Photogrammetry using visible, infrared, hyperspectral and thermal imaging of crime scenes.

Photogrammetry is a method for obtaining virtual 3D models of objects and scenes. The technique is increasingly used to record the crime scene in its original, undisturbed state for mapping, analytical and reconstruction purposes. Recently, it was shown that it is possible to visualize and/or chemically analyze latent traces by using advanced cameras which either operate in wavelength ranges beyond the visible range, and/or are able to obtain spectrally resolved images. The combination of these advanced cameras and photogrammetric techniques enables the 3D registration of valuable information. We successfully explored the feasibility to obtain visible, infrared, hyperspectral and thermal 3D registrations of simulated crime scenes using photogrammetry, and demonstrate the possibilities and practical challenges for use in forensic practice.

Visual characteristics for sequencing of overlapping bloodstain patterns.

The deposition sequence of overlapping bloodstain patterns can be valuable reconstructive information. A formal method for sequencing overlapping bloodstain patterns has yet to be published. We present a method for sequencing overlapping transfer and drip stains using visual characteristics. A survey was held amongst educated bloodstain pattern analysts to determine whether the newly acquired method will assist them in correctly sequencing these overlapping bloodstain patterns. Results showed a significant improvement of expert decisions: the percentage of overlapping stains correctly sequenced by participants increased from 57 to 79% using the visual characteristics defined in this study. These results suggest that a decision support system can be built, which helps investigators at the crime scene to sequence overlapping bloodstain patterns.

Hyperspectral imaging for non-contact analysis of forensic traces.

Hyperspectral imaging (HSI) integrates conventional imaging and spectroscopy, to obtain both spatial and spectral information from a specimen. This technique enables investigators to analyze the chemical composition of traces and simultaneously visualize their spatial distribution. HSI offers significant potential for the detection, visualization, identification and age estimation of forensic traces. The rapid, non-destructive and non-contact features of HSI mark its suitability as an analytical tool for forensic science. This paper provides an overview of the principles, instrumentation and analytical techniques involved in hyperspectral imaging. We describe recent advances in HSI technology motivating forensic science applications, e.g. the development of portable and fast image acquisition systems. Reported forensic science applications are reviewed. Challenges are addressed, such as the analysis of traces on backgrounds encountered in casework, concluded by a summary of possible future applications.

Comparison of brain tissue and local cerebral venous gas tensions and pH.

Neurosurgical monitoring devices have recently become available which are capable of measuring cerebral tissue gas tensions and pH. Brain tissue sensors have not been conclusively demonstrated to correlate with other measurements of regional cerebral gas tensions or pH. The present study was undertaken to correlate sensor values for pO2, pCO2 and pH with blood samples taken concurrently from local cerebral veins. Adult mongrel dogs were anesthetized and a craniotomy was performed. A small gyral vein was isolated and cannulated. Adjacent to the venous catheter tip, a Neurotrend brain tissue probe was inserted in an intracortical location. Each subject received a sequence of manipulations in inspired oxygen and end tidal carbon dioxide conditions. Under each experimental condition, samples of arterial and gyral venous blood were obtained and blood gas analysis performed. Concurrent brain probe measurements of tissue pO2, pCO2 and pH were recorded. Statistical analysis determined that local tissue and cerebral venous blood values for pO2, pCO2 and pH were highly correlated (R(s) = 0.62-0.82; p < 0.001). This indicates that there exists a confirmable monotonic relationship between tissue values and conditions in the post-capillary venous bed. Tissue sensors such as the Neurotrend probe can offer reliable trend indications in brain tissue gas tensions and pH.

Cerebral hypoxia after etomidate administration and temporary cerebral artery occlusion.

UNLABELLED: Neurovascular surgical procedures often require temporary cerebral arterial occlusion. Although clinical validation is lacking, etomidate has often been used to attenuate the effects of cerebral ischemia in this setting. The purpose of this study was to evaluate the effects of etomidate and temporary cerebral arterial occlusion on human brain tissue oxygen pressure (PO2), carbon dioxide pressure (PCO2), and pH during intracranial aneurysm surgery. We studied nine patients presenting for cerebral aneurysm surgery. A Paratrend probe was used to determine brain tissue pH and gas tensions. Etomidate was administered to produce electroencephalographic burst suppression before temporary cerebral arterial occlusion. After etomidate administration in nine patients, brain tissue PO2 decreased 30% compared with baseline (P < 0.05). During temporary brain artery occlusion in 8 patients, tissue PO2 decreased 32% below preclip values (P < 0.05) in conjunction with a tissue PCO2 increase of 23% (P < 0.05) and a 0.1-unit decrease in pH (P < 0.05). In patients in whom PO2 decreased below 10 mm Hg during temporary clipping, tissue pH decreased, compared with patients in whom PO2 remained above 10 mm Hg (P < 0.05). These results demonstrate that etomidate administration during cerebral aneurysm surgery decreases tissue PO2 and that in these patients, tissue PO2 does not increase with increases in inspired oxygen concentration. Low tissue PO2 during temporary clipping significantly increases the risk of tissue acidosis. IMPLICATIONS: Etomidate administration alone resulted in cerebral deoxygenation. Subsequent temporary cerebral artery occlusion resulted in additional tissue deoxygenation and acidosis. These results suggest that etomidate enhances hypoxic risk in the setting of cerebral ischemia.