Martin A. Afromowitz

Multispectral imaging of burn wounds: a new clinical instrument for evaluating burn depth

A real-time video imaging system called the imaging burn depth indicator (IBDI) is described; IBDI can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period. The analysis can be performed on or about the third day postburn on debrided burn wounds. The relative diffuse reflectivity of the burn-wound is measured in the red, green, and near-infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities. Over 100 burn wound sites were studied. Burn sites were evaluated on day three postburn by the IBDI and by the attending physician. Overall, the IBDI was found to be more accurate in predicting burn healing than were the attending physicians.<<ETX>>

Development of medical pressure and temperature sensors employing optical spectrum modulation

Fiber optic Fabry-Perot sensors have been developed whose optical reflectance varies with optical cavity depth (pressure) or with change in a materials refractive index (temperature). These sensors employ a unique combination of features: they are interrogated by an LED; they are designed to operate within a single reflectance cycle; and their returned light is analyzed by a dichroic ratio technique. The sensors use a step index glass fiber and are relatively insensitive to absolute light levels and fiber bending. They have an expanded linear operating range and can be built for low cost disposable applications. Sensor performance meets or exceeds established medical requirements.<<ETX>>

Burn Depth Estimation—Man or Machine

A Burn Depth Indicator, utilizing reflectance ratios of red, green, and infrared light, has been devised and clinically tested for 18 months at our Burn Center. Using the endpoint of wound healing in less than or more than 3 weeks, clinical assessment by two experienced surgeons of intermediate depth wounds was compared to readings from the BDI . In about one third of cases the surgeons were unwilling to commit themselves to a prediction. In the cases where the surgeons were willing to make a prediction, they were incorrect about 25% of the time. The BDI was significantly more accurate than the clinical assessment in those predicted not to heal by the surgeons and maintained an accuracy of 79% in the wounds where the surgeons would not make a prediction. The BDI is portable, noninvasive, and provides an immediate reading. It may have utility as a triage tool for emergency rooms or combat situations, and has utility at present in our Burn Center as a more accurate tool than our clinical judgment in predicting which wounds should be excised and grafted during the first few days after injury.

Photoacoustic measurements of spatially varying optical absorption in solids: A theoretical treatment

The effect of a spatially varying optical‐absorption coefficient on the photoacoustic signal of a solid sample is discussed. A procedure is described for calculating the spatial variation of the optical‐absorption function from the frequency dependence of the photoacoustic signal.

Clinical Evaluation of Burn Injuries Using an Optical Reflectance Technique

In a multiyear clinical study, the authors tested the reliability of an optical technique for diagnosing tissue damage on burn wounds. Optical reflectivity was measured using a convenient, bedside, noninvasive instrument (the Burn Depth Indicator), which was designed and built by one of the authors. The results show that this optical technique is more accurate than conventional methods for predicting the healing time of burn wounds which are otherwise difficult to assess. The optical properties of burn wounds were modeled using a three layer Kubelka-Munk model. We found that eschar thickness and the volume fraction and oxygen saturation of blood in the dermis determine the optical properties of the burn. These factors, in turn, are known to correlate with the burn depth and healing potential.

Fiber optic polymer cure sensor

An in situ method is presented for monitoring the curing of polymeric compositions, including epoxy- and polymide-based composites. The sensor measures the difference between the refractive index of the cured and uncured composition, with the index increasing as polymerization proceeds. The method differs from all existing methods in that it relies on a self-referential differential measurement rather than on an absolute measurement, the sensor is totally independent of curing conditions and is sensitive to the extent of cure even at the latest stages. It can be used within the body of large composite structures undergoing curing in an autoclave, and it can indicate the end of cure without calibration of any kind. >

Applications of Photoacoustic Spectroscopy to Problems in Dermatology Research

The technique of photoacoustic spectroscopy (PAS) was applied in two areas of dermatology research: 1) drug detection and drug diffusion rates in skin, and 2) thermal properties and water content of skin. The drug studies involved detection of the drug tetracycline in the skin and determination of the diffusion rate of the drug through the skin. The water content studies involved determining the thermal properties of the epidermis as a function of water content and the effect of the water concentration gradient across the epidermis. A multilayer model for the photoacoustic effect was developed to account for the nonuniform thermal properties of the intact skin arising from the water concentration gradient. This model was used to determine the width of the region comprising the diffusional barrier in skin. The width of the barrier region was found to correspond to that of the outermost layer of the epidermis, the stratum corneum. This finding coincides with previous research indicating that the stratum corneum comprises the primary barrier to the diffusion of water through the epidermis.

Fiber-optic epoxy composite cure sensor. I. Dependence of refractive index of an autocatalytic reaction epoxy system at 850 nm on temperature and extent of cure.

We discuss the behavior of the refractive index of a typical epoxy-aromatic diamine system. Near 850 nm the index of refraction is found to be largely controlled by the density of the epoxy. Models are derived to describe its dependence on temperature and extent of cure. Within the range of temperatures studied, the refractive index decreases linearly with increasing temperature. In addition, as the epoxy is cured, the refractive index increases linearly with conversion to the gel point. From then on, shrinkage in the volume of the epoxy is restricted by local viscosity. Therefore the linear relationship between the refractive index and the extent of cure does not hold beyond the gel point.

The optical properties of curing epoxies and applications to the fiber-optic epoxy cure sensor

Abstract An in situ fiber-optic technique for determining the endpoint of cure of a thermoset polymer has previously been demonstrated and described. The technique requires no calibration and is readily used as a cure detector in epoxy-based composite materials. The sensor depends upon the relative difference in refractive index between a fully-cured epoxy fiber and the curing epoxy matrix of the composite. In this paper, we present data on the change of the index of refraction of typical aerospace thermoset resin during cure at several elevated temperatures. The measurements were made using a fiber-optic Fresnel reflection technique.

Fiber-optic epoxy composite cure sensor. II. Performance characteristics.

The performance of a fiber-optic epoxy composite cure sensor, as previously proposed, depends on the optical properties and the reaction kinetics of the epoxy. The reaction kinetics of a typical epoxy system are presented. It is a third-order autocatalytic reaction with a peak observed in each isothermal reaction-rate curve. A model is derived to describe the performance characteristics of the epoxy cure sensor. If a composite coupon is cured at an isothermal temperature, the sensor signal can be used to predict the time when the gel point occurs and to monitor the cure process. The sensor is also shown to perform well in nonstoichiometric epoxy matrices. In addition the sensor can detect the end of the cure without calibration.