Characteristic of a T2 weighted image is the high signal intensity of water. Pathology is often associated with edema/fluid and therefore a T2 sequence is very suitable to detect pathology (fig. 15).
Figure 15. Brain tumor with surrounding (reactive) edema frontoparietal left. Both the tumor and the edema have high signal intensity on T2. PA diagnosis: lymphoma.
As in a T1 weighted image, air and calcifications have very low signal intensity.
Tip: you are unsure whether you are seeing air or calcifications? Try to find the structure on an X-ray/CT scan!
Figure 16. Signal intensities in T2 weighted image. Liver, pancreas and adrenals may have low or intermediate signal intensity (SI) caused by variation in individual fluid contents.
Tip: always look for fluid-filled structures (CSF, gallbladder, bladder) to decide whether you are looking at a T1 or T2 weighted image. Fluid has a high signal intensity on T2 weighted images. Note: fat is a less reliable marker to distinguish between T1 and T2 (especially in view of the development of new types of MRI sequences).