Medical devices and methods that provide for improved accuracy when positioning of a synthetic structure, such as a MEMS device or a stent, within a biological feature of a patient, such as a blood vessel, are disclosed. A blood vessel sizing device is configured for placement on the skin of a patient near a feature of interest (e.g. a blood vessel to be imaged). The device may include one or more radiopaque elements, including a target element, and one or more positioning markers having known sizes. A clinician may use the radiopaque elements to identify a portion of a blood vessel suitable for positioning of the synthetic structure.
