Recipient Organization
UNIVERSITY OF TENNESSEE
2621 MORGAN CIR
KNOXVILLE,TN 37996-4540
Performing Department
Small Animal Clinical Sciences
Non Technical Summary
Living organisms consist mainly of the six basic elements: C, H, O, N, P, and S. These elements are combined to form the four major classes of biological macromolecules found in living matter: proteins, nucleic acids, polysaccharides, and lipids. After death, tissue undergoes sequential changes consisting of organic and inorganic phase variations, as well as a gradual reduction of tissue water content. While carbon dominates the chemistry of biological tissues, hydrogen atoms are the most abundant element. Hydrogen nuclei scatter thermal and cold neutrons more strongly than any other atomic nucleus. These two facts ensure that hydrogen is the primary contributor to neutron contrast in biologic specimens. The principle of neutron imaging is based on the attenuation, both scattering and absorption, of a directional neutron beam by the matter through which it passes. Neutron imaging is complementary, rather than competitive with X-ray imaging. Since X-rays are scattered and absorbed by the electrons, the attenuation increases monotonically with atomic number. Neutrons interact with atomic nuclei, and their attenuation does not scale in a regular way with atomic number. Thus, unlike other imaging methods, neutrons are strongly attenuated by hydrogen (the predominant elemental constituent of biological materials) which is manifest as contrast in an image. These contrast differences in neutron scattering and imaging can readily be applied in a forensic context to determine small changes in hydrogen concentrations. Since human decomposition starts approximately 4 minutes after death, structure and hydrogen concentrations change with time. We propose to study the decomposition of fresh animal tissues (for example, skeletal muscle tissue) and fixed tissues using neutron imaging techniques as a method to estimate the time of death. Since neutrons have yet to be used for forensic research, a broad selection of tissue samples is required to investigate which tissues will best show changes in neutron contrast due to hydrogen concentration changes and the structural changes of the tissue. In addition, we will investigate the effect of different environmental conditions (temperature and humidity) to simulate a corpse exposed to the elements. Neutron imaging data will be collected on tissues from fresh to several days of exposure. These results will be compared to imaging techniques commonly used in forensic research such as histology with light microscopy. In conclusion, the main hypothesis of our study is that as the hydrogen content of degrading tissue changes in time, neutrons can quantitatively measure changes in the hydrogen content of the tissues and identify structural changes as they happen through time. Hence, models may be built to determine more accurately the time of death for human beings and adjust for the environment to which they were exposed.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Purpose: The purpose of this research is to determine the role for neutron imaging by measuring changes in structure and hydrogen concentration in decaying animal tissues in different field conditions. Goal: The goal of this research is to develop an objective technique using neutron imaging to better estimate the post-mortem interval from several different tissues. The data analysis will provide new tools to understand the decomposition of biological tissues as a function of time, temperature and humidity in order to provide a more accurate post-mortem interval. Objectives: This proposal had following objectives: 1) Intact tissue samples for neutron imaging in the early stages of decomposition will be identified and prepared. A series of animal tissue samples including heart, lung, pancreas, liver, kidney, skeletal muscle tissue and bones will be extracted from carcasses available through the University of Tennessee, College of Veterinary Medicine, Knoxville. Neutron imaging measurements will be performed on fresh, formalin, ethanol and deutherated ethanol fixed canine tissues. 2) Investigate the effect of different environmental conditions (temperature and humidity) to stimulate a corpse exposed to the elements. Neutron imaging data will be collected on tissues from fresh to several days of exposure. These results will be compared to imaging techniques commonly used in forensic research that are available at the UTCVM. 3) Models will be constructed using the data collected in order to more accurately determine the post-mortem interval. The requirements for a system that is not cost prohibitive for local law enforcement agencies will be determined for known neutron generations techniques such as D-T generators. Such systems may be configurable as a portable device.
Project Methods
The tissues used in this study will be obtained from animal subjects supplied to the Department of Pathobiology, University of Tennessee, College of Veterinary Medicine, Knoxville, TN by a certified animal control agency. Several tissues were collected, fixed, and imaged using neutrons from dog carcasses. We studied skeletal muscle, heart, pancreas, kidney, bone, and lung tissues of thicknesses varying from 1 to 4 mm. In the context of forensic research, death, and crime scene evidence, skeletal muscle tissues survive the longest as compared to other soft tissues when a body is decomposing. We investigated the effects of commonly used tissue fixatives (i.e. formalin and ethanol) on neutron transmission characteristics in radiographs of tissues with different thicknesses compared to fresh tissues. Samples were placed on a translation/rotation stage for alignment and tomography purposes. Detectors for the CG-1D beamline were (1) an ANDOR DW936 charge coupled device (CCD) camera with a field of view of approximately 4 cm x4 cm and ~ 50 micron spatial resolution and 1 frame per second time resolution, and (2) a Micro-Channel Plate (MCP) detector with a 4 cm (radius) field of view and a 40 micron spatial resolution. Small pieces of canine tissues were dissected from dog carcasses followed by either 24h-fixation in 10% neutral-buffered formalin, 70% ethanol, or 70% deuterated ethanol in D2O (ethanol-like fixative where hydrogen atoms are replaced by deuterium atoms that scatter neutrons less than hydrogen). These tissues were imaged using neutrons and compared to neutron radiographs of similar fresh dissected tissue samples. Hydrogen changes were measured temporally (from hours to days) by neutron radiography in different types of tissues. Two types of measurements were performed at the neutron facility: (1) extraction of tissue samples and temporal measurements at the neutron imaging beamline and (2) extraction of tissue samples on a regular basis and measurement of canine tissue extracted using the 2 mm diameter biopsy needle from one dog carcass during 2 weeks period of decomposition at the ARF.