HARDWARE

A 6 inch surface coil is able to receive signal 3 inches deep into the patient SNR penetration depth =_____ coil diameter.

(SNR penetration depth = ½ coil diameter)

The measurement of radiofrequency absorption is know as what?

- Specific Absorption Rate (SAR) is delineated as Watts per kilogram (W/kg).

Table OK? The purpose of this question is to verify accuracy of laser light to table position. Periodically, the MRI technologist / MR physicist should verify the accuracy of the isocenter position in the magnet. Simply ensure the center of the phantom image is positioned ±0-2mm in the H-F or S-I dimension by placing the crosshair / isocenter mark at the top edge of the dark vertical bars (orange arrow below). T/F

true

High field scanners typically have field strengths greater than or equal to _____Tesla.

1.5

Utilizes the goal of maintaining a desired level of consistency and image quality requirements within Radiology. It asks the question, "Are we operating the devices or equipment correctly?"

Quality Assurance (QA)

Asks the question, "Is the equipment operating correctly?", and reflects the set of activities and/or techniques used to fulfill the requirements for quality

Quality Control (QC) a

The local ____ coil used to image a human brain is typically located/kept in the magnet room.

RF

_____ varying magnetic fields (gradient) 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. EPI (Echo Planar Imaging) sequences can have more of a detrimental effect on patients with regards to time varying magnetic fields.

Time

This test is done after establishing the resonant frequency of the system. Values are usually recorded in units of decibels (dB). • Establishing the transmitter gain levels is important in MR imaging because this provides information relating to the proper flip angles. Accurate flip angle measurements ensure appropriate SAR calculations in addition to consistent expected image contrast. • Fluctuations in the transmitter attenuation levels suggest problems with the radiofrequency chain. • The ACR MRI phantom is used and the transmitter attenuation is displayed on the scanner console. • The MRI technologist records the value displayed in column 5 on the Data Form • If action limits are exceeded, the technologist reports the problem to the qualified physicist or MRI scientist.

Transmitter Gain or Attenuation

If a sagittal slice plane has been selected, the ____ gradient is enabled to alter the magnetic field around the patient's body

X

The ____ cycle is defined as the time the gradients are on during a TR period, the "gradient working time." Parameter changes affecting the pulse duty cycle include: 1. Increased # slices 2. Employment of fat suppression pulses (SPAIR requires increased TR compared to SPIR) 3. Utilization of presaturation slabs/bands 4. Increased ETL

duty

parallel imaging phase direction.

iPAT

The gradient ____ ____ 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). Equally synonymous as the units of gradient strength measurement -- 10 mT/m = 1G/cm

rise time

The patient image display with sequence parameter visualization is located in the ____ _____ room on the operator console.

scan control

Utilize _____ ETL possible while enabling flip angle modulation techniques, where applicable. Flip angle sweep methods - Philips: refocusing control; GE: VERSE, tailored RF; Siemens: Hyperecho, Restore; Toshiba: T2 Plus

shortest

A coil that is not properly tuned to the correct magnetic field strength will result in what?

signal loss.

iPAT2 : parallel imaging phase and ____ dimensions

slice

Should you Minimize use of presaturation slabs / fat suppression pulses, in addition to using the least # of slices within a given TR period?

yes

Geometric Accuracy: Using the Sagittal localizer - top-tobottom measurement ensures accuracy of ____ gradient Results should = 148mm ±2mm

z

RF (radiofrequency) energy is low energy non-ionizing radiation. SAR is proportional to the power of ___ for the resonant frequency. Doubling field strength results in fourfold increase in SAR potential. The primary biological effect of radiofrequency fields is tissue heating

2

Transmit gain is a quality measure evaluating for?

Accuracy of flip angles

_________ would be used to contain the RF in an MR magnet room.

Copper

Which of the following sequences would be more at risk for the effects that time varying magnetic fields can cause? FSE EPI

EPI

RF (radiofrequency) energy is low/high energy?

