An apparatus, method, system, component kit and protective sheath for cannulation of blood vessels are disclosed. The apparatus comprises a sensor assembly to provide ultrasound images of at least one blood vessel in a portion of a patient's body in two perpendicular planes. The sensor assembly may have graphic markings on an exterior surface thereof to facilitate orientation of the sensor assembly on the patient and guidance of a needle towards a desired target vessel during the cannulation procedure. The sensor assembly may also include associated structure to cooperate with a reference location element to place, align and secure the sensor assembly to the patient's skin at a desired location.