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Reflectance from a turbid biological tissue is discussed for a diffusive light source illuminating the surface of the medium, and is related to the optical property distribution within the medium and to photon propagation through the medium. A three-dimensional photon diffusion model with closed form is developed to describe the photon diffuse intensity in a homogeneous medium. The solution is extended by numerical methods to the medium with layered structure. The concepts of photon flux paths and of reflectance indexes are utilized, together with reflectance data, to extract information about the internal optical properties of a medium. The flux path concept was corroborated by successfully detecting in vivo and ex vivo layered differences in optical properties within the biological medium. These studies suggest that the optical properties of subdermal tissue can be measured from light reflectance and that the effect of the upper skin layers can be eliminated. >

Sodium fluorescein is an in vivo blood perfusion indicator for soft tissue. When fluorescein dye is introduced into the blood, it distributes throughout the vasculature and the extravascular space. Incident light from an external source causes the dye to fluoresce, the level of which is monitored by a photodetector placed over the tissue. In this study, theoretical analysis incorporating a multicompartmental model for dye distribution is applied to describe the relationship among perfusion, dye kinetics, and fluorescence readings. Errors in calculating perfusion from fluorescence are related to dye concentrations and to measurement errors. These error sources are minimized by selecting the measurement time. The alternatives of measurement during wash-in or during wash-out of dye are compared, as well as the alternatives of introducing dye by bolus injection or by constant infusion. Compensation of wash-in measurements for differences in skin pigmentation is accomplished by the matching of skin optical properties between incident and fluorescing wavelengths. A laboratory study at 80 measurement sites (from ten graded perfusion canine flaps) demonstrated a correlation of wash-in and wash-out perfusion data ranging from 0.88 to 0.96 at typical levels of fluorescein in blood. Since wash-in can be completed in a matter of a few minutes, this is likely to be preferable in the clinical setting to wash-out which can take much longer to complete.

In vivo skin and underlying tissue is a layered structure, suggesting that it will have a layered distribution of optical properties. This study assesses in vivo tissue optical properties using multiwavelength light reflectance. A ratio is introduced to compare the reflectance at red (660 nm) and infrared (880 nm) wavelengths. The concept of photon flux paths is introduced to account for the effect of layering on reflectance. In vivo measurements indicate that the reaching depths of these flux paths are approximately the same for the red (660 nm) and infrared (880 nm) light at any given source-detector separation. The results of the study suggest the possibility of spatially resolving or imaging the distribution of optical properties from non-invasive multiwavelength reflectance measurements.

An ex vivo biological model constructed from layers of subcutaneous fat and dermis over a thick layer of muscle provides a biological medium for demonFtrating the influence of tissue layering upon diffusive light reflectance measurements. Reflectance was measured as a distance from the light source. The source was incident over a 4 mm diameter region on the surface of the model. Index curves defined as the log ratio of reflected intensities were calculated as a function of source detector separation. Since the index includes ratios of reflectances from a layered medium and from a muscle sample, it describes the effects of the layers above muscle upon measurements from muscle. The study demonstrated that the increase in the index at smaller separations and the constancy of the index at larger separations is consistent with diffusion model results for layered media.

The transient response of a polarographic probe which is used to measure metabolically inert hydrogen gas concentration is characterized. The purpose is to permit development of quicker estimation procedures for measuring concentration when H/sub 2/ is used as the tracer in blood perfusion studies. Probes are inserted into the thigh muscle and the lumbar area of anesthetized beagles and the resulting responses analyzed by multiexponential curve fitting and analysis of variance. Time constants and weightings are not significantly different with changes in H/sub 2/ level or ischemia. However, a dependence on the type of tissue is observed. The results suggest that predictive methods are possible for reducing measurement time for a given tissue type. >

A study is presented of viscoelastic changes in the limb in the presence of the compartment syndrome, which can occur when muscle tissue swells following trauma. In a series of laboratory studies with elevated compartment pressure, the measured viscoelastic properties on the surface of the limb became more purely elastic when compared with baseline. The noninvasively measured viscoelastic departure from purely elastic behavior at mid-pressure-cycle (60 mm Hg) dropped from 156 mm/sup 3/ to 32 mm/sup 3/ as compartment pressure increased from 6 mm Hg to 63 mm Hg. Measurements were also taken in study of ten normal human subjects. The use of matched sites was found to provide compensation for differences in fat content and muscle tone among subjects. >

