ASMIRT -MRI ACCREDITATION EXAM TEST
BANK 2025/2026 WITH ACTUAL CORRECT
QUESTIONS AND VERIFIED DETAILED
ANSWERS |CURRENTLY TESTING
QUESTIONS AND SOLUTIONS|ALREADY
GRADED A+|NEWEST|GUARANTEED PASS
What does the frequency encoding gradient do and what will it's strength depend on?
The frequency encoding gradient is switched on as the echo is received and will produce a
frequency shift dependent on position along this axis. This will allow the signal to be resolved in
one direction. The strength of the frequency encoding gradient required will depend on:
• the field of view
• the receiver bandwidth - i.e. the range of frequencies used to span the FOV
What does the phase encoding gradient do?
The phase encoding gradient is pulsed on briefly after the excitation pulse to produce a phase
shift between adjacent rows of pixels. This is repeated as many times as there are pixels in the
phase encoding direction. With each step, the strength of the gradient is varied slightly from a
maximum positive value though zero to a maximum negative value. This will produce a different
phase shift between pixel rows for each step. The gradient strength required for these
maximum steps will depend on: • the field of view • the number of pixels in the phase encoding
direction
To maximize spatial resolution, what needs to occurs between the steepest positive and
negative steps?
To maximise spatial resolution, the steepest positive and negative steps will need to create a
180 degree phase shift between adjacent columns since this will produce the maximum possible
phase separation.
The strength of the phase encoding gradient depends on
1|Page
,The gradient strength required for these maximum steps will depend on:
• the field of view
• the number of pixels in the phase encoding direction
What is sampling?
The echo is sampled and digitised in the presence of a frequency encoding (or read-out)
gradient. This is known as analog to digital conversion. The results are stored in an array known
as k-space. (
What is ADC, reference sampling rate and Nyquist theorem?
Converting the analog waveform into a digital signal requires us to sample the waveform at
multiple different points. In order to represent this waveform accurately we must sample the
waveform at a high enough rate. This is known as the sampling rate. The sampling rate used in
MRI is known as the Nyquist frequency and relates to The Nyquist Theorem. The Nyquist
Theorem is important to MRI and it dictates that any signal must be sampled at least twice per
cycle to represent it accurately
What is the sampling time, the sampling rate and receiver bandwidth?
• The sampling time is the duration of the gradient while 256 or 512 frequencies are sampled.
(eg. 8 msec)
• The sampling rate is the rate at which these samples are taken.
• The receiver bandwidth is the range of frequencies sampled during read-out (eg 16 kHz
What does reducing bandwidth do in terms of trade-offs?
Reducing the bandwidth will:
• increase sampling time
• increase SNR
• increase echo spacing for FSE scans and increase blurring
• increase chemical shift and susceptibility artefact.
What is a fourier transform?
Fourier analysis allows any time varying signal (such as a spin-echo) to be represented as a
spectrum of the frequencies present. Fourier Transformation converts RF intensity vs. time into
Signal amplitude vs. frequency thus allowing us to reconstruct images. The mathematical
procedure relating the functions of amplitude against time and amplitude against frequency is
known as Fourier Transformation - if one is known, the other can be readily calculated. This
process is ideally suited to MR image reconstruction which uses frequency shifts to spatially
localise the signal.
2|Page
,What is k-space?
K-Space is simply an array of numbers whose Fourier Transformation is the MR image. Simply K-
Space is best thought of as temporary image space, which is used to digitize MR signals during
acquisition.
In 2DFT imaging, the position of the values tells us what about where they were collected in
echo?
In 2DFT imaging, each horizontal row of K-space corresponds to the echo data obtained by
digitising the signal from one phase encoding step. The values at the left of each row are
collected early in each echo those at the right are obtained late. The centre of the row will
correspond to the centre of each echo and will therefore contain the largest values.
Why do rows of k-space data at the periphery ie. very top and bottom contribute most to spatial
resolution?
Each row of k-space data is obtained by varying the amplitude of the phase encoding gradient.
The rows at the top and bottom of the k-space grid are obtained with steep gradient slopes. This
will cause smaller signal amplitudes due to gradient-induced dephasing, however this will
maximise the phase separation of adjacent points. These lines therefore contribute most
towards the spatial resolution of the image.
Why do rows of k-space data at the centre contribute most to contrast?
The central rows are obtained using shallow gradient slopes so the echo amplitudes will be
larger due to little gradient induced dephasing. These lines will contribute most towards the
contrast of the image.
Does every cell in k-space correspond to an individual pixel?
It should be remembered that individual cells in k-space do not correspond to individual pixels
in the image - each pixel is represented in every k-space cell.
