Can measurements of heroin metabolites in post-mortem matrices other than peripheral blood indicate if death was rapid or delayed?

Measurements of heroin-metabolites in cardiac blood, pericardial fluid and vitreous humor provide information comparable to that of peripheral blood regarding rapid and delayed heroin deaths, e.g. M3G/morphine ratios <2 indicate a rapid death while ratios >3 indicate a delayed death. However, considerable overlap in results from rapid and delayed deaths was observed, and measurements in muscle appeared less useful. Furthermore, matrices other than peripheral blood can be used to investigate morphine/codeine ratios, but vitreous humor seems less suited.