Greek Common Greek symbols used in medical imaging. (If Greek symbols are MRI related, yellow marked links lead to definitions at MR-TIP.com. π (pi) Ratio of the Circumference of the Circle to its Diameter (~3.1415) τ (tau) Time Delay Anybody can sympathise with the sufferings of a friend, but it requires a very fine nature to sympathise with a friend's success. - Oscar Wilde |