Hardware QA/QC
RF
Employ longer and lower amplitude transmit ____ pulses (base behind low SAR sequences).
phase encoding
Employ parallel imaging techniques to reduce workload of the ______ _____ gradient.
increased
Larger patient = ______ SAR
amplifier
The RF power ______ is located within an equipment room.
rise time
The gradient ______ _____ is defined as the time it takes for the gradient to reach its full amplitude.
gradient amplitude
What is defined as the strength of the gradient?
350 Gauss/centimeter (G/cm) Move decimal two places to the right or multiply by 100
Convert 3.5T/m to Gauss/Centimeter (G/cm)
Z-gradient
If a transverse/axial slice plane has been selected, the __-gradient is enabled to alter the magnetic field around the patient's body.
superconductivity threshold
If the coil temperature rises above the _____ _____ (Tc), the windings suddenly develop a finite resistance. The several-dozen amperes of circulating current passing through this elevated coil resistance create heat. This heat causes a sudden, explosive boil-off of liquid helium.
4
If you double the field strength, SAR is ___ times greater.
RF Coils
In a cross sectional view of MRI system coils, the ____ coils are closest to the patient.
turns, current, spacing
In a superconducting magnet, the magnetic field strength is increased by increasing the _____ of wire, _____ in the wires, or by reducing the ________ between the wires.
sheet, blanket
In exams with high SAR (increased fast spin echo usage I.e. spine, long bone extremity work, pelvis...etc) be mindful of _____ and ____ use. Create a means for the heat to escape, as SAR/body temp correlates to the amount of thermal induction minus escaped heat.
metallic
It is important to know the Gauss/cm for every ______ implant! (Manufacturer guidelines are found at MRIsafety.com)
low
RF (radiofrequency) energy is ___ energy non-ionizing radiation.
echo train lengths
RF heating is more of a concern in fast spin echo sequences due to the multiple ____ ____ ____, leading to potential increases in tissue heating.
2
SAR is proportional to the power of ___ for the resonant frequency.
body coil
The ____ coil is an integrated part of the magnet design that acts as its own transceiver coil, with large FOV capabilities, but lacking high SNR of localized coils.
slew rate
The gradient ____ ___ is the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative. or The gradient ___ ____ is the strength of the gradient over a specific distance.
slew rate
The gradient ____ ____ is the amplitude divided by the rise time (msec).
4.0
The intensity limit for a static magnetic field in clinical use is limited by the FDA (Food and Drug Administration) to _____ Tesla (T) field strength for all patients, but 8 Tesla for all patients over 1 month of age.
tissue
The primary biological effect of radiofrequency fields is ______ heating.
superconducting, horizontal
This is a high-field ________ short bore magnet, ______ field direction.
vertical
This is a high-field superconducting _____ field open magnet.
EPI (Echo Planar Imaging)
Time varying magnetic fields (gradients) have been documented to cause muscle contractions, cardiac arrhythmias, mild cutaneous sensations and visual light flashes (magnetophosphenes). Current FDA guidance limits the Time Rate of Change of Magnetic Field (dB/dt) to levels which do not result in painful peripheral nerve stimulation. ____ _____ ____ sequences can have more of a detrimental effect on patients with regards to time varying magnetic fields.
1 Tesla/meter = 100 Gauss/cm
To convert vendor spatial gradient map into manufacturer conditions chart: _Tesla/meter = _Gauss/cm
magnet bore
Use vendor-specific positioning pads separating patient from _____ _____ edges, especially in bariatric patient imaging.
FOV, SNR
Utilization of surface coils (linear coils) yields a more localized, smaller ____ capability, with increased ______.
shortest
Utilize ______ ETL (echo train length) possible while allowing flip angle modulation techniques, where applicable. Flip angle sweep methods: -Philips: refocusing control -GE: VERSE, tailored RF -Siemens: Hyperecho, Restore Toshiba: T2 Plus
results in longer minimum TE, requiring a longer TR value = longer scan time
What is a disadvantage of using longer and lower amplitude transmit RF pulses?
duty cycle
What is defined as the time the gradients are ON during a TR period? AKA "gradient working time"
40%
When going from a linear coil to a quadrature coil, SNR is increased by ___%.
3"
A 6" surface coil is able to receive signal ___" deep into the patient. (SNR penetration depth = 1/2 coil diameter)
linear
A CP coil yields better signal-to-noise than a _____ coil.
phased array
A ______ ______ coil is comprised of multiple coil elements combined with multiple receiver channels.
signal
A coil that is not properly turned to the correct magnetic field strength will result in _____ loss.
opposite
A low SAR is ______ to vendor-built fast scan options.
parallel
A recent development in MRI are advanced multi-element phased array coils which are capable of acquiring multiple channels of data in ______.
SAR, increased
Consider Transmit/Receive coil, producing lowest ____ levels. Con on this is -significantly ______ scan time.
65-75°F, 50-70%, air
Consistent room temperature of ___-___°F, humidity of ___-___%, and sufficient ___ flow in the MR scan room is recommended to make patients less vulnerable to the RF heating effects.
SNR (signal to noise ratio)
Doubling the magnetic field strength will double the _____.
quench
During a ______ of the MR system, patients and employees should be evacuated from the scan room to avoid asphyxiation, frostbite, and/or damage to tympanic membranes.
520 G/cm
How many G/cm in 5.2 T/m?
X-gradient
If a sagittal slice plane has been selected, the __-gradient is enabled to alter the magnetic field around the patient's body.
solenoid
Permanent magnets with a vertical magnetic field use surface coils that are ______ because the secondary magnetic field (B1) created by the RF coil must be perpendicular to the orientation of B0.
radiofrequency
The MR signal in MRI is produced by the process of resonance, which is the result of __________ coils.
main magnet
The MRI system component that produces the magnetization of proton spins (alignment) is known as the _____ ____.
gradient system
The MRI system component that provides the ability to perform spatial encoding is the ______ _____.
array processor
The ____ _____ is responsible for reconstructing the collected MR images/data using the Fourier Transform, and is located in the MR equipment room.
