What happens if TI is set to a point where a tissue’s T1 curve crosses the zero line?

When the inversion time (TI) is set to a point where a tissue's T1 recovery curve crosses the zero line, it indicates that the longitudinal magnetization has reached its null point or minimum. At this point, the tissue in question will not contribute any longitudinal magnetization, which is essential for producing a signal in MRI. Therefore, if TI aligns with the zero crossing on the T1 curve, the tissue will appear dark or have very little signal on the resulting MR image because the recovery of magnetization has not occurred enough to register a detectable signal. This phenomenon is often employed in specific imaging sequences, such as inversion recovery techniques, to nullify the signal from particular tissues based on their T1 properties. This precise timing is critical for optimizing contrast in MRI scans, which is why this understanding is key in interpreting MRI images effectively.