonance imaging systems realize an SNR boost of:
30-40%
The FDA has set a limit on gradient field interactions to a level at which:
The peripheral nerve stimulation becomes unbearable and the patient stops the exam
Each additional 180° RF pulse in FSE implements ____ times the SAR power compared to the initial 90° RF excitation pulse
Four
__________ is a similar variation to Halfscan, reducing phase encoding steps while maintaining spatial resolution, using conjugate symmetry techniques
Fractional NEX
No phase wrap or anti-aliasing options typically _____ the NSA/NEX as the price for oversampling, eliminating wrap artifacts
Halve
Two main advantages of selecting parallel imaging options
- Reduction in gradient switching
- Lack of additional RF power required performing the acceleration technique
Image based Parallel Imaging
Reconstruct images from each coil element within a reduced FOV then merge the images with the knowledge of collected coil sensitivities (reference scan)
K-space based Parallel Imaging
Explicitly calculate missing k-space lines before Fourier transformation of the raw data
Two prerequisites for Parallel Imaging
- Gradient echo based reference scan or calibration scan is prerequisite to collect tissue data within phased array coil elements (should not be used for metal reduction)
- A dedicated, RF phased array coil
Parallel imaging artifacts occur when:
- FOV is too small for the parallel imaging factor selected, resulting in a misrepresentation of the patient’s tissue, typically in the central portions of the image (usually occurs in the phase direction)
- Parallel imaging reduction factor too high for the parameters and FOV selected (most often this occurs in the phase encoding or slice select dimensions)
Corrective measures for Aliasing
“No phase wrap” or “anti-aliasing” options, or an increase in phase dimension sampling
Corrective measures for Parallel imaging artifacts
Increase FOV or reduce parallel imaging factor
PI Artifact Correction - Increase FOV and maintain voxel size
-Time increases
-Spatial resolution unchanged
(Longer time with increased matrix)
PI Artifact Correction - Increase FOV and maintain phase matrix
-Time unchanged
-Spatial resolution decreases
(Maintain time with decreased details)
PI Artifact Correction - Decrease PI factor
-Time increases
-Spatial resolution unchanged
(Longer time, SAR increases)
Sequences requiring metal reduction not good for PI because:
Calibration scan for PI is GE based
Influences causing artifacts:
- Patient (Primary)
- System equipment such as magnetic field inhomogeneity and machine hardware (Secondary)
Reducing motion artifacts
- Triggering,
- Radial k-space acquisition techniques
- Reduction in signals averages
- Parallel imaging techniques
Chemical shift
- Occur because fat and water precess at different frequencies
- Primarily occurs along frequency axis
- Higher field strength will increase chemical shift
- Higher bandwidth will decrease chemical shift (due to shorter sampling time, less time for artifact to enter slice)
When the TE is shortened, susceptibility artifacts:
Decrease because shortened TE’s allow less time for dephasing thus reducing signal loss
Magnetic susceptibility Reduction
- Smaller voxels
- Shorter TE
- Increased receiver bandwidth
- Fast spin echo (longer ETL) and spin echo sequences (additional 180° pulses)
Doubling the receiver bandwidth at 3.0 Tesla restores the artifact to levels observed at:
1.5 Tesla
A leak in the RF shielding can appear as a:
Zipper artifact in the phase or frequency encoding direction
Gibbs truncation artifact
- Caused by undersampling
- Reduced by increasing phase matrix or reducing FOV (while maintaining matrix)
Dielectric artifacts
- Causes an increase in inhomogeneity
- Caused by local eddy currents due to increased conductivity of body tissues
- Shows aa areas of shading or signal loss
- More prominent in 3T body imaging with large FOV
BLADE/Propeller/MultiVane can
- Reduce motion
- Reduce flow artifacts
- Reduce crosstalk
Cross Excitation artifacts
- Similar to Cross Talk, but deal more with subsequent, consecutive slices
- Signal loss due to partial saturation in adjacent slices
