Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-05-19
2001-11-27
Casler, Brian L. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
Reexamination Certificate
active
06324417
ABSTRACT:
This invention relates to a method for the non-invasive measurement of skin histology and is particularly, but not exclusively, concerned with a method for identifying and measuring the presence and depth of dermal invasion of melanin. The presence and extent of dermal invasion within a skin cancer is considered to be the most important factor governing a patient's prognosis. The present invention is considered to be potentially useful for the preliminary screening of patients to identify those who should be referred to an appropriate clinician for diagnosis and further to assist the clinician in diagnosis.
The present invention is based on the findings reported by Symon D'O Cotton in “Do all human skin colours lie on a defined surface within LMS space”, University of Birmingham Technical Report, Dec. 30, 1995. The disclosure of such Technical Report is included herein by reference. In this Technical Report, the relation between healthy skin and the colour of the skin represented in LMS, a particular colour space, is reported, and is discloses that, for healthy skin, the coloration, regardless of race or amount of tanning, lies on a defined curved surface within a three-dimensional colour space. This, if used with a correct colour measurement system, can measure and quantify the amount of melanin and blood at any particular point at which this measurement is made. If the skin is sampled as an image, then corresponding images showing the variation of blood and melanin across the skin can be obtained. In the above Technical Report, it is disclosed that melanin can sometimes penetrate into the dermis producing the characteristic hues of melanoma and that this melanocytic descent has been quantified by Clark et al (“The Histogensis and Biological Behaviour of Primary Human Malignant Melanomas of the Skin ”, Cancer Research, 29, 1989) into five levels of tumour invasion, in which level 1 corresponds to confinement within the epidermis, level 2 corresponds to invasion into the papillary dermis, etc. In an alternative system, the extent of tumour invasion in mm from the cornified layer is expressed as the Breslow thickness. The above Technical Report also acknowledges that, in the case of melanoma, C. D. Neville (“Melanoma: Issues of Importance to the Clinician”, British Journal of Hospital Medicine, Mar. 1985) discloses the existence of a strong relationship between this level of invasion and prognosis. However, the above Technical Report does not disclose in detail any method suitable for taking the necessary measurements.
According to the present invention, there is provided a method of non-invasively analysing skin structure, comprising the steps of:
(i) measuring infrared radiation from a plurality of locations over an area of skin under investigation so as to give an indication of the variation in papillary dermis thickness over said area;
(ii) measuring the skin colour coordinates at a plurality of locations over said area of skin;
(iii) using data obtained in measuring steps (i) and (ii) to calculate corrected skin colour coordinates over said area which corresponds to a predetermined papillary dermis thickness, and;
(iv) comparing the corrected skin colour coordinates obtained in step (iii) with a reference colour coordinate range for healthy skin of the same predetermined papillary dermis thickness.
The method can be used for locating and measuring the properties of a skin abnormality, in which case the method further comprises the steps of;
(v) identifying an abnormal location (i.e. a region where melanin exists within the dermis) within said area of skin where the corrected skin colour coordinates lie outside the reference colour coordinate range;
(vi) calibrating the corrected skin colour coordinates of said abnormal location with the corrected skin colour coordinates of at least one skin location having colour coordinates lying within said reference colour coordinate range for normal skin, and;
(vii) using the skin colour coordinates to assess the degree of abnormality of said abnormal skin location.
It is to be understood that using this method, it is possible to reconstruct a full 3 D model of the skin architecture which conveys information grossly comparable to the available through microscopical examination of biopsied skin tissue.
It has been found that the papillary dermal skin thickness can change markedly with some skin lesions which are not otherwise of concern. This throws the coloration of the skin off the surface of predicted coloration and so can give rise to false measurements of the histology of such skin lesions. It is for this reason that papillary dermis thickness is measured first, and subsequent calculations are based on the skin colour coordinates corrected to a predetermined papillary dermis thickness. Any arbitrary value for this thickness may be chosen, such as 2.0×10
−4
m which is the average value for healthy human skin.
The thickness of the papillary dermis may be obtained by utilising the property of human skin to vary its absorption of infrared radiation with varying papillary dermis thickness. In general, there is an inverse relationship between absorption and thickness. The fact that infrared radiation is also absorbed by other materials within the skin, particularly melanin and blood, is a complicating factor. However the effect on absorption of varying blood and melanin content is far smaller than the effect of papillary dermis thickness, and so the latter may still be measured. This can be done by obtaining two infrared images, each at a different wavelength. The chosen wavelengths are not important, but one should be further into the infrared (ie at longer wavelength) than the other. Suitable wavelength bands are 800-1000 nm and 600-800 nm, in that readily available infrared films and filters may be used. The brightness of points within the image obtained at the longer wavelength is affected to a greater extent by variations in the papillary dermis thickness. Conversely, the image obtained at shorter wavelength will be affected to a greater extent by other materials such as melanin and blood. By predicting the brightnesses of points of differing papillary dermis thickness and amounts of epidermal melanin which absorb near-infrared radiation at the two different infrared wavelengths, a reference graph (
FIG. 1
) can be obtained which consists of lines of constant papillary dermis thickness, wherein Primary 1 is the measurement made at the longer (800-1000 nm) wavelength and Primary 2 is the measurement made at the shorter (600-800 nm) wavelength. The absorption of blood within these wavelengths is very small (a hundredth of its peak value for visible wavelengths at 600-800 nm and even less for 800-1000 nm) and to a first approximation may be ignored. The presence of dermal melanin does introduce a small error in the range of low values for both primaries, but this is insignificant in practice. Thus, by comparing values obtained at these wavelengths with this graph, it is possible to ascertain the papillary dermis thickness. However it is within the scope of the present invention to measure brightness at such a long infra-red wavelength eg. 1100 nm that the brightness would vary to such a negligible extent with melanin and blood content that it would effectively depend solely on the papillary dermis thickness. This would also reduce the error introduced by the presence of dermal melanin. In such a case only one set of brightness measurements would be required. Furthermore, a transformation can be calculated which allows an image of the skin to be created which represents how the skin would appear if it had a papillary dermis thickness of any predetermined value.
In a preferred embodiment, the reference colour coordinate range for normal skin at the predetermined papillary dermis thickness is obtained as disclosed in the above-mentioned Technical Report as a curved surface lying within a three-dimensional colour space, with one of the bounding axes relating to the amount of melanin within the epidermis and the othe
Casler Brian L.
Michael & Best & Friedrich LLP
Optiscan Limited
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