Biomedical subjects

S Tomatis

Publications and source records attributed to S Tomatis.

14 recordsLinked to original sources

PubMed2006

Optical devices used for image analysis of pigmented skin lesions: a proposal for quality assurance protocol using tissue-like phantoms.

Different technological tools have been developed to aid in the diagnosis of pigmented skin lesions, including cameras working with conventional RGB colour systems, epiluminescence microscopy and spectrophotometric methods using visible and near infrared wavelengths. All the different procedures should provide in an objective and reproducible fashion quantitative measurements of the colour and shape features of a given skin mole. At present, many devices have been introduced in experimental stages for clinical diagnosis, mainly used to provide to the clinicians an objective, computer-assisted second opinion. As for any diagnostic instruments, optical devices should also be subjected to a dedicated quality assurance protocol in order to evaluate the response repeatability of each device (intra-instrument agreement) and to check the accordance among the responses of different devices (inter-instrument agreement). The aim of this study was to design a quality assurance protocol for optical devices dedicated to image analysis of pigmented skin lesions and, in case, to detect cutaneous melanoma by using suitable tissue-like phantoms as standard references that enable testing of both hardware and software components. As an example, we report the results of intra-instrument and inter-instrument agreement when the protocol was applied on a series of 30 SpectroShade instruments, a novel optical device based on multi-spectral image analysis of colour and shape features of pigmented skin lesion.

Biophysical Phenomena↗

PubMed2006

Dose imaging with gel-dosemeter layers: optical analysis and dedicated software.

In radiotherapy involving thermal and epithermal neutrons, the knowledge of dose distributions, with separation of the contribution of each secondary radiation component, is of utmost importance. Layers of Fricke-Xylenol-Orange-infused gel dosemeters give the possibility of achieving such requirements because, owing to the layer-geometry, enriching or depleting the gel matrix of suitable isotopes does not sensibly alter neutron transport. The dosimetry method has been critically re-examined with the aim of improving its suitability to boron neutron capture therapy (BNCT) requirements, as it applies to the protocol of measurement and analysis, the sensitivity of the method and the range of the linearity of the dosemeters. Software has been developed and studied to obtain automatically the images of the various dose components with the established separation procedure.

Algorithms↗

PubMed2006

Micro-melanoma detection: a clinical study on 206 consecutive cases of pigmented skin lesions with a diameter < or = 3 mm.

BACKGROUND: Very small pigmented lesions may represent an important diagnostic challenge to the clinician. OBJECTIVES: The aim of the present study was to establish the diagnostic value, in terms of sensitivity and specificity, of both clinical and dermoscopic examinations in a population of patients with unselected consecutive pigmented lesions with a maximum clinical diameter of 3 mm. PATIENTS AND METHODS: Two hundred and four consecutive patients bearing 206 pigmented skin lesions with a maximum diameter of 3 mm were seen and operated on. Twenty-three of these lesions were melanomas. Each lesion was subjected to both clinical and dermoscopic evaluation before surgery. The results were expressed in terms of sensitivity and specificity of both kinds of evaluation. RESULTS: Clinical evaluation produced a diagnostic sensitivity of 43% and a specificity of 91%. Dermoscopy resulted in a sensitivity of 83% and in a specificity of 69%. The comparison between the sensitivity values of the two diagnostic methods showed a significant difference (P < 0.01). A high value of significance was also obtained comparing the respective specificity values (P < 0.001). CONCLUSIONS: Detection of very small melanomas is feasible by accurate visual inspection. Dermoscopy appears to be an important aid to diagnosis, provided that physicians are aware of this type of lesion and maintain the index of suspicion at a high level.

Adolescent↗

PubMed2002

Optical imaging and automated melanoma detection: questions and answers.