Summary form only given. A study was made of viscoelastic changes in the limb in the presence of the compartment syndrome, which can occur when muscle tissues swell following trauma. Measurements were made of the applied pressure-volume displacement curves with a 1.4-cm/sup 2/ indenter placed on the limb surface above the compartment. The noninvasively measured viscoelastic departure from purely elastic behavior at mid-pressure-cycle (60 mm Hg) dropped from 156 to 32 mm/sup 3/ as compartment pressure increased from 6 to 63 mm Hg. Measurements were also taken in a study of ten normal human subjects. The use of matched sites was found to provide compensation for differences in fat content and muscle tone among subjects. In continuing studies of patents with the compartment syndrome, matched differences in A2 have been observed to correlate well with differences in compartment pressure. The noninvasive test provides an easy-to-use approach for diagnosing the compartment syndrome and for evaluating the time course of pressure changes in the limb. >

The effect of exercise on optical properties of the limb is of interest when the optical properties can be related to changes at depth within the limb. Such information may suggest ways in which noninvasive optical methods can be used to monitor exercise. In the present study, a source-detector arrangement was connected to a computer for collection of data at approximately 7-s intervals during sitting, standing, walking, and jogging. Repeatable changes with exercise were observed, and an oxygen index was calculated for subdermal optical data. The data obtained were consistent with a flow-limited system in which exercise had the effect of increasing oxygen availability at the measurement site. >

A comparison of the mechanical properties of limb soft tissues during edema and during the internal limb pressure elevation of the compartment syndrome with measurements from subjects having healthy limbs is discussed. Measurements were taken noninvasively on the anterior surface of the lower limb over the muscle mass. Tissue displacement was recorded against indentation pressure. From the resulting curves, parameters of tissue softness and departure from linear elastic behavior were calculated. Statistically significant differences in the mechanical properties of soft limb tissue in the presence of edema and in the presence of compartment syndrome compared to normal limb tissues are observed. >

Interest in the study of photon migration through biological tissue was prompted by the rapid development of optical devices used in the field of diagnostic and therapeutic medicine. These optical devices depend upon the behavior of biological tissue in response to irradiation by ultraviolet, infrared and visible light sources. The optical properties of tissue can be studied extensively using computer simulation methods. A Monte Carlo model has been developed to study photon diffusion in a homogeneous diffusive isotropically scattering tissue medium. The depth distribution of the photons within the simulated medium confirms the use of surface optical measurements to access deep tissue optical properties.

The pressures at the surface of the residual lower limb during ambulation are affected by the prosthesis fit and by the material choices in the prosthesis. This study is concerned with the design and application of a data acquisition system for use in studying the pressures in the below-knee amputee during ambulation. The goal was to develop a system that could be easily used with a number of patients and not interfere with the normal fit of the prosthesis. Data was collected from 10 patients, and demonstrated that the measurement system is capable of obtaining data using the patient's own prosthesis. The system has potential for use in the improvement of material choice and prosthetic fit to reduce discomfort and tissue damage. >

Ten patients with moderate to severe arterial peripheral vascular disease (PVD) were monitored during treatment with inductive pulsed electromagnetic diathermy therapy. The therapy consisted of 20 daily treatments lasting one-half hour each per day and spread over one month. The application of the electromagnetic energy to the mid-anterior thigh and plantar surface of the foot of the treated leg was accomplished by the use of two inductive application heads and resulted in tissue heating. Patient measurements included surface temperature, transcutaneous partial pressure of oxygen (tcpO/sub 2/), segmental Doppler blood pressure, and superficial blood flow measured with a laser Doppler flowmeter, in addition to the patients subjective assessments of their overall condition. Temperature measurements indicated a repeatable heating pattern for each patient. The maximum temperature was not reached within 20 minutes of heating at the maximum output, while at 10% of maximum output for 10 minutes after maximum output a temperature plateau was reached. TcpO/sub 2/ indicates that the non-treated limb was also affected by the treatment. Sixty percent (60%) of the subjects indicated their belief that the therapy had some discernible therapeutic effect on their condition. The remaining 40% of the subjects experienced no perceptible change during or after the treatment. Based upon the small sample of patients the studies suggest that there is a maximum heating rate applicable to long duration heating using this modality of diathermy. The principle effect on PVD for the subjects studied appears to have been the stimulation of vasodilation. >

