On a T2-weighted fast spin-echo image, the basilar artery appears black. What is the main reason?

Fast blood leaves the slice before the refocusing pulse

The arterial wall contains calcium that gives no signal

The fat-suppression pulse also nulls the blood

Blood has a very short T1 that removes its signal

A patient with a spinal implant needs fat-suppressed imaging at a Doha hospital, and chemical fat saturation is patchy near the metal. What is a good alternative?

STIR, because it does not depend on field homogeneity

A longer TE only, because a longer echo time lets fat decay away more quickly than water

When the b-value of a diffusion sequence is raised from 500 to 1000 s/mm2, which change is expected?

Greater diffusion weighting with lower signal-to-noise ratio

T1 weighting becomes dominant over the whole image

No change in diffusion weighting but a lower signal

Less diffusion weighting with higher signal-to-noise ratio

MRI physics and sequences

56 Gulf Prometric Radiographer (DHA, DOH, MOH, SCFHS, QCHP) practice questions on MRI physics and sequences, part of MRI. The first 25 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Medium
On a T2-weighted fast spin-echo image, the basilar artery appears black. What is the main reason?
1. AThe arterial wall contains calcium that gives no signal
2. BThe fat-suppression pulse also nulls the blood
3. CBlood has a very short T1 that removes its signal
4. DFast blood leaves the slice before the refocusing pulse
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Answer: D · Fast blood leaves the slice before the refocusing pulse
In spin echo, protons must receive both the 90 degree and the 180 degree pulses to produce an echo. Fast-flowing blood excited by the first pulse has left the slice before the refocusing pulse, so it gives no signal; this flow void is normal in a patent artery. Loss of the flow void can suggest slow flow or thrombosis.
- A: The black area is the lumen, not calcium in the wall.
- B: A flow void appears with or without fat suppression.
- C: A short T1 would make blood bright on T1, not black on T2.
Remember this
Fast arterial flow gives a black flow void on spin-echo images.
Question 2 · Medium
A subacute haematoma, about a week old, appears bright on T1-weighted images. Which substance is mainly responsible?
1. AOxyhaemoglobin
2. BExtracellular methaemoglobin
3. CDeoxyhaemoglobin
4. DHaemosiderin
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Answer: B · Extracellular methaemoglobin
Extracellular methaemoglobin is paramagnetic and has a short T1, so it gives a bright signal on T1. Deoxyhaemoglobin and haemosiderin shorten T2 and appear dark on T2 or T2*. Oxyhaemoglobin is not paramagnetic.
- A: Oxyhaemoglobin is diamagnetic and not bright on T1.
- C: Deoxyhaemoglobin is dark on T2 and isointense on T1 in the early subacute phase.
- D: Haemosiderin appears as a dark rim on T2 and gradient echo images.
Remember this
Extracellular methaemoglobin shortens T1 and is bright on T1.
Question 3 · Hard
At 1.5 T the fat-water shift is about 220 Hz. The receiver bandwidth is plus or minus 16 kHz (32 kHz total) over 256 frequency-encoding points. About how many pixels is the fat displaced?
1. AAbout 0.9 pixels
2. BAbout 7 pixels
3. CAbout 3.6 pixels
4. DAbout 1.8 pixels
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Answer: D · About 1.8 pixels
Bandwidth per pixel = 32,000 Hz / 256 = 125 Hz per pixel. Displacement = 220 / 125, which is about 1.8 pixels. Doubling the bandwidth would halve this, and at 3 T the shift in hertz doubles.
- A: 0.9 pixels would result from a bandwidth twice as high.
- B: 7 pixels would need a bandwidth of only 32 Hz per pixel.
- C: 3.6 pixels would apply at 3 T, where the shift in hertz is double.
Remember this
Chemical shift in pixels = shift in Hz divided by bandwidth per pixel.
Question 4 · Medium
A patient with a spinal implant needs fat-suppressed imaging at a Doha hospital, and chemical fat saturation is patchy near the metal. What is a good alternative?
1. AA longer TE only, because a longer echo time lets fat decay away more quickly than water
2. BA shorter TR only
3. CSTIR, because it does not depend on field homogeneity
4. DIncreasing the matrix
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Answer: C · STIR, because it does not depend on field homogeneity
Frequency-selective fat saturation relies on a uniform magnetic field, which implants disturb. STIR suppresses fat based on its T1, using an inversion time, so it stays reliable in non-uniform fields. Its disadvantages are lower SNR and not being usable after gadolinium.
- A: TE changes T2 weighting and does not suppress fat.
- B: TR changes T1 weighting and does not suppress fat.
- D: A larger matrix changes resolution only.
Remember this
STIR is reliable near metal because it relies on T1, not on field uniformity.
Question 5 · Medium
When the b-value of a diffusion sequence is raised from 500 to 1000 s/mm2, which change is expected?
1. AGreater diffusion weighting with lower signal-to-noise ratio
2. BT1 weighting becomes dominant over the whole image
3. CNo change in diffusion weighting but a lower signal
4. DLess diffusion weighting with higher signal-to-noise ratio
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Answer: A · Greater diffusion weighting with lower signal-to-noise ratio
The b-value summarises the strength and timing of the diffusion gradients. A higher b-value makes the signal more sensitive to water motion, but every tissue loses signal, so the signal-to-noise ratio falls and distortion increases.
- B: The b-value is the parameter that sets diffusion weighting.
- C: Signal-to-noise falls rather than rises at higher b.
- D: Lower weighting would result from a lower b-value.
Remember this
Higher b-values increase diffusion contrast but reduce signal.
Question 6 · Medium
A gradient-echo sequence shows black blooming spots in the brain. Which feature of the sequence explains the high sensitivity to small haemorrhages?
1. ANo 180° rephasing pulse, so T2* effects from susceptibility are not corrected
2. BA very high b-value
3. CA short inversion time
4. DThe use of a very long TR, which allows every tissue to recover fully before the next pulse
Answer and explanation in LearnFree account