Early detection and prompt excision of cutaneous melanoma is of paramount importance to improve patient survival, and the clinician should be aware of the clinical features that suggest the presence of a malignant lesion. The clinical diagnosis is mainly based on observation of the colour and shape of a given skin lesion. Unfortunately, evaluation of a pigmented lesion is to a large extent subjective and is closely related to the experience of the clinician. To overcome this problem, optical imaging techniques using different instrumentation (i.e. colour video camera, epiluminescence microscopy, reflectance spectrophotometry) and computer image analysis have been proposed in an attempt to provide quantitative measurements in an objective and reproducible fashion. The different procedures employed to perform the diagnosis automatically all have a common denominator: mimicking the eye and the brain of the clinician by image processing and computerized analysis programs, respectively. Sensitivity and specificity data reported in the literature suggest that the computer-based diagnosis of melanoma does not greatly differ from the diagnostic capability of an expert clinician, and is independent of the optical acquisition method employed to analyse the lesions. Most of the computer-processed morphometric variables useful in automated diagnosis are not recognizable nor can be objectively evaluated by the human eye, except that of lesion dimension. However, several questions should be answered before assessing the actual usefulness, including the potential and limitations, of computer-based diagnostic procedures. The purpose of this study was to briefly review the different kinds of instrumentation being used to diagnose melanoma, and to raise questions and whenever possible provide answers in an attempt to establish whether there will be a future for these computerized systems.

Automation↗

PubMed2001

A phantom with tissue-like optical properties in the visible and near infrared for use in photomedicine.

BACKGROUND AND OBJECTIVE: Modeling of light transport in tissue requires development of theoretical models and experimental procedures, as well as tissue-simulating phantoms. Our purpose was to develop a phantom that matches the optical characteristics of human skin in the visible and near infrared spectral range. STUDY DESIGN/MATERIALS AND METHODS: The phantom consists of a transparent silicone rubber in which Al(2)O(3) particles and a cosmetic powder are embedded. Layers with thickness as thin as 0.1 mm can be made. The optical properties of Al(2)O(3) particles and cosmetic powder, i.e., total attenuation, absorption and scattering coefficients, and phase function, have been determined in the visible and near infrared spectral range, by using direct and indirect techniques. RESULTS: By varying the concentration of scattering and absorbing particles, tissue-like layers can be produced with predictable optical properties. In particular, mixing at suitable concentration Al(2)O(3) particles and cosmetic powder with the silicone rubber, the optical properties of human skin have been simulated over a range of wavelengths from 400 to 1,000 nm. The comparison between the phantom diffuse reflectance spectrum and that of human skin, averaged over a sample of 260 patients, showed a good agreement. CONCLUSION: The proposed technique allows to produce a stable and reproducible phantom, with accurately predictable optical properties, easy to make and to handle. This phantom is a useful tool for numerous applications involving light interaction with biologic tissue.

Culture Techniques↗

PubMed1999

The ABCD system of melanoma detection: a spectrophotometric analysis of the Asymmetry, Border, Color, and Dimension.

BACKGROUND: The ABCD (Asymmetry, Border, Color, and Dimension) criteria represent a commonly used clinical guide for the diagnosis of early melanoma. The authors revised these criteria in the light of objective measurements of the features of pigmented skin lesions obtained by telespectrophotometric analysis (TS) in the visible and near-infrared wavelengths. METHODS: This study involves a consecutive series of 186 patients with 195 cutaneous pigmented lesions (53 melanomas and 142 nonmelanoma lesions). Each lesion was subjected to TS in vivo, before surgery. For this purpose, the authors used four spectrophotometric parameters that could be closely related to the four criteria of the ABCD guide, namely, roundness (an estimate of how a lesion contour resembles a circle), smoothness (an indicator of the regularity of a lesion border), mean reflectance (the ability of a lesion to diffuse or reflect the incident light), and size (the greatest dimension of a lesion). RESULTS: When melanomas and nonmelanoma lesions were compared by univariate analysis, all four spectrophotometric parameters considered proved to be significantly different (P=0.05). Multivariate logistic analysis showed that mean reflectance in the infrared (P < 0.01) and size (P=0.03) were parameters independently associated with melanoma. Melanoma showed lower reflectance and greater size than benign lesions. CONCLUSIONS: Information provided by TS substantially validates the importance of the ABCD clinical guide and suggests that color is the most important parameter in discriminating melanoma from nevi. In particular, melanoma appears darker than other pigmented lesions.

Adolescent↗

PubMed1999

Monte Carlo simulation of light fluence in tissue in a cylindrical diffusing fibre geometry.

