hardware control

In acquiring ACR QA data, Image 211 is used to evaluate for what quality measure?

Geometric accuracy -- X/Y gradients

Utilization of surface coils (linear coils) yields a more

localized, smaller FOV capability with increased SNR

CP coil (circularly polarized) transmission or receiver coil with two orthogonal transmission and/pr reciver channels, also known as a quadrature coil, yields

better SNR than liner coils

RF heating is more of a concern in _

fast spin echo sequences due to the multiple echo train lengths, leading to potential increases in tissue heating

The 180° RF pulse is _ the power of the initial 90° RF pulse.

4x

gradient rise time is defined as the time it takes for the gradient to reach its full amplitude measured in

microseconds- mT/m or G/cm

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.

Measured in mT/m/msec or T/m/sec

The shorter the rise time, the faster the gradients and therefore echo spacing. Gradients with a shorter echo spacing will have

better resolution capabilities and more available slices per TR period

1 T/m= _ G/cm

100 Gauss/cm

The MR signal in MRI is produced by the process of resonance, which is the result of radio frequency coils. They consist of two electromagnetic coils, the_ generating and receiving electromagnetic fields

transmitter and receiver coils

when going from a linear coil to a quadrature coil, snr is increased by

40%

The primary biological effect of radiofrequency field is _

tissue heating

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

In acquiring ACR QA data, Image 212 is used to evaluate for what quality measure?

Geometric accuracy -- Z gradient

Which of the following is NOT a magnetic field associated with MR imaging?

• Static magnetic fields

• Oscillating magnetic fields (RF)

• Time varying magnetic fields (gradient)

• Gravitational earth magnetic fields

Gravitational earth magnetic fields

The _____ is located within an equipment room.

RF power amplifier

The liquid cryogens are cooled in a superconducting magnet at a temperature of _________?

4 Kelvin

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

4 tesla

The duty cycle can be viewed as the:

time the gradients are on during a TR period

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

copper

The CPU used to plot and adjust slices in an MR sequence is located:

scan control room on the operator console

The unit of measurement of the magnetic field surrounding the periphery of the MR scanner is expressed as:

Gauss

The local RF coil used to image a human brain is typically located/kept in the __________.

magnet room

Referring to SAR impact on the patient, all of the following parameter changes negatively impact pulse duty cycle EXCEPT:

• Presaturation slab employment

• Reduction in # slices

• Decreased TR

• Fat suppression selection

• Increased ETL

Reduction in # slices

What type of magnet is used with most systems currently manufactured?

superconducting

Image 78 is an example of what type of MR scanner?

open magnet

The liquid cryogens most often used to maintain field strength in a super conducting MR system are:

helium

Doubling field strength will result in what impact on SAR potential, if any?

quadruple SAR

The patient image display with sequence parameter visualization is located in the _________.

scan control room

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

copper

In acquiring ACR QA data, Image 213 is used in evaluating what quality measure?

low contrast spatial resolution

In a cross sectional view of the MR magnet design, which coils are closest to the patient?

Radiofrequency coils

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 purpose of shimming the magnet is to:

Make the B0 field as homogenous as possible

___________ 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; passive

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

In acquiring ACR QA data, Image 210 is used to evaluate for what quality measure?

High contrast spatial resolution

Passive shielding can be accomplished by lining the MR room with ___________.

steel

Doubling the magnetic field strength will:

Yield an increase of double the SNR

The direction of the magnetic field in Image 79 is:

horizontal

Image 82 was acquired at what field strength?

1.5 Tesla

When acquiring ACR QA data, the slice correlating to Image 213 requires what visual discernment?

10 visible spokes of 3 discs each

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

Image 79 is an example of which MR system?

Superconducting magnet

Field strength at magnet isocenter is measured in units of:

Tesla

Active shielding can be defined as:

Superconducting windings within the MR scanner, reducing the fringe magnetic field

Transmit gain is a quality measure evaluating for?

Accuracy of flip angles

The array processor is responsible for:

Reconstructing the images using the Fourier transform

In order for energy to be efficiently transferred between a transmitter and receiver, the two must be at the same:

frequency

High field scanners typically have field strengths greater than or equal to:

1.5 tesla