Embodiments described relate to a medical device including an invasive probe such as a guidewire that, when inserted into a duct (e.g. vasculature) of an animal (e.g., a human or non-human animal, including a human or non-human mammal), may be used to aid in diagnosing and/or treating a lesion of the duct (e.g. a growth or deposit within vasculature that fully or partially blocks the vasculature). The invasive probe may have one or more impedance sensors to sense characteristics of the lesion, including by detecting one or more characteristics of tissues and/or biological materials of the lesion. There is further described a method of assembling such a medical device.