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T1 and T2 mapping are quantitative MRI techniques that measure the absolute T1 and T2 relaxation times of tissues on a pixel-by-pixel basis, generating parametric maps.

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Unlike conventional weighted images, mapping yields quantitative values in milliseconds, improving detection, characterization, and monitoring of various pathologies, especially in cardiac, hepatic, and musculoskeletal imaging.

Underlying Physics

• T1 (Longitudinal relaxation time): Time taken for protons to realign with the magnetic field after excitation.
• T2 (Transverse relaxation time): Time taken for protons to lose phase coherence in the transverse plane.

Mapping sequences sample these relaxation behaviors at multiple time points to generate voxel-wise T1 or T2 values.

Techniques

T1 Mapping Sequences

• Modified Look-Locker Inversion Recovery (MOLLI): Most common for cardiac imaging.
• ShMOLLI (Shortened MOLLI): Faster, better for breath-holding.
• SASHA (Saturation-recovery single-shot acquisition): Less sensitive to heart rate, slightly less precise.

T2 Mapping Sequences

• Multiple T2-prepared SSFP images with different echo times.
• Turbo spin echo (TSE) or gradient echo-based sequences may be used in non-cardiac applications.

Applications

Cardiac Imaging

• Primary clinical domain for mapping