Two-dimensional dielectric imaging for dermatologic screening: a feasibility study.

BACKGROUND/PURPOSE: The diagnosis of skin neoplasia can be very challenging, given the low sensitivity and specificity of traditional methods of diagnosis which are based on visual appearance. Techniques which are based on the dielectric properties of cells can improve the diagnostic accuracy of screening techniques; as an example, point-contact coaxial probes for dielectric measurement can improve diagnostic accuracy. Unfortunately, these probes are not well suited for two-dimensional spatial imaging of the skin surface, given that they must be manually scanned over the skin surface. METHODS/RESULTS: An electronic scanning probe was developed and fabricated to simulate an open-ended coaxial probe suitable for two-dimensional dielectric imaging of human skin in real time. A clinical study was undertaken to demonstrate proof-of-concept for the instrumentation. A select group of normal healthy subjects as well as a subject with diagnosed squamous cell carcinoma participated in this study. The electronic scanning probe was found to be a potentially useful tool for providing two-dimensional images from diseased skin. CONCLUSION: The electronic scanning probe used for the present study addresses existing limitations with current coaxial probes. Measurements of healthy and diseased areas of skin are provided to illustrate the feasibility of the approach.

Vaginal evisceration after hysterectomy: a literature review.

The purpose of this review is to highlight the risk factors, clinical presentation, and different surgical management options for vaginal evisceration after vaginal, abdominal, or laparoscopic hysterectomy. We identified all reports of vaginal evisceration after these procedures using sources in the literature from 1900 to the present. We found that a total of 59 patients were reported, 37 (63%) had a prior vaginal hysterectomy, 19 (32%) had a prior abdominal hysterectomy (2 of which were radical hysterectomy), and 3 (5%) had a prior laparoscopic hysterectomy. The majority of these patients were postmenopausal women. Also, the precipitating event was most often sexual intercourse in premenopausal patients and increased intra-abdominal pressure in postmenopausal patients. In addition, the small bowel was the most common organ to eviscerate. Most of the patients presented with vaginal bleeding, pelvic pain, or a protruding mass. We conclude that vaginal evisceration after hysterectomy remains a rare event. It is more often seen after vaginal hysterectomy than after other types of hysterectomy. It can also occur spontaneously or following trauma or vaginal instrumentation, or any event that increases intra-abdominal pressure. Vaginal evisceration represents a surgical emergency, and the approach to therapy for it may be abdominal, vaginal or a combination of the two.

Two-dimensional dielectric spectroscopy: implementation and validation of a scanning open-ended coaxial probe.

Dielectric spectroscopy is a powerful tool for characterizing and classifying materials based on their electrical properties. In order to perform dielectric measurements on a sample with spatially varying properties, the measuring probe typically is repositioned manually on the surface of the sample for each measurement. In this paper, we present a novel technique, based on a reconfigurable multielectrode array, which facilitates the recording of measurements at various different spatial locations without physically moving the measuring electrodes. By electronically selecting one of the electrodes as the inner line and connecting the remainder of the electrodes together to form the outer line, an open-ended coaxial probe is created, which can be repositioned by simply selecting different electrode combinations; hence the name of a "traveling" coaxial probe. The geometric factor, or the cell constant, of each coaxial probe in the array was estimated from measurements on saline solutions with known electrical characteristics. In order to validate the setup for measurement of dielectric properties of biological cells, the plasma membrane capacitance and cytoplasm conductivity of yeast cells suspended in aqueous solutions were measured and compared to results from published reports. Dielectric spectroscopy imaging was carried out on tissue phantoms made of an agar gel with inclusions consisting of concentrated yeast cell suspensions. Measurements were performed on the phantoms, and the dielectric data were spatially mapped with respect to electrode location. The spatial electrical data correlated precisely with locations of yeast cell inclusions within the phantoms.

Instrumentation for small-animal capnometry.

Monitoring of human vital signs - heart rate, respiratory rate, hemoglobin oxygen saturation and others - has become an indispensable part of the standard of care in a hospital setting. For example, vital sign monitoring during administration of general anesthesia is essential, given the role that the anesthesiologist plays in assuming physiologic control. In veterinary settings, however, vital sign monitoring under anesthesia is less common, and may consist simply of a visual assessment of respiratory rate. Vital sign monitoring is especially challenging in small animals, given the high metabolic rates and small volumes under consideration. In this paper, we present a unique nose-cone design and associated instrumentation which allows for measurement of respiratory parameters - e.g., anesthesia gas concentration, inspiratory and expiratory O(2), and inspiratory and expiratory CO(2) (capnometry). Such instrumentation facilitates a physiologic assessment of small animals undergoing general anesthesia, an increasingly important consideration as small animals play a greater role in in vivo biomedical studies. In addition, the techniques proposed herein are suitable for measurement on small respiratory volumes associated with neonatal monitoring.

Implementation of a fast reconfigurable array for tissue impedance characterization.

