What is thermal relaxation time?

As the data obtained from the medical centres says that the time it takes for an object to cool down from 100º C to 50ºC. It is a rule that a smaller object cools faster than a larger object of the same material and shape which means that the smaller target has a shorter thermal relaxation time. This fact is important when the tissue needs to be heated to a desired temperature at a certain fluence setting. If the pulse width is too long, the tissue will start cooling itself via thermal conduction prior to the completion of a pulse causing a negative clinical effect. The second parameter that should be taken into consideration when estimating the TRT is the shape of the target tissue. A sphere (skin cells) having 360 degrees of cooling surface area cools faster than a cylinder (hair follicles). This allows hair follicle to retain its heat while the skin cells can cool itself much more efficiently. For this reason, parameters can be selected to destroy the follicle without causing damage to the skin. For targeting smaller structures, a shorter pulse duration and higher fluence are recommended.