Low energy non-ionizing radiation

Magnetic field inhomogeneity is expressed in:

Parts per million

Geometric Accuracy: Using slice #5, of ACR axial T1, measuring phantom horizontally and vertically ensures accuracy of ___ and ____gradients. Results should = 190mm ±2mm

X and Y

If a coronal slice plane has been selected, the ___ gradient is enabled to alter the magnetic field around the patient's body.

Y

If a transverse/axial slice plane has been selected, the ___ gradient is enabled to alter the magnetic field around the patient's body in a patient lying supine in the bore of the magnet.

Z

The _____ processor is responsible for reconstructing the collected MR images/data using the Fourier transform, and is located in the MR equipment room.

array

In a cross sectional view of MRI system coils, the RF coils are ____ to the patient. Therefore, utilization of multiple, powerful RF pulses (Fast Spin Echo sequences) can lead to increased SAR induction in a patient. The 180° RF pulse is 4x the power of the initial 90° RF pulse.

closest

Radiofrequency (RF) shielding can be achieved by lining the scanner room walls with _____.

copper

Parallel imaging R factor : parallel imaging reduces scan time _____ proportional to reduction -R- factor

directly

Doubling the magnetic field strength will _____ the SNR (signal to noise ratio). However, for field strength, SAR is proportional to the power of 2 for the resonant frequency. Therefore, doubling field strength results in a fourfold increase in SAR potential.

double

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

The shorter the rise time, the _____ the gradients and therefore echo spacing. Gradients with a shorter echo spacing will have better resolution capabilities and more available Trapezoidal gradient pulse utilized in conventional pulse sequences slices per TR period.

faster

For energy to be efficiently transferred between a transmitter and receiver, the two must be at the same _____.

frequency.

The body coil is an integrated part of the magnet design that acts as its own transceiver coil, with large FOV capabilities, but lacking the high SNR of localized coils. ▪ 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 _____ system

gradient

Using vendor-specific positioning pads separating patient from magnet bore edges, especially in bariatric patient imaging reduces SAR. _____

increased

Tracking of system performance can be accomplished by quantitative data entries into an accrediting body-approved (ACR, IAC, etc.)____ l sheet. By gathering extensive data, variations from the expected norm can be addressed.

log

All of the following are magnetic fields associated with MR imaging: • Static magnetic fields • Oscillating magnetic fields (RF) • Time varying magnetic fields (gradient)

memorize

Applying two gradients simultaneously during slice selection would produce an ____ slice, such as the employment of a YX gradient combination in a coronal oblique of the shoulder, parallel to the supraspinatus tendon.

oblique

Magnetic field inhomogeneity is expressed in _____ ____ _____ (ppm)

parts per million

Permanent magnets with a vertical magnetic field use surface coils that are solenoids because the secondary magnetic field (B1 )created by the RF coil must be _______ to the orientation of B0 .

perpendicular

Parallel imaging SENSE: P reduction = scan time reduction in _____ dimension

phase

A ____ _____ coil is comprised of multiple coil elements combined with multiple receiver channels.

phased array

The_____ function of the MRI technologist is to evaluate the overall image quality, by running a series of repetitive (daily vs. weekly) images, recording specific values, and flagging deviations from the normal range. The myriad of categories tracked regularly include system center frequency, transmit gain, geometric accuracy, and low/high contrast spatial resolution. Testing can be performed on a manufacturer-supplied phantom for SPT/PIQT testing, whereas ACR regulations require imaging acquired on a specific phantom providing multiple regions of targeted testing.

primary

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. This refers to the sudden loss of superconductivity when its temperature is raised. In the superconducting state, the resistance of the magnet coil windings is zero and hence no energy is required to maintain current flow.

quench

Employ parallel imaging techniques to _____ workload of the phase encoding gradient.