The shape of surface reflectance curves is compared for a test medium and for the surface of the human limb. A modulated light spot was incident on the surface of the media and mean reflectance was measured at light source-detector separations ranging from 2.5 mm to 34.5 mm. The in vitro model was constructed to approximate a diffusive layered biological medium. The diffusive properties of the model were changed at depth. Both the in vitro and in vivo results are compared with those predicted by diffusion theory for a uniform diffusive medium. The results indicate that the in vitro medium appears to capture the optical behavior of an in vivo medium for surface measurements out to five diffusion lengths. In addition, the data from both media are matched to the uniform diffusive medium predicted by diffusion theory with good agreement at large source-detector separations. >

Presented is an analysis of changes in reflectance at the tissue surface resulting from heat-induced hyperemia and from applied pressure at the skin surface. Optical reflectance measurements are at wavelengths of 660 nm (red) and 880 nm (infrared). Human subject data consist of in vivo measurements from the calf of the leg. An index is calculated which is a logarithm of the ratio of reflected light intensity before and after stimulus application at each wavelength. The slope of the index curve, plotted as a function of source-detector separation, is related to the expected depth dependent physiological changes, in tissue blood fractional volume and tissue blood oxygen saturation. >

Reflectance from a biological medium with multiple layers is influenced by the distribution of optical properties in the medium. A reflectance index is introduced to assess the layered optical properties. The index consists of the logarithm of reflectance ratios and is applied to in vitro layered media with different optical properties and to in vivo tissue. The measurement index varies with separation of source and detector. Blood volume changes in human skin in response to local heating are detected and related to index changes. The measurements at locations with a thick subcutaneous fat layer suggest minimal changes in the dermal blood fractional volume, indicating a different vascularization at these locations. >

Rectification maps provide a means for comparing different methods of fitting prosthesis to limb. In this study, statistical analyses of rectification maps are described for the purpose of quantitative comparison of prosthesis fitting strategies. An example of-differences between fitting by a prosthetist and by a computer-automated system are used to illustrate the descriptive statistical methods.

The results of photon diffusion modeling are applied to the measurement of oxy-hemoglobin at depths up to 10 mm in a layered tissue medium, continuous wave spectroscopy methods for measurement based on diffusion theory and the modified Lambert-Beer Law are not applicable to absorption differences in layered media. The authors examine differences in hemoglobin absorption through a finite difference solution to the Boltzmann equation for layered diffusive media. An effective photon attenuation pathlength (PAPL) is determined by matching to an analytical solution for an equivalent homogeneous medium. The PAPL provides a characterization of the optical properties in the layered medium since it is a function of the medium's absorption and scattering coefficients. While the authors found that reflectance profiles from the layered models for biological tissue resemble those of a homogeneous medium, the effective PAPL was a unique function of the lower layer PAPL, the layered thickness, and the PAPL of the top layer. These results indicate that the PAPL can be monitored for deep tissue hemoglobin absorption when the depth and PAPL of the superficial tissue layer are measured.

Noninvasive clinical assessment of limb oxygen is examined for tcpO/sub 2/ and differential light reflectance spectrography measurements during flow restriction in the limb. The comparisons are made using the compartment representation of oximetric responses. The study included femoral/iliac occlusion in the canine and limb tourniquet studies in primates. Laser Doppler was also recorded but did not correlate with the oxygen responses. Results from canines were variable presumably due to only partial occlusion of flow and the extensive collateral circulation present in the canine limb. The tcpO/sub 2/ data (partial pressure response) showed less variation among subjects than the reflectance data (saturation response). The difference is attributed to differences between oxygen partial pressure responses and oxygen saturation responses. The reflectance method was easier to use.

In contrast to the traditional classroom environment that promotes passive learning, the multimedia-based studio approach is considered to be a more effective tool for delivering course content as it increases active in-class involvement, teamwork experience and cooperative learning (Wilson 1994). More significantly, the studio environment provides a plethora of opportunities to include case studies that promote hands-on experience and problem-solving, illustrate real-life problems and increase student interest in the course content (Starrett and Morcos 2001). In general, engineering courses benefit from the availability of simulation and analysis software in a multimedia studio environment. Biomedical engineering courses including biomechanics, however, are not always amenable to simulation and often require the setting of complicated and expensive tests involving human subjects and hazardous materials. Furthermore, unlike traditional medical courses, biomedical engineering departments do not have extensive teaching laboratories and students have little or no clinical exposure.

