From Siemens Medical Systems;
70 cm + 125 cm + 1.5T and Tim - a combination never seen before in MRI ... MAGNETOM Espree™s unique open bore design can accommodate more types of patients than other 1.5T systems on the market today, in particular the growing population of obese patients. The power of 1.5T combined with Tim technology boosts signal to noise, which is necessary to adequately image obese patients.

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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.

The number of data points collected in one, two or all three directions. Normally used for the 2D in plane sampling. The display matrix may be different from the acquisition matrix, although the latter determines the resolution. Measurement time may be saved by not acquiring raw data lines corresponding to high resolution. Not measured rows are filled with zeroes prior to the image calculation. A square image is the result of an interpolation in phase encoding direction. See also Zero Filling.

The chosen matrix size effects scan time, resolution and SNR. Reduced measurement matrixes decrease the scan time and the resolution by increased SNR.

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Ferromagnetic metal will cause a magnetic field inhomogeneity, which in turn causes a local signal void, often accompanied by an area of high signal intensity, as well as a distortion of the image. They create their own magnetic field and dramatically alter precession frequencies of protons in the adjacent tissues. Tissues adjacent to ferromagnetic components become influenced by the induced magnetic field of the metal hardware rather than the parent field and, therefore, either fail to precess or do so at a different frequency and hence do not generate useful signal. Two components contribute to susceptibility artifact, induced magnetism in the ferromagnetic component itself and induced magnetism in protons adjacent to the component.
Artifacts from metal may have varied appearances on MRI scans due to different type of metal or configuration of the piece of metal. The biocompatibility of metallic alloys, stainless steel, cobalt chrome and titanium alloy is based on the presence of a constituent element within the alloy that has the ability to form an adherent oxide coating that is stable, chemically inert and hence biocompatible. In relation to imaging titanium alloys are less ferromagnetic than both cobalt and stainless steel, induce less susceptibility artifact and result in less marked image degradation.

Remove the metal when possible or take a not so sensitive sequence (a SE or another sequence with a rephasing 180° pulse).

See also Susceptibility Artifact.