Explain how 2D k-space filling occurs
2D volumetric acquisitions fill one line of K-space for slice 1 and then fill the same line of K-
space for slice 2 etc. When one line of K-space has been filled for all slices the next line of K-
space is filled and so on until all the Kspace data has been acquired for all slices. Once the
sequence is finished all of the slices are reconstructed and displayed at the same time. This is
the most common method of K-space filling.
Explain 3D volumetric k-space filling
3|Page
, 3D volumetric techniques acquire data from an entire volume of tissue. The excitation pulse is
not slice selective rather the whole prescribed imaging volume is excited. As such K-space is
three dimensional. At the end of the acquisition the volume slab is divided into slices using an
extra gradient called the slice select gradient. A 3D FT is then used to reconstruct the images. An
example of this technique is a 3D T2* C-spine.
How can k-space be manipulated and why?
K-Space can be manipulated to suit the needs of the MRI examination under progress. Many of
these techniques are made possible due to the mirrored halves of K-Space. That being the top
and bottom halves as well as the right and left halves of K-Space mirror each other. This can be
advantageous to the operator and patient as manipulation of k-space can decrease scan times.
What is Partial / Fractional Echo?
• Relies on echo symmetry from left to right sides of K-space
• Only the right hand side of the echo is read by the frequency encoding gradient - the
remaining portion is calculated. (ie sample the right half of k-space and calculate the left)
• Allows the peak of the echo to occur closer to the RF excitation pulse so shorter TE's are
possible for MRA, T1 spin-echo and fast GRE.
What is partial fourier transform?
• Also relies on symmetry - this time between the positive and negative phase encodings or
halves of K-Space
• Sample the top half of K-space and calculate the bottom half.
• Actually need to sample slightly over half for phase correction.
• Reduces the acquisition time by nearly one half.
• Reduces the SNR to about 70% of a full acquisition (1/√2)
Why might a rectangular FOV be used and how does it affect image quality?
• Can be used for rectangular anatomical areas (eg. axial pelvis, sagittal spine)
• The field of view and the image matrix in the phase encoding direction are both reduced - eg.
to ½ or ¾ - this will cut down the imaging time accordingly.
• The gradient increment between each phase encoding step is increased to maintain spatial
resolution - ie. for ½ FOV the increment will be doubled so that the steepest phase encoding
steps are still performed.
• SNR will be reduced because of the reduction in the number of phase encodings.
What is SNR?
4|Page
BANK 2025/2026 WITH ACTUAL CORRECT
QUESTIONS AND VERIFIED DETAILED
ANSWERS |CURRENTLY TESTING
QUESTIONS AND SOLUTIONS|ALREADY
GRADED A+|NEWEST|GUARANTEED PASS
What does the frequency encoding gradient do and what will it's strength depend on?
The frequency encoding gradient is switched on as the echo is received and will produce a
frequency shift dependent on position along this axis. This will allow the signal to be resolved in
one direction. The strength of the frequency encoding gradient required will depend on:
• the field of view
• the receiver bandwidth - i.e. the range of frequencies used to span the FOV
What does the phase encoding gradient do?
The phase encoding gradient is pulsed on briefly after the excitation pulse to produce a phase
shift between adjacent rows of pixels. This is repeated as many times as there are pixels in the
phase encoding direction. With each step, the strength of the gradient is varied slightly from a
maximum positive value though zero to a maximum negative value. This will produce a different
phase shift between pixel rows for each step. The gradient strength required for these
maximum steps will depend on: • the field of view • the number of pixels in the phase encoding
direction
To maximize spatial resolution, what needs to occurs between the steepest positive and
negative steps?
To maximise spatial resolution, the steepest positive and negative steps will need to create a
180 degree phase shift between adjacent columns since this will produce the maximum possible
phase separation.
The strength of the phase encoding gradient depends on
1|Page
,The gradient strength required for these maximum steps will depend on:
• the field of view
• the number of pixels in the phase encoding direction
What is sampling?
The echo is sampled and digitised in the presence of a frequency encoding (or read-out)
gradient. This is known as analog to digital conversion. The results are stored in an array known
as k-space. (
What is ADC, reference sampling rate and Nyquist theorem?
Converting the analog waveform into a digital signal requires us to sample the waveform at
multiple different points. In order to represent this waveform accurately we must sample the
waveform at a high enough rate. This is known as the sampling rate. The sampling rate used in
MRI is known as the Nyquist frequency and relates to The Nyquist Theorem. The Nyquist
Theorem is important to MRI and it dictates that any signal must be sampled at least twice per
cycle to represent it accurately
What is the sampling time, the sampling rate and receiver bandwidth?
• The sampling time is the duration of the gradient while 256 or 512 frequencies are sampled.