The propagation of light emitted by a linear light diffuser in a cylindrical hollow organ was investigated by means of the Monte Carlo (MC) method. The height and radius of the cavity, scattering (mu(s)) (or reduced scattering, mu'(s)) and absorption (mu(a)) coefficients, anisotropy (g), and refractive indices of the media involved (n1, n2) are required as input data by the MC code, as are characteristics of the light diffuser (length, delivered power and emission profile). Results of our MC model were tested by measuring the light fluence rate in a tissue-simulating phantom (mu(a) = 0.5 cm(-1), mu(s) = 23 cm(-1) and g = 0.75) irradiated at 633 nm with a cylindrical diffuser. Since geometric and optical parameters determine the behaviour of light propagation in tissue, MC simulations with different sets of input parameters were carried out to provide qualitative as well as quantitative data useful in planning photodynamic therapy. Data are reported on light penetration and fluence rate build-up at mu(a) and mu'(s) values ranging between 0.1 and 5 cm(-1) and 2.5 and 50 cm(-1), respectively. Furthermore, results suggest that a shift and spread could occur in the isofluence curves along the symmetry axis, which depend on the diameter of the treated lumen as well as on the emission profile of the light diffuser. Using our data it is possible to estimate how inaccuracy in knowledge of the optical coefficients can affect (i.e. usually by increasing) the light dose scheduled at a certain depth into tissue.

Anisotropy↗

PubMed1998

Spectrophotometric imaging of cutaneous pigmented lesions: discriminant analysis, optical properties and histological characteristics.

Reflectance imaging spectroscopy at 17 selected wavelengths in the range 420-1040 nm has been applied as a method to discriminate melanoma from other pigmented cutaneous lesions. Reflectance images are acquired for 18 primary melanomas and 33 benign naevi in 44 patients. From each spectral image, four parameters related to lesion reflectance (mean value of reflectance, variegation, area and roundness of lesion) are derived at the corresponding wavelength. A discriminant function between the two groups of lesions is determined by using a stepwise discriminant analysis, resulting in a test with a sensitivity of 89% and a specificity of 88%. Since analyses are carried out on the same data set used to obtain the discriminant function, our results should be interpreted with caution. Moreover, in an attempt to assign a physical and/or physiological meaning to the lesion image descriptors, some histological features (i.e., lesion thickness, degree and uniformity of pigmentation) have also been analysed, and their correlations with the image descriptors investigated. Neither degree nor uniformity of pigmentation can fully explain the variations observed in the lesion image descriptors. It is hypothesized that the presence of pathologically related biological components such as lymphocytes and highly aggregated cells may play an important role. The actual performance of the spectrophotometric imaging system should be proven in an additional, unselected number of cases before being used as a diagnostic adjunct for physicians in the clinical detection of melanoma.

Diagnosis, Differential↗

PubMed1996

The invisible colours of melanoma. A telespectrophotometric diagnostic approach on pigmented skin lesions.

Reflectance images of 43 pigmented lesions of the skin (18 melanomas, 17 common melanocytic naevi and eight dysplastic naevi) were acquired by a telespectrophotometric system and were analysed in the spectral range from 420 to 1040 nm, to discriminate melanoma from benign melanocytic entities. Different evaluations were carried out considering the whole spectrum, the visible and the near infra-red. A total of 33 (76.7%) lesions were correctly diagnosed by the telespectrophotometric system, compared with 35 (81.4%) correct clinical diagnoses. Reflectance in the infra-red band appears diagnostically relevant. A larger study is needed to prove the validity of this diagnostic method.

Diagnosis, Differential↗

PubMed1995

Natural fluorescence of normal and neoplastic human colon: a comprehensive "ex vivo" study.

BACKGROUND AND OBJECTIVE: A microspectrofluorometric analysis on "ex vivo" samples from normal tissue and adenocarcinoma of the human colon has been performed to characterize the histological, biochemical, and biophysical bases of the autofluorescence. STUDY DESIGN/MATERIALS AND METHODS: Differences between normal and tumor tissues are found that concern both the intensity distribution and spectral shape of the autofluorescence emission. The different pattern of the fluorescence intensity can be related to the histological organization of the tissue, and involves mainly the arrangement of the submucosa, the most fluorescent layer. RESULTS: The most evident differences in the spectral shape found in the 480-580 nm range involve the stromal compartment, seem to be due to the presence of different fluorochromes, and are possibly related to the host response to the tumor. CONCLUSION: The nature and the extent of the autofluorescence modification between normal and tumor tissue in sections explain at least partly the evidence of the "in vivo" analysis and highlight the importance of excitation for full exploitation of the potentials of autofluorescence in diagnosis.