- Reduced by increasing gap or using interleaving
Metal artifact reduction
- Use TSE over Gradient Echo
- Use STIR instead of Fat Suppression techniques
- Utilize Wide rBW
- No parallel imaging or image uniformity correction
- Thin slices
- Small pixel size/large matrix
- High TSE factor/ ETL
- Add NEX/NSA to buy back signal, restore IQ
Moire Fringes artifact
- Caused by interference of aliased signals at different phases
- Most often seen in 3D gradient echo images at higher field strengths, when larger field of views are utilized
Free Induction Decay (FID) artifact
- Give the appearance of Gibbs-like artifacts, but originate from an incompletely crushed FID signal from an RF refocusing pulse
- Common in FSE / TSE sequences because of their pulse sequence design and their high SNR
- Contributing factors leading to fine line artifacts are reduced refocusing pulses, increases in FOV, and decreases in slice thickness
FID artifact reduction
Increase in NEX and/or the enabling of Flow Compensation
Magic Angle artifact
Occurs when a tendon or ligament is positioned approximately 55° to the direction of the main magnetic field, and a short TE value pulse sequence is utilized
Annefact (cusp) artifact
- Caused by active RF elements in a phased array coil outside the scanning FOV
- Primarily occurs in the phase encoding direction
- Can be corrected by simply de-selecting the element(s) outside the scanning range
Aliasing occurs because tissue outside the selected FOV is:
Undersampled
Magnetic resonance imaging (MRI) uses ________ separate magnetic fields to perform the task of routine image acquisition
3
DWI susceptibility artifacts in or around strong air tissue interfaces can be minimized by:
Increasing parallel imaging acceleration factor
In what anatomical region would you expect to see chemical misregistration the least?
Chemical shift misregistration artefact manifests as bright or dark outlines predominantly at fat / water interfaces. This can present problems in the detection of subtle abnormalities of the optic nerve or small disc herniations in the thoracic spine, or kidneys for example
Most anterior heart chamber
Right ventricle
Most posterior heart chamber
Left atrium
Fastest vessel for carrying blood
Aortic arch
Connects the inferior surface of the aortic arch to the root of the left pulmonary artery
Ligamentum arteriosum
Representative of atrial muscle contraction (systole)
P wave
Representative of ventricular systole (muscle contraction)
QRS complex
Representative of ventricular diastole (muscle relaxation)
T wave
ECG recording during an MRI examination is affected by:
- The magneto-hydrodynamic effect
- Currents induced by gradient variation, RF pulses and breathing, which alter the ECG trace
Trigger delay
- Delay after the system detects the R wave, before transmitting RF to the intended slice
- Purpose of this delay can be to postpone slice acquisition until the heart is diastolic, which is the relaxation period of the heartbeat
Trigger window
- Interval between the end of data acquisition and the next R wave (waiting period before each R wave)
- Expressed as percentage
- Typically 10-15% of the R-R window
- Prospective-gating sequences will exclude late diastole due to trigger window
Common problems with ECG-triggered acquisitions
-Poor or inaccurate R wave detection (e.g., triggering off a prominent T wave) —–Patient arrhythmias
Prospective gating
- Most common
- Triggered by R wave
- Utilizes an arrhythmia rejection method of pausing sequence data collection for the purpose of allowing variations in the subject’s heart rate
Retrospective gating
- Useful in patients with arrhythmias because data from irregular heartbeats can be rejected
- No trigger window and the full cardiac cycle is imaged
- Cine sequences collect data continuously during a cardiac cycle
- Particularly helpful if peripheral pulse gating is used
Best method to evaluate a cardiac infarction:
Perfusion cardiac imaging
R-R interval calculation (ms TR)
60,000ms / BPM
Imaging time in MR cardiac gated sequence Formula
R-R Interval - (trigger window + trigger delay)
Which sequence is best suited for cardiac imaging?
