Helical winding of current-carrying wire that produces a magnetic field along the axis of the helix.

A coil of wire wound in the form of a long cylinder. When a current is passed through the coil, the magnetic field within the coil is relatively uniform. Solenoid RF coils are commonly used when the static magnetic field is perpendicular to the long axis of the body.
The reason against a solenoidal coil is that the signal is missed when the axis of the solenoidal coil is coaxial with the horizontal magnetic field Bo. If the coil's axis can be put near a right angle (60° to 90°) with the principal field, so the loss in the signal is greatly dismissed, and good SNR can be achieved.
The two forms are single turn solenoid and multiple turn solenoids.

The not measured distance between the slices. For some sequences there is a slightest space of e.g. 10-20% necessary. A lower spacing can introduce more noise into adjoining slices.

Measure of resolution (lp/mm or lp/cm).
A dimension of the Fourier transformation space (k-space representation of an image), having units of inverse distance. Higher values of spatial frequencies correspond to finer detail in the image.

An effect of chemical shift is that of spatial misregistration. Because the frequency displacement caused by chemical shift cannot be differentiated from intended spatial frequency encoding misregistration of the resultant signal may occur along the frequency-encoding direction. This artifact can be seen in a FFE or SE sequence as a bright or dark band at the edge of the anatomy.

See Chemical Shift Artifact.