reduce

The MR signal in MRI is produced by the process of ______, which is the result of radio frequency coils. They consist of two electromagnetic coils, the transmitter and receiver coils generating and receiving electromagnetic fields. Atomic nuclei of interest in MRI studies have their own resonant frequencies, in the radiofrequency portion of the electromagnetic spectrum.

resonance

Yielding lowest allowable SAR levels result in what Penalty?

significantly increased scan times

The gradient ___ _____ 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 strength of the gradient over a specific distance is another way to define this.

slew rate

Parallel imaging SENSE: S reduction = scan time reduction in ____ direction (3D acquisitions)

slice

The liquid cryogens are cooled in a superconducting magnet at a temperature of ____ Kelvin. (-270° Celsius / -452° F!!) The liquid cryogens most often used to maintain field strength in a super conducting MR system are ____.

4 Helium.

The intensity limit for a static magnetic field in clinical use is limited by the Food and Drug Administration (FDA) to _____________?

4 Tesla

The intensity limit for a static magnetic field in clinical use is limited by the Food and Drug Administration (FDA) to _____Tesla (T) field strength for all patients, but ___ Tesla for all patients over 1 month of age.

4.0 8

When going from a linear coil to a quadrature coil, SNR is increased by ___%.

40

Consistent room temperature of ___-___°F, humidity 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 50-70%

When performing ACR quality assurance, using the ACR-approved phantom, specific measures can be attained via evaluation of specific slices. Adhere to rigorous parameter settings and planning regimens to ensure accurate measurements taken. Each of the 11 transverse slices obtained following the sagittal scout has a specific function or purpose that can be evaluated for various aspects within the MRI department QA program.

ACR Phantom Scans

Why do you enter the pts weight before starting scan?

Always enter patient weight correctly, to allow for accurate system SAR calculations.

Circularly polarized transmission or receiver coil with two orthogonal transmission and/or receiver channels, also known as a quadrature coil. This yields better signal-to-noise than a linear coil.

CP coil

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

The unit of measurement of the magnetic field surrounding the periphery of the MR scanner (fringe field) is expressed as ____.

Gauss.

In acquiring ACR QA data, Image 211 is used to evaluate for Geometric accuracy -- ____ gradient(s).

Geometric accuracy -- X/Y gradients

In acquiring ACR QA data, Image 212 is used to evaluate for Geometric accuracy -- ____ gradient(s).

Geometric accuracy -- Z gradient

Spatial Resolution: _____ contrast spatial resolution: Slice 1 of ACR Axial T1 - 3 sets of holes. Adequate results = observable holes (4) in UL and LR arrays

High Contrast Spatial Resolution:

_____contrast spatial resolution Using slice #8-11, of ACR axial T1, select slice containing the most "spokes" of low contrast holes. (contrast decreases furthest from slice #11). Count complete spokes (all three discs) - adequate ____ contrast resolution = 10 detectable spokes.

Low

Goal: To achieve and maintain a level of consistent, reproducible image quality in a Magnetic Resonance Imaging system, ensuring the safety of patients being scanned. As a segment of an imaging center or hospital's accreditation process, submission of data evidencing timely, adequate monitoring of system performance is a crucial facet to achieving accrediting body approval. Various components encompass a QA program in the MRI suite, including but not limited to: center frequency, transmit gain, SNR and visual inspections. Record keeping of the data collected is an industry standard, producible upon request and accessible to technologists, physicists and radiology managers.

MRI Department Quality Assurance / Quality Control Program

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 skin. The cables should _____ be coiled or looped, as this can lead to RF burns in the patient.

NEVER

Current FDA limits on time varying magnetic fields are:

Once the patient experiences peripheral nerve stimulation

______ magnetic fields (radiofrequency) - primary biological effect is tissue heating/deposition

Oscillating

Magnetic field shielding can be accomplished via active or passive shielding methods. ____ 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. _______ shielding requires the implementation of superconducting windings within the construction of the MR scanner to oppose a portion of the magnetic field.

