Final answer:
Aliasing is the artifact that occurs when the number of samples in k-space is too small, affecting magnetic resonance imaging (MRI) quality by causing image wrap-around or overlap.
Step-by-step explanation:
When the number of samples in k-space is too small, the artifact that occurs is called aliasing. Aliasing manifests as the superimposition of signal from outside the field of view onto the image within the field of view, which results in image wrap-around or overlap. To understand this, consider k-space as a data sampling grid for magnetic resonance imaging (MRI): if k-space is not fully sampled, the reconstruction of the image will lack data, causing repetitions of the image to appear superimposed on the actual image area.
Sampling density is critical for maintaining image quality in MRI. If the sampling density is insufficient, resulting in fewer than the required number of ensembles in k-space, then signal-to-noise ratio (SNR) might suffer, but more notably, spatial resolution can decrease, causing artifact issues like aliasing.