Various tissue properties have been used in the past and present as metrics which can serve to discriminate healthy from diseased tissue. Electromagnetic absorption (of x-rays and optical signals), scattering of near-infrared light, and electrical impedance are a few such parameters. In order to serve as discriminants for diseased (e.g., neoplastic) tissue, the characteristics of these tissues must first be precisely determined. In this paper, we consider the electrical impedance properties of tissues and cell aggregates, and present the design of a reconfigurable electrode array which is capable of providing a well-defined electromagnetic interface to the tissue under study, for characterization in the 0.01-30 MHz range. The configuration of array elements may be easily changed under digital control, allowing for various electromagnetic field configurations to be applied to the tissue under study. The array is designed to interface to four-point as well as two-point impedance instrumentation, and may be used for two-dimensional bioimaging systems based on electrical impedances. The design may be scaled to higher frequencies and smaller dimensions, allowing for studies of electrical properties at the cellular level.

Biomolecular immobilization onto microwave gaas field-effect transistor gate metal - biomed 2009.

Integration of high-frequency solid-state microelectronic devices into biomedical applications is becoming increasingly attractive. The high sensitivity of microwave devices to local changes in electromagnetic fields makes them a logical choice for an impedimetric biosensor, for example; furthermore, incorporation of a biomolecule as a biorecognition element results in high diagnostic specificity. Integration of organic biomolecules into a solid-state sensing platform can be accomplished by various immobilization schemes. The present work describes a general approach by which organic molecules can be immobilized onto a thin-film gate metallization of a Schottky metal-semiconductor field-effect transistor (MESFET), permitting attachment of proteins or nucleic acids.

Fabrication and characterization of microwave immunosensors based on organic semiconductors with nanogold-labeled antibody.

Microelectronic biosensors hold great promise for rapid, sensitive and specific in vitro point-of-care immunodiagnostics. In particular, sensors fabricated using organic semiconductors have attractive advantages-such as ease of manufacture and low cost-in the design and implementation of such devices. Furthermore, immobilization of an antibody or protein antigen as a biorecognition element onto an organic semiconducting film allows for direct transduction of biomolecular binding events into an electronic signal which is readily measured and processed. In previous work, we have demonstrated that an antigen can be bound to organic semiconducting films while retaining enzymatic activity after immobilization. The present work considers organic semiconducting films which are spin-cast onto an interdigitated electrode; antibodies labeled with gold-nanoparticles are applied to the organic semiconducting film and serve as a biorecognition element. The sensor geometry includes a high-frequency coplanar waveguide contact metallization to facilitate direct measurement using microwave wafer probes. Equivalent circuit models are derived from microwave measurements over the frequency range 0.3 MHz to 8.5 GHz.

Polymer semiconductors as a biosensing platform: peroxidase activity of enzyme bound to organic semiconducting films.

Organic polymer semiconductors have unique electronic properties which make them attractive for use in microelectronic and optoelectronic devices fabricated using inexpensive manufacturing processes. In addition, novel chemical and biological sensors have been proposed which make use of the photophysical and electrical properties of conjugated polymer semiconducting films. The work described herein illustrates one such biosensing application by demonstrating successful immobilization of horseradish peroxidase enzyme onto a thin film of the semiconducting polymer MDMO-PPV. Validation of bound peroxidase activity is accomplished through the use of a substrate solution of 3,3'-diaminobenzidine and hydrogen peroxide, which yields a dark brown precipitate in the presence of peroxidase. Photometric measurements are used to derive a quantitative assay of bound peroxidase concentration. This work supports the feasibility of organic semiconducting polymer films as a biosensing platform in microelectronic sensor devices.

Determination of fiber orientation in MRI diffusion tensor imaging based on higher-order tensor decomposition.

High Angular Resolution Diffusion Imaging (HARDI) techniques have been used for resolving multiple fiber directions within a voxel. Using HARDI, a high-order tensor can be obtained through generalized diffusion tensor imaging (GDTI). In this paper, based on the decomposition of the high-order diffusion tensors, a mathematical technique is presented which permits accurate resolution of multiple, randomly-oriented fiber tracts within tissue. A sequence of pseudo-eigenvalues and pseudo-eigenvectors are derived from the diffusion tensor through successive application of a best least-square rank-1 tensor approximation. These pseudo-eigenvalues and pseudo-eigenvectors are used to identify the major fiber directions within an individual image voxel. Results of a numerical simulation are presented to demonstrate the technique.

Design and implementation of dynamic near-infrared optical tomographic imaging instrumentation for simultaneous dual-breast measurements.

Dynamic near-infrared optical tomographic measurement instrumentation capable of simultaneous bilateral breast imaging, having a capability of four source wavelengths and 32 source-detector fibers for each breast, is described. The system records dynamic optical data simultaneously from both breasts, while verifying proper optical fiber contact with the tissue through implementation of automatic schemes for evaluating data integrity. Factors influencing system complexity and performance are discussed, and experimental measurements are provided to demonstrate the repeatability of the instrumentation. Considerations in experimental design are presented, as well as techniques for avoiding undesirable measurement artifacts, given the high sensitivity and dynamic range (1:10(9)) of the system. We present exemplary clinical results comparing the measured physiologic response of a healthy individual and of a subject with breast cancer to a Valsalva maneuver.