JET motion correction is developped to suppress image artifacts in patients who are unable to remain still during scanning. Next it also suppress artifacts due to involuntary motion such as CSF flow. JET is applicable to all anatomical regions and can be acquired in all scan planes. JET not only corrects for in-plane motion but for through-plane motion as well. An example of the motion correction is shown in below image.

Principles of JET sequences
In normal Cartesian filling mode, the readout gradient pulses in a specified pattern are applied to the patient to acquire NMR signals. Sampling points are assigned to the data points in rows parallel to the coordinate axes in the k-space.

In acquisition with the JET sequence, readout gradient pulses in different patterns are applied to the patient to acquire datasets for different multiple blades. In 2D slice imaging, two of the three orthogonal axes of the gradient fields are used. The rows of data points in the k-space can be rotated within the plane by varying the intensity ratio between Gx and Gy while maintaining the absolute intensity values (i.e., by changing the direction only). Thus, the k-space is filled with datasets that are acquired while the intensity ratio between the two readout gradient pulses is varied sequentially during acquisition.

In the 2D JET filling pattern, the blade rotation angle is varied sequentially from 0° to 180° to fill the k-space with data. The figure shows the data filling pattern when the number of blades is set to 6. When the number of blades is increased, the blade rotation angle is reduced and the in-plane filling density in the circumferential direction is therefore increased. At the same time, the image SNR is increased by the noise cancelation effect. Note, however, that even when the number of blades is increased, a resolution higher than that in the readout direction cannot be obtained, because the spatial resolution of the image is determined based primarily on the resolution in the readout direction.

When the number of blades is decreased, the effective spatial resolution in the circumferential direction decreases, resulting in aliasing artefacts near the edges of the FOV. To obtain the effective spatial resolution over the entire FOV, the data acquisition density in the circumferential direction in the k-space should be approximately the same as the data acquisition density in the radial direction. In this package, the minimum number of blades is calculated automatically to satisfy this requirement. Accordingly, when (for example) the matrix size in the readout direction is increased or a sequence with a short echo train spacing is selected, the minimum number of blades is increased. The minimum number of blades and minimum % of the value for "K Space Fill Ratio" are determined.

Principles of JET reconstruction
The normal Cartesian filling technique uses Fourier transformation to reconstruct images. In the non-Cartesian filling technique, however, Fourier transformation cannot be used directly. Therefore, the Cartesian filling data is first obtained from the non- Cartesian filling data in JET reconstruction (this process is referred to as gridding). In the gridding process, the non-Cartesian filling datasets located adjacent to individual Cartesian filling datasets are used. The sampling delay and the phase shift in each blade are eliminated in the gridding process in order to increase the data consistency between blades. This is equivalent to correcting for the delay that occurs in the data acquisition system and the echo shift due to eddy currents.
The reconstruction process after gridding is the same as for the normal Cartesian filling technique. It is possible to apply reconstruction filters, fine reconstruction, and receive coil intensity correction.