A total of 686 consecutive cases were reviewed for comparison between open cholecystectomy (OC) and laparoscopic cholecystectomy (LC). The procedures were performed by the teaching surgical service of a community hospital. Between March 1989 and December 1992, 381 patients had LC, 262 had OC, and 43 patients had attempted LC that was converted to open cholecystectomy (CONV). Postoperative hospital stay for LC was 2.9 +/- 3.7 days (range 12 h to 28 days) and was significantly less than those for OC (12.4 +/- 23.6 days) or CONV (8 +/- 8.3 days) (p < 0.0001). Patients who had LC revealed meaningfully decreased perioperative or postoperative antibiotic use, postoperative temperature elevations, and hospitalization when compared to OC or CONV (p < 0.0001). Bile duct injury was 0.26% with LC and 0.38% with OC. The percentage of postoperative bile leakage was 0.79% and 0.38% for LC and OC, respectively. LC cases were associated with lower complication rates when compared to OC or CONV (p < 0.005). No deaths were observed with LC (0%). However, the mortality rate for OC was 1.5%. The results of LC were more favorable than those of OC and CONV with respect to complications, morbidity, mortality, and length of hospital stay. Based on our experience, the patient outcome for LC was superior to OC.

Recently, researchers have used phase modulation of photons (PMP) at near infrared wavelengths to assess in vivo tissue blood perfusion. The incident light intensity is amplitude modulated in the megahertz to gigahertz range and the phase shift is measured at the detector for the photon waves that have migrated through biological tissue. The obtained phase shift is related to the pathlength for the detected photons. In the past, the models for this process have not considered the effect upon phase produced by inhomogeneities within the in vivo tissue. The phase shift is a function of the distribution of the optical properties within the medium. We used a simple experimental model to investigate the effect upon phase shift of the location for optical changes. A mathematical model has been developed to describe this effect. The results demonstrate that a measured phase shift depends upon the location at which the optical properties are changed, as well as upon the magnitude of change in the optical properties. In vivo tissue is inhomogeneous so that its optical properties are also inhomogeneous. It is therefore important to consider the optical property distribution of the in vivo tissue when assessing blood perfusion using phase modulation measurements.

The goal in this study is to assess instrumentation and methods for measuring the pressure and deformation of soft body tissues. The design of an instrument and the form of the resulting data are discussed in this paper. Applications include the evaluation of edema, the compartment syndrome, monitoring of peripheral vascular disease and the evaluation of pressures associated with use of a prosthesis with the residual limb following amputation.

Previous studies have examined the relation of light reflectance to changes in optical properties at depth within the tissue. The effect of exercise on reflectance is of interest, when these changes can be related to optical properties and when the optical properties can in turn be related to physiological differences at depth within biological tissue. Presented in this paper is a study of changes in reflectance at the tissue surface during exercise. Optical reflectance measurements are at wavelengths of 660nm(red) and 880nm(infrared). A source-detector arrangement and a data acquisition computer collected human subject reflectance measurements on the calf of the leg. The data demonstrate the ability to measure consistent changes in tissue optical properties during exercise.

Light reflectance from soft tissue has been utilized in noninvasive clinical measurement devices such as the photoplethysmograph and the reflectance pulse oximeter. Incident light on the skin travels into the underlying layers and is in part reflected back to the surface. This paper describes the reflectance of light from in vivo tissue for wavelengths in the range from 420 to 940 nm, based on photon diffusion theory and on experimental results from studies of 17 subjects. The results show a minimum reflectance and a peak sensitivity to the blood pulsations in the wavelength range from 510 to 590 nm. Skin pigmentation is seen to attenuate reflectance rather than altering the character of the modulation spectra. Based on the model introduced in this paper, the dependence of modulation spectra on mean blood fractional volume as well as wavelength is also described theoretically, and corroborated by further experimental data at 570 and 630 nm. At these latter wavelengths, the signal-to-noise ratio was calculated for the blood volume pulsation signal in the presence of physiological noise. The median for calculated ratios of reflectance modulation by blood pulsation and ratios of signal to noise between the two wavelengths were 13.1 and 7.5, respectively, for 93 sites in nine subjects. These results are seen to be consistent with the theory.

Covers the broad issues involved in the care of spinal cord injured patients. Scope includes diagnostic and evaluation methods, spinal cord injury, pathophysiology, medical/surgical management of complications of treatment, and issues of specialized care.