EPI
Where do the coronary arteries originate from?
Aortic root
The chamber of the heart with the thickest myocardium is the:
Left ventricle (also the largest)
Isotropic diffusion:
Water molecules move the same way in every direction
Anisotropic diffusion:
Water molecules clearly move in a preferred direction
Diffusion
Thermally induced motion of water molecules in tissues
Higher B-value
- Stronger diffusion weighting
- Increased signal loss
Calculation of the ADC requires:
2 or more acquisitions with different diffusion weighting
Diffusion-weighted imaging (DWI) can be performed by:
- Using diffusion gradients on each side of the 180° pulse when using very fast, single-shot spin-echo echo-planar sequences with varying b-values
- The first pulse dephases the spins, and the second pulse rephases the spins if no net movement occurs
Perfusion Imaging
- A means to establish “vascularity” of a given process
- Comparing “vascularity” at a particular point compared with internal reference (normal white matter)
- Unit of measurement: relative Cerebral Blood Volume (rCBV)
- rCBV is proportional to degree of neovascularity or capillary density
- Final result is a set of calculated images which indicate various flow characteristics
Uses of Perfusion:
- Differentiating tumor from non-tumor, and primary brain neoplasm from secondary lesions (e.g. metastasis)
- Glioma grading
- Stereotactic biopsy guidance
- Differentiating tumor recurrence from radiation necrosis
Perfusion Protocol:
- Ultra Fast Gradient Echo sequence with bolus injection IV Gadolinium @ 4cc/sec
- Exponential Time Curves generated on separate workstation, with multiple ROI’s generated to calculate specific rCBV’s
- NAWM (Normal appearing white matter) established as the control and the area(s) of pathology/edema are compared to the NAWM to determine vascularity
Dynamic Susceptibility Contrast (DSC)
T2* gradient echo Perfusion imaging, utilized in Brain Perfusion studies
Dynamic Contrast Enhancement (DCE)
Basic T1 perfusion imaging (pituitary or prostate dynamic sequences, longer acquisition times/dynamic compared to DSC)
Functional MRI
Imaging technique that employs a very rapid pulse sequence while the patient is at rest or performing a task
Spectroscopy
- Able to obtain biochemical information about the chemical components in tissues
- Final result is a spectrum of specific metabolites detected
N-acetyl Aspartate (NAA)
2.02 ppm (D)
Choline
3.2 ppm (I)
Creatine & phosphocreatine
3.0 ppm (IDA)
Lipids
0.9-1.5 ppm (I)
Lactate
1.33 ppm (P)
Myo-inositol
3.56 ppm (I)
Glutamate and Glutamine
2.2-2.4 ppm (I)
At 1 Tesla the difference in precessional frequencies between fat and water is:
147 Hz
At 1.5 Tesla the difference in precessional frequencies between fat and water is:
220 Hz
As magnetic field strength increases, chemical shift:
Increases
Pixel Shift calculation
Bandwidth x 1000 (to convert to Hz) ÷ matrix, then divide chemical shift by answer
28.2 x 1000 = 28200 Hz; 28200 ÷ 256 = 110;
220 ÷ 110 = 2 pixel shifts between fat an water
The Ernst angle can be defined as the optimal _________ that yields the _________ signal for a particular spin in the least amount of time
Flip angle; maximum
The phase encoding step is performed:
Prior to frequency encoding
A major advantage of a 2D time of flight over a 3D time of flight sequence is the ability to:
Image larger areas without saturation of flowing blood
A disadvantage of TOF MRA is high signal in some background tissues. To minimize signal from background tissues, TE should be selected that enable the signals from fat and water to be:
Out of phase (minimize signals from background stationary tissues in time of flight MR angiography)
Phase contrast MRA techniques produce images in which the signal intensity within the vessel is dependent upon the:
Velocity of the flowing blood
When imaging a geriatric patient, while performing a PCA MRA sequence, what imaging parameter might the operator adjust?
