A system for injecting a shaped marker in an image of an ultrasound scanner, the system comprising: an ultrasound scanner configured to generate an image and a video-out signal; a probe connected to the ultrasound scanner for transmitting and receiving ultrasonic energy to and from a volume; a marker device configured to respond to a received ultrasonic signal transmitted by the probe and to emit an ultrasonic signal after a delay, the ultrasonic signal including one or more pulses which when rendered in the image generate a marker of a given size at a position within the image; a medical instrument configured to be disposed in the volume, wherein the medical instrument includes the marker device; and a memory comprising a control module, wherein the control module is configured to interpret the ultrasonic energy received from the probe and from the marker device, to determine a three dimensional location of the medical instrument, to highlight the three dimensional location of the marker device with the marker in the image, and to extract a frame repetition period T of the imaging mode used by the ultrasound scanner, and a time of arrival t o of a maximum signal from the probe to the marker device; characterized in that the ultrasonic signal emitted from the marker device is configured to be injected at times t 0 +nT+S i, where n is an integer and S i is a time delay corresponding to the emission of the one or more pulses which when rendered in the image correspond to a predetermined shape of the marker, such that the video-out signal of the ultrasound scanner, together with the injected signal, can be analysed to quantitatively estimate the internal beamforming and scan conversion parameters of the ultrasound scanner. an ultrasound scanner configured to generate an image and a video-out signal; a probe connected to the ultrasound scanner for transmitting and receiving ultrasonic energy to and from a volume; a marker device configured to respond to a received ultrasonic signal transmitted by the probe and to emit an ultrasonic signal after a delay, the ultrasonic signal including one or more pulses which when rendered in the image generate a marker of a given size at a position within the image; a medical instrument configured to be disposed in the volume, wherein the medical instrument includes the marker device; and a memory comprising a control module, wherein the control module is configured to interpret the ultrasonic energy received from the probe and from the marker device, to determine a three dimensional location of the medical instrument, to highlight the three dimensional location of the marker device with the marker in the image, and to extract a frame repetition period T of the imaging mode used by the ultrasound scanner, and a time of arrival t o of a maximum signal from the probe to the marker device; characterized in that the ultrasonic signal emitted from the marker device is configured to be injected at times t 0 +nT+S i, where n is an integer and S i is a time delay corresponding to the emission of the one or more pulses which when rendered in the image correspond to a predetermined shape of the marker, such that the video-out signal of the ultrasound scanner, together with the injected signal, can be analysed to quantitatively estimate the internal beamforming and scan conversion parameters of the ultrasound scanner.