An interleaved saturation recovery/inversion recovery (SR/IR) pulse sequence allows the sign of the IR signal to be retained even if images are formed from the magnitude of the two-dimensional complex Fourier transforms of the raw data. Synthesis of images by a linear combination of SR and signed IR pixel values has proved a valuable method of relaxation time (T1) contrast manipulation without the need to re-image the slice. Linear combination has also allowed IR images with a wide range of time-to-inversion (TI) values to be synthesized from an SR/IR pair obtained with TI = 200 ms and time-to-recovery (TR) = 1000 ms, thus avoiding the need for computationally intensive calculations based on complicated relaxation equations.
Redpath, T. W., Smith, F., & Hutchison, J. M. S. (1988). Magnetic resonance image synthesis from an interleaved saturation recovery/inversion recovery sequence. British Journal of Radiology, 61(727), 619-624. https://doi.org/10.1259/0007-1285-61-727-619