Measuring Area and Volume of Leg Ulcers by Structured Light

  • Peter Plassmann

    Student thesis: Doctoral Thesis


    Ulcers of the human skin are difficult to cure and a massive burden to patients. Their treatment costs in the UK are in excess of £100 million annually (1989). Both suffering and costs can be reduced significantly by establishing if an ulcer is responding to treatment. Any measurement device must not make any contact with the patient in order to avoid pain, damage or infection of the wound.

    This work describes a novel non invasive measurement method for superficial skin ulcers. Measurement is carried out using a new version of colour coded structured light method to obtain three dimensional surface data. A set of parallel stripes of light is projected onto the ulcerated skin and observed by a camera. The stripes are displaced by an amount which is related to the shape of the skin. It is shown how stripe parameters such as colour, distance, width and coding may be optimised with respect to the object of interest to maximise the performance of the method. Two newly developed stripe extraction algorithms ensure that the centre positions of the projected stripes are found with a precision better than 0.1 mm. From the position of the stripes on the skin a computer then calculates a representation of its shape by triangulation. This is stored in a three dimensional surface map. The volume of a skin ulcer is the difference between the measured base of the lesion and the original healthy skin. The work demonstrates that the original shape may be simulated by a specialised spline interpolation method which is based on the surroundings of the ulcer.

    The technique is implemented in a portable instrument which is capable of measuring the area and volume of a wide range of different ulcers and pressure sores with a standard deviation of less than 5% of the total figure. With the current equipment the measurement is made in half a second and its result is available after less than 5 minutes.

    The technique works well in subdued ambient lighting and on most ulcers. In cases where the ulcer is wet, specular reflection may cause problems but the system is usually able to correct for them. The instrument is suitable for a large variety of ulcers but is not able to measure wounds which undermine the skin, extend outside the normal field of view or are highly flexible.

    Date of AwardSep 1992
    Original languageEnglish

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