In single shot techniques (used for EPI, TSE, FSE, RARE, HASTE), the entire raw data set is acquired with a single excitation pulse. The magnetization of a fully relaxed spin system is used. Each of the subsequent echoes is given a different phase encoding. For improved SNR, spatial resolution or FOV, the needed raw data are acquired over a number of sequence repetitions. Each repetition then collects a fraction of the complete raw data set. Only slightly more than a half of the raw data is acquired. The image is obtained through half Fourier reconstruction.
A single shot sequence is useful in cases where movement is to expect e.g. in abdominal Imaging or fetal MRI.

See also Half Fourier Acquisition Single Shot Turbo Spin Echo.

The Dixon technique is a MRI method used for fat suppression and/or fat quantification. The difference in magnetic resonance frequencies between fat and water-bound protons allows the separation of water and fat images based on the chemical shift effect.
This imaging technique is named after Dixon, who published in 1984 the basic idea to use phase differences to calculate water and fat components in postprocessing. Dixon's method relies on acquiring an image when fat and water are 'in phase', and another in 'opposed phase' (out of phase). These images are then added together to get water-only images, and subtracted to get fat-only images. Therefore, this sequence type can deliver up to 4 contrasts in one measurement: in phase, opposed phase, water and fat images. An additional benefit of Dixon imaging is that source images and fat images are also available to the diagnosing physician.
The original two point Dixon sequence (number of points means the number of images acquired at different TE) had limited possibilities to optimize the echo time, spatial resolution, slice thickness, and scan time; but Dixon based fat suppression can be very effective in areas of high magnetic susceptibility, where other techniques fail. This insensitivity to magnetic field inhomogeneity and the possibility of direct image-based water and fat quantification have currently generated high research interests and improvements to the basic method (three point Dixon).
The combination of Dixon with gradient echo sequences allows for example liver imaging with 4 image types in one breath hold. With Dixon TSE/FSE an excellent fat suppression with high resolution can be achieved, particularly useful in imaging of the extremities.
For low bandwidth imaging, chemical shift correction of fat images can be made before recombination with water images to produce images free of chemical shift displacement artifacts. The need to acquire more echoes lengthens the minimum scan time, but the lack of fat saturation pulses extends the maximum slice coverage resulting in comparable scan time.

The number of series of 180° RF rephasing pulses and their corresponding echoes for a fast or turbo spin echo pulse sequence.

See Fast Spin Echo.