A manually operated preferential looking grating acuity test was modified to include a micro-computer for controlling both stimulus presentation and data acquisition, storage, and analysis. The computerized test requires only one observer-operator and minimizes several testing biases and errors of the manual test. A technique was developed to keep the observer-operator masked during the generation of a transformed staircase. The monocular test time of about 8 min, and the success rate—81% for 224 children aged 2–39 months—compare favorably with our experience with the manual two-operator test. For 39 pairs of age-matched children without visual pathology, grating acuities were 0.6 octaves better with the computerized test. The computerized version was used to measure acuity in 120 children who had, according to clinical examination, poorer vision in one eye than in the other. The suspect eyes showed an average of 0.8 octaves poorer grating acuity. The improvements of computerization were realized without loss of the advantages of the manual test.

We have developed an iterative computer-based algorithm which determines Pso while avoiding direct inversion of the relationship between blood oxygen partial pressure and oxyhemoglobin saturation. Blood sample measurements and the value of P50 are used, together with carboxyhemoglobin data, as necessary, to calculate blood oxyhemoglobin saturation and oxygen content.

Measurements of local tissue blood flow using a technique of hydrogen clearance were used to examine the effect of lumbar sympathectomy on skeletal muscle blood flow. Polarographic recordings on 25 hydrogen desaturations were obtained with platinized platinum electrodes. Lumbar sympathectomies were done on five canines leaving the contralateral limb as a control. The hydrogen clearance data were modeled with biexponential curves: the initial rapid component and the second slow component yielded a weighted average perfusion through tissue. Average volumetric blood flow in the control limb was 6.08 +/- 0.45 ml/min/100 g tissue while the sympathectomized limb averaged 9.54 +/- 0.61 ml/min/100 g tissue (p less than 0.005). Average blood flow increases ranged from 33 to 83 percent in the sympathectomized limb over the control limb. This significant increase in muscle blood flow following lumbar sympathectomy, if of prolonged duration, may be cause for re-evaluation of the role of sympathectomy in the management of arteriosclerotic occlusive disease.

This paper constitutes a presentation to health care managers on the clinical engineering role in the hospital. Guidelines are covered that were issued in 1976, by the Joint Commission for the Accreditation of Hospitals: the engineering problems, goals, and solutions addressed in the clinical engineering function; the education of the clinical engineer; and the alternative methods of delivering engineering support services to the hospital. The material included in this paper can form the basis for presentations intended to increase awareness of the role of clinical engineering, improve compliance with JCAH requirements, and to stimulate action to make effective use of engineering.

Data from a patient receiving ventilatory assistance are processed by computer to calculate pulmonary shunt, dead space/tidal volume ratio, oxygen uptake and delivery, and carbon dioxide elimination and delivery. The computations are based on routines described by Kelman and by Severinghaus, but modified to match limitations of testing imposed by the requirements for ventilatory assistance. Analyses are performed sequentially on arterial and venous blood samples and on respiratory gas samples. The output of the blood gas analyzers is fed on-line to a computer together with other data, such as patient identification, which are manually entered at a keyboard and with thumb-wheel switches. The computer processing begins with determining the concentration of oxygen and carbon dioxide in whole blood and of bicarbonate in plasma. The shunt equation is used to calculate a virtual shunt at therapeutic concentrations of inspired oxygen. Dead space/tidal volume ratios are corrected for mechanical dead space in the respiratory circuit. The analyzed results are returned to the operator within seconds via a video display. Since the data include blood samples from multiple patient sites, a cross-comparison is made by the computer and the operator is informed of unusually large differences in values.

Publisher Summary This chapter presents details of experiments conducted to study monitoring of argon gas transport in tissue. In the study, the diffusion process is employed in a technique for withdrawing gas from tissues to challenge the tissue environment around a monitoring probe. Withdrawal is accomplished using silicone or Teflon membrane tipped probes coupled by a high vacuum line to a mass spectrometer. Argon is the monitored gas in this study. Because it is not metabolized, any changes in argon gas tension readings must be because of the changes in supply of inspired argon or alteration in delivery to the probe due to changes in perfusion and/or diffusion. The mass spectrometer probes consisted of slotted stainless steel tubes covered with a silicone or Teflon membrane. The slits in the steel tubes allow gases to diffuse into the inner part of the tube that is maintained at a high vacuum by the mass spectrometer.

This paper includes sections written by the current or former Clinical Engineering coordinators of five universities on common problems faced by Clinical Engineering (CE) educational programs and the different solutions adopted on various campuses. The problems discussed include student recruitment, financial support, containment of student credit hours and faculty time, retention of CE graduates in the profession, and differentiation between Clinical Engineering and Biomedical Engineering Technology.