05) Instrumentation
18.
The term “metadata”, as used within the DICOM environment, refers to the information about:A) the image data (pixel values) contained in an image DICOM file
B) the MR protocol used to scan the patient
C) the scanned patient
D) the facility performing the scan
E) all of the above
E) all of the above
19.
The term “lookup table” (LUT), refers to the laser camera calibration process that accounts for:
A) the nonlinear features of the human visual system
B) the imperfections of laser camera hardware
C) the performance characteristics of the film
D) the brightness and contrast settings (window and level) used by the technologist to film the image
E) the way the MR scanners formats the image pixel data sent to the laser camera
A) the nonlinear features of the human visual system
20.
The main task of the reconstructor engine in the MR scanner is to:A) cleanup errors and imperfections in the raw data acquired during scanning
B) perform the discrete Fourier Transform (DFT) of the MR data
C) cleanup the MR image by removing imperfections related to hardware performance limitations
D) filter out parasitic signals that are not a part of the MR image
E) reformat the MR images for proper display and archiving, including DICOM compliance
B) perform the discrete Fourier Transform (DFT) of the MR data
1.
A magnet that has two sets of windings with currents flowing in opposite directions, with one set close to the patient, the other farther away, is:
A) an unshielded design
B) a passively shielded design
C) an actively shielded design
D) a hybrid (mixed) shielding design
C) an actively shielded design
2.
Which of the following is measured by the SAR?
A) the rate of change of the gradient fields
B) the strength of the static field
C) the size of the signal read by the RF receiver
D) the RF energy deposited in the patient
E) the number of RF pulses applied during an exam
D) the RF energy deposited in the patient
3.
The term “phased array coil” refers to which of the following?
A) sequential excitation of multiple coils
B) use of multiple coils and multiple data channels
C) the “birdcage” coil geometry
D) use of two coils to develop phase coherence
E) electronic detuning of surface coils during RF excitation
B) use of multiple coils and multiple data channels
4.
The strength of the magnetic fringe field associated with a MRI unit falls off with distance R from the center of the field in proportion to
A) R
B) one over R (1/R)
C) one over R squared (1/R2)
D) one over R cubed (1/R3)
E) one over R to the fourth power (1/R4)
D) one over R cubed (1/R3)
5.
Eddy currents are induced by which one of the following?
A) cardiac ECG leads
B) high strength magnetic fields (i.e., > 0.5 T)
C) time varying gradient magnetic fields
D) patient motion
E) blood flow
C) time varying gradient magnetic fields
6.
Which of the following is NOT a feature of eddy currents?
A) they counteract field generated by the gradient coils
B) they depend on gradient coil geometry
C) they can be reduced by active shielding
D) they can be reduced by modification of gradient waveforms
E) they can be reduced by passive shimming
E) they can be reduced by passive shimming
7.
A primary limiting factor in the implementation of fast MR imaging sequences is the switching rate of magnetic field gradients. This limitation is due to:
A) inability of the gradient amplifiers to generate the required current
B) insufficient current ratings of the gradient coils
C) electrical characteristics (such as self-inductance) of the gradient coils
D) excessive acoustic noise generated by gradient fields
C) electrical characteristics (such as self-inductance) of the gradient coils
8.
A quench can be used to:
A) improve the image quality in MRI
B) rapidly remove the superconductivity and the magnetic field
C) maintain the homogeneity of the magnetic field
D) terminate the exam abrubtly if the patient suffers claustrophobia panic attack
E) improve the stability of the magnet
B) rapidly remove the superconductivity and the magnetic field
9.
Coils least commonly used in modern MRI scanners are:
A) linear transmit coils
B) linear receive coils
C) quadrature receive coils
D) quadrature transmit coils
E) phased array receive coils
B) linear receive coils
10.
The main advantage of the superconductive magnet design is:
A) low cost
B) minimal maintenance requirements
C) an ability to produce a very homogeneous magnetic field
D) an ability to produce a very stable magnetic field
E) an ability to produce a very strong magnetic field
E) an ability to produce a very strong magnetic field
11.
The main advantage of the permanent magnet design is:
A) low cost
B) minimal maintenance requirements
C) an ability to produce a very homogeneous magnetic field
D) an ability to produce a very stable magnetic field
E) an ability to produce a very strong magnetic field
A) low cost
12.
The reduction of image artifacts caused by eddy currents is achieved by using:A) a self-shielded magnet
B) an actively shielded magnet
C) a set of self-shielded MFG coils
D) a set of actively-shielded MFG coils
E) a set of quadrature MFG coils
D) a set of actively-shielded MFG coils
13.
The eddy current compensation scheme, used to reduce the image artifacts caused by eddy currents, consists of:A) an alteration of MFG pulse shape, called “pre-emphasis”
B) an alteration of the MFG pulse duration, called “pro tempore”
C) a change in polarity of consecutive MFG pulses called “gemini swap”
D) an implementation of nonlinear gain in gradient amplifier, called “affine distortion”
E) special software post-processing routines
A) an alteration of MFG pulse shape, called “pre-emphasis”
14.
Typical RF power used with a dedicated head transmitting coil on a 1.5T MRI scanner is about:
A) 50 W
B) 100 W
C) 200 W
D) 400 W
E) 800 W
D) 400 W
at 1.5T, typical sequences that use the body coil to transmit RF pulses require about 12–14 kW of instantaneous RF power, while using a much smaller head coil for the same task requires much less power, about 400 W or so.
15.
Typical RF power used with the body coil on a 1.5T MRI scanner is about:
A) 4 kW
B) 8 kW
C) 14 kW
D) 20 kW
E) 30 kW
C) 14 kW
at 1.5T, typical sequences that use the body coil to transmit RF pulses require about 12–14 kW of instantaneous RF power, while using a much smaller head coil for the same task requires much less power, about 400 W or so.
16.
In two scanners, one operating at 1.5T and the other at 3T but otherwise identical, the RF power requirements to drive the transmit coils of the same effective volume, are:
A) two times higher for the 3T system
B) two times higher for the 1.5T system
C) four times higher for the 3T system
D) four times higher for the 1.5T system
E) the same for both systems
C) four times higher for the 3T system
It is important to realize that the requirements for the RF power increase in proportion to the coil volume and to the square of the main magnetic field.
17.
The dwell time of the analog–to–digital converter (ADC) determines:
A) the analog bandwidth of the MR signal
B) the digital bandwidth of the MR image
C) the lower limit of available digital bandwidth range
D) the number of samples collected during a single data acquisition window
E) the number of samples collected within a single phase-encoding run, called a “view”.
B) the digital bandwidth of the MR image