Inversionrecovery

Inversion recovery is an MRI pulse sequence technique that uses an initial 180-degree inversion pulse to invert longitudinal magnetization, followed by a waiting period called inversion time (TI) before excitation. By selecting TI to match the T1 relaxation of a target tissue, the net longitudinal magnetization of that tissue is driven toward zero at the moment of signal collection, effectively nulling its signal. This allows selective suppression of specific tissues or contrast enhancement between tissues or pathology depending on the TI and sequencing strategy.

Common variants include FLAIR (fluid-attenuated inversion recovery), which nulls cerebrospinal fluid signal to improve detection of brain lesions near fluid spaces, and STIR (short tau inversion recovery), which nulls fat signal to enhance lesion conspicuity in musculoskeletal imaging. In cardiac MRI, inversion recovery sequences are used with gadolinium contrast to null normal myocardium, producing bright areas of scar or fibrosis in late gadolinium enhancement (LGE) imaging. Inversion recovery can be implemented with different readouts, such as spin-echo or gradient-echo, and TI is adjusted for the magnetic field strength and the intended tissue nulling.

Practical considerations include the need for accurate TI, which may be influenced by field inhomogeneities or patient factors such as heart rate in cardiac imaging. Some variants require contrast agents, and inversion recovery sequences can have reduced signal-to-noise ratio or be sensitive to motion. The primary advantage is improved lesion conspicuity and tissue contrast by suppressing unwanted signals, facilitating more reliable detection and characterization of pathology.