(TE) The echo time represents the time in milliseconds between the application of the 90° pulse and the peak of the echo signal in spin echo and inversion recovery pulse sequences.
(TEeff) The contrast and the SNR of an MR image are determined primarily by the temporal position of the echo at which the phase encoding gradient has the smallest amplitude. The echo signal in this case undergoes minimal dephasing and has the strongest signal. The time period between the excitation pulse and this echo is the effective echo time.