Quick Overview
Please note that there are different common names for this MRI artifact.

The Gibbs or ringing artifact appears as a series of lines in the MR image parallel to abrupt and intense changes in the object at this location. This artifact does not occur visibly on smooth objects. This artifact is caused by the Gibbs phenomenon, an overshoot or ringing of Fourier series occurring at discontinuities.
In the spinal cord, a small syrinx can be simulated by the Gibbs phenomenon. Gibbs artifacts are also seen in other regions, for example the brain//skull interface.
Fine lines visible in an image may be due to undersampling of the high spatial frequencies, respectively incomplete digitization of the echo.
With more encoding steps the Gibbs artifacts is less intense and narrower. Therefore, e.g. the artifact is more intense in the 256 point dimension of a 256x512 acquisition matrix.

This problem can only be resolved by smoothing filters (LanczosSigmaFactor, 2-D Exponential Filtering, Gegenbauer Reconstruction etc.) or with a higher acquisition matrix and/or a smaller FOV, to smooth the object.

See also Gibbs Phenomenon and Apodization.

Inhomogeneity is the degree of lack of homogeneity, for example the fractional deviation of the local magnetic field from the average value of the field. Inhomogeneities of the static magnetic field, produced by the scanner as well as by object susceptibility, is unavoidable in MRI. The large value of gyromagnetic coefficient causes a significant frequency shift even for few parts per million field inhomogeneity, which in turn causes distortions in both geometry and intensity of the MR images.
Manufacturers try to make the magnetic field as homogeneous as possible, especially at the core of the scanner. Even with an ideal magnet, a little inhomogeneity is always left and is caused in addition by the susceptibility of the imaging object. The geometrical distortion (displacement of the pixel locations) are important e.g., for some cases as stereotactic surgery. Displacements up to 3 to 5 mm have been reported. The second problem is the undesired changes in the intensity or brightness of pixels, which may cause problems in determining different tissues and reduce the maximum achievable image resolution.

General strategies for reducing field inhomogeneity induced artifacts:
Increasing the strength of the gradient magnetic field.
Decreasing the echo time.
Improving the image resolution. Phase encoding. Postprocessing.

With an open configuration MRI system neurosurgical procedures can be performed using image guidance. Open MRI can be used to guide interventional treatments or procedures, such as a biopsy.
Intraoperative MRI allows lesions to be precisely localized and targeted. Constantly updated images, correlated with images obtained pre-operatively, help to eliminate errors that can arise during framed and frameless stereotactic surgery when anatomic structures alter their position due to shifting or displacement of, e.g. brain parenchyma.
Intraoperative MRI can help with the identification of normal structures, such as blood vessels and is helpful in optimizing surgical approaches, achieving complete resection of intracerebral lesions, determining tumor margins and monitoring potential intraoperative complications.

Quick Overview
Please note that there are different common names for this artifact.

Machine imperfection-based artifacts manifest themselves due to the fact that the odd k-space lines are acquired in a different direction than the even k-space lines. Slight differences in timing result in shifts of the echo in the acquisition window. By the shift theorem, such shifts in the time domain data then produce linear phase differences in the frequency domain data.
Without correction, such phase differences in every second line produce striped ghosts with a shift of half the field of view, so-called Nyquist ghosts. Shifts in the applied magnetic field can also produce similar (but constant in amplitude) ghosts.
This artifact is commonly seen in an EPI image and can arise from both, hardware and sample imperfections.
A further source of machine-based artifact arises from the need to acquire the signal as quickly as possible. For this reason the EPI signal is often acquired during times when the gradients are being switched. Such sampling effectively means that the k-space sampling is not uniform, resulting in ringing artifacts in the image.

Such artifacts can be minimized by careful setup of the spectrometer and/or correction of the data. For this reasons reference data are often collected, either as a separate scan or embedded in the imaging data. The non-uniform sampling can be removed by knowing the form of the gradient switching. It is possible to regrid the data onto a uniform k-space grid.

Quick Overview

The magic angle is a precisely defined angle, the value is approximately 54.7°. Hence, two nuclei with a dipolar coupling vector at an angle of approximately 54.7° to a strong external magnetic field have zero dipolar coupling.
Magic angle spinning is a technique in solid-state NMR spectroscopy, which employs this principle to remove or reduce dipolar couplings, thereby increasing spectral resolution. In MRI, the magic angle effect visualizes as bright spots through an increased T2 time on short echo time (TE) images, for e.g. collagen fibers of tendons and ligaments, which are oriented at the magic angle of approximately 54.7° to the magnetic field.

Take care that tendons and ligaments are not oriented at about a 54.7° angle to the main magnetic field.