Question 7 · Easy
In an MRI sequence, TR (repetition time) is the time between:
1. ATwo consecutive echoes in an echo train
2. BSuccessive excitation pulses applied to the same slice
3. CThe start of the scan and the first echo
4. DThe excitation pulse and the centre of the echo
Answer and explanation in LearnFree account
Question 8 · Hard
A department moves a FLAIR protocol from a 1.5 T to a 3 T scanner. T1 relaxation times of tissues are longer at 3 T. How should the sequence be adjusted?
1. AShorten TI and lengthen TE only
2. BKeep all timing the same, because T1 does not depend on field strength
3. CShorten both the inversion time and TR, because the tissue T1 values are shorter at higher field
4. DLengthen both the inversion time and TR, so CSF stays nulled and recovers fully
Answer and explanation in LearnFree account
Question 9 · Medium
In a diffusion-weighted acquisition, the b-value:
1. ASets the repetition time
2. BSets the pixel size and the field of view of the diffusion-weighted image
3. CSets how strongly the sequence is sensitive to water motion
4. DSets the number of slices
Answer and explanation in LearnFree account
Question 10 · Medium
A radiographer wants to suppress the bright CSF signal on a T2-weighted brain image so that periventricular lesions are easier to see. Which sequence is chosen?
1. AFLAIR
2. BT1 gradient echo
3. CSTIR
4. DProton density spin echo
Answer and explanation in LearnFree account
Question 11 · Medium
A patient cannot hold his breath for an upper abdominal scan, and the images show ghosting along the phase-encoding direction. Which option best reduces this artefact?
1. AUsing a smaller field of view to cut the scan time
2. BRespiratory triggering or compensation
3. CIncreasing the receiver bandwidth to shorten the readout
4. DIncreasing the slice thickness to gain more signal
Answer and explanation in LearnFree account
Question 12 · Easy
A STIR sequence is used mainly to:
1. ASuppress CSF using a long inversion time
2. BMeasure diffusion of water
3. CShow the signal of iron
4. DSuppress fat signal using a short inversion time
Answer and explanation in LearnFree account
Question 13 · Hard
A sequence with a 24 cm field of view and a 256 x 256 matrix is changed to a 20 cm field of view, with everything else unchanged. By about how much does the SNR change?
1. AIt falls to about 70% of the original
2. BIt rises to about 144% of the original
3. CIt rises to about 120% of the original
4. DIt falls to about 83% of the original
Answer and explanation in LearnFree account
Question 14 · Easy
Cerebrospinal fluid is normally:
1. ADark on both T1 and T2
2. BBright on both T1 and T2
3. CBright on T2 and dark on T1
4. DDark on T2 and bright on T1
Answer and explanation in LearnFree account
Question 15 · Hard
Fat has a T1 of about 260 ms and fluid a T1 of about 4,000 ms. For the strongest T1 contrast between them in a spin-echo sequence, which settings are best?
1. ATR 4,000 ms, TE 100 ms
2. BTR 4,000 ms, TE 15 ms
3. CTR 500 ms, TE 15 ms
4. DTR 500 ms, TE 100 ms
Answer and explanation in LearnFree account
Question 16 · Medium
A Dixon sequence is used for fat suppression in a knee with a small metal staple. How does the Dixon method separate fat from water?
1. AEchoes in phase and out of phase are combined
2. BA long TE allows the fat signal to decay first
3. CA short inversion time nulls the fat signal
4. DA narrow RF pulse saturates the fat peak only
Answer and explanation in LearnFree account
Question 17 · Easy
On a T1-weighted spin-echo image, how does subcutaneous fat appear?
1. ASignal void
2. BIntermediate grey like muscle
3. CDark (low signal)
4. DBright (high signal)
Answer and explanation in LearnFree account
Question 18 · Medium
A gradient-echo sequence uses a short TR and a large flip angle of about 70 to 90 degrees. The resulting weighting is mainly:
1. AT2* weighting
2. BDiffusion weighting
3. CT1 weighting
4. DProton density weighting
Answer and explanation in LearnFree account
Question 19 · Medium
What is the main effect of using an echo train length of 16 in a fast spin-echo sequence, compared with a conventional spin echo?
1. ASpatial resolution is reduced to a quarter
2. BScan time is reduced by about 16 times
3. CSNR is raised by 16 times
4. DScan time is doubled
Answer and explanation in LearnFree account
Question 20 · Medium
Parallel dark and bright lines appear next to a sharp border between CSF and spinal cord on a sagittal image. This is a truncation (Gibbs) artefact. Which step helps most?
1. AReduce the matrix to shorten the acquisition time
2. BUse a thicker slice to average the interface signal
3. CIncrease the matrix in the phase-encoding direction
4. DShorten the TE to reduce the signal decay at the edge
Answer and explanation in LearnFree account
Question 21 · Easy
Which combination of TR and TE gives a T1-weighted spin-echo image?
1. AShort TR and long TE
2. BShort TR and short TE
3. CLong TR and short TE
4. DLong TR and long TE
Answer and explanation in LearnFree account
Question 22 · Easy
T1 relaxation in MRI describes the:
1. ATime between two excitation pulses
2. BDecay of transverse magnetisation
3. CRecovery of longitudinal magnetisation
4. DPrecession frequency of the protons
Answer and explanation in LearnFree account
Question 23 · Medium
For a proton-density weighted spin-echo image of the knee, which timing is chosen?
1. AShort TR and long TE
2. BLong TR and long TE
3. CShort TR and short TE
4. DLong TR and short TE
Answer and explanation in LearnFree account
Question 24 · Medium
A patient in a Dubai hospital with sudden left-sided weakness has an MRI. A diffusion-weighted image shows a bright area in the right middle cerebral artery territory, with low values on the ADC map. What does this indicate?
1. ASusceptibility artefact
2. BA normal variant
3. CIncreased diffusion, consistent with chronic infarct
4. DRestricted diffusion, consistent with acute ischaemia
Answer and explanation in LearnFree account
Question 25 · Hard
A sequence with 2 signal averages takes 3 minutes. A radiographer wants to double the signal-to-noise ratio by changing only the number of averages. What will the new scan time be?
1. A24 minutes
2. B6 minutes
3. C9 minutes
4. D12 minutes
Answer and explanation in LearnFree account

