Alternative light source (polilight®) illumination with digital image analysis does not assist in determining the age of bruises

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Abstract

The age of a bruise may be of interest to forensic investigators. Previous research has demonstrated that an alternative light source may assist in the visualisation of faint or non-visible bruises. This project aimed to determine if an alternative light source could be utilised to assist investigators estimate the age of a bruise. Forty braises, sustained from blunt force trauma, were examined from 30 healthy subjects. The age of the bruises ranged from 2 to 231 h (mean = 74.6, median = 69.0). Alternative light source (polilight®) illumination at 415 and 450 nm was used. The black and white photographs obtained were assessed using densitometry. A statistical analysis indicated that there was no correlation between time and the mean densitometry values. The alternative light source used in this study was unable to assist in determining the age of a bruise.

Introduction

The determination of the age of a bruise has been a longstanding issue in forensic medicine. Previous research has indicated that it may be possible to indicate if a bruise is recent or old from direct observation or viewing of photographs [1], [2]. However, estimation the age of a bruise by visual inspection is subjective and susceptible to variations in perception [3], [4]. Therefore, objective methods for assisting the determination of the age of a bruise are required.

Techniques have been developed for assisting the examination of bruises. Diaphanoscopy may identify areas within the skin that contain subcutaneous haematomas that are not visible to the naked eye [5]. Study of CIE L × a × b values obtained from spectrophotometry [6] has been performed to determine if the depth of the haemorrhage can be determined from the colour of the bruise. However, these techniques do not provide objective information that may assist with estimating the age of a bruise.

A bruise forms as a result of blunt trauma. When the blood vessels within the skin are torn, red blood cells are released into the surrounding tissue. Red blood cells contain haemoglobin, which has an absorption peak at 415 nm [7], [8]. Macrophages (phagocytes) accumulate within the bruise as part of the inflammatory (healing) response to the injury. Macrophages convert haemoglobin to bilirubin [9], which has a broad absorption peak that is maximal at 460 nm [7], [8]. As a result a decrease in the absorption of light at 415 nm and an increase of absorption of light at 460 nm would be expected as a bruise ages. The potential application of spectrophotometry to provide objective information for the estimation of the age of bruises was investigated by Klein et al. [10] and we have published a technical note describing practical application of reflectance spectrophotometry for the study of bruises [11].

An alternative light source illuminates the skin with light of a specific wavelength. Light that is absorbed may be re-emitted at a larger wavelength (with lower energy) [12]. In order to observe the fluorescence it is necessary to separate it from incidental light by using filters or goggles [13]. It has previously been demonstrated that injuries viewed using an alternative light source revealed greater detail, contrast and extent compared to their appearance under natural light [13]. The application of an alternative light source permitted the visualisation of faint or non-visible bruises in children that otherwise would not have been apparent [14].

This study sought to determine if objective information regarding the age of a bruise could be gained using a polilight® as an alternative light source. The polilight® was chosen as it is utilised by the regional police crime scene investigators. The polilight® units that were available had set emissions at 415 and 450 nm. Light at 415 nm is optimal for detecting haemoglobin, which has a narrow peak around this value. Illumination at 450 nm will still be significantly absorbed by bilirubin as it has a broad absorption curve.

Section snippets

Methods

Volunteers with a bruise of known age and cause were recruited. The alternative light source used in this study was a polilight® model PL10A (Rofin, Australia). The bruise and adjacent non-bruised skin were illuminated by the polilight® set at 415 or 450 nm. The intensity of the light source was kept constant for all subjects.

The output of the polilight® was channelled though a fibre-optic cable to a jig, which also held a Minolta XG-M camera with a 50 mm lens. The camera was fitted with an

Results

The age of the bruises examined ranged from 2 to 231 h (mean = 74.6 h, median = 69.0 h). The mean grey value obtained with illumination at 415 and 450 nm for each of the 40 bruises in shown in Fig. 1. A statistical analysis indicated that there was no correlation between time and the mean densitometry value at 415 nm, (coefficient of correlation = 0.00, Pearson correlation = −0.038) or at 450 nm, (coefficient of correlation = 0.00, Pearson correlation = −0.046). However, there was correlation between the 415 and

Discussion

Haemoglobin has an absorption peak at 415 nm and bilirubin has a broad absorption with a peak at 460 nm [7], [8]. Therefore, it was proposed that a recent bruise would have a higher area densitometry value at 415 nm than an old bruise, and that an old bruise would have a higher densitometry value at 450 nm than a new bruise. However, after statistical analysis it was found that there was no correlation between time and the area densitometry values at 415 or 450 nm.

Fair skinned individuals were

Conclusion

Currently, clinicians may age a bruise by visual inspection, stating that a bruise is not recent if it contains the colour yellow. This study investigated the application of an alternative light source (polilight®) for the estimation of the age of bruises. However, no useful information for the ageing of bruises was obtained using this method.

Acknowledgements

We would like to acknowledge the various units of the NSW Police Service who supported this project by lending our department the polilight units.

References (15)

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