System for determining a position of an interventional device respective an image plane defined by an ultrasound imaging probe of a beamforming ultrasound imaging system in which the position of the interventional device is determined based on ultrasound signals transmitted between the ultrasound imaging probe and an ultrasound transducer attached to the interventional device, the system comprising: an image reconstruction unit configured to provide a reconstructed ultrasound image corresponding to an image plane defined by the ultrasound imaging probe; a position determination unit configured to: compute a lateral position (LAP TOFSmax, θIPA) of the ultrasound transducer respective the image plane based on a time of flight (TOF Smax) of a maximum detected intensity (I Smax) ultrasound signal transmitted between the ultrasound imaging probe and the ultrasound transducer; compute an out-of-plane distance (D op) between the ultrasound transducer and the image plane, based on the intensity (I Smax) and the time of flight (TOF Smax) of the maximum detected intensity ultrasound signal; wherein computing the out-of-plane distance (D op) comprises comparing the maximum detected intensity (I Smax) with a model having only one-dimensional calibration data describing an expected variation of in-plane maximum detected intensity (I SmaxInplane) with time of flight, at the time of flight (TOF Smax) of the maximum detected intensity (I Smax) ultrasound signal; and to indicate the out-of-plane distance (D op) in the reconstructed ultrasound image. an image reconstruction unit configured to provide a reconstructed ultrasound image corresponding to an image plane defined by the ultrasound imaging probe; a position determination unit configured to: compute a lateral position (LAP TOFSmax, θIPA) of the ultrasound transducer respective the image plane based on a time of flight (TOF Smax) of a maximum detected intensity (I Smax) ultrasound signal transmitted between the ultrasound imaging probe and the ultrasound transducer; compute an out-of-plane distance (D op) between the ultrasound transducer and the image plane, based on the intensity (I Smax) and the time of flight (TOF Smax) of the maximum detected intensity ultrasound signal; wherein computing the out-of-plane distance (D op) comprises comparing the maximum detected intensity (I Smax) with a model having only one-dimensional calibration data describing an expected variation of in-plane maximum detected intensity (I SmaxInplane) with time of flight, at the time of flight (TOF Smax) of the maximum detected intensity (I Smax) ultrasound signal; and to indicate the out-of-plane distance (D op) in the reconstructed ultrasound image. compute a lateral position (LAP TOFSmax, θIPA) of the ultrasound transducer respective the image plane based on a time of flight (TOF Smax) of a maximum detected intensity (I Smax) ultrasound signal transmitted between the ultrasound imaging probe and the ultrasound transducer; compute an out-of-plane distance (D op) between the ultrasound transducer and the image plane, based on the intensity (I Smax) and the time of flight (TOF Smax) of the maximum detected intensity ultrasound signal; wherein computing the out-of-plane distance (D op) comprises comparing the maximum detected intensity (I Smax) with a model having only one-dimensional calibration data describing an expected variation of in-plane maximum detected intensity (I SmaxInplane) with time of flight, at the time of flight (TOF Smax) of the maximum detected intensity (I Smax) ultrasound signal; and to indicate the out-of-plane distance (D op) in the reconstructed ultrasound image.