HARDWARE QA/QC Flashcards
The location of the coils installed in the MRI scanner, from the inner point closest to the patient to the outer most edge, are:
- RF radiofrequency coils
- gradient coils
- shim coils
- main magnet
The gradient rise time is defined as
the time it takes for the gradient to reach its full amplitude
measured in microseconds — mT/m (milliTesla/meter) or G/cm(Gauss/centimeter).
The** gradient slew rate** is
the speed rate of ascent or descent of a gradient from zero to its maximum amplitude, either positive or negative
Which is the amplitude divided by the rise time in msec. Measured in mT/m/msec or T/m/sec.
The duty cycle is defined as
the time the gradients are on during a TR period
“gradient working time”
Parameter changes affecting the pulse duty cycle include:
- Increased # slices
- Employment of fat suppression pulses (SPAIR requires increased TR
compared to SPIR) - Utilization of presaturation slabs/bands
- Increased ETL
The primary cause of the noise in the MR scan room is
the rapid, successive switching of the gradient coils
RF heating is more of a concern in ________ sequences due to the multiple echo train lengths, leading to potential increases in tissue heating.
fast spin echo
Doubling field strength results in ____ increase in SAR potential.
fourfold (4x)
The primary biological effect of radiofrequency fields is
tissue heating
Consistent room temperature of ____________ and sufficient air flow in the MR scan room is recommended to make patients less vulnerable to the RF heating effects.
65-75°F, humidity of 50-70%
For energy to be efficiently transferred between a transmitter and receiver, the two must be
at the same frequency.
Utilization of ___________ yields a more localized, smaller FOV (field of view) capability, with increased SNR, thus providing opportunity for improved image quality on most systems.
surface coils (linear coils)
A 6 inch surface coil is able to receive signal ____ inches deep into the patient
3
(SNR penetration depth = ½ coil diameter)
Circularly polarized transmission or receiver coil with two orthogonal
transmission and/or receiver channels are
CP coil, also known as a quadrature coil
This yields better signal-to-noise than a linear coil
When going from a linear coil to a quadrature coil, SNR is increased by
40%
A ________ is comprised of multiple coil elements combined with multiple receiver channels.
phased array coil
The patient image display with sequence parameter visualization is located in the
scan control room on the operator console
The CPU used to plot and adjust slices in an MR sequence is located in the
scan control room at the technologist operator console
The array processor is responsible for reconstructing the collected MR
images/data using the Fourier transform, and is located in
the MR equipment room.
The RF power amplifier is located within
an equipment room
Radiofrequency (RF) shielding can be achieved by lining the scanner room walls with
Copper
________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.
Passive
_______shielding requires the implementation of superconducting windings within the construction of the MR scanner to oppose a portion of the magnetic field.
Active
What is the magnetic field surrounding the periphery of the
MR scanner?
Fringe Field
The unit of measurement of the fringe field is expressed as
Gauss
FDA limit for static magnetic field in clinical use is
4.0 Tesla (T) field strength for all patients, but 8 Tesla for all patients over 1 month of age
The most commonly used system in MR imaging today is the
Superconducting magnet
In a superconducting magnet, the magnetic field strength is increased by
- increasing the turns of wire
- increasing current in the wires
- by reducing the spacing between the wires.
The orientation of the main magnetic field in a high field, superconducting, short bore magnet is
horizontal
The liquid cryogens are cooled in a superconducting magnet at a temperature of
4
4 Kelvin (-270° Celsius / -452° F!!)
The liquid cryogens most often used to maintain field strength in a super
conducting MR system are
Helium
During a quench of the MR system, patients and employees should be evacuated from the scan room to
- avoid asphyxiation,
- frostbite,
- and/or damage to tympanic membranes
A quench refers to
the sudden loss of superconductivity when its temperature is raised
All of the following are magnetic fields associated with MR imaging:
- Static magnetic fields
- Oscillating magnetic fields (RF)
- Time varying magnetic fields (gradient)
The MRI system component that produces the magnetization of proton spins (alignment) is known as
the main magnet
The MRI system component that provides the ability to perform spatial
encoding is the
gradient system
Side effects of the Time varying magnetic fields (gradient) have been documented as
- muscle contractions,
- cardiac arrhythmias,
- mild cutaneous sensations
- visual light flashes(Magnetophosphenes)
Side effects of the Oscillating magnetic fields (radiofrequency)
tissue heating
Quality Assurance (QA) utilizes the goal of
maintaining a desired level of consistency and image quality requirements within Radiology
QA (quality assurance) asks the question
“Are we operating the devices or equipment correctly?”
Quality Control (QC) asks the question
“Is the equipment operating correctly?”
____________is an inherent manufacturer quality mechanism by which a technologist, physicist or field service engineer might evaluate the performance of an MRI system.
System Performance Testing (SPT), or PIQT (Periodic Image Quality Test)
In acquiring ACR QA data, Image 210 is used to evaluate for what quality measure?
High contrast spatial resolution
In acquiring ACR QA data, Image 212 is used to evaluate for what quality measure?
ensures accuracy of Z gradient
In acquiring ACR QA data, Image 211 is used to evaluate for what quality measure?
ensures accuracy of X and Y gradients
When acquiring ACR QA data, the slice correlating to Image 213 requires what visual discernment?
10 visible spokes of 3 discs each
Multiple coil elements combined with multiple receiver channels make a:
Phased array coil
Magnetic field inhomogeneity is expressed in:
Parts per million
When going from a linear coil to a quadrature coil:
SNR is increased by 40%
The gradient rise time is defined as the:
Time it takes for the gradient to reach its full amplitude
RF (radiofrequency) energy is
Low energy non-ionizing radiation
Which of the following sequences would be more at risk for the effects that time varying magnetic fields can cause?
A. SE. B. FSE.
C. GE. D. EPI
D. EPI
