Diffusion monitoring protocol for optimized tissue fixation

A system for monitoring diffusion of a fixative into a tissue sample, said system comprising:

• (a) a signal analyzer containing a processor (105) and a memory coupled to the processor, wherein the memory stores computer-executable instructions that cause the processor to perform operations comprising:
• (a1) fitting a time of flight (TOF) trace to a single exponential curve, the TOF trace comprising a plurality of TOF measurements of an ultrasonic signal transmitted through the tissue sample at a plurality of time points the TOF trace, and
• (a2) calculating the rate of diffusion at each time point by:
• calculating a derivative of the single exponential curve;
• and
• optionally, normalizing the derivative by dividing the derivative by an amplitude of the signal at the time point.

A tangible non-transitory computer-readable medium to store computer-readable code that is executed by a processor to perform operations comprising:

• monitoring a time of flight (TOF) of an acoustic wave traversing a tissue sample immersed in a fixative;
• calculating a rate of diffusion based on the (TOF);
• and
• comparing the rate of diffusion with a threshold to determine an optimal time to remove the tissue sample from the fixative.