VENC (velocity encodings) might be adjusted in an elderly (geriatric) patient during a PCA (phase contrast angiography) MRA sequence to compensate for changes in the rate of blood flow
In an MRA sequence, the removal of signal from vessels is accomplished by:
Spatial presaturation
Permanent magnets with a vertical magnetic field use surface coils that are:
Solenoids
The transmit bandwidth of the RF pulse affects:
The transmit bandwidth of the RF pulse affects the slice thickness, which has an effect on resolution and the overall SNR in the MR image
________ sequences use T1 gradient echoes with TR and FA selections to suppress signal from stationary tissues, visualizing flowing blood by flow-related enhancement, whereas __________ sequences use T2 gradient echoes with parameter selections that suppress stationary tissue and rely on velocity-induced phase shifts for vascular signal
TOF MRA; PC MRA
Which of the following, in an MRA sequence, aids in minimizing the loss of signal due to dephasing within a voxel:
Smaller voxel size, short TE
Dynamic enhanced MRA sequences of the mesenteric arteries are performed using:
Incoherent gradient echo
Shimming in MRI can be performed by:
- Adding current to the gradient coils
- Adding metal to different coils within the shim coil
- Changing the current in the shim coil
Which of the following best describes an EPI sequence?
A train of gradient echoes
Magnetic field inhomogeneity is expressed in:
PPM
In what orientation would a tear of the collateral ligaments of the knee be best visualized?
Coronal
A technique utilized to reduce the MRI scan time which requires the use of an array coil is:
Parallel Imaging
The energy used to form MRI images is ______ from the patient’s tissues
Emitted
Increasing the flip angle:
Increases SNR up to the Ernst angle
Which of the following combinations of flip angle (FA) and TR would produce a T2 weighted gradient echo?
450 TR; 30º flip angle
In a Fast Spin Echo (FSE) sequence, acquired with a long TE, yielding T2 weighted images, scan time can be reduced by:
Using longer ETL
When a gradient echo sequence is selected for fast, breath hold dynamic contrast-enhanced imaging of the abdomen, ______ is utilized
Spoiling
When imaging the female pelvis, the most optimal view for evaluation of the ovaries is the:
Coronal
When imaging the spine, to rule out metastatic lesions of the spinal cord, contrast enhancement is used with T1 weighted images because:
Metastatic lesions (in the cord) enhance and normal cord does not
The optimal imaging plane for visualization of a TFCC tear is:
Coronal
MR angiography of the abdominal aorta and runoff of the lower extremities is acquired with dynamic contrast enhancement and:
Stepping table motion from the abdomen down to the feet following the contrast injection
Which cranial artery passes through the sylvian fissure?
Middle cerebral
Brachiocephalic artery AKA:
Innominate artery
Basal vein AKA:
Rosenthal vein
Zygapophyseal joint AKA:
Facet joint
The vertebral body will display a _________ signal intensity on T1 weighted images in the presence of fracture, infection or neoplasm
Hypointense
Breast implant rupture
- Sagittal, small FOV
- Contrast not mandatory
The larger and more direct terminal branch of the popliteal artery is the:
Posterior tibial artery, which supplies blood to the foot, and has a crucial branch known as the fibular, or peroneal artery.
A major advantage of a 3D time of flight over a 2D time of flight sequence is the ability to:
Visualize smaller vessels
Flow before an area of stenosis is defined as:
Laminar flow
Which of the following MR angiography techniques has a scan time short enough to complete an abdominal study in a single breath hold?
