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.

The smallest distance between two points in the object that can be distinguished as separate details in the image, generally indicated as a length or a number of black and white line pairs per mm (lp/mm).
The specific criterion for resolution to be used, depends on the type of test used (e.g., bar pattern or contrast-detail phantom). As the ability to separate or detect objects depends on their contrast and the noise, and the different MR parameters of objects will affect image contrast differently for different imaging techniques, care must be taken in comparing the results of resolution phantom tests of different machines and no single simple measure of resolution can be specified.
The resolution may be an isotropic one. The resolution may be larger than the size corresponding to the discrete image element (pixel), although it cannot be smaller.

A surface coil is essentially a loop of conducting material, such as copper tubing. The in-bore solenoidal sending coil is used as the transmitter of RF energy. This type of receiver coil is placed directly on or over the region of interest for increased magnetic sensitivity. The loop may form various shapes and be bent slightly to conform to the imaged body part. Surface coils have a good SNR for tissues adjacent to the coil and because the signal decrease with the distance, an eligibility homogeneity correction will equalize this over the field of view. A rule of thumb for surface coils is that the sensitivity decreases appreciably beyond a distance equal to the diameter of the coil.
The positioning of the coil is an important determinant of performance. As only the region close to the surface coil will contribute to the signal, there is an improvement in the SNR for these regions, compared to the use of receiver coils that surround the appropriate part of the body. These coils are specifically designed for localized body regions, and provide improved signal to noise ratios by limiting the spatial extent of the excitation or reception.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'

The process of adjusting the transmitter and receiver circuitry so that it provides optimal signal performance at the Larmor frequency. A properly tuned scanner will produce images with a higher signal to noise ratio, and therefore improved diagnostic versatility.
More generally, tuning is the process of adjusting the components for optimal performance, including matching impedances.

Undersampling is the decrease in data to increase image acquisition speed (shorter scan times without loss of quality - increased productivity - reduced cost of equipment). There are different strategies to decrease data without losing quality (e.g. reduction of the FOV in one or more spatial directions - RFOV).
Reduction in data normally is associated with an increase in aliasing (degradation of the SNR through backfolding of the entire noise spectrum), or with other artifact caused by missing data, which results in fine lines.