TI scout (look-locker) MRI

A TI-scout (TI refers to inversion time) is a type of imaging sequence used in cardiovascular magnetic resonance (CMR) to assess the nulling time of normal myocardium after the administration of a gadolinium-based contrast agent. This sequence is crucial for determining the optimal inversion time to null the signal from specific tissues, such as the myocardium, during the delyed PSIR image aqusition.

Here’s a breakdown of how it works:

• Inversion Time (TI): This refers to the delay time after which an MRI sequence is applied following the inversion of magnetization. In the TI scout sequence, multiple images are acquired with different TIs to allow the MRI to capture images at different points of recovery of the longitudinal magnetization.
• Purpose of the TI Scout: In cardiac MRI, particularly when using sequences like Delayed Enhancement or Late Gadolinium Enhancement (LGE), it is crucial to find the inversion time that causes the normal myocardium to appear nulled (dark) in the images. This enhances the contrast between healthy myocardial tissue and pathological tissues (like fibrosis or scars), which do not null at the same TI.
• Process: During a TI scout sequence, multiple images are acquired at different inversion times (ranging from 90 to 800 milliseconds, as in your example). This range is used to progressively see how the myocardium signal intensity changes as the inversion time increases.
• Optimal Nulling Point: By reviewing these images, the radiologist or technician can determine the specific inversion time at which the normal myocardium appears darkest (nulled), while pathological tissues retain higher signal intensity and appear brighter. This inversion time is then used for the late gadolinium enhancement (LGE) imaging sequences to ensure optimal contrast for visualization and assessment of myocardial tissue health.