Magnetic Resonance Imaging (MRI) is a widely used diagnostic tool that provides detailed images of the body’s internal structures. The two fundamental MRI sequences are T1-weighted (T1WI) and T2-weighted (T2WI) images. Understanding the differences between them helps clinicians accurately interpret anatomy and identify disease.
T1-Weighted MRI (T1WI)
T1-weighted imaging highlights differences in the longitudinal relaxation times (T1) of tissues. These images are produced using a short repetition time (TR: 400–600 ms) and a short echo time (TE: 10–20 ms).
T1-weighted images are particularly useful for evaluating normal anatomy because they provide sharp, well-defined structural detail. In these images, fat appears bright (hyperintense), while fluids appear dark (hypointense).
Examples:
- Subcutaneous fat appears bright.
- Cerebrospinal fluid (CSF) within the brain ventricles appears dark.
T2-Weighted MRI (T2WI)
T2-weighted imaging emphasizes differences in transverse relaxation times (T2) of tissues. These images are acquired using a long repetition time (TR: 3000–6000 ms) and a long echo time (TE: 90–110 ms).
T2-weighted images are especially valuable for detecting pathology, as most conditions associated with increased fluid content become more visible. In T2WI, both fat and water-containing structures appear bright, with fluid often appearing very bright.
Examples:
- Cerebrospinal fluid (CSF) appears bright.
- Joint fluid (synovial fluid) appears bright.
MBH/DB