Rotational intravascular ultrasound (IVUS) imaging devices, systems, and methods are provided. The present disclosure is particularly directed to rotary transformers incorporating flex circuits that are suitable for use in rotational IVUS systems. In one embodiment, a rotary transformer for a rotational IVUS device includes: a rotational component and a stationary component. At least one of the rotational and stationary components includes a core formed of a magnetically conductive material and a flex circuit coupled to the core. In some instances, the flex circuit is coupled to the core such that a coil portion of the flex circuit is received within a recess of the core and an extension of the flex circuit extending from the coil portion extends through an opening of the core.
