During investigations of potential child and elder abuse, clinicians and forensic practitioners are often
asked to offer opinions about the age of a bruise. A commonality between existing methods of bruise aging
is analysis of bruise color or estimation of chromophore concentration. Relative chromophore concentration
is an underlying factor that determines bruise color. We investigate a method of chromophore concentration
estimation that can be employed in a handheld imaging spectrometer with a small number of wavelengths.
The method, based on absorbance properties defined by Beer-Lambert's law, allows estimation of
differential chromophore concentration between bruised and normal skin. Absorption coefficient data for
each chromophore are required to make the estimation. Two different sources of this data are used in the
analysis- generated using Independent Component Analysis and taken from published values. Differential
concentration values over time, generated using both sources, show correlation to published models of
bruise color change over time and total chromophore concentration over time.
Visual inspection of intact skin is commonly used when assessing persons for pressure ulcers and bruises. Melanin
masks skin discoloration hindering visual inspection in people with darkly pigmented skin. The objective of the project
is to develop a point of care technology capable of detecting erythema and bruises in persons with darkly pigmented skin.
Two significant hardware components, a color filter array and illumination system have been developed and tested. The
color filter array targets four defined wavelengths and has been designed to fit onto a CMOS sensor. The crafting process
generates a multilayer film on a glass substrate using vacuum ion beam splitter and lithographic techniques. The
illumination system is based upon LEDs and targets these same pre-defined wavelengths. Together, these components
are being used to create a small, handheld multispectral imaging device. Compared to other multi spectral technologies
(multi prisms, optical-acoustic crystal and others), the design provides simple, low cost instrumentation that has many
potential multi spectral imaging applications which require a handheld detector.
The detection and aging of bruises is important within clinical and forensic environments. Traditionally, visual and
photographic assessment of bruise color is used to determine age, but this substantially subjective technique has been
shown to be inaccurate and unreliable. The purpose of this study was to develop a technique to spectrally-age bruises
using a reflective multi-spectral imaging system that minimizes the filtering and hardware requirements while achieving
acceptable accuracy. This approach will then be incorporated into a handheld, point-of-care technology that is
clinically-viable and affordable. Sixteen bruises from elder residents of a long term care facility were imaged over time.
A multi-spectral system collected images through eleven narrow band (~10 nm FWHM) filters having center
wavelengths ranging between 370-970 nm corresponding to specific skin and blood chromophores. Normalized bruise
reflectance (NBR)- defined as the ratio of optical reflectance coefficient of bruised skin over that of normal skin- was
calculated for all bruises at all wavelengths. The smallest mean NBR, regardless of bruise age, was found at wavelength
between 555 & 577nm suggesting that contrast in bruises are from the hemoglobin, and that they linger for a long
duration. A contrast metric, based on the NBR at 460nm and 650nm, was found to be sensitive to age and requires
further investigation. Overall, the study identified four key wavelengths that have promise to characterize bruise age.
However, the high variability across the bruises imaged in this study complicates the development of a handheld
detection system until additional data is available.