As the needles are slowly inserted into the brain cryoprotectant is pumped through them leaving a trail of this solution along the entire length of each needle. The major arteries can be injected with cryoprotectant, but with the capillaries being blocked by coagulated blood no circulation is possible. Something better is needed. Pretend that cryoprotectant perfusion was done and do the usual slow freeze. The result is hamburger.
Microwaves can rapidly penetrate and fix tissue.
Pack the brain with ice and place in a microwave with a turntable, which has been top rated by Consumer's Reports for uniformity of heating. Cook using pulses of radiation until well done. Treat brain with cryoprotectants by storing it in a concentrated cryoprotectant solution for a week. Store in freezer until needed. Freeze brain slowly to -10 C to limit ice crystal damage.