Contrast enhanced
When utilizing time-of-flight (TOF) MRA to evaluate peripheral vascular flow, such as arterial blood flow in the legs, presaturation pulses are:
Positioned inferior to the slice group
In time-of-flight (TOF) imaging, areas of signal void can be seen on the image due to:
Turbulent flow, vortex flow
In order to obtain a time of flight MRA of the IVC a presaturation band would be placed:
Superior
The shorter the rise time:
The faster the gradients and echo spacing
Gradients with a shorter echo spacing will have:
Better resolution capabilities and more available slices per TR period
Array processor and RF power amplifier are located in the:
MR equipment room
In order for energy to be efficiently transferred between a transmitter and receiver, the two must be at the same:
Frequency
Consistent room temperature of 65-75°F, humidity of 50-70%, and sufficient air flow in the MR scan room is recommended to:
Make patients less vulnerable to the RF heating effects
The intensity limit for a static magnetic field in clinical use is limited by the Food and Drug Administration (FDA) to:
4.0 Tesla field strength for all patients, but 8 Tesla for all patients over 1 month of age
At 3 Tesla the difference in precessional frequencies between fat and water is:
440 Hz
A magnetic vector possesses attributes of both:
Magnitude (strength) and direction
What has a higher precessional frequency?
Water
_________ magnets can be “shut off” the quickest in case of an emergency
Resistive
How many radiofrequency pulses produce a FID?
1
Multiple coil elements combined with multiple receiver channels make a:
Phased array coil
Which of the following has been documented to cause muscle contractions, cardiac arrhythmias, mild cutaneous sensations and visual light flashes?
Time varying magnetic fields (gradient)
The strength of the gradient magnetic fields are measured in:
Gauss per centimeter of Millitesla per meter
A coil that is not properly tuned to the correct magnetic field strength will result in:
Signal loss
If a sagittal slice plane has been selected, the __________ is enabled to alter the magnetic field around the patient’s body
X gradient
Applying two gradients simultaneously during slice selection would:
Produce an oblique slice
Which of the following sequences would be more at risk for the effects that time varying magnetic fields can cause?
EPI (train of gradient echoes)
The measurement of radiofrequency absorption is delineated as:
Watts/kg
The strength of the gradient over a specific distance is known as the:
Slew rate
SSFP is an abbreviation for:
Steady state free precession
FA is short for:
Fractional anisotropy or Flip angle
_________ is simply defined as the distance between echoes
Echo spacing
_____________ prevents or reduces motion artifacts in an MR image caused by the beating heart or pulsating blood flow and enables the images to be acquired synchronized to movement
Cardiac triggering
The __________ is the alternating magnetic field generated by the RF in a transceiver coil
B1
An ________ comprises a multiprocessor that is switched in sequence and in parallel while simultaneously performing a computing task
Array processor
What is the term for the echo generated by switching a pair of dephasing and rephasing gradients, without the use of a 180° refocusing pulse?
Gradient echo
Regions of the body that do not quickly dissipate thermal absorption from SAR during MR procedures are:
Eyes and testicles
The primary biological effects of radiofrequency fields are:
Tissue heating and thermal heating
The primary risk of the main static magnetic field is:
Missile or torpedo effect
The primary biological effects of the time varying magnetic fields (TVMF) are:
- Peripheral nerve stimulation, visual light flashes (magneto phosphenes) and muscle contractions.
- The FDA limit on time varying magnetic fields is once the patient experiences peripheral nerve stimulation.
________ is more of a concern in fast spin echo sequences due to the multiple echo train lengths, leading to potential increases in tissue heating
RF heating (due to multiple ETLs)
The pulse sequence that should be utilized the least in a patient with implanted metallic hardware is a:
Gradient echo sequence (lack a 180° RF pulse that aids in correcting local magnetic field inhomogeneities)
Which of the following is used in the MRI suite to monitor patients?
-Blood Pressure
-ECG
-Pulse Oximeter
-End Tidal CO2
(All)
Symptoms of a patient in cardiac arrest might include:
- Pallor and weakness
- Not having a pulse
What items should be worn by a healthcare provider during any direct contact with a patient?
Gloves
The fringe magnetic field:
Can cause nearby medical devices to malfunction
It is ___________ that every patient having an MRI be provided auditory protection in the form ______________
Recommended; earplugs and/or headphones
