This paper aims at introducing a speculative (philosophical) framework to comprehend modern metrology. In classical sense, measurement measures physically existing quantities, such as length, mass, and time. In contrary, modern measurement measures a wide spectrum of objects-to-be-measured, such as imaging biomarker, which is user-defined patterns. Artificial-intelligence (AI-) based diagnosis is another example. If we regard an optical coherence tomography (OCT) device equipped with the diagnostic AI as a comprehensive “measurement system,” the object being measured by this system is a “disease,” which is not a physical quantity but a concept. To comprehend the wide range of modern measurements, we introduce a speculative (philosophical and theoretical) model, so-called “epistemological-metrology model.” In this model, the act of measurement is described as a cascading encoding and decoding processes. In the encoding processes, three types of objects-to-be measured are considered. They include the substance, existence, and concept. The acts of measurements are then classified into “sensing,” “understanding,” and “reasoning,” which measure to the substance, existence, and the concept, respectively. We point out that, the measurements in the understanding and reasoning classes are constructive. Namely, they proactively define the quantity-to-be-measured by the measurement modalities themselves. A speculative method to warrant the relevance of such constructive measurements is presented. Several modern OCT-related measurements, including AI-based diagnosis, some types of polarization sensitive OCT, and attenuation coefficient imaging are investigated by using this this theoretical framework.
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