David B Denham

Publications (6)10.9 Total impact

• Article: In vitro dimensions and curvatures of human lenses.

  Alexandre M Rosen, David B Denham, Viviana Fernandez, David Borja, Arthur Ho, Fabrice Manns, Jean-Marie Parel, Robert C Augusteyn
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  ABSTRACT: The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.
  Vision Research 04/2006; 46(6-7):1002-9. · 2.41 Impact Factor
• Article: Thermal analysis of laser interstitial thermotherapy in ex vivo fibro-fatty tissue using exponential functions.

  Nelson Salas, Fabrice Manns, Peter J Milne, David B Denham, Ahmed M Minhaj, Jean-Marie Parel, David S Robinson
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  ABSTRACT: A therapeutic procedure to treat small, surface breast tumours up to 10 mm in radius plus a 5 mm margin of healthy, surrounding tissue using laser interstitial thermotherapy (LITT) is currently being investigated. The purpose of this study is to analyse and model the thermal and coagulative response of ex vivo fibro-fatty tissue, a model for breast tissue, during experimental laser interstitial thermotherapy at 980 nm. Laser radiation at 980 nm was delivered interstitially through a diffusing tip optical fibre inserted into a fibro-fatty tissue model to produce controlled heating at powers ranging from 3.2 to 8.0 W. Tissue temperature was measured with thermocouples placed at 15 positions around the fibre. The induced coagulation zone was measured on gross anatomical sections. Thermal analysis indicates that a finite sum of exponential functions is an approximate solution to the heat conduction equation that more accurately predicts the time-temperature dependence in tissue prior to carbonization (T < 100 degrees C) during LITT than the traditional model using a single exponential function. Analysis of the ellipsoid coagulation volume induced in tissue indicates that the 980 nm wavelength does not penetrate deep enough in fibro-fatty tissue to produce a desired 30 mm diameter (14.1 x 10(3) mm3) coagulation volume without unwanted tissue liquefaction and carbonization.
  Physics in Medicine and Biology 06/2004; 49(9):1609-24. · 2.83 Impact Factor
• Article: Laser interstitial thermotherapy (LITT) monitoring using high-resolution digital mammography: theory and experimental studies.

  Ahmed M Minhaj, Fabrice Mann, Peter J Milne, David B Denham, Nelson Salas, Izuru Nose, Karsten Damgaard-Iversen, Jean-Marie Parel, David S Robinson
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  ABSTRACT: Laser interstitial thermotherapy (LITT) is a minimally-invasive laser hyperthermia procedure for the treatment of localized tumours. Real-time monitoring of LITT is essential to control the extent of tumour destruction and ensure safe and effective treatments. The feasibility of using high-resolution digital x-ray mammography to monitor LITT of breast cancer was evaluated. Tissue phantoms including polyacrylamide hydrogel and cadaver porcine tissue were heated using a 980 nm diode laser delivered through optical fibres with diffusing tips. Digital images of the tissue phantoms were recorded with a high-resolution digital stereotactic breast biopsy system during heating. The recorded images were processed and analysed to detect heat-induced changes. No changes were detected during heating of the hydrogel. Pixel-by-pixel subtraction of the initial image from images taken during laser heating shows observable thermally-induced changes around the fibre during laser irradiation that correlate with the thermal denaturation zone observed by gross anatomy. These experiments demonstrate that high-resolution digital x-ray mammography can be used to detect heat-induced tissue changes during experimental LITT in fibro-fatty tissue.
  Physics in Medicine and Biology 09/2002; 47(16):2987-99. · 2.83 Impact Factor
• Article: Laser interstitial thermotherapy (LITT) monitoring using high-resolution digital mammography: theory and experimental studies

  Ahmed M Minhaj, Fabrice Manns, Peter J Milne, David B Denham, Nelson Salas Jr, Izuru Nose, Karsten Damgaard-Iversen, Jean-Marie Parel, David S Robinson
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  ABSTRACT: Laser interstitial thermotherapy (LITT) is a minimally-invasive laser hyperthermia procedure for the treatment of localized tumours. Real-time monitoring of LITT is essential to control the extent of tumour destruction and ensure safe and effective treatments. The feasibility of using high-resolution digital x-ray mammography to monitor LITT of breast cancer was evaluated. Tissue phantoms including polyacrylamide hydrogel and cadaver porcine tissue were heated using a 980 nm diode laser delivered through optical fibres with diffusing tips. Digital images of the tissue phantoms were recorded with a high-resolution digital stereotactic breast biopsy system during heating. The recorded images were processed and analysed to detect heat-induced changes. No changes were detected during heating of the hydrogel. Pixel-by-pixel subtraction of the initial image from images taken during laser heating shows observable thermally-induced changes around the fibre during laser irradiation that correlate with the thermal denaturation zone observed by gross anatomy. These experiments demonstrate that high-resolution digital x-ray mammography can be used to detect heat-induced tissue changes during experimental LITT in fibro-fatty tissue.
  Physics in Medicine and Biology 07/2002; 47(16):2987. · 2.83 Impact Factor
• Article: BiOS 2001 The International Symposium on Biomedical Optics

  Ahmed M. Minhaj, Fabrice Manns, Peter J. Milne, David B. Denham, Jr. Nelson Salas, Jean-Marie A. Parel, David S. Robinson
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  ABSTRACT: Experiments on the feasibility of x-ray monitoring of laser interstitial thermotherapy (LITT) of breast cancer are presented. Digital images of heated tissue phantoms (including fatty porcine tissue and polyacrylamide/acrylate hydrogel), obtained from an x-ray stereotactic biopsy system, were analyzed for changes in pixel intensity. Tissue phantoms were heated either by a 980 nm diode laser or by resistive heating elements in a custom-made chamber. Analysis was conducted by evaluating the changes in average pixel intensity of regions of interest. Image constancy and stability of the x-ray system were also investigated. Slight changes (less than 5%) dependent on the temperature of the tissue phantom were observed, while changes caused by heat- induced tissue displacement and/or shrinkage were more significant (greater than 10%).© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
  05/2001;
• Article: Optics, Electro-Optics, and Laser Applications in Science and Engineering

  Peter J. Milne, Rod G. Zika, Jean-Marie A. Parel, David B. Denham, Carl M. Penney
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  ABSTRACT: Photorefractive keratomileusis procedures are currently being evaluated for both direct ablation of the human cornea and for the shaping of synthetic lenticules, with the ArF excimer laser offering the promise of reduced photochemical damage of underlying tissues due to the non-penetrative nature of 193 nm radiation. In order to better consider the possible effects of any secondary luminescence produced by the interaction of 193 nm radiation with these materials, an optical system based on a gated diode array spectrometer was constructed and used to record their fluorescence spectra at known laser fluences. A broadband fluorescence peak centered around 290-330 nm was observed upon irradiation of corneal buttons and collagen-based biopolymers. The optical efficiency of the fluorescence cell was calibrated by the use of a scattering material of known reflectivity allowing estimates of the fluorescence quantum yield of this process to be made.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
  05/1991;