(eg. 8 msec)
• The sampling rate is the rate at which these samples are taken.
• The receiver bandwidth is the range of frequencies sampled during read-out (eg 16 kHz
What does reducing bandwidth do in terms of trade-offs?
Reducing the bandwidth will:
• increase sampling time
• increase SNR
• increase echo spacing for FSE scans and increase blurring
• increase chemical shift and susceptibility artefact.
What is a fourier transform?
Fourier analysis allows any time varying signal (such as a spin-echo) to be represented as a
spectrum of the frequencies present. Fourier Transformation converts RF intensity vs. time into
Signal amplitude vs. frequency thus allowing us to reconstruct images. The mathematical
procedure relating the functions of amplitude against time and amplitude against frequency is
known as Fourier Transformation - if one is known, the other can be readily calculated. This
process is ideally suited to MR image reconstruction which uses frequency shifts to spatially
localise the signal.
2|Page
,What is k-space?
K-Space is simply an array of numbers whose Fourier Transformation is the MR image. Simply K-
Space is best thought of as temporary image space, which is used to digitize MR signals during
acquisition.
In 2DFT imaging, the position of the values tells us what about where they were collected in
echo?
In 2DFT imaging, each horizontal row of K-space corresponds to the echo data obtained by
digitising the signal from one phase encoding step. The values at the left of each row are
collected early in each echo those at the right are obtained late. The centre of the row will
correspond to the centre of each echo and will therefore contain the largest values.
Why do rows of k-space data at the periphery ie. very top and bottom contribute most to spatial
resolution?
Each row of k-space data is obtained by varying the amplitude of the phase encoding gradient.
The rows at the top and bottom of the k-space grid are obtained with steep gradient slopes. This
will cause smaller signal amplitudes due to gradient-induced dephasing, however this will
maximise the phase separation of adjacent points. These lines therefore contribute most
towards the spatial resolution of the image.
Why do rows of k-space data at the centre contribute most to contrast?
The central rows are obtained using shallow gradient slopes so the echo amplitudes will be
larger due to little gradient induced dephasing. These lines will contribute most towards the
contrast of the image.
Does every cell in k-space correspond to an individual pixel?
It should be remembered that individual cells in k-space do not correspond to individual pixels
in the image - each pixel is represented in every k-space cell.
Explain how 2D k-space filling occurs
2D volumetric acquisitions fill one line of K-space for slice 1 and then fill the same line of K-
space for slice 2 etc. When one line of K-space has been filled for all slices the next line of K-
space is filled and so on until all the Kspace data has been acquired for all slices. Once the
sequence is finished all of the slices are reconstructed and displayed at the same time. This is
the most common method of K-space filling.
Explain 3D volumetric k-space filling
3|Page
, 3D volumetric techniques acquire data from an entire volume of tissue. The excitation pulse is
not slice selective rather the whole prescribed imaging volume is excited. As such K-space is
three dimensional. At the end of the acquisition the volume slab is divided into slices using an
extra gradient called the slice select gradient. A 3D FT is then used to reconstruct the images. An
example of this technique is a 3D T2* C-spine.
How can k-space be manipulated and why?
K-Space can be manipulated to suit the needs of the MRI examination under progress. Many of
these techniques are made possible due to the mirrored halves of K-Space. That being the top
and bottom halves as well as the right and left halves of K-Space mirror each other. This can be
advantageous to the operator and patient as manipulation of k-space can decrease scan times.
What is Partial / Fractional Echo?
• Relies on echo symmetry from left to right sides of K-space
• Only the right hand side of the echo is read by the frequency encoding gradient - the
remaining portion is calculated. (ie sample the right half of k-space and calculate the left)
• Allows the peak of the echo to occur closer to the RF excitation pulse so shorter TE's are
possible for MRA, T1 spin-echo and fast GRE.
What is partial fourier transform?
• Also relies on symmetry - this time between the positive and negative phase encodings or
halves of K-Space
• Sample the top half of K-space and calculate the bottom half.
• Actually need to sample slightly over half for phase correction.
• Reduces the acquisition time by nearly one half.
• Reduces the SNR to about 70% of a full acquisition (1/√2)
Why might a rectangular FOV be used and how does it affect image quality?
• Can be used for rectangular anatomical areas (eg. axial pelvis, sagittal spine)
• The field of view and the image matrix in the phase encoding direction are both reduced - eg.
to ½ or ¾ - this will cut down the imaging time accordingly.
• The gradient increment between each phase encoding step is increased to maintain spatial
resolution - ie. for ½ FOV the increment will be doubled so that the steepest phase encoding
steps are still performed.
• SNR will be reduced because of the reduction in the number of phase encodings.
What is SNR?
4|Page
