Rapid and reliable detection of previous freezing of cerebral tissue by computed tomography and magnetic resonance imaging

Stephan A. Bolliger, Doris Tomasin, Jakob Heimer, Henning Richter, Michael J. Thali, Dominic Gascho

Due to slowing or even inhibition of postmortem processes, freezing may make an estimation of the time-since-death very difficult. This is also true in previously frozen and subsequently thawed bodies. Knowledge of prior freezing is important, as it may lead to a different assessment of the time since death. Twelve pig heads were frozen at -20 °C, and 6 heads were either kept at room temperature (approximately 20 °C) or in a cooling cell (approximately 5 °C). The frozen brains and cadavers were thawed at either room temperature or in a cooling cell. All specimens underwent repeated CT and MRI scanning until the brains were sampled for histological examination. Two radiologists assessed the images and two pathologists reviewed the histological slides with regard to thawing artifacts and putrefaction. All raters were blinded regarding whether the samples had been frozen, for how long and how they had been thawed. Imaging revealed distinct, tiny bubble-like artifacts only in previously frozen specimens. Histology also revealed artifacts only seen in such cases, namely very distinct, columnar bubbles in the cerebral cortex. All raters successfully identified previously unfrozen brains (100% specificity) and nearly all previously frozen brains. Our results suggest that initial post-mortem imaging can be of enormous importance in everyday forensic practice by identifying possible cases of previous freezing - cases that would therefore warrant closer scrutiny and thus raise caution regarding the time of death.