CPU
The ____ used to plot and adjust slices in an MR sequence is located in the scan control room at the technologist operator console.
local
The _____ RF coil used to image brain is typically located/kept in the magnet room.
faster
The shorter the rise time, the (faster or slower) the gradients and shorter echo spacing.
1. increased # of slices 2. employment of fat suppression pulses (SPAIR requires increased TR compared to SPIR) 3. presaturation slabs/bands 4. increased ETL
4 parameter changes that affect the pulse duty cycle include: 1. increased # of _______ 2. employment of _____ ________ pulses 3. presaturation ____/____ 4. increased ____
1. static 2. oscillating 3. time
All of the following are magnetic fields associated with MR imaging: _____ magnetic fields ______ magnetic fields (RF) ______ varying magnetic fields (gradient)
SAR
Always enter the patient weight correctly, to allow for accurate system ____ calculations.
oblique
Applying two gradients simultaneously during slice selection would produce an ______ slice, such as the employment of XY gradient combination in a coronal oblique of the shoulder, parallel to the supraspinatus tendon.
shortest
Avoid "________ TR" as this has negative impact on pulse duty cycle (gradient on-time). Instead, increase TR to manageable level, decreasing SAR effect on patient.
quadrature
CP coil: Circularly polarized transmission or receiver coil with 2 orthogonal transmission and/or receiver channels, also known as a _______ coil.
skin, coiled, looped
Cables from local RF coils and gating leads should be braided and positioned straight in the bore, NEVER in direct contact with the patient's _____. They should NEVER be ______ or_____, as this can lead to RF burns in the patient.
Tesla
Field strength at magnet isocenter is measured is measured in units of _____, the SI derived unit of magnetic field measurement.
frequency
For energy to be efficiently transferred between a transmitter and receiver, the two must be at the same _______.
microseconds mT/m (milliTesla/meter) G/cm (gauss/centimeter) 10 mT/m = 1G/cm
Gradient rise time is measured in?
resolution, slices
Gradients with shorter echo spacing will have better _____ more available ____ per TR period.
1.5
High field scanners typically have field strengths greater than or equal to _._ Tesla.
fourfold (4x)
However, for field strength, SAR is proportional to the power of 2 for the resonant frequency. Therefore doubling field strength results in a _____ increase in SAR potential.
Y-gradient
If a coronal slice plane has been selected, the __-gradient is enabled to alter the magnetic field around the patient's body.
million
Magnetic field inhomogeneity is expressed in parts per _____ (ppm).
active, passive
Magnetic field shielding can be accomplished either by ______ or ____ shielding.
presaturation slbs/fat suppression, slices
Minimize use of ________ _____ / _____ _______ pulses, in addition to using the least # of ______ within a given TR period.
tissue heating
Oscillating magnetic fields (radiofrequency) primary biological effect is ______ ______.
copper
Radiofrequency (RF) shielding can be achieved by lining the scanner room walls with ______.
transmitter and receiver
Radiofrequency coils consist of 2 electromagnetic coils, 1. _______ and 2. ______ coils generating and receiving electromagnetic fields.
mT/m/msec T/m/sec
Slew rate is measured in
watts per kilogram (W/kg)
Specific absorption rate (SAR) is measured in ____ per _____ (W/kg).
superconducting
The _______ magnet is the most commonly used system in MR imaging today.
180°, 90°
The ____° RF pulse is 4x the power of the initial ____° RF pulse.
homogeneous
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 ________.
4 Kelvin -270° Celsius -452° F
The liquid cryogens are cooled in a superconducting magnet at a temperature of ___ Kelvin.
helium
The liquid cryogens most often used to maintain field strength in a superconducting MR system are _______.
1 RF (radiofrequency) coils 2 gradient coils 3 shim coils 4 main magnet
The location of the coils installed in the MRI scanner, from the inner point closest to the patient to the outer most edge are: 1 _________ coils 2 ________ coils 3 ______ coils 4 main ______
specific absorption rate
The measurement of radiofrequency absorption is known as ______ _____ ____ (SAR).
horizontal
The orientation of the main magnetic field in a high field, superconducting, short bore magnet is horizontal or vertical?
scan control room
The patient image display with sequence parameter visualization is located in the ____ ______ ____ on the operator console.
gradient coils
The rapid switching of the _____ _______ is the primary cause of the noise in the MR scan room.
Gauss
The unit of measurement of the magnetic field surrounding the periphery of the MR scanner (fringe field) is expressed as _____.
SAR
Therefore, utilization of multiple, powerful RF pulses (Fast spin echo sequences) can lead to increased ____ induction in a patient.
accelerated
This 'parallel imaging' technique uses unique acquisition schemes that allow for _______ imaging.
Quality Assurance (QA)
_____ ____ utilizes the goal of maintaining a desired level of consistency and image quality requirements within Radiology.
Quality Control (QC)
______ _____ reflects the set of activities and/or techniques used to fulfill the requirements for quality.
Passive
______ shielding can be accomplished by lining the MR room with steel or other ferromagnetic plating, thus reducing the scope and distance of the fringe field.
Quality Assurance (QA)
_______ _____ asks the question, "Are we operating the devices or equipment correctly?"
Active
_______ shielding requires the implementation of superconducting windings within the construction of the MR scanner to oppose a portion of the magnetic field.
Radiofrequency
__________ coils are 2 major parts of the radiofrequency (RF) system in the MRI hardware.