Adenocarcinoma↗

PubMed1995

Potential and limitations of magnetic resonance imaging for real-time monitoring of interstitial laser phototherapy.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR) imaging has been suggested as a method to monitor interstitial laser phototherapy (ILP) in deep tissues. Unfortunately, a reliable relation between temperature and MR parameters has not yet been demonstrated. In this study, we examined whether such a relation exists and whether MR imaging can measure absolute temperature or temperature changes. METHODS: We evaluated, in the range of 21 degrees C to 80 degrees C, the temperature dependence of the MR imaging signal and T1 in samples of liver, water, CuSO4, and oil. Spin-echo and fast low-angle shot (FLASH) sequences were used. RESULTS: The MR imaging signal of liver, CuSO4, and water continuously decreased when the temperature was increased from 21 degrees C to 80 degrees C. By contrast, the MR imaging signal of the oil increased with increasing temperature up to 40-50 degrees C and then decreased at higher temperatures. We observed a reliable linear relation only between T1 and temperature in a range' of 30-60 degrees C for oil and CuSO4. CONCLUSION: MR imaging has the potential to measure thermal variations with an uncertainty of approximately +/- 10 degrees C. However, the use of MR imaging to monitor the real-time thermal effect induced in biologic tissues during laser irradiation requires further investigation before it can be applied clinically.

Animals↗

PubMed1995

In vivo spectrophotometric evaluation of neoplastic and non-neoplastic skin pigmented lesions. III. CCD camera-based reflectance imaging.

Reflectance spectroscopy, which allows an objective evaluation of the color of surfaces, has recently been proposed as a useful tool to discriminate cutaneous melanoma from other pigmented cutaneous lesions. A novel spectrophotometric system based on the use of a charge coupled device camera provided with a set of interference filters has been developed to acquire images of cutaneous pigmented lesions at selected wavelengths ranging from 420 to 1040 nm. For each filter, an image was captured, digitized by a frame grabber and stored in a personal computer to perform off-line data handling. Reflectance images were acquired of 22 cutaneous pigmented lesions including melanoma and dysplastic, compound and junctional nevus. From each spectral image, three parameters, i.e. mean reflectance, variegation index and lesion area; were derived at the corresponding wavelength. The wavelength dependence of the three parameters was significantly different when melanoma was compared to the other investigated lesions. Although preliminary, our results suggest that telespectrophotometry gives useful information and could be utilized as an aid in the clinical diagnosis of cutaneous pigmented lesions.

Humans↗

PubMed1994

Ex vivo optical properties of human colon tissue.

Using a spectrophotometer equipped with an internal integrating sphere, the absorption (mu a) and the reduced scattering (microseconds') coefficients of ex vivo human colon tissues were evaluated from reflectance and transmittance measurements. Mu a and microseconds' varied from 47.7 to 1.0 cm-1 and from 14.2 to 6.2 cm-1, respectively, on passing from 300 nm to 800 nm. These results can be used to estimate the optical penetration depths when photodynamic therapy or light-induced fluorescence procedures are used.

Absorption↗

PubMedDate not supplied

Image analysis in the RGB and HS colour planes for a computer-assisted diagnosis of cutaneous pigmented lesions.

AIMS AND BACKGROUND: A study was carried out to evaluate the effectiveness of image analysis performed by the two color representation models when a computer-assisted diagnosis of melanoma is involved. METHODS: Color images of 40 skin pigmented lesions, which included 12 melanomas, were acquired by a standard color RGB video camera and stored in a PC for off-line processing. Image analysis was performed in the red green and blue color representation model and using hue and saturation color components. To describe shape and color characteristics of each lesion, including area, roundness and color variegation, 16 parameters were derived from red, green, blue, hue and saturation color planes and tested as possible variables useful to differentiate melanomas from benign nevi. RESULTS: The test gave a result of significance for six of the 16 derived image descriptors. The general trend of our data was in agreement with clinical observations according to which melanoma is usually darker, more variegated and less round than a benign nevus, whereas lesion dimension of melanomas and benign lesions was not significantly different. CONCLUSIONS: Our preliminary results suggested that image analysis performed on hue and saturation-derived and red green and blue-derived data could better discriminate melanoma from nevi than separately using the two color representation models.

Color↗