Quiz: Physics & Engineering: Compressed Sensing in MRI

When is it possible to reconstruct an image sampled below the Nyquist limit?

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Under what condition is a signal or image said to be “sparse”?

If the object is clearly distinguishable from background noise
Only if it is an angiogram
If, either intrinsically or following mathematical transformation, the overwhelming majority of its elements (i.e., pixels) are zero-valued and information is concentrated within a small subset

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For compressed sensing to work effectively, which two signal domains must be “incoherent”?

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Compressed sensing reconstruction require solving a nonlinear optimization problem. This task can be done:

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What happens if a compressed sensing reconstruction assumes an image to be more sparse than it actually is?

Nothing – the algorithm will adapt and figure out the correct level
The reconstructed image may contain artifacts or exhibit contrast and/or structure degradation
The reconstruction algorithm will fail to converge to a solution

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