Final answer:
The loudest and fastest MRI technique is Echo Planar Imaging (EPI), which is characterized by rapid gradient switching that causes mechanical vibrations and loud noises.
Step-by-step explanation:
The MRI technique that is known for being the loudest and fastest is the Echo Planar Imaging (EPI) technique. It utilizes alternating readout and phase applications, and this sequence allows the entire brain to be scanned in a short amount of time. The speed of EPI is especially beneficial in functional MRI (fMRI), where it captures fast physiological changes. However, its rapid switching of magnetic field gradients is the source of the characteristic loud noises during an MRI scan. These sounds are caused by the mechanical vibrations of gradient coils within the MRI scanner, which result after electrical currents swiftly change direction within the coils.