There is increasing evidence that alterations in the electrical property spectrum of tissues below 10 MHz is diagnostic for tissue pathology and/or pathophysiology. Yet, the complexity associated with constructing a high-fidelity multichannel, multifrequency data acquisition instrument has limited widespread development of spectroscopic electrical impedance imaging concepts. To contribute to the relatively sparse experience with multichannel spectroscopy systems this paper reports on the design, realization and evaluation of a prototype 32-channel instrument. The salient features of the system include a continuously selectable driving frequency up to 1 MHz, either voltage or current source modes of operation and simultaneous measurement of both voltage and current on each channel in either of these driving configurations. Comparisons of performance with recently reported fixed-frequency systems is favorable. Volts dc (VDC) signal-to-noise ratios of 75-80 dB are achieved and the noise floor for ac signals is near 100 dB below the signal strength of interest at 10 kHz and 60 dB down at 1 MHz. The added benefit of being able to record multispectral information on source and sense signal amplitudes and phases has also been realized. Phase-sensitive detection schemes and multiperiod undersampling techniques have been deployed to ensure measurement fidelity over the full bandwidth of system operation.
We have deployed a recently completed spectroscopic electrical impedance tomography (EITS) imaging system in a small series of women (13 participants accrued to date) in order to investigate the feasibility of delivering EITS breast examinations on a routine basis. Hardware is driven with sinusoidally varying spatial patterns of applied voltage delivered to 16 electrodes over the 10 kHz to 1 MHz spectral range using a radially translating interface which couples the electrodes to the breast through direct contact. Imaging examinations have consisted of the acquisition of multi-channel measurements at ten frequencies on both breasts. Participants lie prone on an examination table with the breast to be imaged pendant in the electrode array that is located below the table. Examinations were comfortable and easy to deliver (about 10 minutes per breast including electrode-positioning time). Although localized near-surface electrode artefacts are evident in the acquired images, several findings have emerged. Permittivity images have generally been more informative than their conductivity counterparts, except in the case of fluid-filled cysts. Specifically, the mammographically normal breast appears to have characteristic absolute EITS permittivity and conductivity images that emerge across subjects. Structural features in the EITS images have correlated with limited clinical information available on participants with benign and malignant abnormality, cysts and scarring from previous lumpectomy and follow-up radiation therapy. Several cases from this preliminary experience are described.
We have recently built and tested a 32 channel, multi-frequency (1 kHz to 1 MHz) voltage mode system to investigate electrical impedance spectroscopy (EIS) imaging. We completed a series of phantom experiments to define the baseline imaging performance of our system. Our phantom consisted of a plastic circular tank (20 cm diameter) filled with 0.9% aqueous NaCl solution. Conductors and nonconductors of decreasing width (W5: 3.4 cm, W4: 2.54 cm, W3: 0.95 cm, W2: 0.64 cm and WI: 0.32 cm) were positioned at various distances from the tank edge (1 cm, 2 cm, 4 cm and 8 cm). The results suggest that the detection of objects less than 1 cm in width is limited to the first 1 to 2 cm from the tank edge for absolute images, but this depth can extend to 8 cm in difference images. Larger 3.4 cm wide objects can be detected in absolute images at depths up to 8 cm from the tank edge. Generally, conductor images were clearer than their nonconductor counterparts. Not only did electrode artefacts lessen as the frequency increased, but the system's maximum resolution was attained at the highest operating frequencies. Although the system recovered the value of the electrical conductivity at the correct order of magnitude, it tended to smooth out large property discontinuities. The calculated electrical permittivity in these phantom studies was inconclusive due to the presence of electrode artefacts.
Background: Transnational funders provide up to 80% of funds for medical devices in resource-limited settings, yet sustained access to medical devices remains unachievable. The primary goal of this study was to identify what factors hinder access to medical devices through the perspectives of frontline public hospital staff in Ghana involved in the implementation of transnational funding initiatives. Methods: A case study was developed that involved an analysis of semi-structured interviews of 57 frontline technical, clinical and administrative public health care staff at 23 sites in Ghana between March and April 2017; a review of the national guidelines for donations; and images of abandoned medical devices. Results: Six key themes emerged, demonstrating how policy, collaboration, quality, lifetime operating costs, attitudes of health care workers and representational leadership influence access to medical devices. An in-depth assessment of these themes has led to the development of an enterprise-wide comprehensive acquisition and management framework for medical devices in the context of transnational funding initiatives. Conclusion: The findings in this study underscore the importance of incorporating frontline health care staff in developing solutions that are targeted at improving delivery of care. Sustained access to medical devices may be achieved in Ghana through the adoption of a rigorous and comprehensive approach to acquisition, management and technical leadership. Funders and public health policy makers may use the study’s findings to inform policy reform and to ensure that the efforts of transnational funders truly help to facilitate sustainable access to medical devices in Ghana.
The growing interest in global health electives among medical students as well as the emerging emphasis on capacity building and sustainability of global health programs necessitate the development of new models of global health education. New models will need to address the limitations of former models, which include a lack of bidirectional exchange, cultural isolation, and inadequate psychosocial support. Additionally, early exposure to global health education will be imperative to ensure that students cultivate a strong foundation of agency and commitment to the field.Structure/Method/Design: We implemented a team-based approach to global health education in Harare, Zimbabwe that attempts to address these limitations. The approach is anchored by the principle of peer mentorship, which allows medical students to live and work closely with their resident and attending physician counterparts in the host-country. This model provides capacity building support to foster mutual appreciation between the hostcountry medical system and the visiting medical team as well as a structure capable of promoting cultural immersion and customizable global health education for elective participants.Under the current system, global health electives are not offered to medical students until the fourth year, limiting their ability to establish a lasting commitment to long-term international work. To address this issue, our program enables students to engage in global health education throughout the entirety of their four-years in medical school.Upon selection, students are immediately matched with mentors and participate in pre-departure training to prepare for international placement during the summer after their first-year. This is followed by two years of further training and mentorship. The program culminates in students returning to their original locations during their fourth year for a second international elective.Outcome/Evaluation: This new model engenders a sense of agency amongst student participants. By bridging the gap between interest and capacity, the program fosters a deeper sense of commitment to the field and creates a platform for students to mature into global citizens and emerge as instruments of social change in order to combat the increasing healthcare disparities of society on a global scale.
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