What does it mean if a t2 prolongation on brain mri is getting larger?

Very complicated ans: Without going into the physics of MRI (which I doubt even the most ardent Radiologist could explain), prolongation of the T2 signal (a bright area on T2-weighted images) generally means a higher water content - swelling from stroke, inflammation, tumors, infections can cause this. If you've had multiple MRIs, increasing prolongation may not mean much as each MRI is obtained differently.