MRI is the imaging technique that has most benefited from technological innovation. The many advances have led to improvements in quality and acquisition speed. 
Each sequence is a subtle combination of radiofrequency pulses and gradients. Whatever the type of sequence, the aims are to favor the signal of a particular tissue (contrast), as quickly as possible (speed), while limiting the artifacts and without altering the signal to noise ratio. There are over a hundred different sequences and to complicate things further, manufacturers tend to each choose their own acronyms!