A method of processing a tissue sample, comprising: a. subjecting a first tissue sample to a time of flight analysis based on passing an acoustic signal through the first tissue sample while the first tissue sample is immersed in a first processing fluid; b. determining a first processing time sufficient for a predetermined amount of the first processing fluid to diffuse into the first tissue sample based on the time of flight analysis; c. determining a second processing time sufficient for a predetermined amount of a second processing fluid to diffuse into the first sample, wherein the second processing time is calculated based on: the first processing time determine in step b, and a pre-determined functional relationship for calculating the second processing time from the first processing time, wherein the pre-determined functional relationship represents a correlation of a plurality of data pairs, each data pair comprising first data indicating a measured processing time sufficient for the predetermined amount of the first processing fluid to diffuse into a specific type of tissue sample and comprising second data indicating a measured processing time sufficient for the predetermined amount of the second processing fluid to diffuse into the specific type of tissue sample; and d. immersing the first tissue sample in the second processing fluid for the second processing time. a. subjecting a first tissue sample to a time of flight analysis based on passing an acoustic signal through the first tissue sample while the first tissue sample is immersed in a first processing fluid; b. determining a first processing time sufficient for a predetermined amount of the first processing fluid to diffuse into the first tissue sample based on the time of flight analysis; c. determining a second processing time sufficient for a predetermined amount of a second processing fluid to diffuse into the first sample, wherein the second processing time is calculated based on: the first processing time determine in step b, and a pre-determined functional relationship for calculating the second processing time from the first processing time, wherein the pre-determined functional relationship represents a correlation of a plurality of data pairs, each data pair comprising first data indicating a measured processing time sufficient for the predetermined amount of the first processing fluid to diffuse into a specific type of tissue sample and comprising second data indicating a measured processing time sufficient for the predetermined amount of the second processing fluid to diffuse into the specific type of tissue sample; and the first processing time determine in step b, and a pre-determined functional relationship for calculating the second processing time from the first processing time, wherein the pre-determined functional relationship represents a correlation of a plurality of data pairs, each data pair comprising first data indicating a measured processing time sufficient for the predetermined amount of the first processing fluid to diffuse into a specific type of tissue sample and comprising second data indicating a measured processing time sufficient for the predetermined amount of the second processing fluid to diffuse into the specific type of tissue sample; and d. immersing the first tissue sample in the second processing fluid for the second processing time.