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Digital radiographic imaging systems are becoming more widely deployed in low-resource settings, potentially reducing the inequitable access to medical imaging that persists today. Even when resources are made available to install digital x-ray equipment, challenges remain with respect to ongoing maintenance and recommended quality assurance programs. Recent studies have indicated that a significant fraction of radiographic installations in Africa are not assessed at recommended intervals due to the lack of high-cost x-ray exposure meters. As a result, errors in x-ray exposure parameters (e.g. current, exposure time, or kilovoltage) can lead to suboptimal image quality, repeated exams, and unnecessary radiation exposure to patients and staff. We have developed a low-cost solution for routine x-ray quality assurance measurements, which takes advantage of commercial-off-the-shelf (COTS) electronic components integrated with a low-power microprocessor controller. The device employs four sensitive phototransistors connected to a multiplexed 16-bit analog-to-digital converter. Light input to the optical sensors is provided by a rare-earth phosphor screen (Lanex regular), which emits green light under exposure to x-rays. Estimation of spectral properties is enabled by the use of aluminum filters on two of the four photosensors. Acquisition is controlled by an open-source microprocessor (Arduino Nano 33 BLE) and the total cost of all components is less than $100 USD. Comparisons against a commercial sensor indicate that the optical-based measurements of x-ray exposure are linear and accurate to within ±3%, over the range from 60 to 140 kVp. This project demonstrates the feasibility of providing accurate, robust solid-state x-ray exposure measurements in low-resource settings.
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