31 more MRI physics and sequences questions

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MRI physics and sequences

On a T2-weighted fast spin-echo image, the basilar artery appears black. What is the main reason?

A subacute haematoma, about a week old, appears bright on T1-weighted images. Which substance is mainly responsible?

At 1.5 T the fat-water shift is about 220 Hz. The receiver bandwidth is plus or minus 16 kHz (32 kHz total) over 256 frequency-encoding points. About how many pixels is the fat displaced?

A patient with a spinal implant needs fat-suppressed imaging at a Doha hospital, and chemical fat saturation is patchy near the metal. What is a good alternative?

When the b-value of a diffusion sequence is raised from 500 to 1000 s/mm2, which change is expected?

A gradient-echo sequence shows black blooming spots in the brain. Which feature of the sequence explains the high sensitivity to small haemorrhages?

In an MRI sequence, TR (repetition time) is the time between:

A department moves a FLAIR protocol from a 1.5 T to a 3 T scanner. T1 relaxation times of tissues are longer at 3 T. How should the sequence be adjusted?

In a diffusion-weighted acquisition, the b-value:

A radiographer wants to suppress the bright CSF signal on a T2-weighted brain image so that periventricular lesions are easier to see. Which sequence is chosen?

A patient cannot hold his breath for an upper abdominal scan, and the images show ghosting along the phase-encoding direction. Which option best reduces this artefact?

A STIR sequence is used mainly to:

A sequence with a 24 cm field of view and a 256 x 256 matrix is changed to a 20 cm field of view, with everything else unchanged. By about how much does the SNR change?

Cerebrospinal fluid is normally:

Fat has a T1 of about 260 ms and fluid a T1 of about 4,000 ms. For the strongest T1 contrast between them in a spin-echo sequence, which settings are best?

A Dixon sequence is used for fat suppression in a knee with a small metal staple. How does the Dixon method separate fat from water?

On a T1-weighted spin-echo image, how does subcutaneous fat appear?

A gradient-echo sequence uses a short TR and a large flip angle of about 70 to 90 degrees. The resulting weighting is mainly:

What is the main effect of using an echo train length of 16 in a fast spin-echo sequence, compared with a conventional spin echo?

Parallel dark and bright lines appear next to a sharp border between CSF and spinal cord on a sagittal image. This is a truncation (Gibbs) artefact. Which step helps most?

Which combination of TR and TE gives a T1-weighted spin-echo image?

T1 relaxation in MRI describes the:

For a proton-density weighted spin-echo image of the knee, which timing is chosen?

A patient in a Dubai hospital with sudden left-sided weakness has an MRI. A diffusion-weighted image shows a bright area in the right middle cerebral artery territory, with low values on the ADC map. What does this indicate?

A sequence with 2 signal averages takes 3 minutes. A radiographer wants to double the signal-to-noise ratio by changing only the number of averages. What will the new scan time be?