This happens whenever a structure is only partly within the imaging section, pixel or voxel. The consequence is that the signals of the structure and the adjacent or surrounding structures present in the section, pixel or voxel are averaged.
As a result erroneous pixel or voxel signal values result. This can lead to diagnostic misinterpretations.

See also Partial Volume Artifact.

The partial volume effect is the loss of contrast between two adjacent tissues in an image caused by insufficient resolution so that more than one tissue type occupies the same voxel (or pixel). That may induce a partial volume artifact, dependent on the size of the image voxel. If fat and water spins occupy the same voxel, their signals interfere destructively. A small amount of water signal may be eliminated by a larger lipid signal from the same voxel, resulting in a voxel that appears to contain only lipid. The partial volume effect is minimal with thin slice thickness and sufficiently high resolution, so that fat and water or other different structures are unlikely to occupy the same voxel.

Take thinner slices, and higher resolution (smaller voxel), but remain this may result in poorer signal to noise ratio in the image.

(PRFT) See Partial Fourier Imaging.

(Pa) The SI unit of pressure.
Definition: 1 pascal is equal to 1 N/m2 = 1 J/m3 = 1 kg·m-1·s-2
1 kPa = 0.145 lbf/in2.
Air pressure is measured in hectopascal (hPa), with 1 hPa = 1 millibar.
The unit is named for Blaise Pascal (1623-1662), French philosopher and mathematician.

The term 'passive' refers to any medical device that serves its function without the supply of power. Examples of passive devices include but are not limited to aneurysm clips, shunts, scalpels, IV poles, and oxygen bottles.