Multiecho

Multiecho refers to an imaging technique in which multiple signal echoes are collected after a single excitation. Each echo occurs at a different echo time, producing a series of signals that reflect tissue relaxation properties. By analyzing how the signal decays across the echoed measurements, researchers can estimate quantitative relaxation parameters such as T2 or T2*, and can derive contrast-weighted images from selected echoes.

In magnetic resonance imaging, two common implementations are multi-echo spin-echo (MESE) and multi-echo gradient-echo (ME-GRE). MESE uses a train of refocusing pulses to generate several spin echoes and is primarily used for T2 mapping and high-T2 contrast. ME-GRE relies on gradient echoes produced by successive readouts and is used for T2* mapping and susceptibility-weighted imaging. Some protocols acquire many echoes to enhance quantification, enable myelin water imaging, or improve iron concentration assessment.

Advantages of multiecho approaches include the ability to obtain quantitative relaxation maps without separate scanning, improved efficiency when designed for rapid fitting, and greater flexibility in post-processing. Limitations include reduced per-echo signal-to-noise ratio for longer echo trains, potential increases in acquisition time or SAR with many refocusing pulses, greater sensitivity to patient motion, and the need for robust fitting algorithms to extract accurate parameter estimates.

Multiecho techniques are widely used in neuroimaging, musculoskeletal imaging, and body imaging to characterize tissue properties and support quantitative MRI studies.