Optical characterization of bruises

Bruises develop as a result of a physical impact on the body, most often unintentionally. During the impact, the tissue may be disrupted and this may cause a bleeding. This, together with the immune response providing higher activity to repair the damage, will appear as a bruise. In several situations it would be of interest to characterize a bruise – it is, for instance, important to avoid any bleedings inside the skull, to avoid an increased intracranial pressure, quickly yielding severe consequences. It is thus of importance to be able to measure size and location of such a bleeding quickly. Bruises at other parts of the body may be important from a forensic point of view, to allow an objective characterisation. It may, for instance, be of importance to be able to judge the age of a bruise and being able to use this in crime investigations.

The aim of this project is to discuss and present some modeling results to support the idea of judging the age of a sub-dermal injury by optical spectroscopy.

There seems to be at least two parameters varying as a function of age for a bruise. Firstly the haemoglobin leaking out in the tissue will be metabolised with time and the porphyrin structure of hem will be chemically altered and finally disrupted. This will cause spectral shifts of the bruise. Secondly the haemoglobin will not stay in the same position after the leak, but will diffuse and also move away. This will also provide information of the age of the bruise. In the project you should thus especially consider

• Absorption spectra of haemoglobin and its metabolites
• Transport  and diffusion of liquids in the tissue
• Optical properties of tissue
• Depth of the leakage

The intention is that the project should include the following:

• You are supposed to briefly study the field of optical characterisation of bruises and also other diffuse reflection spectroscopic diagnostic procedures of skin, as for instance bilirubin concentration measurements. This research field is very new and it may be difficult to find much background literature devoted to these questions, The background should be included in the introduction of the report, citing the proper literature.
• You should find the optical properties of the tissues and wavelengths of interest for the project in the literature or measure them during the laboratory exercises. Note though, that skin tissue is very difficult to measure as it is consisting of several very thin layers with very different properties. Also with the equipment used during the labs it is not possible to measure optical properties below 660 nm.
• You should study how haemoglobin is metabolised, and find in the literature the absorption spectra of these compounds.
• You should calculate the diffusely reflected light for different compositions of the bruise and for several different wavelengths (during the computer exercises and by yourself).
• You should find in the literature the mobility of the compounds giving the appearance of a bruise. If you have difficulties finding appropriate values, please make motivated assumptions. You may be able to model this in FEMLAB.
• If possible (if you for instance hurt yourself during a soccer game or something), take a photo of a bruise every day until it disappears.
• Discuss the changes in bruise appearances as a function of age based on the results obtained above. 

Suggested key-words: skin spectroscopy, reflection spectroscopy, bruise characterisation, tissue optics, jaundice