Biomedical subjects

C M Gardner

Publications and source records attributed to C M Gardner.

5 recordsLinked to original sources

PubMed2001

Silicone roll-on suspension for upper limb prostheses: users' views.

OBJECTIVE: To determine the perceived benefit, pattern of use and problems of the ICEROSS socket for upper limb prostheses. DESIGN: Structured questionnaire sent to patients provided with ICEROSS systems. SETTING: NHS artificial limb clinic. SUBJECTS: All patients (20) who have used an upper limb prosthesis with an ICEROSS inner socket between 1995-1999. MAIN OUTCOME MEASURES: Purpose-designed questionnaire. RESULTS: Replies were obtained from 18 patients. Eight (8) amputees continue to use their ICEROSS limb regularly (44%) after a mean of 32 months. Ten (10) amputees stopped using the ICEROSS system. Six (6) developed persistent skin problems, 2 switched to myoelectric prostheses, 1 was unable to put the ICEROSS on independently and 1 amputee stopped using all kinds of prostheses because he did not find them useful. Fourteen (14) amputees complained of phantom pain, 4 of whom reported worsening of the pain with ICEROSS sockets. CONCLUSION: The ICEROSS socket provides good suspension for upper limb prostheses, but its use is limited by skin problems and incompatibility with myoelectric contacts.

Adolescent↗

PubMed1997

Monte Carlo model for determination of the role of heat generation in laser-irradiated tissue.

A Monte Carlo model is described for modeling photo propagation in a scattering medium. The fraction of locally absorbed photons is proportional to the local rate of heat generation in laser-irradiated tissue and the associated distribution of light (fluence rate) is obtained by dividing the rate of heat generation by the local absorption coefficient. Examples of computed distributions of the rate of heat generation are presented for situations where light scattering in tissue is important. The method is applied to analyze treatment of Port Wine Stain and the selection of laser wavelengths for cyclophotocoagulation.

Absorption↗

PubMed1997

Diagnostic potential of laser-induced autofluorescence emission in brain tissue.

Laser-induced autofluorescence measurement of the brain was performed to assess its spectroscopic properties and to distinguish brain tumors from the normal tissues. The excitation-induced emission spectra were plotted on a 2-dimensional map, the excitation-emission matrix, to determine the excitation wavelengths most sensitive for the spectroscopic identification of brain tumors. The excitation-emission matrices of various types of human brain tumors and normal brain samples lead to the selection of three fluorescence peaks at 470, 520, and 630 nm, corresponding excitation light at 360, 440, and 490 nm, respectively for comparing the autofluorescence signatures of brain tissue. The fluorophores most likely related to each of these peaks are NAD(P)H, various flavins, and porphyrins, respectively. In vivo studies of rat gliomas showed that "NAD(P)H", "flavin", and "porphyrin" fluorescence were lower in gliomas than in normal brain. This finding suggests that there are certain relationship between brain tissue autofluorescence intensity and metabolic activity. In vitro human normal brain tissue fluorescence signals were lower in gray matter than in white matter and "NAD(P)H" fluorescence were lower in all measured human brain tumors than in normal brain. "Flavin" and "porphyrin" fluorescence in the neoplastic tissues was lower or higher than normal tissue depending on their nature. In conclusion, the fluorescence spectroscopic diagnostic system might be able to distinguish brain tumors from the normal brain tissue. The results of this study need to be verified and the investigation extended to human brain tumors in the operating room.

Brain↗

PubMed1996

Light transport in tissue: Accurate expressions for one-dimensional fluence rate and escape function based upon monte carlo simulation.

BACKGROUND AND OBJECTIVE: Surface laser irradiation of tissue often produces a fluence rate that varies only with depth. Modeling of laser-induced fluorescence involves an expression for the fraction of fluorescence emitted per unit depth that escapes from the medium. We present accurate expressions for fluence rate and escape function for the one-dimensional case based upon Monte Carlo simulation results. STUDY DESIGN/MATERIAL AND METHODS: Expressions were proposed for fluence rate, phi (z)/E0 = C1exp (-k1z/delta)-C2exp(-k2z/delta), and escape function, G(z) = C3exp(-k3z/delta), that varied solely with depth relative to effective penetration depth, z/delta. The scalar (C) and exponential (k) coefficient values were found by curve fitting the expressions to Monte Carlo simulation results. RESULTS: The coefficients varied as smooth functions of diffuse reflectance, Rd, for the range Rd = 0.01-0.8, and were independent of scattering anisotropy in the range g = 0.7-0.9. Simple expressions approximated the relationship of each coefficient to Rd. CONCLUSION: The proposed expressions have accuracy comparable to Monte Carlo simulations, over an essentially unrestricted range of diffuse reflectance values. The expressions may be combined accurately to portray laser-induced fluorescence measurements of a turbid medium.

Fluorescence↗

PubMed1992

Dynamic optical property changes: implications for reflectance feedback control of photocoagulation.

During laser treatment, coagulation affects the optical properties of the tissue. In particular, the formation of a white lesion significantly increases the scattering coefficient. This change in the optical properties in turn affects the laser light distribution in the tissue. The white lesion formed during photocoagulation of the retina has a dynamic effect upon reflection and fluence rate. This problem has been simulated on a model medium consisting of a thin absorbing layer covered with a 1 cm thick layer of albumin. The albumin layer is subdivided into coagulated (white) and uncoagulated (clear) layers. The optical properties of each layer have been determined and these values have been used to model light distribution in the medium. One-dimensional adding-doubling and three-dimensional Monte Carlo methods have provided light distributions in the medium for varying thicknesses of the coagulated albumin. Computed fluence reaching the absorbing layer decreased in the presence of a 275 microns or thicker coagulated layer. The coagulated layer attenuates light because it is highly scattering; however, this scattering also leads to a sub-surface peak in fluence rate at a level higher than the incident fluence. The latter effect outweighed the former for coagulated layer thicknesses less than 275 microns. Computed reflectance of argon laser light from a semi-infinite coagulated region initially increased linearly as a function of thickness. As the coagulation thickness increased beyond 4-5 optical depths, the reflectance approached a constant value, R infinity, at 9 optical depths (2 mm). Experimentally measured total reflectance is shown to be an inadequate indicator of the thickness of a lesion (finite coagulated volume); however, central reflectance from a lesion measured with a CCD camera confirmed the computed trends. These results provide a theoretical foundation for control of lesion thickness using reflectance images.

Argon↗