Passive Active

Multiple coil elements combined with multiple receiver channels make a _____ array coil.

Phased array coil

The location of the coils installed in the MRI scanner, from the inner point closest to the patient to the outer most edge, are:

Radiofrequency coils, gradient coils, shim coils, main magnet

Employ longer and lower amplitude transmit RF pulses (base behind low SAR sequences). Drawback?

Results in longer minimum TE, requiring a longer TR value - increased scan time. (Low SAR opposite to vendor-built Fast scan options)

Repetitive recording of the SNR value taken from identical pulse sequence acquisitions within the same coil ensures adequate SNR for image quality. Action limits should be set to indicate requirement for service call when recorded values exceed normal threshold.

SNR value

Passive shielding can be accomplished by lining the MR room with ___________. Radiofrequency (RF) shielding can be achieved by lining the scanner room walls with_________. ___________ could be used to line the walls and/or floors of the MR magnet room to reduce the fringe field, and is defined as __________ shielding.

Steel copper Steel; passive

The CPU used to plot and adjust slices in an MR sequence is located in the scan control room at the technologist operator console. T/F

TRUE

The rapid, successive switching of the gradient coils is the primary cause of the noise in the MR scan room. T/F

TRUE

Field strength at magnet isocenter is measured in units of _____, the SI derived unit of magnetic field measurement.

Tesla

The array processor is responsible for:

The array processor is responsible for reconstructing the collected MR images/data using the Fourier transform, and is located in the MR equipment room.

If the coil temperature rises ____ the superconductivity threshold (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.

above

Gradient _____ is defined as the strength of the gradient.

amplitude

A recent development in MRI - ____ _____ -___ phased array coils which are capable of acquiring multiple channels of data in parallel. This 'parallel imaging' technique uses unique acquisition schemes that allow for accelerated imaging.

sophisticated multi-element phased array

Utilization of ____ coils (linear coils) yields a more localized, smaller FOV (field of view) capability, with increased SNR, thus providing opportunity for improved image quality on most systems.

surface

Why should you Avoid "shortest TR"?

this has negative impact on pulse duty cycle (gradient ontime). Instead, increase TR to manageable level, decreasing SAR effect on patient.

Radiofrequency coils are two major parts of the radiofrequency (RF) system in the Magnetic resonance imaging hardware. What are the two coils?

transmit and receive coils

Center Frequency? The purpose of this question is to ensure integrity of MR system operating frequency, at which all system coils will be tuned to. Variations from acceptable range warrant notification to manufacturer service engineers. T/F

true

Console OK? Patient Mic OK? The purpose of this question is to ensure sufficient ability to communicate with patients, via verification of microphone / console functionality. T/F

true

Particularly in exams with high SAR / increased fast spin echo usage (spine, long bone extremity work, pelvis, and any combination of these procedures) be mindful of sheet and blanket use.... Create a means for the heat to escape, as SAR / body temperature correlates to the amount of thermal induction ---minus--- escaped heat. T/F

true

System Performance Testing (SPT), or PIQT (Periodic Image Quality Test) is an inherent manufacturer quality mechanism by which a technologist, physicist or field service engineer might evaluate the performance of an MRI system. Normal ranges are established following installation, and testing is performed daily or weekly to ensure adherence to normal ranges of QA monitoring. T/F

true

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 homogeneous. T/F

true

To convert vendor spatial gradient map into manufacturer conditions chart: 1 Tesla/meter = 100 Gauss / cm MSG given: 3.5 T/m Move decimal two places to the right - 3.5 x 100 3.5 T/m = 350 Gauss / centimeter (G/cm) Example # 2: 5.2 T/m = 520 G/cm Important for every MRI technologist to know Gauss / cm for every metallic implant. T/F

true

The superconducting magnet is the most commonly used system in MR imaging today. In a superconducting magnet, the magnetic field strength is increased by increasing the ____ of wire, current in the wires, or by reducing the _____between the wires.

turns spacing